Torque/Stall Converter Considerations

I know you mechanics out there know this, so this is for us “Laymen/Do it yourselfers”.

There are more than a few options out there available for Torque Converters. Everyone has heard of B&M Trans and TCI is another great option for converters that will be mated to a performance built engine. There is also a need to find a quality replacement if you are content on keeping a stock powertrain. After doing research for my own build, I thought I'd share a few things I've learned & some links that were very helpful.

If you are installing a new "performance" cam in an engine build, chances are you'll need a new converter so you don’t toast your transmission. If the stall speed is too low (or too high) the converter will overheat the transmission fluid, especially if you are just cooling the trans only with your radiator. The key is to find your "optimal range" for this power to transfer properly in order to avoid problems.

I've discovered that the stock converter that is currently on my TH350 will have a stall speed that's approximately 1000 RPM's to low to support my (fairly mild) engine build.

Your cam's peak torque number, your intake valve duration, your rear end gear ratio and tire sizes are all determining factors you need to consider when choosing a converter. When you get a new cam there is a "cam card" that should come with the parts. These are also available online at most reputable manufacturers’ websites as well as "dyno" test information for the particular cam's configuration. For my new cam I’ll need a 2400 stall speed & the original GM converter I have is factory rated at approx. 1400 RPM.

Here are examples. (This is the cam I’m using, not too radical & makes excellent torque @ slightly over 410 ft lbs)
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=86&sb=2
http://www.compcams.com/v002/Pages/388/XE268H-10.aspx

This is a good link to the OEM style units. "Precision of New Hampton" sells through authorized installers or resellers. You’ll have to call to find someone in your area. They also sell performance built units as well. You can look up what you should have by the year & Tans type.

Precision OEM style for GM:
http://www.gopnh.com/Automotive-Manufacturer.cfm?Manufacturer=General%20Motors
Precision Performance for GM:
http://www.gopnh.com/Street-Performance-Stall-Converters.cfm

Here is what I've considered on my build from these two well known manufacturers. After verifying the cam spec's above, I've decided to go with the TCI "Breakaway" type as they are a "stepped-up" version of the factory unit and really all I need. There are other manufacturers out there also and some "racing" supply company's even have their own name brand units.

B&M Racing & performance converters page
http://bmracing.com/?page_id=50
B&M Application guide:
http://bmracing.com/wp-bnmcont/uploads/torque_converter_application_chart.jpg

TCI
http://www.tciauto.com/tc/torque-converters/street-strip.html/?main=1

A much needed upgrade for anyone doing even the smallest upgrade! I currently run a 2500 stall in my elco, and had a 3500 stall behind my big block in my chevelle. I would even recommend one for a stock engine (obviously a smaller 18-2000 stall), as it helps the tranny and helps to shift the power band to a more usable level.

how do you use this info to decide on what stall to get? I am running a ZZ430 engine with a 200-4r trans and 3:73 gears...if this helps. Right now I am also running stock 15" rally rims but I would have to check on the tire size.

Look up the specs on the zz430 cam & note the Peak Torque RPM- in other words; when your cam makes its maximum amount of torque- what RPM is the engine spinning? That will give you a rough idea. The application guide from B&M should help but it's always a good idea to call or e-mail one of the manufacturers to get a recommendation with your specific information as listed above.

The ZZ430 has the GM hot cam in it. I believe the max torque is at like 5600rpm's or something.

My small block will make 413 ft lbs of torque @ 3800 RPM even though the cam will spin to 5500. I don't know the specs for the GM cam in your motor- just using my own build as a guide for others.

If your max torque number is achieved @ 5600 rpm then your motor is probably spinning way more RPM's than mine will. You'll probably end up in the 3000-3500 stall speed range but again- best to check with the manufacturer of the converter with specific info.

I hate to give info from memory; or lack of it. I will look up my dyno graph and see where I hit max torque. I know the cam was good up to 6000rpm's. I thought the torque has pretty high up there also. But let me check. Thanks for all the help, so far.

I hate to disagree with solid info, but I look on this issue a little differantly. You have to consider how the car will be used. Will it be an out and out weekend warrier or will it be a daily driver or will it be a combo of the two where it will be used as a cruiser "look at me" car. When My car was first built I had a 3,000 RPM converter, but I use my car as a cruiser and it has never been on the strip...yet. Whenever I would pull up to a stop sign and take a right turn I would have to give it a lot of gas and it would do nothing and I would keep increasing the gas and then all hell would break loose. I went back to a 2,300 converter and the problem went away. Now if I was just a weekend warrier I could have even went higher than the 3,000 converter, but it would be dangerous on the street. My cam is a very hot Comp roller cam, i forget the specs. JB

That cam making 413 ft lb in a 350 small block is very impressive. In my opinion HP without good torque is not what we need.
I haven't used any of Comp Cams later grinds, but used a bunch of their Magnum series cams.

I liked the choice of this cam & I'll be the 1st to admit that my engine builder helped a lot & knew exactly what to pick for my 4200 pound "mid-sized" car.

It'll be interesting to see how it sounds compared to the stock cam that was in the engine. The "XE" grinds are newer & he considered my cam "pretty tame" compared to what's out there these days. But he promised it would sound really good. We'll see soon enough.

I know we all want to maximize our torque output of the engine, but I'd say the best answer for choosing the proper stall speed should be based on the type of driving that will be done. For daily driving, and no racing, I'd suggest 1800-2000 stall, for performance driving I'd go 2200-2500, and for street and strip action I'd go 3000-3500, and all out strip only, 3500 on up. If you choose a stall convertor based on that, than obviously you got the cam, heads, gears, and carb. to go with that type of driving you will be doing.

Paul -

I would NOT run out and buy a converter until you drive your car with the new powerplant.

Check out this article:
http://www.pontiacstreetperformance.com/psp/twisting.html

It's based around a Pontiac but converters function the same for all. It will fill in the gaps on how things work.

Thanks -

Jerry

Thanks for that, it was a good read. Somewhere out there there must be a mathematical formula to figure out all the "variables", which would probably involve some algebra. LOL

I did plan on using the TCI unit & I'm fairly sure it'll fit the bill- but thanks to that article- I'm going to double check B&M and some others to see what if any differences in recommendations there might be.

I'll have to get it right. I appreciate the advice & that I should drive the car but I'm not keen on removing the Trans & TC once everything is put back in the car.

What rear axle gear are you running?

3.08