I've always heard that you want the torque converter to stall to the torque peak of the engine. Makes sense at first glance, but. . .

There's a local guy that's gone 11.4x with a stock cam, head, intake LS1 and a Yank 4500 converter. I'm pretty sure that's higher than the torque peak of the engine and it works outstanding.

My Vigilange "2800" stalls to 5400 when I run 18 - 20 psi boost. I was just about to change it to a "2400", when I realized that it may not be the best thing.

Would you want engine to spend more time at peak hp (looser converter) or peak torque (tighter converter)? I know they gear race cars so that the engine spends it's time around peak hp, but would that be the case with a torque converter?

Mike

 

You can't generalize. If you already have traction problems, you may want to be well below your peak torque, and so on. But for max accelration, assuming you have the traction, most people say it should a few hundred rpm below peak torque. Doesn't always work that way though.

BTW: this probably belongs in "Drag Racing".

Rich

 

The "few hundred below peak torque" is a good ballpark figure. The stall rating given by the manufactuer is only an estimate. A 2800 stall converter may stall at 2400 behind one engine and 3200 in another. It just depends on how much torque is being put into it.

The only way to know the converters true stall speed is with a transbrake. How do you get a 2800 converter to stall at 5400?

My 8" converter stalls at 5700 on the transbrake but I only launch at 4500. The engine peaks the torque around 5000

 

Rolling along at 30 mph in Drive with 2.73 gears, a TH350 and no kickdown cable. Hit the gas and the tack goes to 5400. Coincidentally, all of my chassis dyno runs don't hit peak torque until 5400.

Sounds like your converter stall is 700 rpm over your torque peak. Seems contradictory to your earlier statement.

 

I was told by PI (makers of the Vig) that for a street/strip car, the stall speed should be around 900 rpm below the torque peak...This is just a general guideline, but its worked fairly well for me...

--Alan

 

Well. . . with a turbo, I don't have to worry about it being a "street" converter. It will drive like any other 2800, but stall much higher when you 363 cid @ 20 psi through it.

 

The first statement also said a ballpark figure. It's not uncommon for a Stock Eliminator or Comp eliminator car to have a 6000+ converter and a 7000+ red line.

I only need peak torque to launch the car. A lot of energy is needed to get a heavy weight moving from a dead stop. After that I want the engine rpm to stay closer to the peak HP numbers because hp is the time it takes to do the work (torque). The higher the HP number, the faster the work gets done. Staying at that high number longer means a quicker run.

Watching my playback tach, the rpms never go below 5500 rpm during the entire run except during the launch.

 

I learned just from talking with guys at the track over the years in some pretty radical cars that typically these guys get a stall around 2000 rpm below their shift points.

 

Sometimes you have to ignore the peak stall numbers. What is really important is the effective stall which pits the weight of the car and the total gearing against the engine torque.
The effective stall is the rpm at which the car just has to move. There is enough power there to overcome the weight thru the gearing. You can have a converter that brake stalls against the trans break at 5700rpm that will drop to 4500 the second that you let off of the brake because the car is moving or the tires are spinning.
My formy with an ST3500 would only stall to 3100 or so in 2nd on the foot brake. Now at the line it would only come up to 2800 max and my logs showed no increase after that. I had to have it loosened up to get the effective stall that I needed.
With all of that being said I would say that your effective stall is too high and that you're car would probably accellerate better with a tighter converter, but it's going to be harder on the tires.