1971 Cutlass problem with trans

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Just rebuilt 350 (edelbrock carb, cam, manifold), new 3500 stall converter (questionable as to who built it, the guy who rebuilt my transmission referred him) and rebuilt transmission w/ heavy duty BM shiftkit.

Engine runs great...starts fine, idles fine, great sounding through all rpm's.
Problem comes when you put the car into gear; the car will go into gear and then it seems as though all the power is gone. NONE whatsoever. I am guessing it might be the 3500 stall converter...maybe too much stall? any comments would be greatly appreciated.

PS. edelbrock rated engine at 420 horses at flywheel so I would think power wouldnt be an issue.
PSS. the trans is a TH-350

posted by  neslorelyks

Raise the RPM's up to 4000 and launch it...in a safe place that is...If it still bogs then it is not the converter. However I think your power should be in gear ,. it 3500 is way too much for that car and engine combo...The guy who rebuilt your tranny and motor should have both suggested a smaller stall converter.

posted by  retrosns

i built the motor and had the trans sent out. for 420 hp, what would be a good stall speed

i do have power when i am in gear, just not off the launch

posted by  neslorelyks

What gears are you running? and what heads are you using to get 420hp?

a 3500 stall converter with steep gears (3.91's or lower) and 420hp, your car should work well.

On the other hand, if you have the car cammed and carburated for the mid-high rpm range and your heads and valvesprings can't support the upper rpm ranges that the cam operates best in, then all you've done is hurt the low end torque of the engine without the offsetting higher rpm gains.


posted by  DPelletier

The heads are stock but machined to allow larger heavy duty dual springs and heavy duty roller rockers (all from comp cams) that are supposed to match the cam. The power range for the motor is supposed to be 1500-5000.
The gearing is stock; whatever that is.

posted by  neslorelyks

I suspect that:
- your gearing is way to high for the cam and stall speed used. Check your gearing.
- I also suspect (not trying to rain on your parade) that you aren't producing anywhere near 420hp. I read where Edelbrock had done some testing on an Olds 350 and with closed chamber heads running W-31 valve sizes, high compression, and thier cam, intake and carb managed to get 370hp out of it.
420 hp is a lot to ask from a 350cu in smallblock running a hydraulic cam and stock heads. I don't have enough information ( compression ratio, cam specs, head porting, etc. ) to make an educated guess on potential hp levels, but based on what you've said, 420 seems high.


posted by  DPelletier

I agree with Dave!!.

Is the converter slipping (RPM higher then the forward motion of the car)? A high stall converter will slip until in nears its stall speed. Is the car bogging due to a locked up converter(no slip). These are all questions you need to present. Like was said above you need to find out what rear gear you have. Does it spin one tire or two? Do you have a tach?

When you order a converter they ask many questions to match your converter to your combination. (Compression/cam/rear gear/Shift RPM/exhaust/heads). I doudt if your putting out 420hp. My guess would be more like 330-370HP max but that's a guess.
With a good set of street gears (3.23-3.73) you could probably run a 2500-2800 stall converter without trouble. The same converter behind a 330HP motor will stall lower then behind a 420Hp motor.

Test: With your foot on the brake, watching the tach, what RPM does the back tire start to brake loose. That's your stall speed.

posted by  fc7gtx

Just for some guidance I ran a Dyno Run for your engine with some a few guesses, here's what I imputed:

stock heads
11.1 cpmpression(yours is probably a lot lower then that)
780CFM carb/w dual plane intake
.504/.479 lift cam 282 duration Hydraulic (advertised) (Your's is probably a bit smaller then that).
Small Tube Headers/w mufflers.

I had to push up the cam/headers/compression #'s even to get what I did, and here's the result. This is just to show that 420HP is not easily attained with that combo.


If I knew that actual compression and cam specs I could get the Dyno a lot closer. If you don't have headers or your compression is lower or the cam is smaller subtract from this Dyno Run but keep in mind its only a computer program and although useful, not real world as far as exact HP levels but close.

posted by  fc7gtx


Yeah, those hp numbers look right. I would guess that he'd need to run at least 3.73's with a 3500 converter (4.10's would be better).

Looking at your sig, on the other hand, I'd estimate closer to 500hp! :mrgreen:


posted by  DPelletier

Yes, the 3.73's are a great gear and the 3500 'tight' converter would work. He has some work to do but it has potential!! :thumbs:

You are very close, at least according to the computer . :thumbs:


posted by  fc7gtx

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