Unloading the rear tires

[imjoesnuffy]

Leaving off the foot brake, car leaves hard. Will even pull the front tires, if at a good track, an inch or two. Leaving at 14 psi, it gets to whatever boost I am set at pretty quick. About 20 feet out from the line as soon as the front end settles back down the rear tires unload and spin. Looking for advice on how to fix it, or I am stuck at 1.50 60' times forever.

275 MT ET streets, Solid tubular lowers and double adjustable uppers, Hellwig bar, QA1 single adjustables on all four corners. Stock original springs all four corners. -4 pinion angle. I have tried all three positions on the Hellwig bar and the car seems to like the middle one best.

Doesn't seem to matter what shock settings I try, it will unload 10-20 feet out, if I leave hard every time.

All four shocks on 1 netted a 1.50
LR 1, RR 4, LF 4, RF 1 1.54
Every other setting I have tried I just spin. I have played with tire pressure from 16-24 psi as well.

Is this a boost control issue, where too much power is being applied too quickly?
Front shocks worn out?
Or do I need to start looking at different setup? Coilovers, DA shocks?

 

[Fachie Motion]

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[Chuck Leeper]

Start with some videos..From the rear, side.......

QA1 singles adjust the extension and rebound to the same settings. Running the rear near full loose, may cause insufficient control...[Squat, then extend.] Remember, girls squat, racecars don't. Videos will allow a longer look at how the suspension is working. [Or not.]
Any data logs?

 

[Scott Atk]

Slow down extension on the front shocks. If you set them real loose it will rise quickly but it takes a bunch of horsepower to keep the front end up. How's the anti-squat? Like Chuck mentioned, you don't want to see the rear spring compress on launch.

 

[imjoesnuffy]

Let's see if I can get this attached. Here is datalog from last night. Left pretty hard, then spun. I had to lift, so it upshifted, then down shifted, so disregard the false knock.

I have video from last year, but I need to edit/compress the file. I don't have any recent video from the right rear. In the video it doesn't spin much but you might be able to see what the suspension is doing. I will try and post it tomorrow.

 

[imjoesnuffy]

https://www.facebook.com/video.php?v=2658181342439

Here is a video from the Nationals last year. I think this was a 1.55, it didn't spin much here, but you get the idea. Seat of the pants dyno says the car is making more power now, but cant confirm. I don't have recent video from the rear, with it spinning.

 

[Alky V6]

She's squating. Relocate the rear upper control arm front mounting point. The easiest way is to use Kevin's buckets and control arms. You need to get the instant center where it will work better. Then worry about shock settings. Fix the IC first.

 

[imjoesnuffy]

She's squating. Relocate the rear upper control arm front mounting point. The easiest way is to use Kevin's buckets and control arms. You need to get the instant center where it will work better. Then worry about shock settings. Fix the IC first.

Who is Kevin and where do I find these buckets?

 

[Slow91z]

I think Donnie is talking about the baseline suspension kit.

 

[Alky V6]

That's correct.

 

[imjoesnuffy]

Are relocating buckets my only option? I don't want to sound unappreciative of the advice, but just want to make this is the only thing that will help my car before I start throwing parts at it.

 

[Alky V6]

Other options would be to move the rear mount of the upper control arm higher, or move the rear mount of lower control arm lower. It's preferred to have the lower control arm as close to level with the ground as possible, so I would not consider moving the rear mount of the lower control arm lower.
Most kits that I've seen that will help move the upper control arm rear mounting higher only have one relocation choice. Kevin's buckets come with optional locations, and you can even bench modify the bucket yourself to come up with a specific instant center location that you choose, if you think it's necessary.

 

[KevinB]

I second the baselinesuspensions.com upper arms and buckets. My car squated bad. Put this kit on my car and tightened my qa1 singles up front and got the car to go from the mid 1.4's to mid 1.3's.

 

[charlief1]

If you remember the SSM bars they did it by using a slightly longer lower and a relocation bracket on the axle. Yes, it made the car hook and also stressed the LCA mounts on the frame to the point where they ripped off.

The other option is to get a pair of offset bushings for the ears on the axle. Speedway motors has them if you want to take a look. Part number is 916-34047 but it only offsets the bushing 1/8". Not a lot but if Donnie would plug the numbers in his calculator to see how much it moves the IC it might be the least expensive option.

 

[Alky V6]

If you remember the SSM bars they did it by using a slightly longer lower and a relocation bracket on the axle. Yes, it made the car hook and also stressed the LCA mounts on the frame to the point where they ripped off.

The other option is to get a pair of offset bushings for the ears on the axle. Speedway motors has them if you want to take a look. Part number is 916-34047 but it only offsets the bushing 1/8". Not a lot but if Donnie would plug the numbers in his calculator to see how much it moves the IC it might be the least expensive option.

That program is on my laptop at work. I can do that tomorrow, but I can tell you right now that 1/8" is not going to do enough.

 

[charlief1]

That program is on my laptop at work. I can do that tomorrow, but I can tell you right now that 1/8" is not going to do enough.

I agree but I'm just wondering how much it might change it since technically it's legal for calss racing since it doesn't exactly change the mounting point of the arm, which is required in most cases.

 

[KevinB]

Technically I think the baseline buckets are considered stock location because they bolt into the stock location and the arms bolt into them.

 

[Phatman]

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[KevinB]

Next time you go out, put the front shocks in the middle. You want to keep as much weight transfer on the rear wheels. When the cars front end pops up real fast and falls back down at the same rate, all that weight transfer goes back to the front, unloading the rears.

On the squat issue, if you look at my pic in my signature, that was before i put the relocation brackets on. Now the clearance between the tire and fender do not change. The good thing about the baseline kit is it adjustable. You can have too much lift, where the rear if the car will separate from the tire, but there are 3 adjustments to get it right. I use the top hole. Haven't had time to plot it out yet but it works great.

 

[johnplogii]

Not to contradict everyone but I am using relocation brackets on the rear end lowers. Been 1.25 60ft on 275 radials. They are supposedly better suited for slower cars.