Stall Speed

Squirrell · 03-09-2016, 06:45 AM

Hi Guys, I have a 1990 chevy Beretta , 572 ci bbc made 893 hp and 756 ft lb torque. 5400 stall, Car weighs 2350 lbs , 180 first gear and 3.90 rear gear and 32 x 14 Mickey Thompsons. I am having trouble hooking up on a marginal track, my question is if I change the convertor to 4200 or 4500 rpm down from 5400 rpm will it stop the wheel spin on the startline ?.
If I lower the launch rpm will that have a similar effect or will it flash up to 5400 and still spin the tire.
We found our tire guage was incorrect . The tire was 4 psi higher than what the tire gauge read , ie, 7 psi was actually 11 psi. We have seen better results with the tire at 7 psi on a good track but it will spin on a marginal track.
The engine makes 748 ft lbs at 4600 rpm and 756 ft lbs at 5800 rpm , would a convertor with 4200 stall still behave the same as the 5400 convertor due to the fact that the engine has a lot of torque down low.
Can I achieve a softer hit with simply lowering the launch rpm ?. Still learning to set the shocks .
Thanks in advance for your thoughts Patrick.

Lenny5160 · 03-09-2016, 02:15 PM

Too many variables to be able to provide exact answers, but I think your converter is already way too tight. I'd be shooting for 6200 stall, minimum. You are making the engine work pretty hard by having stall below peak torque. I'd also put some rear gear in it. 4.30 or 4.56, most likely but it depends where the HP fell off which you haven't stated.

Lowering the launch RPM will soften the hit no matter where the converter is. A lot of tube chassis cars work better when you hit the chassis harder on the starting line to make it work. You can soften the hit with 4-link and shock settings, if needed.

Squirrell · 03-10-2016, 07:20 AM

Hi Tony , thanks for the reply. Max HP was 893 at 6800 rpm. Engine has an 1150 carb but with a 1050 it still made 700 ft lbs at 4200 rpm. Heads are AFR 335 cc. Chassis is a pro stock chromemoly.
We have tried a few 4 link settings and yes still learning the shocks. If we set the launch chip at 4200 , the engine will still flash to 5400 the limit of the convertor but because the trans brake has been released at 4200 will the hit be softer?. Hoping to test the car soon. Remember we are trying to get down a loose track. Interesting you suggested going to 6200 we have tried that and car does great wheelstands but I thought it would be way to aggressive for the loose track.
Thanks again Patrick.

Lenny5160 · 03-10-2016, 11:55 AM

A tight converter will almost always be less consistent than one that is 'correct' (definitions may vary) or a little on the loose side. A loose converter can also be less aggressive on the starting line even though the RPM is higher.

The 'hit' will be softer if you lower the chip, no matter what the converter flash is. The car will begin moving while the engine gets up to the flash point, which will take some bite out of the actual hit when the engine reaches the converter flash stall point.

How you want to set up your car depends on a lot of things. I don't know how bad this loose track is and what percentage of your racing will happen at that track. Looking at it from the outside, my thought is to optimize your combination for a good track and, once that is accomplished, do whatever you need to do in order to make it work on the bad ones. That could be a shock adjustment, pull timing on the starting line, lower chip, shift 0.1 seconds into the run, etc...

rodrocket · 09-22-2016, 08:03 AM

Patrick

Have you tried pulling a couple of degrees out of it on the launch & ramping it back in over 0.5 of a second

03-09-2016, 06:45 AM	#1
Squirrell Junior Member Join Date: Apr 2013 Posts: 33 Likes: 0 Liked 0 Times in 0 Posts	Stall Speed Hi Guys, I have a 1990 chevy Beretta , 572 ci bbc made 893 hp and 756 ft lb torque. 5400 stall, Car weighs 2350 lbs , 180 first gear and 3.90 rear gear and 32 x 14 Mickey Thompsons. I am having trouble hooking up on a marginal track, my question is if I change the convertor to 4200 or 4500 rpm down from 5400 rpm will it stop the wheel spin on the startline ?. If I lower the launch rpm will that have a similar effect or will it flash up to 5400 and still spin the tire. We found our tire guage was incorrect . The tire was 4 psi higher than what the tire gauge read , ie, 7 psi was actually 11 psi. We have seen better results with the tire at 7 psi on a good track but it will spin on a marginal track. The engine makes 748 ft lbs at 4600 rpm and 756 ft lbs at 5800 rpm , would a convertor with 4200 stall still behave the same as the 5400 convertor due to the fact that the engine has a lot of torque down low. Can I achieve a softer hit with simply lowering the launch rpm ?. Still learning to set the shocks . Thanks in advance for your thoughts Patrick.

03-09-2016, 02:15 PM	#2
Lenny5160 Senior Member Join Date: Nov 2015 Location: Inver Grove Heights, MN Posts: 898 Likes: 604 Liked 431 Times in 224 Posts	Re: Stall Speed Too many variables to be able to provide exact answers, but I think your converter is already way too tight. I'd be shooting for 6200 stall, minimum. You are making the engine work pretty hard by having stall below peak torque. I'd also put some rear gear in it. 4.30 or 4.56, most likely but it depends where the HP fell off which you haven't stated. Lowering the launch RPM will soften the hit no matter where the converter is. A lot of tube chassis cars work better when you hit the chassis harder on the starting line to make it work. You can soften the hit with 4-link and shock settings, if needed. __________________ S/ST 51 S/C 53

03-10-2016, 07:20 AM	#3
Squirrell Junior Member Join Date: Apr 2013 Posts: 33 Likes: 0 Liked 0 Times in 0 Posts	Re: Stall Speed Hi Tony , thanks for the reply. Max HP was 893 at 6800 rpm. Engine has an 1150 carb but with a 1050 it still made 700 ft lbs at 4200 rpm. Heads are AFR 335 cc. Chassis is a pro stock chromemoly. We have tried a few 4 link settings and yes still learning the shocks. If we set the launch chip at 4200 , the engine will still flash to 5400 the limit of the convertor but because the trans brake has been released at 4200 will the hit be softer?. Hoping to test the car soon. Remember we are trying to get down a loose track. Interesting you suggested going to 6200 we have tried that and car does great wheelstands but I thought it would be way to aggressive for the loose track. Thanks again Patrick.

03-10-2016, 11:55 AM	#4
Lenny5160 Senior Member Join Date: Nov 2015 Location: Inver Grove Heights, MN Posts: 898 Likes: 604 Liked 431 Times in 224 Posts	Re: Stall Speed A tight converter will almost always be less consistent than one that is 'correct' (definitions may vary) or a little on the loose side. A loose converter can also be less aggressive on the starting line even though the RPM is higher. The 'hit' will be softer if you lower the chip, no matter what the converter flash is. The car will begin moving while the engine gets up to the flash point, which will take some bite out of the actual hit when the engine reaches the converter flash stall point. How you want to set up your car depends on a lot of things. I don't know how bad this loose track is and what percentage of your racing will happen at that track. Looking at it from the outside, my thought is to optimize your combination for a good track and, once that is accomplished, do whatever you need to do in order to make it work on the bad ones. That could be a shock adjustment, pull timing on the starting line, lower chip, shift 0.1 seconds into the run, etc... __________________ S/ST 51 S/C 53

09-22-2016, 08:03 AM	#5
rodrocket Junior Member Join Date: Sep 2008 Posts: 37 Likes: 1 Liked 0 Times in 0 Posts	Re: Stall Speed Patrick Have you tried pulling a couple of degrees out of it on the launch & ramping it back in over 0.5 of a second