watching the tape of my runs at slow motion it appears the front comes up very quikly comes back down a little lower than stock and then rises again. all this happens in about 20 feet im guessing. how do i fix this? the rear does not squat at all. also there is a bit of twisting. rear bumper looks to be about 4" out of level. not pulling the front tire. i know a anti-roll bar would fix this but is it worth the trouble,expence, and most importantly is there any E.T. to be found here? as always thanks Dave

Dave,

How were you launching the car? I found that mine left the best stalling it against the brakes to about 1500 rpm and flashing the converter when the tree came down.

Jason, thats what them guys at the track with me told me to do so i left at 1500. im going to remove the ssm brackets and install the lowers in the factory location (lengthing the instant center) and see if that dosent help. also my c/e shocks are set at 70/30 i guess i could try 90/10 and then maybe the shock nut deal Tom talks about. the e.t. streets had 18.5 lbs on 2 runs and 17.5 on 2 runs. we also tried pushing the car through the lanes and leaving at a cooler temp but none of this seemed to make any difference. Dave

You don't want the back end to squat. When that happens, the rear tires are pulling up inside the body and trying to come off the track. The SSM bar drop down bracket shortens the instant center which causes and anti-squat situation. This pushes the tires away from the body and down to the track surface.

If the front end drops too quickly, then maybe you need a slightly stiffer front shock setting to slow the movement down some. It could also come down to playing with different rear shock valvings as well.

Most all A/G-body cars exhibit some form of body/chassis twist off the line. You can use a heavy sway bar that bolts on the stock location out back as well as playing with air bags and different pressures. Don't expect to level the launch 100% this way though, but it should help traction to a certain degree.

What Carb are you running ? If a Holley, does it have the jet extensions on the rear bowl? My car was doing that a few years back, and thats what I ended up needing. I also played around with the stock 4 bar set up and put ALOT of pinion angle in it and got it to pull 1.46 60's consistantly with a worn out 12-1 355 f/braking it.

They way you described your front suspension reaction it sounds like your front suspension is coming up too quickly. I would put stiffer extension shocks on. Some people have been able to stop it by putting their front sway bar back on.

Sqauting is not where the rearend is trying to come off of the ground. It is the reaction of the acceleration forces of the car overcoming the rear suspension setup (instant center, springs and shock settings)and allowing the body to squat over the rearend.

When power is applied to the rearend the first reaction (regardless of instant center location) of the rearend is push into the ground. This is because the pinion gear is climbing the ring gear.This reaction happens so fast you very rarely see it. This is why extension settings on the rearend is also crucial.

The secondary reaction is created by the suspension setup (instant center location, springs, and shocks) reacting to acceleration forces when the car starts to move. If you have squating setup the g forces of the body over comes the suspension and pushes the rearend down but because the spring rates aren't high enough to counter act the forces the car squats. If your car lifts then the suspension linkages (control arms) are carring the load and not allowing the car to compress the springs.

Anti-squat doesn't determine the amount of force the suspension is putting to the ground. anti-squat determines how much of the acceleration forces are transmitted to the tires thru the linkages and the springs. If you have 70% percent anti squat the linkages will carry 70 percent of the load adn the springs will carry the final 30 percent. Anti-squat percentage alone doesn't determine how much your car will squat. For example, if you have 10 percent anti-squat and 2000 pound springs on each side of your rear do you think it will squat with a 300 hp 283. absolutely not. If anybody's interested i'd be glad to go into this further on a longer post. I have been designing suspension for various types of suspensions and it was one of my majors in engineering at auburn.


Todd

Dave, are you running an air bag on the pass. side?Also a travel limiter on the motor or solid mounts may help as well. I installed a limiter on mine,we'll see what hapens this week.

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Dont waste your time with 90/10 shocks.

Todd and Todd are right Dave. If the front comes up and then the rear unloads you need to slow the rate of rise. You need to go to go in the direction of a 50/50 shock not 90/10. Before you do that though I would put a set of air bags in the rear. Not only will it help level out the car, but effectively increase the rear spring rate. Kind of a band aid, but they are pretty cheap and do work. My car worked best with 15 psi in the passenger side and 10 psi in the driver side.

ok let me go into a little more detail on my suspesion. the front has the moog 6 cylinder springs 5230 (i think) CE 3 ways set at 70/30 15/16 sway bar, poly bushings, the lower control arm bolts are finger tight and double nutted, the uppers have the retainer turned backwards. solid motor mount left, poly right. the rear is stock srings with air bags 14 right and maybe 4 left. CE shocks set at 50/50. metco uppers, pinion angle about 5 degrees down, ssm bars, and 1" sway bar, poly bushings. i appreciate the help guys. dont have a clue to what most of this means but ill try a few things. whay would the first and second choices be? thanks Dave

Set those fronts to 50/50.or buy a set of 25.00 Monroes

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Dave,

What size ET Streets? What gear? I would move the air pressure in the tires down to 16 psi hot and set the front shocks to 50/50.

In addition, you need to put a little heat into the tires with a decent burnout. It sounded like from your description that the burnout was a little lacking. Tire speed is where it's at. Roll through the water box. Stop just at the edge of where it's dry/wet. Put the trans in second and quickly snap the throttle while applying the brakes/linelock. As soon as you get the RPMs to come up go to third gear and hold around 5000 RPM. When you see smoke or hear/feel the engine lug down, release the brake and power out and move directly to the line. You don't need a John Force burnout, but you do need at least 5-6 seconds. M/T says you don't need much of a burnout with the ET Streets, but mine seemed to work best with a decent burnout.

Also, make sure you line up in the "groove." Makes a big difference.

BTW - 1.61 60' aint all that bad graemlins/thumbsup.gif

Jason, 4.11 gears with 15x12.50x28 et streets. i run through the gears heating the tires up. went to about 5k for several seconds 2 times i got smoke 2 times i did not. the better burnouts produced the 1.61 times. thanks

opps dp

Stock type suspensions and lower powered cars are real succeptible to anything that lets the suspension bind or top out too soon. Like front shocks running out of upward travel, rear shocks topping out, front upward suspension limiters, etc. If anything tops out early or binds, it sends a slight jolt thru the chassis and unloads the tires. Then the nose falls, the car recovers and does it again.
The lower powered the car, the looser the suspension needs to be to go quick.
Also, you need to keep power applied to the tire to keep them planted. If it has even a SLIGHT dropoff in acceleration, the tires become unapplied and the nose falls.
You may work with the pump shooter size and volume to help carry the car out further.

What you're seeing when the nose falls is a slight loss in the rate of acceleration whether from tires unloading momentarily or power being lost momentarily.
JMO thru experience. I'm not an engineer, just a racer.

Randy

ok i think im getting a feel for whats going on. i think. if i understand correctly the front end is rising so quickly that it is rebounding off the shocks and literaly bouncing back towards the ground? so if i go with a stiffer shock that extends slower it will rise slower and hopefully prevent this. Dave

Dave.. OK here is the dumb question of the day..
Im not familiar with the metco upper arms. Are they double adjustable while installed like the Dick Miller uppers? If so, did you set your preload after setting up you pinion angle? Maybe I missed it but I didnt see any mention of it in the thread.

sorry it took so long to reply. my puter is down and am having to barrow one. yes the metco uppers are double adjusable. the pinion angle is about 5 down and dont have a clue what you mean about preload? what is it and how do i set it? if i get the anti-roll bar installed do i still need to set the " preload"? will prlaod help plant the tires? thanks Dave

My car was pulling the fronts 4 to 6 inches then dropping, launching forward and spinning the tires. I changed my 3 way shocks from 90/10 to 50/50 and it now has all forward motion, pulls the driver front about an inch and once it sets the tire down, the front stays up. On a hooking pass with the 90/10 setting I ran a 1.72 60'. With the 50/50, I run 1.67 60's.