I have already replaced the exhaust and beefed up my rear end with bigger gears and a new differential, now it time to start on the motor. I have a 305TPI motor and i wanna get it in low 300's range in horsepower and mid to upper 300 range in torque. Any of you guys have any good suggestions on what to go with? I want to avoid stroking it because i plan on droping in a 350 somewhere down the road. Any help with this would be great. Also a buddy of mine wants to sell me a set of corvette aluminum TPI heads, my question is will they work on my 305?
thanks in advance

 

IK86,

You've already taken care of one of the big items - the exhaust.

Forget the aluminum L98 heads - they have larger chambers that will cost you compression and power, and you would likely experience valve clearance problems.

If your replacement 350 will use the TPI system from your 305, you can do some work there that will pay off a little now, and a LOT with the 350. Remove and port the plenum behind the throttle body. Enlarge and match the openings where the plenum and runners mate together, and where the runners join the intake base.

If you're still usig the stock ECM, change the PROM to the upgraded GM PROM that was part of the TSB campaign. It helps a lot with power enrichment, idle and low-end issues, and overall performance. It could be the best $50 you spend on your stock car.

If you want a little more, you can install a cam, lifters, springs, and timing set. The stock cam is really a hindrance to any kind of flow, and the weak stock springs are a similar problem at any RPM over about 4,300.

After that, an adjustable fuel pressure regulator will help you make the most of your improved intake and better cam profile. Short of burning a custom PROM, this is the quick-and-dirty method of tuning for WOT power. The plenum and intake work, and the AFPR will transfer directly to your 350 when you install it. The cam, lifters, and springs may or may not be appropriate for your 350, but will set you back only about $250 if you shop right. That's a lot of power potential for the money.

As for changing heads, you can if you want, but anything that works well on your 305 will generally not work nearly as well with a 350. I suppose you could always sell off the unneeded parts once the 350 is in, but, why?

 

Vader is right about the cam.... the exhaust is the first restriction in a 305 TPI car, the next is the cam. After that (or actually at the same time as a cam install), I would recommedn porting the heads.

Beyond those things, about anything you do won't transfer to another motor, or will cost too much money for too little results.

 

not on the 86 305 tpi trans am, my stock exhaust is the same as a 89 350 tpi , measered it, as for the peanut cam that has to be the most restrictive in a 305 tpi, i'm sure putting some headers will help but what exhaust what i have flows pretty decent for a stock 86 tpi

 

You're right, it's the same as a 350 TPI.... and it chokes one of those even worse.

Headers are the main thing that it needs. The rest of the exhaust system isn't too bad. Some people, especially people with TPI (for which the flow requirements aren't that great in the first place), report essentially zero gains from a low-restriction cat-back. Probably not worth the money unless your old one is worn out and needs replacing anyway.

 

Those are a 58cc chamber, they are considered a budget swap by most people as they have the benefits of being lighter (save 50+ lbs) and they already have 1.94/1.50 valves in them.

They would be perfect, the only issue is they do not have a EGR passage I believe and require an external one, similar to the Vortec heads.

 

What is the TSB campaign?? Can the new prom be purchase at a GM dealer??

 

Drakar is right. Those heads wouldn't be too bad for your engine.
There would be no valve clearance problems as long as they are 1.94/1.60
If you are getting them for next to nothing, they would be great.
You could also port the ones you have and install bigger valves and get good results. Do a search on 305 heads.

 

just use the d@mn corvette heads already.

 

O.K. - ALUMINUM heads. Compression may not be an issue, but what about valve edge clearance and shrouding? If I understand correctly, the stem centers on a L98 head are wider than the 305 heads, correct? I know a 1.94 fits a 305, but in a 305 head. Also, there's the EGR passage issue. then there's the question about what head gasket to use, since the 305 gasket can interfere with the valves, and a 350 gasket will cause a compression loss.

Yes, the factory upgrade PROM can be purchased at the dealer parts department. For 1986 TPI cars, there was a TSB regarding some "bugged" EPROMs and performance, error code, and driveability problems. Mine was among those that had problems. The TSB covers all TPI cars made in the 1986 model year:



PONTIAC ROUGH IDLE, CHUGGLE, LOW SPEED. Page: 1
86-6(GAS)-66 Issued: 10/17/86
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
1986 FIREBIRD VEHICLES WITH 5.0L LB9
TPI ENGINE (ENGINE CODE F)

New service calibrators (Ref: Called Mem-Cal In Shop Manual) have been
released for the 1986 Firebirds with the 5.OL TPI engine. These new
calibrators will address the following customer comments:

1. "Rough Idle" on both hot and cold engine - the idle speed is raised to 650
plus or minus 50 RPM.

2. "Chuggle or Shudder" at low speeds - torque converter clutch (TCC)
engagement speed is raised to 41 MPH.

3. "Hesitation" on light acceleration with a hot engine.

4. "Cold Driveability" - New calibration eliminates light to moderate sag on
cold driveaway.

5. "Service Engine Soon" Lights - Eliminates the following false Codes:

A. Code 32 - EGR System failure
B. Code 33 - Mass Airflow Sensor Voltage High
C. Code 34 - Mass Airflow Sensor Voltage Low
D. Code 43 - Electronic Spark Control
E. Code 44 - Lean Exhaust Indication

If normal engine diagnostics and repair do not correct the above conditions,
it will be necessary to replace the calibrator in the ECM. Below is a listing
of the new calibrators and their usages.

ON AIR CONDITIONING (C-6O) FIREBIRDS

With QYZ (P215/65 R 15/N 15" Tire) Use - 1228290 Calibrator
With QAC (P235/60 VR 15N Tire) Use - 1228291 Calibrator
With QDZ (P245/50 VR 16N Tire) Use - 1228291 Calibrator

ON NON-AIR CONDITIONING (C-41) FIREBIRDS

With QYZ (P215/65 R 15/N 15" Tire) Use - 1228292 Calibrator
With QAC (P235/60 VR 15N Tire) Use - 1228293 Calibrator
With QDZ (P245/50 VR 16N Tire) Use - 1228293 Calibrator

Use Applicable Labor Time and Operation Numbers.

 

I think that SDPC sells an egr kit that will fix your problem for only like 75 bux.

 

vader
should i just put a 1989 chip in my 86 305 tpi ta, what will be the best for me, i got a hypertech chip right now in there, the funny thing is the stock 86 chip out performs it,

 

I found the same thing with a HyperTech Thermomaster PROM. The upgrade GM PROM actually does better.

GM L98 Aluminum, 163cc runners, 58cc chambers, 1.94/1.50 valves, 186cfm/140cfm. Valve spacing is 1.935". Considering the 0.055" offset of the valves toward the exhaust side, that makes the valve perimeters 3.653", allowing only .025" around the edge of the exhaust valve (shrouded, and close to interfering with the gasket bore).

Let us know how it works out.