Building first race car and have some questions

[cohny]

This fall/winter I'm going to be converting my mildly prepped E36 M3 into a race car. The plan is to build the car for NASA's ST5 class which limits the power to 14 lbs/hp and has some other restrictions for tires, aero, etc. As I'm starting to plan out my build I have a few questions/ideas for the motor and suspension I could use some help with:

Motor: I have a pretty unique situation here. Right now I'm also finishing up an E34 I'm building for a DD. I was going to build up the M50tu it came with into an S52 and have already acquired an S52 crankshaft, S52 camshafts & trays, S52 pistons, and S52 rods for that motor.

One option is to move foward as originally planned and build this M50tu up for the E34 and refresh the S52 in the M3 for the ST5 build. Recently, however, I was thinking another option would be to just swap the S52 from the M3 into the E34 and build up a motor for the ST5 build. If I went in that direction I could get creative and was thinking it would be pretty sweet to source an aluminum M52 block from a Z3, source some M54 rods/pistions, and build an aluminum 3.0L with S52 cams. I have to build one motor for one of the cars so the cost is somewhat of a wash either way.

I ran this idea by the one guy I know who races and his opinion was that the lower weight of the aluminum motor wouldn't be worth the trade off in displacement, but 14 lbs/hp comes out to around 215 whp at my target race weight of 3000 lbs. It seems to me that a 3.0 could easily make that but the calculation is an average and the larger engine would have slightly better area under the curve.

Thoughts?

Suspension: I've heard that the subframe/differential mounts should all be solid aluminum and that all of the control arms/RTABs should be spherical joints. Is this true? Is there anywhere else besides the engine and transmission mounts that I should run something with give like a high durometer polyurethane etc? I have always thought that new/OE bushings are better than poly joints etc. but obviously when you get to the point where you're running slicks the forces are far higher. I just don't want the car to be twitchy feeling.

[ScotcH]

Motor: 2.8L will easily put out 215 rwhp, so a 3.0L is no problem. you'll need M54 crank/pistons to make it work, not M52 (for 3.0L). They are good engines, and since your power level is low, they should last. However, your weight is pretty high, so the aluminum might be a wasted expense. Gutted e36 rac cars are typically around 2700 lbs without driver, so you'll be bolting in weight anyway

Suspension: Solid everything for a proper race car. Reinforce the important points (subframe mounts, engine mount points, RTABs, etc). This is the only way to ensure a consistent setup and alignment that does not dynamically change. It is amazing how much more precise a solid chassis feels compared to a compromise (ie, poly or rubber).