Drag race rear suspension advice needed!

DIV1RACER-2

Well Known Member
Supporting Member 12
Some pics of my car and other coil spring cars , they are hard to stop the RR squating w/ a nearly stock rear supension , i do not have any pictures of Brian's car ... his leaves nearly level; ... Maybe he can post a pic of his car ! :dunno2
 

de31168

Well Known Member
Dan

Explain rear end housing separate from body??

In the simplest of explanations, with the calculator on the website I shared above, the math and geometry will give you a percentage. 100% is perfectly balanced. Anything under 100% means when you launch the car, the rear end will want to come up and compress the springs. This takes pressure off the tires. Anything over 100% and it will want to go down or separate, i.e. expanding the springs therefore pushing the tire harder to the pavement. It doesn't mean its going to throw the rear end out of the car or anything, its very fine adjustments in some cases. GM cars by design always tend to have squat to them or the under 100% style. If you've ever watched a 60's Mopar launch you can see the back bumper actually go up from the track, because they are designed to push the tire down with their setup.

Just because a car has separation doesn't mean it will not still be able to wheel stand and launch like any other car. The only real way to pay attention, if you have a level launch, is to look at the wheel in the wheel well area to see if it is being tucked in or you can see more of the top part of the tire.

Hope this helps.
 

Iowa 409 Guy

Well Seasoned Member
Supporting Member 15
In the simplest of explanations, with the calculator on the website I shared above, the math and geometry will give you a percentage. 100% is perfectly balanced. Anything under 100% means when you launch the car, the rear end will want to come up and compress the springs. This takes pressure off the tires. Anything over 100% and it will want to go down or separate, i.e. expanding the springs therefore pushing the tire harder to the pavement. It doesn't mean its going to throw the rear end out of the car or anything, its very fine adjustments in some cases. GM cars by design always tend to have squat to them or the under 100% style. If you've ever watched a 60's Mopar launch you can see the back bumper actually go up from the track, because they are designed to push the tire down with their setup.

Just because a car has separation doesn't mean it will not still be able to wheel stand and launch like any other car. The only real way to pay attention, if you have a level launch, is to look at the wheel in the wheel well area to see if it is being tucked in or you can see more of the top part of the tire.

Hope this helps.

Thanks, I see. I'll look at the suspension link you posted, on my PC when I get a chance.
 
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Steve "wully bully"

 
Supporting Member 1
Looking at the picture you posted, I would say your lower bar needs to be moved lower in the front. Your upper bar needs to be raised on the rear end housing and lowered on the frame mount. The factory set-up on these cars had a terrible instant center for racing, but ideal for a nice cushy ride. The factory set was well below 100%. Instant center is the theoretical point that these bars would cross if you extended them out. We have found with our car that the instant center should be around the middle to rear of the rocker panel, or lower if possible. We run with about a 110% set up, so it wants to separate and "push" the slicks into the pavement. As Denny pointed out, it is virtually impossible to get these cars to not twist, so when you look at the drivers side, you see excess separation, and on the passenger side you see very little. Notice in the pictures how hard the tire is being squashed. That is the effect of over 100% "anti squat". We have had a best of 1.38 60' times, with a 3680lb car on 10.5 slicks. In the videos we just posted onto facebook from Mason Dixon this past weekend, you can see the separation in action. The video where Philip is in the right lane, which was qualifying pass, he had a 1.400 60' time. In the final, where he is in the left lane, it was a 1.417. These both were with a bog during the wheelstand, which we have been fighting for years. 6-24-2018-MD-533.jpg6-24-2018-MD-534.jpgFacebook Page
 

de31168

Well Known Member
Steve, is yours an auto or a manual trans? I know that is another ingredient in how you'd set the car up because of the clutch settings and the manual leaving harder. Our car is currently set somewhere in the 80% range (all my setup notes are at the shop) and launches similarly with a best of 1.33 at 3605lbs and 10.5 slicks. This past weekend it was in the 1.41-1.44 range because it was hooking so hard it was pulling the motor down. Bottom line for the original poster.. there are many ways to get similar results! Just have to find what your car likes.... and have the adjustability to get it there.

20861946_1414014972046245_4643853817579643874_o.jpg
 

johnnyriviera

Well Known Member
Thanks again for the input! Great stuff!

I have some videos some friends took of the car launching, I will post them when he they send them to me.
My front shocks should be here soon, as many have said I need to get the front dealt with first. The brackets Global West makes lowers the front mounts of the upper arms, and that is still on my radar. Looking to get back out to the track on the 7th.
 

RussC

Well Known Member
Steve, is yours an auto or a manual trans? I know that is another ingredient in how you'd set the car up because of the clutch settings and the manual leaving harder. Our car is currently set somewhere in the 80% range (all my setup notes are at the shop) and launches similarly with a best of 1.33 at 3605lbs and 10.5 slicks. This past weekend it was in the 1.41-1.44 range because it was hooking so hard it was pulling the motor down. Bottom line for the original poster.. there are many ways to get similar results! Just have to find what your car likes.... and have the adjustability to get it there.

20861946_1414014972046245_4643853817579643874_o.jpg

Sounds like you have everything working well. In the dead hook situation you describe...with our stick car...we back the clutch down. We look for two things on launch. First the drive shaft speed needs to jump immediately to 1200 rpm...you have wheel speed. The tire hooks and the clutch separates... the motor stays in the power band...as the motor rpms increase the clutch locks up. The second thing we look for is clutch separation for .6-8 seconds.

Not sure how to handle the dead hook with an auto...probably change the converter... but I don't understand "torque confusers"

Keep up the good work!
 

chevytaylor

Well Known Member
Supporting Member 2
This is a great thread!!:beer

A good way of finding out where your IC is, is to loft it out to scale. For example, I used 5mm - 1". My IC is about 34" forward of the rear axle centre line and about 15" up from ground level and about 8.5"- 9" above the line of force. This is a dead hook slush box car.
 
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Steve "wully bully"

 
Supporting Member 1
We run a Mcleod sof lok clutch and a GForce trans. Russ, yes, I have the clutch set too tight. I plan to soften it some before our next event. With Philip's minimal experience with stick, I wanted to give extra clutch in case he needed to slip it extra driving slow. Also important in this discussion, make sure you have the correct slicks. Never run radials with stick. I am curious to see the videos, as you stated it spins after launch. If you are hooking well on launch, something is unloading the tires, which could be a multitude of issues.
 

RussC

Well Known Member
We don't look for the tire to hook until driveshaft speed is around 1200 happens in the first hundredth.

I know guys running radials with a stick. A soft clutch must be the secret. I'm not trying it.

We run a GF2400...4 speed and a dual 7" from Rob Youngblood. You are right always start with a tight clutch
 

Ishiftem

Well Known Member
Supporting Member 2
I don't have a data logger but I know my car does best if it slips the tire for about a revolution before it its glued to the track. I also know of some people running a stick and radials. You have to dead hook it and it seems the clutch has to be spot on for the track conditions. I'll stick with my stiff sidewall bias plys. An adjustable clutch is like an infinitely adjustable torque confuser..................except it's more fun! That and the fact that an adjustable converter doesn't exist.
 

de31168

Well Known Member
Sounds like you have everything working well. In the dead hook situation you describe...with our stick car...we back the clutch down. We look for two things on launch. First the drive shaft speed needs to jump immediately to 1200 rpm...you have wheel speed. The tire hooks and the clutch separates... the motor stays in the power band...as the motor rpms increase the clutch locks up. The second thing we look for is clutch separation for .6-8 seconds.

Not sure how to handle the dead hook with an auto...probably change the converter... but I don't understand "torque confusers"

Keep up the good work!

Im glad to hear that because that was my next plan of attack, back the clutch off more. However, like Dan, we dont have a data logger either. Just tune from what the tach says on the video and how the motor sounds and tires look and what the time slip says. The guy that did our clutch said he knows we dont want to be in the bellhousing all the time so always err on the tire side instead of the clutch slipping.
 

jim_ss409

Well Known Member
Supporting Member 5
Our X frame cars tend to have the instant center too far ahead, but on many leaf spring cars, the instant center is too high and too far back. Those leaf spring cars will crush the tires and lift the body, but the hit is often too violent, causing the tire to rebound and the suspension to hit the end of the shock travel. That causes lots of problems too.

Leaf spring car...
zcimg363.jpg

If the instant center is way off in either direction, you usually have to tighten up the shocks and use stiffer springs.
If you get the instant center into the right ballpark, the shocks and spring rates become less critical.
 

BSL409

Well Known Member
Supporting Member 6
Dave & Dan I think your rears are more backed haved ? Then the rest of us ware we are hooked at stock upper & lower locations of the control arms. Steve helped me out on my 62 instant center and was spot on! My best has been 1.39 60ft I took those same locations and used them on my 61 with a Best
60 ft of 1.28 so far on 10.5 stiff side wall it can be done !!
 
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