[prbush]

I am just starting to modify a L78 pontiac 400 engine and would appreciate any help on which way I should go. The Trans am is stock in all respects and I would like to keep the rear end stock as well as not have to change the converter. It has an automatic transmission)Tryingto decide which parts to change out to give the engine more power (it is a stock, low compression and has all the smog controls on it). I would appreciate any comments or help on the following questions: I do not want to mess with the bottom end.
1. Should I eliminate the egr and air pump and add an rpm intake? If so what size cam should I use and what brand? I do not want a rough idle as the car will be a daily driver I would like the idle to be as smooth as possible.
2. Should I use a performer intake (if so should I use the one with the egr or eliminate the smog items and use the one without? If so what type and size of cam should I use?
3. Should I use the stock rochester quad or is it too limited due to the emissions and if I should change it out what brand and what size?
4. Should I use the stock distributor or change it out to something else and if so what type.
5. Are there any other modifications that I can make that would help with the torque and horsepower? As I said earlier I will be driving it daily and it will not be used for racing.
The engine had been severly limited in its horsepower due to the emission controls that were put in place and I want to try to bring back as much horsepower and torque as possible.
The engine was just re-built stock and therefore I do not want to go and redo pistons,etc.
I am so new to doing this that any help or information will be greatly appreciated. Hopefully I have not asked too many stupid questions....Thanks....................
FYI, the car is a 79 Trans am, 400 L78 engine, automatic transmission, etc.....

[prbush]

I am just starting to modify a L78 pontiac 400 engine and would appreciate any help on which way I should go. The Trans am is stock in all respects and I would like to keep the rear end stock as well as not have to change the converter. It has an automatic transmission)Tryingto decide which parts to change out to give the engine more power (it is a stock, low compression and has all the smog controls on it). I would appreciate any comments or help on the following questions: I do not want to mess with the bottom end.
1. Should I eliminate the egr and air pump and add an rpm intake? If so what size cam should I use and what brand? I do not want a rough idle as the car will be a daily driver I would like the idle to be as smooth as possible.
2. Should I use a performer intake (if so should I use the one with the egr or eliminate the smog items and use the one without? If so what type and size of cam should I use?
3. Should I use the stock rochester quad or is it too limited due to the emissions and if I should change it out what brand and what size?
4. Should I use the stock distributor or change it out to something else and if so what type.
5. Are there any other modifications that I can make that would help with the torque and horsepower? As I said earlier I will be driving it daily and it will not be used for racing.
The engine had been severly limited in its horsepower due to the emission controls that were put in place and I want to try to bring back as much horsepower and torque as possible.
The engine was just re-built stock and therefore I do not want to go and redo pistons,etc.
I am so new to doing this that any help or information will be greatly appreciated. Hopefully I have not asked too many stupid questions....Thanks....................
FYI, the car is a 79 Trans am, 400 L78 engine, automatic transmission, etc.....

[Gary S.]

I have nearly the same car.1978,though.
Firstly,don't use the stock intake manifold,as it is restricted on the secondaries.You can tell this by the D-shaped holes for the secondaries.The better manifolds have a round shape.
A real good intake is the circa 1969 Pontiac.All the aftermarket ones would be an improvement over the stock one you have,too.
Keep the Q-Jet,but rebuild it the way it oughta be.You can have it built with the intention of freeing up the restrictions like the gasket,etc.Just tell the builder what you are wanting.It's a great carb,it was just toned down because of emissions.
Also,get yourself a Summit 2801 cam,if you don't wanna change the rear axle.It moves the power band up a bit,because there is no sense wasting it down low.You can't get a good launch with a 2.41 rear or anything similar anyway.

[BillyGoat]

I take it from your questions that do are not required to pass any emissions tests. If so, eliminate all of the emissions crap, air pump, egr, restricted intake. I don't have a TA but I believe there are some clearance issues with the Performer RPM, so go with the Performer. The q-jet you have is one of the best performers for a street car if set up properly by one of the q-jet guru's like Cliff R. You already have an HEI. Did you ever consider headers? You need to get your engine to breath. Intake, modified q-jet and headers would be a good starting point. Those are the easiest mods without going internally into the engine, however a cam change would also be beneficial.

[Doug Christie]

You might want to give your engine a little more compresson by milling your heads to closer to 90 cc's or buy a new set with smaller chambers and do some pocket porting. Your intake and carb should be OK, although, if your going with a bigger cam ([email protected]) you may have to modify the carb somewhat.

The extra air/fuel going through the engine will need to get out, so headers are a good bolt on along with 2 1/2 exhaust through good flowing mufflers. Your gearing is going to hold you back, so upgradeing to 3.42:1 posi will wake your ride up nicely.

Almost forgot, your HEI dist. is fine for street or strip, but gains can be had by recurving it.

[COLETTE]

Another angle would be to eliminate HP losses from your pully system such as fan, water pump. (fuel pump, A/C) Switch over to electrical. Probably just a modest gains though. My uncle just put in some sort of transistor distriutor in his TA and even though he raved good things about it for 2 hours I can't remember the name; just "no moving parts... blah blah". There is alot of good ones out there though.

[prbush]

Thanks for the information and help that I have received so far. It has really started me thinking about the direction I need to go so that I eliminate as many mistakes as possible.
After some of the posts I think that I will reconsider and will probably upgrade the rear end. Also, If I go with a 69 intake will I have to make any modifications or will it be a direct bolt on to my 6x heads? Also, would the 69 intake give me the same performance boost as a performer or performer rpm would?
Is there a website for Cliff R. to contact about rebuilding the carb or are there some other people that I could contact to do the work? Also, would 2 1/2" be about as large an exhaust that I should go with?
Thanks again for the great replies and information. I want to make sure that I get this right the first time. I don't want to do something and then have to re-do it again and again......

[wk wood]

Phillip, I just did basically the same thing to a 1973 Grand Am, which is quite a bit heavier than your Trans Am. I left the bottom end alone (400 motor), but changed just about everything else. I kept the original 3.23 gears and did not change the transmission or torque converter. I also wanted a smooth idle. The only thing I would have done differently is I should have had the cylinder heads milled slightly to increase compression, as my compression is around 8.2 to 1. The trade off is I can run 87 or 89 octane gas just fine which is nice since gas is so expensive.

Be very carefull which camshaft you install. I would suggest that you stay with a conservative profile. The first camshaft I installed, was too aggresive. The car was a dog off the line and I was very unhapply with the performance. Some suggested that I change the torque converter and rear gears to compensate for the loss of low end torque, but I did not want to get caught in that trap. Instead, I bit the bullet and put in a different camshaft (more mild). It made such a difference, the motor idles smoother, and it has better low end torque and throttle response. As previously suggested, the Summit 2801 would be a good choice.

You check out my two posts to get more details on what I did. The first was "Low Cylinder pressures" and most recently "H.P. gain in low compression 400".

[bmpmdf]

I would mill the heads about .040", and on the intake side too, then get a Melling SPC-7 cam, as my experience is it will out perform the summit cam. Use 1 .6 rockers on the intake side. You will have a good performing car with the stock Q-jet and a performer intake, and not have hood scoop fitting issues, although Larry's air cleaner set up looks like a very good design and will help the carb flow better. Also with the Melling cam, you will have the same type vacuum as stock for the power brakes. You won't with the summit cam. You will also not have to change convertors. Put 4 tube headers on it with a 2 1/2" exhaust with Magnaflow mufflers, and it will perform great without being too noisey.

[Cliff R]

The lack of power is mostly due to the low static compression ratio. If stock type cast pistons were used during rebuilding the compression ratio is lowered even more. Get the static compression ratio up over 9 to 1 and put in a well matched camshaft. The stock q-jet is an excellent carb, I use a 1977 T/A carb on my 455 running well into the 11's with just a few modifications. The stock intake, even the blocked off EGR versions aren't as bad as one might thing, aside from being very heavy. We'd be glad to help with your carb needs if you dont' mind the wait, very, very busy here.....Cliff

[Mr. P-Body]

Between a well built Q-Jet, Performer, good headers (4-tube, not 3), a "curve kit" in the distributor, and a Comp XE262H cam, will really wake it up. Raising compression can also give it more, but the cam/intake/exhasut combination will do more, without requiring the removal of the heads.
To use the '69 intake, you must take steps to block the cavity above the heat crossover in the middle of the heads, as the early intakes have a larger hole on the passenger's side. Agreed, though, the early intakes are very good.
The Comp XE grinds offer better performance in a lower compression application than any other grinds we've tried. The 262 will have good idle and plenty of low-end, and still rev to 5,500-plus. Beware of trying to compare them directly to other cam grinds. Due to the asymetric lobe designs, the @.050" numbers aren't as easy to cross. They effectively act like a cam with 5 degrees less duration at low speed, and 5 more on the high end. Vacuum signal will be very good.

[prbush]

According to the previou message, to use a 69 intake manifold with 6x heads and a 79 400 I have to take steps to block the cavity above the heat crossover in the middle of the heads. Would someone tell me exactly how this is done and what steps I need to do. I have never done anything like this but would like to give it a try......Remember that I am a complete novice with this so would appreciate specific instructions. If this process is more than a novice should try are there any other early pontiac intakes that would boost performance and would be direct bolt ons................Thanks

[Doug Christie]

You can do do search on this topic by useing the "find" button at the upper left hand of any post. Here's a link to one of the post's.

http://forums.performanceyears.com/g...481#9186071481

PS, say high to your DAD and wish him luck in the election.

[bmpmdf]

The exhaust mismatch might be a very good reason for you to go with a Performer intake if you are not comfortible doing the modifications.

[prbush]

Thanks, I think that this is very do-able after looking at the links..... I have one final question and then I should have the information that I need to get started....

If I use a 69 intake and then use a 69 carb would there be any modifications that I would have to make to use the carb instead of the 79 carb that is in the car; would it hook right up to the different linkages??

[Doug Christie]

Linkage will be different but will probably work with a few mods. Why do you want to go to the 750 CFM?

[prbush]

I guess I was thinking that if a 69 intake would give me better performance over a 79 that a 69 carb would also give me better performance over the 79 carb.... Am I off base on this???
I notice in looking at prices that the edelbrock q-jet for 69 is about 100.00 less than the 79 so if there is an advantage and I decide to buy one instead of having it rebuilt then I would go with the 69 over the 79. Unless I am totally wrong in my thought pattern.

[Mike P.]

Getting rid of that 2.42 gear for something 3.23 or probably above will make a huge difference in acceleration. I'm running 3.55 w/my 400 and the jump from the 2.73's was amazing. Do the other mods Mr. P-Body suggests. I think you can get it to run good with out getting too much other work, if you do the headers etc.. and decide you still need more, you'll already have what you need in place to support smaller chamber heads and a rowdier cam. At some point torque converter might come into the equation too.

[Thumpin455_GTO]

Is it the original engine? If it has a Pontiac engine in it, then its not original. There were no 400 Pontiacs installed with automatics 79. They were all 4 speeds. If its the 403 Olds engine(that was only paired with automatics), then everything that has been said on here doesnt apply. If its a transplanted engine, then the sky is the limit, isnt it?

Still an easy upgrade to the exsisting engine, would be cam, intake, headers, recurve the distributor, and 3.08-3.55 gears. You can run a TH400 "High stall" converter, its functionaly the same as an L88 converter, stalls a bit higher but doesnt burn up gas, create heat, or slip as much as other stalls do. Plus the high stall is cheap (usually). You can do that with either the 403 or the 400, can you post a pic of the engine? That way we know what it is.

[Thumpin455_GTO]

Does your engine look somewhat like this one? Albeit prettier?