Stall speed

[Harris]

Hello All,
Another question. I'm putting a beefed up C4 behind my 347 stroker motor (being built) The Ford cam calls for a manual transmission. For many reason, mainly foot box room, I am going to use the C4. I haven't weighed my car but I assume around 2500 lbs+-. I don't know what stall speed converter I should use. I'm also guessing I have a 3:50-3:70 final drive Ford 9" rear end. I don't anticipate any track use. Just for cruising, but with the ability to hold my own with almost anything. Have had suggestion of 3000 , but I think 2000-2200 would be better.
My engine should put out 450 HP. I want to be comfortable cruising the freeways at 65-70 mph. I will put a trans and oil cooler on the car.

Thanks in advance,

Larry Harris

[Tom Wells]

Hello Larry,

Stall speed is a tough one because there are so many factors. Here's a URL that might get you started:

Torque converter intro

Beyond that I'd suggest you go on line to the various torque converter mfrs. Most of them have a form you fill out and submit, and then they recommend a stall speed.

It'd be especially enlightening I suspect, to give several of them your specs and see if the recommendations come back similar

Here are a couple of mfrs to get you started:

Performance Automatic

Edge Racing

There are plenty of others too such as B&M, TCI etc etc.

Hope this helps!

Tom

PS: I ended up with the Edge unit after having problems with the TCI. So far, so good

[Mr.Fixit]

Anything over 2500 is not really good for the street. I run a 2600 stall in my chevelle, it is almost too much stall speed for around town driving. The car gets up and boogies with a 3500, but that doesn't work out well in the real world. You need less stall speed cause your car is light

[GREENSNAKE]

Hey Larry! What cam are you using? The B, E,F,X,or Z Motorsport cam? Im running the F-Cam in mine but have the C-6 behind it. My stall is 2600-2800 Works great ! But just Bought a Built C-4 and im running 3000 Stall now ill see how it does and let ya know Later (Greensnake)

[donjohn]

I have a 3000 stall in my car it works great 390 C6 with shift kit

[Excaliber]

WHOA!!!! If your rear end ratio is that low you will really be disappointed with the HIGH rpm you will be running on the street! Automatics have a high slip ratio in 1st and 2nd and if your not using a lock up torque converter the slip ratio still applies in third.

Slip ratio: Motor rpm turns the torque converter and the converter turns the trans gears. Figure 10 to 15% "slip". That is why auto trans cars ALWAYS come from the manufacturer with a higher rear end ratio than a stick shift.

Stick might be 3:50, auto will be more like 2:73, a BIG difference! You need to NAIL DOWN that rear ratio before you can begin to calculate stall speed! With a really low rear (3:50 to 3:70) I wouldn't go with a stall beyond STOCK! As far as that goes, I wouldn't use a rear ratio THAT low with an automatic unless I was strictly drag racing!

Am I a pain in the butt or what? Hey, just adding my 2 cents, lol.

Ernie

[HighPlainsDrifter]

Larry,
A couple things determin the stall speed. Converter size; 12"-stock, 11" street performance, 10"- street strip, 8 or 9" race converers. Take a 11" street performance converter, the vanes inside can be angled slightly different so that it is rated at 2400 to 2800 rpm. That doesn't mean it will stall at that point , engine torque and vehicle weight determine where that converter will stall. A light car 2,200 lbs will not stall as high as a 2,800 lb car,you don't load the converter as much. The other big factor is low end torque. My big block makes over 500 ft/lbs of torque right at 3,000 rpm,thats where my coverter stalls. Put that same converter behind a stock smogger 220 hp big block and the torque is 360 ft/lbs and will stall about 2,500 rpm. Your 347 should make decent power at 2,500 rpm but not huge torque numbers, so you could go with a 11" street converter rated at 2,400 to 2,600 rpm and still lock up at freeway speeds, just run a good B&M 18,000 lb trans cooler. I have no problem with my trans temperatures.
Good Luck,
Perry.

[dkjos]

Larry,

From all I have read and heard, the C-6, while it is a strong piece, will soak up a lot of horsepower(like 75 HP) unless it is "rollerized". Why don't you take a look at Lentech and Baumann Engineering to see what can be done with the Ford AOD/AODE. They will give you lower parasitic losses and the advantage of an overdrive top gear.

[boxhead]

Listen to Excaliber, with that type of ratio in the final drive you really would be better of with a lower stall speed especially if you will use it for street driveing mainly
Also with a diff ratio like yours and a hi stall speed you will be creating alot of heat in the trans, so make sure you fit a good quality cooler with a hi flow rate.
Also the lower stall speed will improve the fuel economy.

[speed220mph]

I haven't read all the suggestions, but the answer is simple: Go with a stock stall speed simply because of the Cobra's light weight, certainly not over 2,500 rpm. You won't be sorry.