c3_dk

Hi,

I have a friend that has a 1971 Corvette, he would like to have a new converter.

Today he has 3.08 rear, but maybe it will be 3.70 soon.

Can anyone tell me what stall speed would be correct for him? (stall speed if he goes for 3.08 and if he goes for 3.70)

The car is a street fighter, 0-60 mph car, not 1/4 mile/race car.

New 383 engine.
AFR 195
EZ-EFI 1.0
Comp Cams 12 466 8
1.6 rocker arms
G-team 7530 intake
Headers and 2½" exhaust
TH400 transmission, with shift kit installed.
3.08 OR 3.70 rear
255-60-15 tyre

Thx,
John

C3 Stroker

If the only change is the rear gear ratio, there is no reason to change the stall speed converter. The converter should be changed to match the engine characteristics......specifically, the cam. Some cams require a higher stall speed to keep the engine's RPMs OK at idle, especially a street car.

You list a performance cam with your specs........Comp Cams specs that cam as 1800-5800 rpm range, their largest recommended for a stock converter. A 2500 rpm converter will give you more "zip" out the hole and will probably be more fun than stock, but is not mandatory regardless of which rear gears you choose.

Grumpy 427

A 10" 2500 stall will work. The 383 will make some torque, so converter will most likely flash to 2800-3000 and still be tight enough to drive around without making too much heat.

TimAT

And the higher stall converter will generate more heat, making trans temperature a factor- as in a temp gauge, bigger trans cooler and more frequent fluid changes.

You can pickup a little bit by putting a converter from a TH350 equipped car in that TH400..

TedH

Agree. Unless the new cam says higher stall, the stock 2000rpm converter in your vette will launch hard. It will even like the better gears. Save yourself the added heat unless you need an even harder launch. But, you may have more breakage (half shafts, diff, etc.) to consider if you boost stall speed above 2000rpm.

I run 2000rpm stall with 700R4, retro roller cam, 3.54 gears in my warmed over L48 (haven't installed the 4-bolt yet). It launches HARD (good) from a dead stop and runs like a scalded dog. Barks/spins thru 1-2 shift too.

c3_dk

Thx all.

So you are saying 2000 would be fine, but he can go to 2500, but it make a bit more heat = add a cooler.
The converter he has today is the factory 71 converter.
If he decides to go for the 2000 stall speed, will it then be better to buy a new modern 10" with 2000 compared to the factory 71?
If yes, what will he gain?

I tought the factory stall speed was 1400 or 1600, but it's 2000?

HeadsU.P.

I'm with you. I thought factory stall was 12-1400. A 2,000 is aftermarket.
And if you were to go to all the trouble of pulling the convertor, I sure wouldn't buy & install a different GM unit just to save a few bucks over after-market.

c3_dk

The engine is on its way out, it's a 350 today, but will be a 383 soon.
So he is in there anyway.

Grumpy 427

More torque will make a converter flash higher. In my 80 vette, i have a stock lock up converter the local tranny shop reworked to stall at around 2000 rpm. I have an external trans cooler just to keep the trans heat out of the rad.

My duster i have a 10" TCI 3500 stall flashes to 4000 drives fine on the street doesn make any more heat. Once to get into the 8-9 " inch units 4500 stall and up you need to worry about heat.

I had a Coan glide in my 77 BBC Camaro with a 5000 stall and a brake. After a couple passes the trans temp got warm, but not overtemp. I had a gauge tapped into the pan. drove that on the street with no issues.

7t9l82

I run a 9.5 in 2800 Stahl with 3:55 gears it takes drag radials to keep from destroying the tires. The smaller diameter cuts rotating mass and the engine revs quicker making just driving around snappier. Just more to consider

BKbroiler

This is an often overlooked advantage of higher stall speed converters, with smaller diameter and much less weight.

63mako

TH400 trans in Corvettes was a 2000 stall factory. Other uses were lower stall. That cam is an 1800-5800 cam in a 350. In a 383 drop that 300 RPM at least. I would not touch the convertor. A TH 400 with a shift kit and that engine will be a beast with the 3.08. It will be noticeably better with the 3.70

C3 Stroker

I used a 2500 rpm 10'' TCI in my 383 before eventually a custom Art Carr 3000 w/4300 flash. The 2500 was great on the street and drove like stock. It enabled the engine to idle without surging, and gave me a great holeshot. I did install a trans cooler. You may not have problems, but heat will increase if only a little. I'd recommend a cooler with any converter upgrade from stock.

REELAV8R

Couple of reasons for a higher stall as a street motor.

One is to get the engine farther up in the rpm range where it’s developing more torque for more power to the wheels.

Second is to allow an engine with a large cam to idle.

Neither of these seems to be an issue with the cam spec’d for this engine.

I would say the cam is relatively short for a 383 so it will develope lots of torque down low. DCR should be computed to see how high it’s gonna be based on the CR so as to not have issues with detonation.
It should also idle very easily and not require a higher stall converter.

c3_dk

Again thx all !!

So lets say he keeps it @2000 (I think he will, when he reads this)
But will he benefit anything buying a new converter, and go down to 9.5 or 10"

c3_dk

Or will there be any benefit from buying a new factory 2000 stall converter (can a converter be worn out?)

c3_dk

DCR = 8.37 with 1094

Dyno says (again with 1094):

REELAV8R

There would be a benefit in buying a new converter just from the technology in a modern converter.
Less slippage better more rugged construction.
A torque converter of the 70's is likely less efficient (more slippage) and may not be able to handle the torque developed by the new engine.
A new torque converter should be furnace brazed, have a anti-balloon plate or at least a larger hub center and will handle the torque of the new engine.
Your current 2000 stall converter may not stall until 2800 with the 383. Stall depends on the torque developed by the engine.

Personally I would not use a stock unit on a much higher powered 383.

REELAV8R

Lots of torque to spare down low peaks near 3500 and starts falling off at 4500. HP starts falling at about 5500.

So it could use a longer duration cam or a narrower LSA if a guy wanted and get the torque peak around 4200 or so. Allowing the HP to climb all the way to 6000 to 6200.
Just my personal preference really. I feel one of the advantages of greater displacement is being able to run a bigger cam and not lose the bottom end in the process vs a smaller displacement.

DCR looks good as long as aluminum heads are used.

I'm running 8.8 DCR but at 3500 to 5500 feet and have no issues with detonation even on 87 to 88 octane.

c3_dk

This is with 12 66 8 (EFI cam due to EZ-EFI 1 installed)