front wheel drop

[kjkens]

On a 1971 pontiac firebird with a 1000 hp big block chevy any one have any thoughts on how much to limit the drop of the front wheels at the launch and whats the best way to do this. On the first 2 runs I had a chain with eye bolts to limit the wheels from dropping over 2 inches but at the hit the car pulled the wheels slightly which was fine but the impact of those chains was an abrupt stop that loaded the rear suspension and then the car porpoised several times before settling down. Other wise it went straight as an arrow. The next time out I took the limiters out and just let the wheels drop to the factory bumpers and the initial hit was fine then around 1/4 second into the run when the front end came back down the car pulled to the right slightly and then when it shifted to 2nd gear it seemed to pull to the left which it did not do any of this when I limited the front wheel drop. Any ideas or comments would be appreciated. This car is a back half car with a 4 link rear suspension and stock front suspension

[automotive breath]

Front wheel drop and rate of drop requirments are different for
each chassis/power/track combination.

An ideal way to limit drop is to weld nuts over the bump stop holes in
the upper control arms and screw a bolt in from the underside. This
makes adjustments very easy.

[Nwguy]

Adjustable rebound shocks will control the rate at which the nose comes up. More rebound = slower rise. Watch a Pro stock car....the nose doesn't move much.

[kjkens]

Right now lifting the front end with a jack under the center of the front crossmember and measuring inches of lift at the fender wheel opening and with scales under the rear tires we have about 7" of lift before the front tires come off the ground. With 200# in the drivers seat to simulate the drivers weight, up until 4" of lift the weight is 100# heavy on the LR tire vs the RR. At 5" of lift the rear weight moves to even across both rear tires, at 6" the weight is about 100# heavy on the RR and at 7" right before the wheels leave the ground the weight returns to LR 100# heavy. I forgot to mention earlier the car has an antiroll bar in the rear in addition to the 4 link. I know this does not take into consideration engine torque but thought this additional information might help. Also I thought that this 7" of front wheel drop is excessive but I do not know what would be an acceptable amount of travel

[beth]

I thought that this 7" of front wheel drop is excessive but I do not know what would be an acceptable amount of travel

The amount that works best is what is acceptable in my experience. Make it adjustable and compare 60 foot times at 2" then 3" then 4" etc. until you get the best result. A tighter shock will lessen the shock to the chassis at the travel limit.

[automotive breath]

The key to suspension set up is adjustability. What works on a pro stock
car won’t work on a back half car. On the same car what works today
might not work tomorrow as track conditions change.

Here’s what I use to limit front suspension travel. Combine something
like this with a fully adjustable shock with final setup determined at the
track.

[kjkens]

Thanks for the replys. On the bolt setup in the picture is there something on the bottom portion of the bolt such as a rubber bumper, flat washer welded to it etc. or does the lower portion of the bolt just contact the frame with a 1/2" or so contact area?

[automotive breath]

Yes I couldn't get a picture of it. I cut the head off and welded a flat washer
to the bottom of the bolt and drilled and taped to to accept a traction bar
rubber bumper. My car needs plenty of suspension travel, the bumper ended
up limiting travel so I don't use it. With a car that needs a small amount of
travel the bumper would soften the hit. The bumper can be cut back to say
1/2" or so.