big end tire spin

We are having a on-going problem with tire spin downtrack in my son's pro-mod chassis. Power is a 548 bbc w/8-71 at 20# of boost. Trans is a B&J 3 speed with converter drive and 4:56 rear gears,& 34.5 Hoosiers. Just before the shift to high gear the tires start to spin and continue through the traps. I'm going to put some more wing in the car and lower the tire pressure to 5 1/2 #. Just wondering if anyone has other possible solutions. He does not have any system to take timing out at this time. He is also using a msd 7al-2 ignition which seems to be working very well. Best et is 7.29, but skating all over the place. Launching at 4400 on trans brake. Any help will be greatly appreciated. Thanks, Les

 

Try this forum: http://promodzone.com/forumindex.php

 

Les, what do you have for a chassis, and more important, who's shocks/struts do you have. I would make sure you have the car set up correctly before you try to take power away. While there are times that adding wing and taking timming away are the correct choices, remember that most teams that are running well are looking to make more power and spending time learning to apply it.

Pirate

 

you could probley do it with the four link adjustment to keep the tires planted

 

tire spin downtrack

Thanks for the input guys. I must confess I don't know much about four-link, as I have always run solid rear in altered and dragsters. What type of adjustment will help stop spin on the big end? The car launches straight and stays untill it starts to spin. 60ft is around 1.11. The car stays hooked up until the top of 2nd gear. Can you suggest which way to go with adjustment?
The corner weights are right on. Could we possibly need more tire speed to get up on the tire sooner? Thanks, Les

 

I think it is a shock or wing issue, not a 4 link setting.

See what Mike Canter says when he checks in...

EDB

 

depending on the weight of the car you may need to go up on the air presure to make sure the tires are not rolling up in the center some times more air presure will give you a better foot print any way it could be several things try the things that dont cost money at first before you spend alot of money on the shocks once you understand the way a four link principle works there are many adjustments to help you out from the starting line to down track

good luck jim

 

Thanks again guys. The chassis is a Pro-Max Venom, built in Clinton, Tennessee. The shocks and struts are from Strange. One more thing to add, we are getting ready to change rear gears from 4.56 to 4.29. Also in a photo a friend took, at a distsnce past the 60ft.line the rear tires were still so wrinkled you could not read the Hoosier name. As the car seemed to be really hooked up and didn't shake, I don't know if the wrinkleing is significant. How soon should the car be "up on the tire"? Will adjusting the 4-link help on the traction problem down-track when the car is leaving straight and not moving around untill the half-track point? We won't get to try another run until the third weekend in August so hopefully we'll get this figured out. All input greatly appreciated.

 

Where is your IC Point? If it is long and low, the car can have a tenacy to spin down track. Espescally if it is a front heavy car

 

the 4.29 gear will be a better gear i would think in my opion you should already be up on tire before then which needs to get the wheel speed up converter ( torqe multiplier )cars can be trickier to get down the race track a 4.29 will calm the car down leaving should help get up on the tire

IC -INSTANCE CENTER -WHERE THE TOP BAR INTERSECTS WITH BOTTOM BAR

amagine 4-link in an easy terms its a trick way to think of making 3-link longer are shorter by either bringer the top and bottom bar closer together are futher apart and where they intersect tells you were the leverage is are instance center thats just my opion and how i look at it and remember you can get way off base messing with the 4-link if your not careful a small adjustments can change alot

 

Unless your 4-link is way out, and I mean wayyy out, it’s not the problem. The changing of the gear is not going to be of any help either. As Jim said this is strictly opinion as I am not there looking at your car. What is the history of your rear shocks. Are they Elec. or Pneumatic. What is the spring rate, and what are the settings on the comp. and rebound, assuming they are dbl adj. It sounds like you need to loosen up the rebound. I am not a fan of Strange stuff, but you should be able to make it work safely.

Take a peek under the car and make sure the bottom bar isn’t pointing to the ground, or up at the sky either. It should be somewhat parallel with the car. The instant center should be up in the middle of the car, to the firewall somewhere. The shorter the IC, the more aggressive it is. All cars and combos are different, and the answer that you need on your final settings won’t come from this forum as there are too many variables.

One last thing, make sure your tire pressure gauge is good. When you have figured out what your car likes, it’s just a number, but when you are trying to figure out a problem it becomes more important. It sounds like you really need to add some air to the rear tires as a converter car generally doesn’t hit the tire as hard as a clutch car.




Good Luck

 

well said if the car worked before the 4-link hasnt changed its hard to help when your not there watching the car are looking at the underside such as the shocks, spings , air preasure ,there are so many varibles

what low gear is in the car a 456 seems lowto me i ran a blown chevy years ago started with 4.56 gears and you couldnt hardly drive the damn thing spinning ,skating all over the place are shaking my brains out went to a 4.30 it calmed down and went faster good luck with what ever you do

 

Compare your tire gage with someone elses? We had a shake problem earlier this year, turns out my moroso gauge got beat up over the winter and was showing 8, was really 6.75