I posted in the 'general fbody' forum about a mild 10 second ls1 buildup, more or less to see responses on what everyone thought it would take to scratch 10's in the 1/4. Half the people didn't even read what I listed would go in the car, others claimed that my stall was too low, etc, mostly regurgitated information you find all over the internet, which is fine I guess, well, sorta. What did I expect eh?

My main problem has to do with the general thought on choosing the right torque convertor. The general idea of "A bigger stall will give you better times and lower 60.'" is not correct.

You choose a torque convertor stall speed that correlates with your peak torque rpm. This is so when you launch, you are at peak torque, which will provide peak acceleration.

For instance, on a nitrous'd ls1 that is spraying at 3500rpm-6500rpm, 99.9% chance peak torque is going to be at 3500rpm. So at which rpm would you want to launch? 3500rpm. If it was spraying 3200rpm-6500rpm, you'd want to launch at 3200rpm. This means you would want to have a torque convertor that stalls to either 3500rpm or 3200rpm respectively.

There are plenty of heads/cam cars making peak torque at ~4000rpm, and are using ~4000rpm stall respectively, and pulling sick 60' times. But this doesn't mean that a 4000rpm stall would work best for a car that makes peak torque at 3200rpm.

Now picking a torque convertor that has a slightly higher stall speed than your peak torque is not 'bad' to do, especially if it's only 100-300rpm higher, because chances are, the torque will still be 97-99% of the peak torque number, and you'll still get VERY close to your peak acceleration, in fact at this point if your suspension/tires aren't set up perfect you wont notice a difference anyway because you'll never reach full acceleration anyhow.

In conclusion, if you are serious about your times, pick your convertor stall speed according to YOUR engines torque curve, and don't ever think 'bigger is better'.

I hope that my ramblings mean something to someone.

 

I disagree with you.

Personally, I would consider a 4500 stall and start spraying at 4500. You will be able to pill it up a bit without having to worry about killing the motor.

Anyway, with an LS1 that pulls to 6500, you won't be under 4000 RPM much at all. You make more power at 4500 than you do at 3500, right? Doesn't it make sense to keep it in the range where you make the most power?

But what do I know? I was one of the first LT1 impala folks to run a 3000+ stall converter with the stock motor. It actually flashes to around 3800 which is way past the torque peak.

Do you think that if I put in a converter chosen under your logic that my car would still be able to pull 1.6 sixty foot times?

 

The only reason for launching at an rpm that is much higher than your torque peak rpm would be to utilize the automatic transmissions 'torque multiplication' feature for a longer amount of time. For instance on the n2o powered ls1 I described above, launching at 4500rpm would mean that you would have 100+ ft-lbs less during your launch (less acceleration off the line and first 30 or so feet), BUT your torque multiplier will stay in effect longer, so you could make up for "lost acceleration" by maintaining a higher average acceleration.

So I guess I could rephrase the above post and say that the blanket statement "a bigger stall isn't ALWAYS better".

 

You have the concept of torque all wrong.

If you stick to that logic, you're not going to pick the proper torque converter
for your application.

There is a post started by Cajun_Z which is pages long concerning
HP vs. Torque.

http://www.gmthunder.com/main/module...ewtopic&t=4575
http://web.camaross.com/forums/showthread.php?t=228048

 

I think bigger is better when it comes to converters, I have never seen a car go slower with a looser torque converter. Of course there is a limit where you lose streetability and aren't gaining any ET.

You cannot compare a nitrous motor to a naturally aspirated motor as far as choosing a torque converter- its apples and oranges.

3500-6500 rpm powerband would be great, if it made it's peak torque at 3500 rpm and its peak horsepower at 6500 rpm- however I dont think this is realistic.

A car that is peaking power at 6500 rpm is going to be peaking torque over 4000 rpm, probably more like 4200-4500 rpm.