Combination Synergy



Engine Block  Turbos   Air Filters  Intercoolers  Heads  Intake/Plenum  Throttle Bodies  Cam Shafts  Headers  Down Pipes/Exhaust Systems  Cold Air/Ram Air  Torque Converters  Chips  Compression Ratio   

Examples of some Basic Combinations

Combination Examples

Following are a couple of drive train combinations that should work as described.  By no means are these meant to be the definitive combinations of parts.  These are merely examples.  There are so many turbo varieties, etc. these days that it would be extremely presumptuous for me to say this is the absolute way to do it.  Note that these are aimed at Daily Drivers, not race cars. 

Both of these should be capable of running in the elevens in basic trim and average over 20 mpg with the AC going with intelligent driving.  Stop and think.  How few cars on the street can actually run in the elevens? In reality, not very many.  Many seem to run better when parked than when moving.  A properly running turbo Buick should have no problem running reliably in the elevens for many miles IF

if the car is mechanically and electrically solid, if the owner takes the time to learn something about the car and how to tune it, and if he is mature enough to understand the need for support equipment such as scan tools, and has enough commonsense to not beat on it beyond reasonable limits, or when it does not seem to be running properly.

Please note that parts installation is only one facet of the experience.  Someone made me laugh the other day when he posted that a 12 second car was sometimes the combination of 10 second parts with a 14 second owner.  My experience says that is very true.

Before you start any modification program, if the car has more than 75,000 miles on it, change the timing chain/gears, install new valve springs, a good fuel pump, hot wire kit, and an adjustable regulator, scan tool, and an accurate boost gauge (the factory gauge is probably not accurate, and it does not read high enough).  Make sure the engine is running properly and the sensors are all good.  Be sure the oil pressure is good and responds quickly to movement of the gas pedal.

I don't discuss transmission work below but the 200 r4 is an outstanding transmission that was built to handle 250-300 hp when delivered from the factory.  As soon we start doubling the engine output, the tranny starts to go away.  A wise investment is a rebuild by someone that actually knows our particular version with its unique valve body.  You will most likely be very unhappy with a job built by the local shop that thinks it is just another Monte Carlo.  Spend the money correctly the first time and have the work by someone with a reputation for turbo Buick trannies.  Don't trust someone that has not built a name doing it.  It will be money well spent.  These trannies are excellent when built properly with the right parts and internal mods.  Don't waste your time and money swapping it out for another type if you have a street car.

After all these years, I have come to this conclusion.  To optimize the combination, one must use a converter that matches the turbo so that it puts the most power to the ground in the quickest possible time. Be warned that this converter will not be cheap.  Don't be tempted to cheap out on the converter.  It's gonna be close to a $1000.  Don't convince yourself to buy something cheap because you cannot afford a good one.  Wait and save your money.  You will be glad that you did.

With regard to turbos, don't be tempted to buy a cheap unit from overseas.  The explosion may be spectacular.  Again, wait and save your money.  For the track, a conventional, cheaper journal bearing turbo will work well when matched up with a good converter.   For the street, a ball bearing turbo will spool quicker with a tighter, lower stall speed converter, but, again, it has to be matched up.  Look at what is working for others and save your money until you can do it right.


Version 1-Upper Elevens

A Scanmaster (Go ahead and buy a PowerLogger as well.  You will learn a lot faster and others will be able to help you much easier)
A fuel pressure gauge and an adjustable fuel pressure regulator
An accurate analog boost gauge
A 2.5" free flowing exhaust kit
An open K&N air filter
A modern, programmable chip
A 340m fuel pump, or, equivalent
A fuel pump hotwire kit
A TA49 or TE44 turbo or  5831   (the 44 and 49 have been superceded by the 5831)
*A 2600-2800 rpm stall torque converter
A set of 60 lb injectors
**A single nozzle alky kit
***A set of 275/60-15 drag radials

I also suggest buying a PowerPlate and installing it for better air distribution.

****Options-ported iron heads and/or an aftermarket stock location intercooler, Powerlogger

*If tuned well, a stock converter may work ok, particularly on the street.  It may be a bit slow to spool from a stand still, but it will work well from a roll.  The programmable chip will help in optimizing the  launch from a stand still.

**Instead of spraying alky, one could run race gas, but that gets old trying to always have race gas in the tank so one can keep the boost turned up all the time.

***These are 28" tall tires and may be a bit too much for a stock converter from a stand still.  275/50-15s which are 26" tall may be better for launches with a stock converter.

****both ported iron heads and a better intercooler will improve flow and make it easier to get more air into the cylinders.  Certainly not required to run in the upper elevens, but, it may do it with a bit less effort.  Powerlogger makes it much easier to examine all the run information after the fact as well as to share it with others.  It is one of those things-if you know what your are doing, it is not necessary, but, if you don't know what you are doing, it can really help you get to the point and learn how things work.

Turbo Note:  These are old school turbos but I really have not seen much that I would consider better in this intended range.  Tried and Proven many times over.  On the other hand, it looks like the 44 and 49 are the 5831 which gives basically the same performance...don't get confused by the array of options...you don't need anything ultra-fancy in this range.

Why didn't I include a 3" downpipe in this combination?  Frankly, I have not seen much in the way of verification that one makes a big improvement versus the investment at this point.  I added one in the next version.  It will not hurt, it may help a little, it is your money.  Make sure the one you buy has a good record when it comes to "fit".

Note that some have managed to push similar combos to the mid-11s, or even faster.  I would not say this was the rule because most that did were very experienced and very determined.

Version 2-High Tens/Low Elevens

Version 2-mid Ten Potential

A Scanmaster plus a *PowerLogger
A fuel pressure gauge and an adjustable fuel pressure regulator
An accurate boost gauge
A 2.5" free flowing exhaust kit
An open K&N style air filter
A modern, programmable chip
A 340m fuel pump, or, better
A fuel pump hotwire kit
A 6262 turbo.  If you can afford the ball bearing version, grab it. (A T66 bb converter is also a great turbo if you find a good deal on it)
**A 3200-3400 rpm stall torque converter
A set of 60-80 lb injectors
***A single nozzle alky kit
An aftermarket stock location intercooler or a front mount if you will be hot lapping frequently.
A set 28" slicks
A 3" downpipe
****Ported iron heads

Again, I also suggest buying a PowerPlate and installing it for better air distribution.

*****Options-a mild cam in the range of 206-210 degree duration at 0.050" lift.

*I added a PowerLogger here simply because it is so nice to be able to log a run and see what happened all the way down the track.  Even more useful may be its use in troubleshooting and/or info sharing with others.  The more I try to help people, the more I believe a PowerLogger is absolutely required for guys that don't have 25 years of experience with the cars.  You will learn faster, and, save a lot of money by preventing disasters.

**The converter must be matched stall-wise with the turbo in order to get good spool up without losing anymore of the power band than required to get the car moving.  When I say 3200 rpm stall, I mean being able to see at least 12 psi of boost on the gauge at this point.  If you choose a bb turbo, you may be able to run a few hundred rpm lower stall converter than if you go with a journal bearing unit.  For the street, bb turbos provide more streetability than do the journal units because the converter can be tighter and the car will respond to throttle input faster. Again, please remember I am talking about street cars and a particular converter.  It is probably more correct to refer to the rpm point where one sees the zero boost point on the gauge and better converter vendors that have turbo experience often use this reference.  They have to have knowledge of various turbos in order to do this successfully.  You will need a well built transmission that can handle the power and I prefer a non-lock up converter. Take your time and see what some of the racers are running.

***I say single nozzle because alky is usually much easier to tune with a single nozzle than with dual nozzles-particularly on street cars in the range we are discussing here.  Again, race gas could be used if one is prepared to keep the boost down low when unleaded 93 is in the tank.

****Ported iron heads are often worth some where around 3 tenths in this range.  One cannot make power unless one can get the air/fuel mix into the cylinder when the valve is open.  I do not advocate aluminum heads on daily drivers due to the lousy thermal efficiency of aluminum.  One needs more compression to make them work properly.  The additional cost does not justify it either.  I will hold to this thought until well into the tens.

*****As one draws close to 11.0, a mild cam works well with the ported heads and becomes increasingly beneficial, I think, in the very low elevens.  More than one stock cam/short block as run into the tens so don't look for magic...a slightly bigger cam should just make more power in the 5000-5800 rpm range.

Turbo Note:  There are many modern turbos with ball bearings and/or billet wheels that are excellent units that will work on a street car.  Some of them will allow you to run a tighter converter and spool better with excellent results.  6262 because it is a proven unit that will provide great results.  Do your research and don't get conned into a turbo that can run Nines just because someone gives you the old, "you won't have to upgrade again" line.  The large majority of people will probably never dip deeply into the tens and will never be beat on the street so use some common sense.  Get a turbo that spools fast with a tight converter that will provide great drivability and response on the street.  These cars are a blast to drive when the combination is right. 


At the sake of being redundant, these cars are all about combination and there are no magic parts-only parts that work well when complemented with other parts that match up.  This includes the engine, transmission, and suspension.

Let me repeat that for any car to perform up to standard, the basic drivetrain must be in good condition.  Engines with flat lobes on the cam, excess slack in the timing chain or missing teeth on the cam gear, low compression, burnt valves or weak valve springs, etc.  simply won't run as they should.  The same can be said about the transmission and differential.  If they are not in good shape, the car will not perform well.  It's as simple as that.  Bolting monster turbos, etc. on a sick car is simply a waste of time, not to mention good money.

Likewise, trying to make ones car perform without the proper accessories-scantool, fuel pressure gauge, accurate boost gauge, etc. is a pointless exercise.

For the purpose of this discussion, I am going to stick to the engine block, turbo, torque converter,  intercooler, heads/intake, camshaft, and associated items.

Now, let's talk about what one should expect performance-wise from the car.  The intent is not to state how the car has to be built, but, to provide an idea how the parts should work with one another and to give some basis for analyzing current performance and planning future mods.

The factory combination was almost ideal.  Turbo size, injectors, fuel pump, intercooler, heads, converter, etc. all seemed to match each other to a tee.  There was not a great deal to expand on performance-wise without beginning to change things.  It's amazing how much power was extracted from base components without changing out everything for specialty items.

A stock drivetrain should approach 110 mph (low 12's) with alcohol injection (or race gas) and a modern chip, 2.5" exhaust, K&N air filter, good fuel pump/adjustable fuel pressure regulator, fuel pump hotwire, and drag radials, - nothing more.  It should be around 103 (low 13's) on 93 octane without alky on decent tires and may sneak into the upper 12s.  Note that the stock turbo is pretty much all in by 21-23 psi of boost with a stock factory location intercooler (spraying alky helps).  Some claim to run more boost without detonation, but, 17-18 psi is often about as good as it gets on straight 93.  Proceed with caution.

Mph is a better indication of horsepower than times as mph is less dependent on driving technique.  Go Here and look at Joe Lubrant's chart for mph and times.  I think his suggestions for injectors are a bit small, but, the e.t.s and mph can be very useful when analyzing performance.

Yes, I know, the bulletin boards are full of people with every product sold by vendors,  including 70 size turbos, that cannot get out of the 12s.  Some of them even own a scantool.  On the other hand, there are many that perform as I describe above.  There must be a reason!  If the car does not approach the mph associated with the above times then it is time to discover why not rather than buying more stuff to add on.

There is more than one way to achieve ones performance goals, and, it would not be much fun if every car was built identically to the next.  On the other hand, certain criteria must be met if there is to be the required synergy between the various components and value is to be received for the money spent.  Spending a ton of money on go fast parts and the car does not respond as expected is no fun at at all unless one is simply a Drive-In racer.

It is important to understand the basic science involved in order to make intelligent decisions if one is to achieve the desired goals.

When one sets out to improve the performance of his Buick, it is important to establish  aspirations for the car.  Is it going to be a daily driver that is mostly street driven?  Is is going to be a week end street racer where ultimate drivability is not that important, or will it be a race car where drivability is not a real consideration? 

I am not sure how to approach the subject of synergy so I will try to discuss the various common components that make up the drive train and attempt to point out what must be considered when upgrading.  I am ignoring the transmission, itself, for the most part, but, see my cautionary warning down in the Examples section.

Engine Block

What does the block have to do with it?  Everything, if you want to crank the horsepower up and keep it in one piece.  Typically a stock block is safe to the vicinity of the vicinity of 11.0 secs assuming that one has assembled the engine according to good practice (that's another topic altogether) and avoids detonation.  Beyond that, the wise typically install engine girdles and steel main caps.  Yes, there are a few guys that may be pushing 650 hp or so and don't run girdles....Personally, I think those guys probably get dressed in a phone booth.  I suspect they don't make a lot of passes every week like some do, either.

These days, there is another consideration as well.  Age and the number of cycles on the crank and rods are taking their toll.  What was good for 525 hp a few years ago may not be good for 425 today.  Stuff happens as they say and there is no guarantee.  My first choice would be a properly installed girdle.  The next improvement would be steel main caps and these have to be properly installed with careful machine work by an experienced shop.  Given the age, a steel crank and rods would be a wise investment on a car that was going to be pushed into the Tens very far, very often.

It is absolutely critical that one uses good parts, good assembly practices, and avoids detonation if one wants to extract maximum life.  The faster one wants to go, the more one is going to have to spend to do it reliably.  As my friend, Steve Yaklin, says, "Cubic money beats cubic inches".

It is a waste of money to buy the parts to make 600 hp and have them blow the bottom out of the block.


Once, turbos were listed by flow in cfm.  Sometimes, potential  horsepower is also listed.  A general rule of thumb that can be used to compute this theoretical horsepower is:  CFM x 0.069 x 10 = maximum horsepower that the turbo can theoretically support.

Now it is important to understand what a turbo can support and what your engine can generate are often two entirely different things.  In other words, just because your turbo can flow enough air to theoretically support 600 hp does not mean that your engine is capable of making 600 hp.  Unless the engine is a built with all the necessary components required for complete synergy, it is likely that from a practical standpoint,  the actual horsepower will be somewhat less than the theoretical prediction.

When selecting a turbo there are two important parts of the drivetrain that must be matched to the turbo.  It should be obvious that the fuel injectors must be of sufficient size to provide the required fuel at the maximum boost/airflow that the turbo will run or the engine can generate.  These days, there are plenty of good injectors available and it is easy to go buy a set of injectors that will work well from the 14's to the 10's with a modern, matching chip.  These days, many simple suggest stepping up to a minimum of 60# injector when upgrading as these will take one to 10.0 in combination with the proper alky injection system.  If alky is not being used, they are good for high tens. 

Once fueling has been covered, a torque converter with a stall that matches the spool up characteristics of the turbo is a necessity.  In general, the larger the turbo, the higher the rpm required to get the turbo into the boost domain.  In order for a quick transition to boost, the torque converter must provide sufficient stall to allow the turbo to spool.  This means that monster turbo which is so much fun to brag about may require so much stall in the converter that the car is not a lot of fun to drive on the street due to slippage in the converter, and, may actually be slower from a roll, or, off the light than your friend's car with a smaller turbo that does not take five seconds to get spooled up.  Modern ball bearing turbos, altho expensive, often require less stall to spool and may restore some of the drivability once lost.

Now, the question of synergy arises.  How well is your chosen turbo going to work within your combination of parts?

Let's say one has stock heads, cam, and intercooler and you want to go to a large turbo.  A suitable high stall converter and matching injectors are no problem as you don't mind the extra slippage and potentially slushy low speed throttle response.  Will you get your money's worth when you put on that TE70 turbo?  Obviously it has the capability of flowing a lot more air than a stock or TA49 sized turbo.  It ought to be a real kick in the pants at wide open throttle.  BUT, the stock heads, cam, intercooler become  real bottlenecks that prevent the big turbo from living up to its credentials.  It may be able to flow a lot of air, but, not with the bottlenecks between it and the cylinder.

The combination does not work well.  It may seem obvious, but, it is not that uncommon to come across such a combination running no faster, and sometimes slower, than a near stock set up.

An obvious problem is with the stock cam that is pushing the rev envelope at 5200 rpm.  Put a 3600 stall converter on to match the big turbo and more than a 1000 rpm of usable street power band has been lost in order to use that big turbo, and the engine is not capable of turning the rpm required to absorb the flow capability of the turbo anyway.

Same with the heads as the turbo may easily out flow the capability of the ports at any given lift.  Think about it.  These heads are the same heads as used on low performance naturally aspirated engines. Using a turbo to push more air through the ports works to a certain extent, but, there are limits to what is efficient, and, beyond that, it becomes ridiculous.  As an analogy, consider the case where one wants to pour a gallon of gas into the fuel tank and uses a funnel with a half inch outlet to pour it through.  It goes fairly well.  Now, consider the case where one has a five gallon jug of race gas to pour into the tank.  That small funnel becomes a real hindrance in this case and a funnel with an one inch outlet makes the job go a lot faster.  That is similar to the problem when one installs a 70 series turbo on an engine with stock heads.

Air Filter

Yep, air filter.  If you want the turbo to spool properly, and, deliver advertised performance, the inlet side must not be a restriction.  On a ten second, or quicker car, this is probably a 4" inlet pipe and a 12" filter.  Below are some guidelines provide by K&N to Chuck Leeper who kindly passed them on to me.



Will the turbo give you what you paid for if you don't address all the weak links in the chain?  You have to be able to supply enough inlet air to the turbo so that it can do its job.  No sense having choked off.


One issue to keep in mind is that small turbos often seem to like higher timing on race gas/alky while larger turbos that produce higher density air charges tend to like less.  Trying to crank more boost out of a smaller turbo may be a wasted exercise as the compressor moves out of its better efficiency zone on its compressor map which then causes undue heating of the charge which then creates a less dense charge-in other words, a wasted effort.  Turning the timing up in this case is then a better alternative.  On a large turbo, 20-22 degrees of timing and cranking the boost up more may be more optimum.  If one does not experiment, one will not know.  Hey, that sounds like Tuning!


Intercoolers are an interesting subject because there are so few facts readily available with regard to performance enhancement other than bigger is generally better if one has reached the point of diminishing returns with the current unit.  Determining this point is the difficult thing.  Unfortunately, vendor hype often does not do much to clarify the issues. 

I have found that intercoolers with larger volumes may interact badly with some turbos as excessive turbo compressor surge may be encountered at low throttle openings...this is hard on the turbo and terrible for drivability.  Nothing like trying to ease around someone in traffic and having the car shake like a wet dog and refuse to accelerate because the compressor wheel in the turbo is stalling.  In my own experience, I have found that a V2 front mount and a Craig 45 turbo (T63E) was not a lot of fun to drive due to the compressor surge at light throttle.  Yet, when I installed the T66bb which is larger, the surge is 99% gone and the car drives virtually like a stocker.  On the other hand, my other car with a TE44 was surge free with the stock intercooler, but, it has some surge at times at light throttle after I installed the larger V4 slic.    Go figure...it has to be related to the turbo compressor map.

Intercoolers are very difficult to effectively test even when one has a lot of sophisticated equipment.  Red Armstrong spent a year testing intercoolers and promising to post the results and it never happened as he could not quantify results in a meaningful manner.

There has been only one scientific comparison test of which I am aware.  It was conducted by Bob Dick and posted in The Source.  Bob is a mechanical engineer with a Master's Degree from Villanova concentrating on thermodynamics and he made a valiant effort to scientifically compare several intercoolers on a mid 12 second car (stock intercooler) equipped with a PTE-51 running 21# of boost on 100 octane.  This may not be representative of the Ricky Racecars amongst us, but, the results provide plenty of food for thought.  It's worth reading and understanding the complete write up so go here when you have the time.  Please note that a couple of columns are reversed in the temps provided for the stock intercooler in the table included in the article.

Also, here is an article by an unknown author which was posted by Ed Baker on www.turbobuicks.com.  This article contains some theory and discussion of intercooler design and performance.

If one reads Corky Bell, or other turbo experts, one learns that the magnitude of the pressure drop across the intercooler is generally more important than the amount of heat transfer capability of the intercooler.  To clarify, the LESS the pressure drop across the intercooler, the better.    Obviously there has to be some trade off between the two (pressure drop versus heat transfer) as a three inch straight pvc pipe in place of the intercooler would minimize pressure drop to almost zero, but, would not cool the charge at all and we would be back to hot air cars!

Now, why is the magnitude of the pressure drop important?  Boost pressure is measured in the plenum.  If the stock intercooler has almost 6# of pressure drop across it at 21# measured in the plenum, that means the turbo is actually pumping 27# of pressure at its outlet. 

The heat generated by compressing air to 27# at the turbo outlet is considerably greater than it would be if the turbo only had to make 23# at the outlet to have 21# at the plenum.  Why is the temperature important?  Two reasons, air density and detonation.  Remember that it is not the pressure of air going into the cylinder that makes power, but, rather, the density of the air.  The denser the air, the more molecules of air, and, that is what counts.  Therefore, if we can reduce the boost at the turbo outlet, the air entering the intercooler will be cooler and the air exiting the intercooler will be also cooler which means our 21# of boost in the plenum will actually be denser and we can make more power at the same boost than before.  That is what it is all about.  Detonation which is the auto-ignition of the end gases in the cylinder occurs more easily as the air temperature rises and colder air is a major asset in avoiding this problem as well.

Now, what did Bob Dick determine when he compared the thermal and track performances of a stock intercooler, a Duttweiller Big Neck conversion of a stock IC, a CAS V4, a Cotton stock location IC, a PTE front mount, a ESP front mount, a CAS V2, and, a Cotton front mount?  Remember, this was a low 12 second street car with a stock IC and a small PTE-51 turbo with limited airflow capability.  Most of these units have been replaced in the market these days so these numbers are mostly for comparative purposes only.

Stock IC                    5.52 psi pressure drop               4.2 Flow Coefficient

Big Neck                    3.62 psi pressure drop               2.5 Flow Coefficient

Cotton stock location   3.16 psi pressure drop average    1.8 Flow Coefficient

CAS V4 stock location  3.02 psi pressure drop average    1.69 Flow Coefficient

ESP front mount          4.10 psi pressure drop average    2.1 Flow Coefficient

CAS V2 front mount      3.62 psi pressure drop average   1.53 Flow Coefficient

PTE front mount           1.77 psi pressure drop average   0.93 Flow Coefficient

Cotton front mount       1.64 psi pressure drop average   0.84 Flow Coefficient


Now, it is not so simple as merely looking at pressure drop or we would be using that piece of pvc that I mentioned above.  In fact, it is not simple at all.  Restriction within the the intercooler slows down the path of the air thru the intercooler which means the thermal efficiency of the intercooler with regard to heat transfer may be greater. 

Mass air flow thru the intercooler must also be taken into account and the Flow Coefficient relates pressure loss and flow.  Lower is better.  This is a more meaningful number than simple pressure drop, and we see the big front mounts are five times better in this category.  If one is running in the Nines, or faster,  this is more important than if one is running in the Elevens.

An efficient turbo compressor that does not generate as much heat as another may actually perform better with a slightly more restrictive intercooler that removes more heat when the air density entering the cylinder is compared (this is the reason that the temperature at the turbo outlet of a TE44 is lower than that of a stock turbo at 20# as measured in the plenum--more efficient compressor).  One has to be very careful in trying to make decisions based simply on one parameter or another, and one has to remember that the above numbers were measured from a PTE-51 turbo with limited volume and not a T-88 that would really stress the smaller units' capabilities.

In a nutshell, it is not the boost that is being run that determines the power that can be made, but, rather, the amount/density of the air that enters the cylinder on each intake stroke.

At the bottom of this section are the numbers for the thermal performance of the various intercoolers comparing air temp measured at the throttlebody to air temp at the turbo outlet.  Note that the front mounts average 30-50 degs cooler at the throttlebody.  To be fair, one should be aware that the V4 is fairly old technology today and the Cotton's stock location is made from old factory cores.  Today's units are usually better with regard to flow coefficients.  However, a front mount typically offers more surface area to cooler ambient air which indicates that it should perform better if constructed well.  We know that some have been into the nines on stock location intercoolers made from old cores.  What we don't know is how fast they would have gone on a new tech front mount.  Few vendors, if any,  provide any scientifically measured data to support performance claims.  Again, what may be an improvement on a Nine second car may not be measurable on an Eleven second car.  Keep that in mind when someone is trying to sell you an unit that costs twice what you can buy another unit for.

Studying the tests performed by Bob Dick, I have come to the conclusion that the factory intercooler was well matched to the boost provided from the factory on the stock turbo and that a Duttweiller Big Neck conversion will work well for the money on a stock, or near stock, turbo.  After all, the flow coefficient on the above test clearly shows the poor flow coefficient of the factory unit when the boost is cranked up.  If we typically believe that the factory turbo is all done by 21 # of boost, anything we do to reduce the intercooler bottleneck should extend the useful range of the turbo as the reduction of loss in the intercooler will allow the turbo to run at a lower turbo outlet boost to obtain the desired plenum boost at a cooler temperature.

If we go to larger turbos, it is very obvious why we are not getting our money's worth with the factory intercooler.  It becomes a bottleneck fast altho alky injection does minimize this a bit.

Now, one could easily come to the conclusion that a good front mount is the best solution by far.  There are some caveats, however.  First, there could be a potential overheating problem if one lives in a hot climate as air flow to the radiator is restricted by the presence of the front mount.  This is at its worst when the AC is running.  A good radiator backed up by dual fans, a high volume water pump, and perhaps, an overdrive water pump pulley is usually a big help in this department.  Then we have a problem, potentially, with larger turbos and the larger volume of the tract between the turbo and the throttle body which may cause  compressor surge  which can make the car more difficult to drive at light throttle in some cases as mentioned prior.  It is a good idea to seek the experiences of others running similar combinations before forking over your money.  Finally, we may have a bit more lag before spool up as we have a larger volume of air to get moving in the system.

Practically speaking, a modern, stock location intercooler should perform on par with a front mount at least well into the 10s.  I am a bit dubious that they will duplicate the performance on a hot day due to the reduction in air flow thru the core with any streetable duct system no matter what various vendors claim, but, I suspect the difference is not much more than a tenth if tuned properly for both.  If one is running alky injection, then I would expect no difference at all.

The main point of all of this is that the stock unit is a serious bottleneck when it comes to larger turbos and/or more boost as evidenced by the provided numbers, and intercooler improvement should be considered along with turbo size increases, etc.  When running a smaller turbo such as the TA49 or TE44 and alky injection, it may not be the problem it seems, however.

Here are the temperature differences measured in Bob's tests of the various units.


As stated above, the factory heads that came stock on the turbo Regals have the same ports as the naturally aspirated heads and were not designed for high performance.  With a small turbo, however, they work quite well.  The turbo pushes the additional air thru them without significant resistance and the small ports are not a real bottleneck in the greater scheme of things.  Once larger turbos are used, the small ports begin to provide serious hindrance to the flow potential of the turbo.  See my analogy above comparing funnel sizes.

Small ports provide good velocity and throttle response when the engine is not under boost and are good for both performance and fuel economy.

Once the boost is cranked up, a bigger turbo capable of flowing more air, a better intercooler, etc. come into play, the stock heads begin to be an impediment to making power.  By the time the car enters the eleven's, better flowing heads will improve virtually any combination.  The larger the turbo, the better the intercooler, the quicker the stock heads become a bottleneck.

Daily drivers don't need, or benefit much from, significant metal removed from the ports, but they do respond well to pocket porting and cleaning up the short side radii of the intakes entering the pocket.  Normal clean up and port matching along with the aforementioned work will deliver 85% of the performance of a $1200 set of commercially done heads-particularly for those running in the 11s while maintaining low speed performance and fuel economy.  One has the option of doing his own work, having them done by a professional, or looking for a used set from someone moving up to a set of aluminum heads. 

Cast iron factory heads have run into the nines and a full blown set of fully ported commercial heads are certainly adequate for running well into the tens if the rest of the combo matches up well.

Aluminum heads are available for those that are serious about  getting everything possible out of the engine.  However, they are more susceptible to damage, cracking, and due to the poorer thermal performance of aluminum, more compression should be added.  I consider the current crop of aluminum offerings to be more suited to the cars that are largely used for the strip. 

I consider a set of mild iron heads as very helpful on any engine that has a TA-49 or larger if it typically runs much above 20 psi of boost on 93 and alky, or race gas.  There is very little downside if the porting was done properly... Properly meaning reasonable sized ports and consistency between cylinders.  Lots of performance improvement for a reasonable expenditure of money makes them attractive to me and they are not instantly obsolete when larger turbos, etc. are added to the combination.

Don't be surprised if a good set of heads picks up three tenths in the quarter with no other changes once the car is in the elevens.


Intake Manifold/Plenum

The stock intake is fairly well designed and aftermarket units don't provide much, if any, performance gains for stock blocks.  Port matching to the heads won't do any harm, but, may not provide measurable performance gains, either. Once one is approaching the Nines, larger should help to some degree.

The weakness in the stock manifold comes in air distribution and the problem probably lies more within the physics of the plenum design.  Air entering the throttlebody, and into the plenum, tends to travel to the rear of the intake and is biased toward ports five and six.  As a consequence, these two ports tend to run leaner than the other four.

Hemco, PTE, and Kenne-Bell/Accufab have redesigned the plenum in an attempt to better balance the air flow distribution between the cylinders with some improvement.

In addition, RJC Racing has designed the Power Plate that goes between the plenum and the manifold that works extremely well in equalizing flow between cylinders and is in use on many of the nine second stock blocks as well as more normal performers.  It allows one to tune A/F's for all six cylinders rather than targeting an adequate mixture for five and six which leaves the other four too rich.  Power Plates are available for the stock plenum as well as the PTE and KB/Accufabs.  Testing indicates the PTE and PTE Power Plate are probably the best overall combination for even distribution.  There is also an unit for the BGC manifold if one is making a 1000 hp or more.  Initially there was a lot of controversy over the Power Plate as many "eyeball" engineers looked at it and dismissed it a simple restriction.  Dyno tests, six probe egt readings, and, most importantly, track results have demonstrated that it does work as advertised even into the upper nines.

Throttle Bodies

One of the most popular upgrades, and often, one of the most useless from a performance standpoint is the addition of a larger throttlebody.  I have yet to see any convincing numbers that demonstrated that an increase from the stock 58 mm throttlebody to a 62, 65, or 70 mm unit has increased speed on a mid-ten second car or slower.  Some offer improved throttle response as evidence of improved performance.  A larger unit appears to have better response, but, it is due to the increased area of the throttleblade which has to be opened less to provide the same airflow.

Now, having stated that larger units don't normally add to performance there are a couple of benefits.  First, the original units may have worn seals around the shaft and be the source of vacuum leaks which affect idle.  Also, the 70 mm units match up well with those intercoolers that offer 3" outlets.  That makes plumbing the IC to the TB easier without a trick hose.

 Steve Monroe also does the conversions of stock units to 62 mm and he may be contacted HERE.  Might even be a better bang for the buck.  Drop him a line and find out.


One of the beauties of a good turbo street car is that it drives very well when not under boost and has good low in torque in normal driving, and is almost seamless in the transition from no boost to wide open throttle/full boost.  Much of this is due to the ability to use a mild cam that is good for low rpm street driving with nice bottom end acceleration and then use the turbo to stuff more air thru the system than normal.

The factory cam is an excellent design that allows for nice unboosted performance from a 231 cubic inch engine and yet has run into the tens for some.  My own experience/observations lead me to believe that it is a great choice for combinations aimed down to the mid-elevens.  At that point some benefit may be obtained from larger cams if the other components in the combination match up.  If one needs a new cam, some in the duration range of 206-208 degs at 0.050" lift will add some rpm range into the 5500 rpm range without hurting the bottom end too badly for normal driving.

As noted before, big turbos generally are restricted in performance if the engine cannot turn the rpm required to be able to ingest the amount of air the large turbo can produce.  The factory cam is pretty much done (along with the turbo) at 4800 rpm, or so.  We may run it out in third gear thru the lights to 5400-5600 rpm at times, but, we are not making much power-just saving a shift.

Going to a longer duration cam (flat tappet or roller) of of 206-212 degrees on the intake may not hurt the bottom end torque significantly and should extend the usable rpm range  to the 5500-6000 rpm area and add considerably more power to the shift point with a bigger turbo.  Makes good use of those ported heads as well.

In the above, I am mostly referring to flat tappet cams.  Over the years, there have been numerous reports of flat tappet cams with wiped lobes.  Experienced engine builders seldom have this problem. 

Looking at the engine readily shows a potential problem.  Normally, the lifter should be situated to one side of the cam lobe in order that the taper ground across the lobe and the convex base of the lifter combine so that the rotation of the cam causes the lifter to rotate.  When one looks down the lifter bores of the Buick engine at the cam, one will see that some bores are almost centered over the cam lobes rather than being offset properly.  Number 3 exhaust is particularly bad in this respect.  Is it a problem with the block casting, or is the problem with the cam blank?  People argue both ways and I have never tried to measure to see which has the problem.  It does not really matter.  It is a problem that must be dealt with by the user.  Those lifters which are not properly offset will not rotate properly and are subject to early wear along with the cam lobe.

Why do experienced builders seem to have a far smaller rate of failure?  First they take great care to follow proper break in procedures and secondly, they stay away from excessive spring pressures.  The factory springs are rated at 78 lbs +/-4 lbs at an installed height of 1.727".  Going to a spring that is significantly stiffer will do little for the rpm range of the cam and nothing for the power band, but, it may shorten the life of your cam considerably as well as contribute to wear on the front cam bearing.

LT1 springs often exert 100-105 lbs of pressure when the valve is closed and may be simply too much.  They were suggested in the early days when the problem was not well understood, or, recognized.  Some still tout them and it is difficult to prove they create problems..  Today, the Comp Cam spring # 980 is an excellent choice when the cup is omitted.  This spring is slightly stiffer and includes a damper that helps eliminate spring harmonics at upper rpm ranges.  Similar springs are available from Sealed Power, etc. 

Using a spring of the proper range along with good break in procedures goes a long way in avoiding cam problems.  Some companies such as Lunati may increase the the taper ground into the lobe in an effort to increase lifter rotation.  Whether this helps, or not, when the lifter is centered on the lobe, I don't know.  I don't think it can hurt.  Dry lubing the lobes certainly helps as does using plenty of moly paste on the lobes and lifter bottoms during installation.  Priming the engine so that oil is fully circulated thru the engine definitely helps as well as running the engine at the rpm suggested by the cam manufacturer for at least the minimum time stated is also vital.

Recently, there have been many discussions in the magazines about the lack of zddp in modern oils and the problems created in race engines with very stiff valve springs and cheap imported lifters.  Normally this does not apply to our engines.  But, soft, imported lifters may be a problem no matter what the spring tension is.  The original GM lifters had a stellite base which did not easily fail.  I have not seen a modern GM replacement lifter to see if they are similarly built, or not.  I have heard that the lifters from TA performance are good quality.

An alternative to a conventional flat tappet cam is a roller cam.  This largely eliminates the chances of lobe wiping.  There are some downsides, however.  First and foremost is pricing.  The cost can be four times that of a flat tappet cam set up.

Secondly is the stronger spring pressure required.  Most seem to require a spring of some 135 lbs which puts more pressure on the front cam bearing and on the rocker shafts.  Heavy Duty bearings and shaft reinforcements should be used (or roller bearing lifters).  Billet cams require more rigging to adapt to our engines.  In recent years, non billet roller cams that are similar to current engine design have become available and seem to work well.

I really like the performance of my roller which has 210 degs of duration at 0.050".  It has almost the same torque off idle as the stocker and allows much more flow at higher rpm than the flat tappet lobe designs which don't provide as much "area under the curve".  Roller cam lobes are much more square (less peaked) than flat tappet lobes and the valves stay open more for a given duration due to the rapid opening and closing of the valve.

Due to the hydraulic roller lifter, spring tension, weight of the lifter, etc., rpm is limited to 5800-6000.  There is a Comp Cam lifter available that sets with almost zero preload that reportedly adds a few hundred rpm to the band.  I have not used it.

No matter which cam one selects, three things are imperative.  1) degree the cam in properly.  2) Set the lifter pre-load properly.  3) Break in the flat tappet cams carefully.

Match the cam operating power band to the torque converter, heads, turbo, etc.  Installing a cam with long duration that does not begin to make power until somewhere past 3000 rpm does not do anything for drivability and insures that a higher stall converter be used to get the car moving off the light.

Remember that a combination that takes seconds to spool won't be too impressive on the street.


The factory headers are the equal of after market units until well into the tens.  As long as the originals are not cracked to such an extent that they cannot be repaired, they tend to perform better on slower cars and just as well as aftermarket units for stock block cars.

If one is gung ho, the factory headers can be welded around the tube entry to the flange and then ported out to match the heads.

Hooker headers were available for our cars at a reasonable price, but, they had larger tubes which killed exhaust velocity and often were much weaker at lower speeds than factory headers.  They also lacked the turbo brace and sometimes contributed to a very short life for the factory oil return line from the turbo which would crack from the vibration.  I would avoid them like the plague other than for race cars..

All in all, expensive headers provide very little for the money and may not fit with your current down pipe.  If you need them, the TA Performance headers are well built.  The cheap, Chinese headers are often poorly made, may not fit at all, and don't last long.  I believe TA Performance also makes a replacement drivers side header as well.

Down Pipes/Exhaust Systems

Once one has arrived in the elevens, a good 3" down pipe should begin to make a difference.  A turbo car does not like back pressure.  The closer one gets to zero back pressure, the quicker the turbo will spool and the faster it will go on top end.  Once, this was one of the automatic suggestions for an upgrade.  There were few actual head to head comparisons offered to demonstrate the benefit and it is my opinion/experience that it is one of the secondary things to be changed once the car is becoming fast.  The Chinese knock offs that sell for a low price seem to have their share of fit problems.  If you buy one, buy it from someone that will guarantee its fit, or replace it if it does not.

A good 2 1/2" mandrel bent exhaust system works very well down into the 11's.  People run even faster on them, but, a larger diameter system may do even better at that point when running thru the mufflers.

From a cost stand point, it is difficult to beat the cost of the Hooker 2 1/2" aluminized system altho the mufflers that come with it can be improved upon if you are going all out.  I prefer the straight thru designed mufflers that flow better such as Ultra-Flos or Maxflows.  Pypes also makes a good stainless steel system for the money.  I don't like Flowmasters which generally don't flow as well and I dislike the sound.

If one wants to spend the money there are some excellent 2 1/2-3" systems available in stainless steel.  Larger diameters are generally louder and I don't like the single shot style as they sound like the UPS truck to me.  Not much fun to cruise around with and listen to the stereo.  But, heck, I am getting pretty deaf so it may not matter?



Cold Air/Ram Air Kits

The factory air filter in the canister is restrictive and becomes worse as the boost is turned up and more power is generated.

There have been at least three different attempts to improve upon the factory implementation. 

The first involves the removal of the factory filter and canister and simply placing a K&N style cone shaped filter at the end of a metal maf pipe situating it above the charcoal canister and behind the large hole in the radiator support.

The second is to use a Kenne-Bell set up where the filter is located similar to the first, but is enclosed in a canister that has an outlet attached to a 4" hose that picks up air from behind the air dam beneath the bumper.

The third involves locating the filter in front of the radiator support hanging down behind the bumper.

The Kenne-Bell method is quite restrictive as the canister fits quite snugly around the filter and most of the air flow comes from the four inch opening to the hose.  Tests long ago showed this set up to be slower than an open element in the first 1/8th mile and then picking up some speed as air was rammed in at high speed.  Some people cut off much of the cannister leaving enough of it to attach the hose to.  Others threw the canister away and merely left the hose in the  radiator support hole so that it directed outside air over the filter when the car is moving.  The downside to either is that a lot of dirt, leaves, etc. are blown into the engine compartment.

I don't think that the air in a moving car is much hotter directly behind the radiator support inside the engine compartment than in front of it.  I believe the air going thru the turbo is heated far more than the difference between outside air and the underhood air at this particular location.  Driving down the road, the air going into the throttle body on my car measures ten degrees warmer on average than the outside air temperature in the summer.  Remember that the air temperature just above the pavement is often much higher than the actual air temperature measured a few feet off the ground and this is the air being picked up.  For serious purposes, one can add a hose when racing to direct outside air across the filter and remove it at other times to avoid trash coming into the engine compartment.

I like this technique combined with a 4" maf pipe for faster cars/bigger turbos. 

When running, alky injection the inlet temps to the plenum are often colder than the intake pick up point temps, as well.

Torque Converters

As stated under the turbo section, it is very important to match the turbo to the effective torque converter stall speed in order to obtain adequate turbo spool up.

Now, stall speed is a very imprecise matter as it depends not only on the blade angle and diameter of the converter, but, also on the power the engine makes.  If a converter stalls against the brake to 3000 rpm, and one improves the horsepower of the engine by another hundred, then the same converter may now stall to 3400 rpm with no other changes.

Altho' one can buy a converter rated at a certain stall, one won't be sure what it actually stalls to until it is in the car.  We also have the problem of defining stall.  If we use brake stall (what rpm will it go to when you plant your foot on the brake and stand on the gas until the wheels try to turn), then that is probably most common...but, we may find that one car tries to turn the rear wheels at 3# of boost and another can reach 12# of boost before the wheels turn.  As that is probably considerably more horsepower, that will push the rpm even higher.....again, the joys of defining and measuring stall.  I guess the best measure of stall would be the rpm when the boost gauge is reading zero boost.  This is more meaningful if one knows how that relates to a given turbo.

The factory converter measures 12" in diameter and stalls in the vicinity of 2200 rpm depending upon the power made by the engine and the quality of the rear brakes.

The factory converter that stalls in this range is usually adequate for the factory turbo or a TA-49/TE-44 with a good tune from the chip.  Many have run into the lower 11's on the original converters.  If the chip is not programmed well, the factory converter may be a bit sluggish off a standing launch.  Many prefer a converter that will stall around 2600-2800 for both street and strip.

Now, most of the factory style replacement converters don't seem to have the right stall speed for our cars and are often down around 1800 rpm in stall.  That will not get the job done very well-certainly not for the slightly larger turbos.  For this reason, if one needs to replace his converter due to age, problems, etc., then I suggest one go ahead and buy a 12" converter stalled to 2600-2800 rpm if one has nothing larger than a TE-44 turbo.  On a well tuned car, one may have to leave at a slightly lower boost to keep from blowing street tires or drag radials away, but, that just makes it more fun.

I do not recommend 12" converters stalled higher than 2800 rpm.  In order to achieve the desired amount of stall, the fins have to be bent so much on a large diameter converter that the converter will then slip excessively on the top end and generate more heat and less top end mph.  I know there are cheap 12" converters on the market that are rated at 3000-3200 rpm, but, it goes against the laws of physics and they are simply too inefficient.

If one wants/needs a stall above 2800 rpm, then it is time to go to a smaller diameter converter where the angle of the fins can be less and the converter will have less slip at wide open throttle going thru the lights.  There are good 10" converters available for stalls in the 3000-3400 rpm range and 9/9.5" that will cover this range and above.  A good converter will allow you to build spool without taking all day and yet be acceptable in everyday driving unless one has gone out of the ball park on turbo size.

For a daily driver, I prefer a lock up converter.  For a serious street/strip car, I think a non locking converter is the better choice.  Good converters are not the cheapest, and, the cheapest are seldom satisfactory.  The problem gets worse as the car gets faster.  I suggest that one checks with the more experienced users and try to find out what has a solid reputation before putting the money down.

Used converters are often a risky proposition unless they have been cut open and cleaned out.  Never, ever, install an used unit that came from a car with a bad tranny as it will probably be full of debris and will soon take yours out as well.  It is a very good idea to have any used converter opened up and cleaned out by a professional converter builder if you feel the need to buy a used one.  By the time you are finished, it may be close to the same price as a new one.



The old school, non programmable chips have been replaced by far better programmable units from Bob Bailey and Eric Marshall.  There is simply no comparison between the old and the current day offerings.  In order to get the utmost from these chips, one needs to learn a bit about tuning.  That is a good thing.

I have no use for aftermarket systems like FAST on street cars.   Total waste of money is my opinion, and you end with something that will need to be tuned by a pro unless you are willing to devote the time to learning and can afford to deal with the mistakes you make.  Aftermarket systems come into their own on faster race cars...not street cars.

Compression Ratio

Okay, this is not a part, but it is a vital link in the combination.  Long ago, Ricardo demonstrated that lower compression ratios make more horsepower than do higher ones in forced aspirated implementations.  People often point this out when the subject arises as a "fact".  Too some extent, it is.

What Ricardo did not take into account was effective cylinder pressures and the effect of compression ratio on power "under the curve" as compression, camshaft duration, and size of turbo are all considered.  I linked to an article under the Basic section on compression which makes for interesting reading and contemplation.

Peak horsepower is of interest primarily to those guys who like to run their car on a dyno and talk about it.  Power under the entire curve is more important to those that are trying to extract the best all around performance from their car, particularly for daily drivers that operate across a wide rpm band.

In essence, the longer the duration of the camshaft, the lower the cylinder pressure and the more compression that can be run without running into detonation.  Larger turbos that heat the charge less under boost also improve the situation.

As we increase the cam duration and the cylinder pressure drops, an increase in compression tends to offset the loss and maintain the low end power which is nice on the street for good throttle response and quick spool.  This is well understood in building conventional engines, but, is often ignored on our turbo engines by many with the exception of people like Lawrence Conley and Kenny Duttweiller who often build 9-1 engines for the street.  If we get much past 9-1 on a stock cam, we may begin to incur some detonation when not under boost due to excessive cylinder pressures.

Even engines with stock cams seem to benefit with a bit more compression on the street even if total boost may be a bit less.  Low timing chips seem to like it as well.

The easiest way to approach 9-1 is to use a single shim gasket rather than the thicker composites as used on the 86-87's.

If one is running aluminum heads, then something like 9.5-1 is in the desirable range.