Re: why SC and not turbo M cars? (archive)

: someone posted a few sites of stuff about M cars, and i only found SC kits available for the M coupe/roadster. you'd think that with the already nice low-end of the 3.2, a turbo would be a more desirable top end boost.
: or is the dinan SC kit a vortec centerfugal (sp?) type supercharger?
: do any of you drive turbo M's?

Brace yourself for a long rant... ;)

As far as I know, all of the supercharger kits that are available for the S52 motor (M3 and M Coupe) are centrifugal superchargers. Centrifugal blowers are, IMHO, the worst of both worlds.

Roots-type blowers (and "Whipplechargers" like the Autorotor) give nice boost down low, but have horrid thermal efficiency, and being positive displacement "pumps" suffer boost loss with an intercooler.

Centrifugal blowers are just the opposite. They don't have the boost loss problem with intercoolers, but they don't make any boost down low.

Turbos combine the good thermal efficiency of the centrifugal blowers and the ability to get boost at lower revs of the positive displacement blowers.

The on-off behavior that some folks have described is really a function of some designs of high-boost systems. The early Porsche Turbos were classic examples of this, where the ultra-low compression motor made no power off-boost, and the turbos were sized for high boost at the top of the range. The result was that all hell broke loose at 4k rpm. Fine if you're always above 4k, but not very streetable.

Good design can create very nice, smooth power curves, with lots of torque in the midrange and lots of power up high. These designs sacrifice ultimate power for driveability.

For S52 turbos, there are three that I know of:
Active Autowerke has kits for M3s, but they're obscenely expensive for OBD2 cars.

Bell Engineering has an M3 kit in the works, and I've been corresponding with Corky Bell about adapting the kit for the Coupe. That's a little ways off yet, but I've offered my car as the prototype. ;) I've driven Miatas with Corky's turbos, and the best thing I can say is that Corky has destroyed the old saw "There's no replacement for displacement." There is, and it's well managed boost. Aside from the odd whooshes and pops, there's no hint that these are turbo cars.

-Zandr

Follow Ups:

Let me try that again...one little HTML typo. ;) Zandr 13:47 6/19/2000 (2)
- will the S52 c.r. be low enough for boost? Chris Sawatsky 18:38 6/19/2000 (1)
  - Some boost, yes... Zandr 19:25 6/19/2000 (0)

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