Lowering the steering rack

[grannyknot]

If you take a stock 72 240z lowered 1" with lowering springs then cut off the steering rack mounts and built new ones 1.75" lower than stock, what would be the effect on steering/ handling?

I'm still trying to find a way to shoehorn in this BMW engine without screwing things up too much.

Dropping the steering rack would give crank balancer a place to live.

Thanks,

Chris

[Namor]

Essentially it will be like you lowered your car 2.75" as far as your steering geometry is concerned.  I think you are going to have bumpsteer unless you do something to correct for it.  There are already Roll-Center Adjusters on the market (aka bumpsteer spacers) that drop the steering knuckle to help restore the stock geometry after lowering to minimize bumpsteer.  I think they make them up to around 1.5" thick and you might be able to get some thicker ones if you have clearance with your wheels.  I know my swastika style wheels definitely wouldn't have the clearance for anything that thick.  

[74_5.0L_Z]

Can you get the balancer behind the rack? 

 

Unfortunately, the way to improve the bump steer on an S30 is to raise the rack or lower the outer tie rod.  At the stock rack height, the front suspension has a bit of toe out on bump (~0.5 deg per inch of bump).  A small amount of toe out on bump for the front suspension is safe and here is why:

 

You are driving down the road and hit a bump with one front wheel.  The suspension on the one front wheel compresses and the bumped front wheel steers outward.  This causes the car to slightly steer toward the bumped wheel and lean away from the bumped wheel which causes the bumped wheel to return toward it original position and the opposite wheel's suspension to compress. The overall effect is that the suspension wants to get back to its original  steady state configuration.

 

If you lower the rack 1.75 inches , the front suspension will toe in severely in bump (more than 1 degree per inch of bump).  This will make the car dangerous to drive. This is dangerous because the bumped wheel will steer the car away from  the bump which will cause the suspension to compress further which will make the car steer even more inward.  At low speeds, you may be able to compensate with steering.  However, at high speeds you will reach a point where you cannot compensate.  This is called the critical speed.

 

If you can't get the engine behind the rack, move the rack forward. If you move the whole crossmember, then you will add caster and give yourself some clearance.  If you still need more room then move the rack forward independent of the crossmember.  You will lose a bit of Ackermann, but you can live with that.  You might not live with severe toe in during bump in the front suspension.

 

And bump steer spacers will not help this situation at all.

Edited August 7, 2016 by 74_5.0L_Z