Repost of Part II below (m) (archive)

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Well, I don't like imagining, so lets assume
you run 5psi of boost (which would give you
the same combustion pressures as the dinan stage 1 supercharged E36M3, and given the E46's better head design, roughly the same resistance to detonation.

In 6th gear at 5psi of boost near redline, the M3 is generating roughly 304ft-lbs of torque, a number that would stay roughly constant from around 6000rpm to roughly 8000rpm (the engine breaths better at 6k, but the blower only develops ~3psi of boost at 6k, so the roughly 10% increase in the stock torque curve from 8k to 6k is compensated by a roughly 10% decrease in intake charge density (in fact, this is conservative becuase the higher boost heats the air more, so the curve is more skewed to the low end, a good thing for centrifugal blowers). So assuming the M3 develops 304ft-lbs of torque (supercharged) from 6k to 8k rpm, that works out to 907ft-lbs to the road in 6th gear, or a 11% increase over the 5th gear torque of the stock E46M3. This would equate to a rough top speed of 180mph (in 6th gear) at 6800rpm. If you changed the rear end gearing to a 3.97 (which is what I have put forth as an interesting option in past archived posts), the M3 would put 990ft-lbs of torque to the road, equating to a top speed of 186mph at 7660rpm. The maximum top speed of this theoretically supercharged E46M3 would occur with a rear end gearing that would give the maximum speed at redline in 6th gear (solving some equations relating the increase in rear end torque linearly with ratio increase and drag increasing with the square of the speed and speed increasing linearly with rpm) you get a rear end ratio of 4.09, so the car would have a top speed of 196mph at redline in 6th gear with 5psi of boost

To back up that boost number look at it this way:
E36M3 US motor runs 6psi on the Dinan SC. So the combustion pressure is roughly (14.7psi + 6psi) *compression (10.5:1) 217.4psi

The new motor is 11.5:1, limiting boost to 4.2psi for the same combustion pressure, however, the improved cooling on the M3 cylinder head could probably handle the additional 0.8psi w/o detonation.

Oh, as a random other note, if you incorporated an aftercooler on the supercharger allowing 7.5psi of boost (based on the fractional boost increase allowed by the vortech aftercooler used by RMS), the M3 would be running a true boost of 6-6.5psi (1-1.5psi drop through the aftercooler) for a torque of 327ft-lbs at redline or, with a 3.99 rear end, a top speed of 200.9 mph.

So, for all those that want that beautiful 200mph top speed, based on the educated guess here, the E46M3 motor with a 6.5psi vortech w/ aftercooler (oh, and btw, the max torque of the motor being only like 327ft-lbs is relatively great news, as that small of an increase over stock 58ft-lbs (over the Euro E46M3 motor) should be easy for the internals, clutch, etc to take, as this is roughly the peak torque of the E36M3 US supercharged motor.

Now, running that aftercooled 6.5psi motor with a 3.99 rear end, will give you some impressive acceleration figures.

The car will put 3248ft-lbs of torque to the ground in 2nd gear (the stock US version puts 3907 in 1st! (20% more, but 1st vs. 2nd gear!)

Based on very very rough calculations, this hypothetical M3 would run 0-60 in (assuming 0.3s per shift and 60mph at redline in 2nd and traction limited 1st gear at 3900ft-lbs traction limit) roughly .6s less than the stock M3, or about 4.2s

The 1/4 would also improve by about a second, to roughly 12.2s @ ~120mph or so (Z06 type numbers)

Ok, now I looked back and I think I made a small error in the rpm vs. mph numbers, but only about 1-2%, so all the top speeds should still be accurate +/-3-5mph

(random other note, that asymmetric twin turbo motor I was thinking about would run a top speed of 220mph with a rear end ratio of ~3.5, but since I wanted to run the M5 rear ratio of 3.15, the actual top speed would be ~210 instead...the reason for the 3.15 is otherwise the car would be traction limited in 2nd gear as well as 1st, and by putting the taller (numerically lower) rear in the car, the mph in each gear is considerably higher, increasing drivability with the increased torque, and that car would run 11.5-11.7 @ 125mph or so on the strip)

Just my $0.02, please email me if you want to flame and now that I'm a little lower stressed at work, expect a few more posts from me

Thanks
Marc
98 M3/2
750SS
01 M3/2 (march)
01 996 (march)
01 R34 GTR (october, heavily modified)

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