My buddy has a big block and his tranmission guy says lower stall for drag racing.
 

Hey LT1 guys help me understand something. I am tired of argueing with my buddy. But his tranmission guy says that a lower stall is better for drag racing because you don't want a loose stall because you are losing horsepower. My buddy's engine makes 500lbs of torque at 2500rpms and 600lbs of torque at 4400rpms at the flywheel. The tranmission guy says he needs a 2500 stall. Why would he say this for drag racing? Wouldn't he want close to a 4000 stall since it is near his peak torque. Am I right or is the transmission guy right? Also this is based on that he can get traction.

Also please don't say it depends on gears, weight, etc. or that a big block is different unless you can explain why. Because if you want a 2500 stall, the reason your converter builder needs the gears, weight, etc is so that they can build the converter correctly so it will stall at your requested rpm. The gears, weight, etc is not going to make a 2500 stall beat a 4000 stall as long as you can get traction.

I do not disagree with the transmission guy, since as you say "if you can get the traction"
Theres part of the picture missing in your post. What is the rest of the setup such as suspension and tires etc. Maybe he sees the greater benefit of the lower stall based on what he has in front of him.

In my humble opinion, theoretically the higher stall may the the correct choice, practice however can be slightly different.


my $0.02

If it makes a crap ton of torque down low then maybe he doesn't need to rev higher to get in the fat part of his torque range. And it's going to slip that converter pretty good with all that torque anyway. Maybe that's what he's talking about.

But the transmission guy is basing it off that he can get traction. Because he said the higher stall will help with your 60' and take off but you will lose the race at the end of the track. I hope you see this, I forgot to type that in my first post.

Interesting.... but does not belong in "LT1 Based Engine Tech".

Moving........

I run a loose 3600 stall on my 383 stroker. You want the estimated stall to happen for maximum torque. If the big block make power at a lower rpm a lower stall is appropriate. Traction, in my opinion, is whether or not you can utilize the torque efficiently.

Yes there are other variables such as gearing and tire size to be considered if you want to do it the proper way, but informally you simply want to maximize the hp the engine makes for maximum torque. The other choice is whether or not you want a lockup or non-lockup converter and that choice will also need to consider whether or not the car sees any street duty.

The 4000 stall will be closer to correct. Any decent converter builder will want
a lot more information about the engine and car though. Engine Dyno sheets
are the best way. Weight, gearing, tire size, camshaft profile, etc. all play a role in determining the best converter set up. But the short answer is still the
4000 stall is the better choice.

Talk to the converter manufatcturers. They will likely side with you, as would I, and I build transmissions as well. Ive worked in a few shops that had pro drag cars in both outlaw class and a rail car that ran 7's. Like others have stated, I was taught you want the converter to stall at or near peak tq, by an engine builder thats been in the game longer than I am old, and the owner/operators of the other stated dragsters. Sounds like this guy is basing his opinion on something else, or hes just an idiot.

In general, a loose converter is bad, and so is a tight converter. The optimal choice no matter what gearing, weight, vehicle useage, etc is for peak ENGINE tq. As the O.P. stated, the other variables you guys are mentioning are for the converter builder to accurately stall your converter for the load you put on it from both ends. Now if the car is handicapped by traction or whatever, then thats a WHOLE diff. story. Having a stall at peak tq allows the vehicle to get moving faster and pull as hard as it can out of the hole and get you down the track. Now a poor converter thats not efficient after the initial launch may very well slow you down afterwards because its not transferring all the energy. Think about it this way; If you had a stick, and yer at the line waiting to launch, considering you have great traction, are you going to let the clutch out early and let the engine bog out? Of course not, but if you rev it to where you know its making peak tq and then dump the clutch and hook, its bogs a tad and then pulls like crazy. This is what your after with the stall.

Im guessing hes basing his opinion/choice upon this as well as the fact that we all know a converter has the tendency to flash higher than the stall rating on the launch. So IMO, he may not be entirely wrong about a lower stall making the vehicle a little quicker in the 1/4 mile. Hope this didnt confuse the situation as I know alot of folks dont really understand how converters work. To summarize, if the engine makes peak tq at 4k stall, I would probably have them build the converter to stall at 3800. If its a little loose yer still ok, if its a little tight, you can decide to re-stall it or let it ride. On the other hand if you ask for a 4k stall and its loose, you have no choice as it will feel like a dog, like the trans is slipping its ballz off, especially out of the hole. So I would guess thats what the trans. guy is trying to say.