Suspension tuning - brake dive

[Vince@Meanstreets]

Originally Posted by manny z

Just look at these to start. Put up the answers to the questions I asked.

manny you got to break that up, didn't see your advice till now....maybe change the color?

[gerno]

Thanks for the replies. I extracted many of the questions and here are they details.

Ok, for one what kind of QA1 coilovers are you using? Did you just get them "off the shelf"? or were they built for YOUR car? What spring rate are you running on these coilovers?

They are off the shelf parts. I used HAL-GMP3350-3 which is spec'd below.

Suspension Height Adjustment Stock
Coil-Over Kit Position Front
Recommended Front-End Weight 1,701-1,900 lbs.
Shocks Included Yes
Adjustable Valving Yes
Internal Design Twin-tube
Gas Charged No
Number of Valving Selections 12
Shock Body Material Aluminum
Shock Body Finish Clear anodized
Bushing Material Polyurethane
Bushing Color Black
Coil-Over Springs Included Yes
Spring Rate (lbs/in) 350 lbs./in.


Instead of changing your pedal ratio, why not use a proportioning valve? Or do you know what size the piston is in your MC? You know one of the issues you could be having is, the MC piston might be a little to small, and creating to much pressure when you step on the brakes, making your brakes to touchy.

I have an adjustable proportioning valve for the rear but the issue is that the pedal is too stiff. The MC has a 1 1/4 bore off an astro van and I have an extra MC sitting around off an S10/Regal/Malibu that has a smaller bore. Based on what I was reading I beleive the smaller bore makes the brake less touching. For some reason I always get confused with the efffect of MC ratio on the brakes.

No offense but, if you are not well verced in suspension set-up, you are just going to make you car not fun to dirve.

I agree completely which is why I'm asking the questions now. Before I start buying all new stuff I'm hoping a little advise on my current mismatched parts will point me in a better direction.

I agree, look to matching your spring rates up first. Being QA1's I'd assume the standard 350 lbs spring.
Most likely coming down on your bump stops and unloading the rear end.

If you are serious in performance stiffen up the subframe and look into a different spring and shock set up. Rear should be fine.

Support down bars for the front, cross bar right above the sway bar and weld up your subframe seams.

I'd like to see a video of your runs.

I'm also thinking the light coilovers aren't helping me. I have the subframe fairly stiff but have not welded the seams as of yet. I did add some down bars and also welded in a supprt bar near the sway bar.

I have some video but they didn't turn out well at all and you can't really see what's going on. I wish my Replay XD had a video screen so I could test in advance.

[manny z]

Originally Posted by gerno

Thanks for the replies. I extracted many of the questions and here are they details.

Ok, for one what kind of QA1 coilovers are you using? Did you just get them "off the shelf"? or were they built for YOUR car? What spring rate are you running on these coilovers?

They are off the shelf parts. I used HAL-GMP3350-3 which is spec'd below.

Suspension Height Adjustment Stock
Coil-Over Kit Position Front
Recommended Front-End Weight 1,701-1,900 lbs.
Shocks Included Yes
Adjustable Valving Yes
Internal Design Twin-tube
Gas Charged No
Number of Valving Selections 12
Shock Body Material Aluminum
Shock Body Finish Clear anodized
Bushing Material Polyurethane
Bushing Color Black
Coil-Over Springs Included Yes
Spring Rate (lbs/in) 350 lbs./in.


Instead of changing your pedal ratio, why not use a proportioning valve? Or do you know what size the piston is in your MC? You know one of the issues you could be having is, the MC piston might be a little to small, and creating to much pressure when you step on the brakes, making your brakes to touchy.

I have an adjustable proportioning valve for the rear but the issue is that the pedal is too stiff. The MC has a 1 1/4 bore off an astro van and I have an extra MC sitting around off an S10/Regal/Malibu that has a smaller bore. Based on what I was reading I beleive the smaller bore makes the brake less touching. For some reason I always get confused with the efffect of MC ratio on the brakes.

No offense but, if you are not well verced in suspension set-up, you are just going to make you car not fun to dirve.

I agree completely which is why I'm asking the questions now. Before I start buying all new stuff I'm hoping a little advise on my current mismatched parts will point me in a better direction.

I agree, look to matching your spring rates up first. Being QA1's I'd assume the standard 350 lbs spring.
Most likely coming down on your bump stops and unloading the rear end.

If you are serious in performance stiffen up the subframe and look into a different spring and shock set up. Rear should be fine.

Support down bars for the front, cross bar right above the sway bar and weld up your subframe seams.

I'd like to see a video of your runs.

I'm also thinking the light coilovers aren't helping me. I have the subframe fairly stiff but have not welded the seams as of yet. I did add some down bars and also welded in a supprt bar near the sway bar.

I have some video but they didn't turn out well at all and you can't really see what's going on. I wish my Replay XD had a video screen so I could test in advance.

I am going to start from the top. BRAKES: With the brakes you are using, the MC piston size is a little on the large side. When I first set up the wilwoods on my charger, I had a 1 1/8" MC piston size, it wound up being the big. I down sized to a 1", and the brakes feel better. Are you manual brakes, or power?

You front shocks, get those 350 lb springs, and use them to hold your hood up. lol.. < just some humor. Way to light for that car man. I would start with at least a 650-700 spring. Like was mentioned, with that small of a sring rate, you are more then likley diving pretty hard, and unloading the rear of teh car.

[manny z]

Originally Posted by Vince@MSperfab

manny you got to break that up, didn't see your advice till now....maybe change the color?

I know. I set it on red, but it came out black. haha..

[gerno]

Thanks for the guidance. I'll be swapping the MC this week to the smaller bore. I had forgotten I had an extra one sitting around. I'll also swap my smal block (600lb) Hotchkis springs in this week for the QA1 coilovers. I figured since many other people were using them they would be ok but apparently not so much. For now I'll use the shocks alone with the other springs but will eventually sell the coilovers and get some good shocks

[Smoker03]

With a small block and the QA1 coilovers, you can get them to work very well. You have the 350lb spring which is a little light. Up the spring on the coilover to 450 or 500 max and it will work great. You do not need 700lb springs on a coilover. If you had a separate spring and shock in the stock location, a 700lb spring would be a good option. I would keep the coilovers and up the spring rate to 450 and see how it does. The rear sounds fine. I also agree with goin down in size on the MC.

[Sieg]

Originally Posted by gerno

Thanks for the guidance. I'll be swapping the MC this week to the smaller bore. I had forgotten I had an extra one sitting around. I'll also swap my smal block (600lb) Hotchkis springs in this week for the QA1 coilovers. I figured since many other people were using them they would be ok but apparently not so much. For now I'll use the shocks alone with the other springs but will eventually sell the coilovers and get some good shocks

Call Tobin at Kore3.com for a brake system recommendation. I went with a 7/8" Wilwood manual from factory '69 power and couldn't be more satisfied with the modulation and pedal effort.

[JRouche]

Hmmm? Ok Ill go off a lil. Ok wait? Ill stay on track for a second. The 350lbs springs are a lil light for your car. I like the advice with the 450lbs springs. And like smoker said, 700lbs (I think yer 600lbs are too tight) is not needed.

I dont mind too much load transfer (front end dip). It loads the front end up so it can really work. Too light up front and the car will be loose. And YES!! Loose in racing can translate to fast track times. But ONLY if its a track only car. Race cars are NOT street cars.

I personally like a loose car for the track if I know the car. But I never want a loose (read light on the rear and basically a level feeling car) for the street.

For you I would stiffen up the front springs some and focus on the rear shocks a lil. If they are adjustable I would tighten them up for rebound. Make them hold the rear end compressed for just a second while the car is turning and braking. Something as simple as the shocks will help with an apparent dive issue.

And I say apparent dive issue (with braking). I dont have a problem with it. And Im talking about a STREET car that likes to see the track sometimes.

I have driven front heavy street cars to their maximum adhesion on a closed track. Big heavy (on the front cars). Driven them to the point of major understeer, basically trying to rip the front tires off the rims with turns and braking. LOL Tires never came off but Im sure alot of rubber did.

At first during this training session I was slow. But after a few more laps and understanding the car I was able to increase the lap speeds and bring the times down.

My point? Even supposed heavy front end cars can dig their way around the track. Dont worry to much about how it seems to dig in cause you might be actually hitting the track at a decent speed.

A car can feel out of shape and look out of shape but the clock will ALWAYS tell the true story. JR

[gerno]

I agree Tobin is the brake expert. Since I have the other MC already I'll give it a shot first. I used it before with the same brakes but not the hydroboost so I know it matches well with the calipers so it should work. I only have the current large bore becuase it came with the hydroboost.

I'll work on adjusting the rear shocks a little. They are only single adjustables but I'll play with them a click at a time and see what happens. The 600lbs springs I have are not coilovers, they are standard full sized springs. Since I already have them I was thinking to give them a shot but I just noticed the cost of new QA1 springs is not too bad.

At this point I am actually waiting on my new trans to be delivered and the car is inoperable for a while. I'll focus on the brakes and the shock adjustments first then after the new trans is installed will decide if I'll use the 600lbs or purchase some new coil over springs.

[Chassisworks]

Gerno,
A couple of us from Chassisworks were out at Mather the same day as you. We noticed your car porpoising around the course and commented that you definiately needed either a better set of shocks or some serious adjustment. I agree that the 350# front springs are too light, assuming they are 9"-10" free length.

Also, most of the time on a car like yours we would recommend either a 1" or the 7/8" master so you're going in the right direction.

If we see you out there next time we'll make sure to introduce ourselves and maybe we can help you out a little.