Front Subframe Spacers

[rinmak]

Hi SAU,

I have dropped an RB25det into my 180sx and it fits but I need to drop it lower to clear the bonnet etc. Im going to slot the engine mount brackets down abit which should give me 10-15mm but im also interested in putting some spacers inbetween the front crossmember and the chassis rail.

What im after is some input as to how this would affect the front suspension of the car. Would it make a difference at all?

Regards

[Sydneykid]

Hi SAU,

I have dropped an RB25det into my 180sx and it fits but I need to drop it lower to clear the bonnet etc. Im going to slot the engine mount brackets down abit which should give me 10-15mm but im also interested in putting some spacers inbetween the front crossmember and the chassis rail.

What im after is some input as to how this would affect the front suspension of the car. Would it make a difference at all?

Regards

Negative effects on bump steer, Ackerman and dynamic camber change.

Cheers

Gary

[rinmak]

Thought as much.

I guess my next question is: would these effects be very dramatic if I was only to use a small amount (say 3-4mm) of spacing?

Also,

Is there any way to counter these effects?

[salad]

Will also lower your roll centre.

Basically, it's like having the front of your car lower (geometry gets worse), but you don't have the gain in lowering the CG (well, not as much as lowering the whole front down).

As for how dramatic the change would be, it depends on how low the car is now, but even then, it's hard to say without modelling in a suspension analysis program. Or, someone with lots of experience (like Gary) can tell you how it would feel having all this stuff changed.

[Sydneykid]

Thought as much.

I guess my next question is: would these effects be very dramatic if I was only to use a small amount (say 3-4mm) of spacing?

Also,

Is there any way to counter these effects?

The front lower control arms should always point slightly downwards (to the ground) towards the wheel. So by whatever amount you lower the inner front lower control arm pivot point you must also lower the outer front lower control arm pivot point. That fixes the dynamic camber change problem.

The Ackerman problem can be fixed by moving the steering rack and/or the steering arms (on the upright). The latter is usually the easiest.

The bump steer is usually corrected with spacers at the outer tie rod ends. Start with the same thickness spacer as you used to lower the outer front lower control arm pivot point.

This is why people change the inlet plenum and/or the bonnet.

Cheers

Gary