I called Procharger to see what they recommended for pulleys to make 10 lbs of boost at 5800 RPM....

They said with my 7.5" crank pulley to run a 5.25" blower pulley.. Puts me at 36,789 rpm impeller speed at 5800 rpm...

Don't think I'll have to worry about belt slip.

I ran 12 psi on 93 with my 598 it made 1200 hp and I ran 32 deg timimng I also ran a m4 with a cog belt drive

You will have to watch for it there to...even 5-6psi belt needs to be kept very tight and watch for black dust

Im turning my procharger 8 to 10,000 rpms past its rating because of the hp level im at, really in m4 or m5 territory but never upgraded. With 12 rib i never had belt problems at 48 000 to 50,000 rpms, at 58,000 everything has to be perfect and i had to re-enforce mounting bracket to eliminate flex and was still marginal, fwiw, Smitty

What ? A 5.25 upper pulley

7-lbs of boost and I'd have an efi system that can knock retard.thats why I like the mefi4b,you can watch the knock sensor and spot problems.I use the knock and o2 sensor to dial the tune in.

Great discussion. Is there a preferred system or plug and play setup for knock sensing especially on a low tech carb setup without efi/computers?

I have a pair of 572s with 14-71s on top, intercooled and twin 850 carbs in between 1000-1100hp running 93 and Boostane to get it around 99octane for safety. I really wanna add the O2s (have the FAST kit already), but love the idea of knock sensing, and how to prevent bad things from happening. I am by no means an engine expert, and had them built for me, just curious, might be a nice add-on before I start running the thing hard.

When I dynoed the procharger head unit it was static boost throttled to achieve same load as it would be on motor at wot. I DO disagree on your opinion of "load" from supercharger. I dont really care how much hp it would take to free spin a old school roots, I am talking about under a load. So back to BSFC's, two identical motors, cams, heads etc, one with a centrifugal with BSFC's in the .520 range, the old school roots blower motor with bsfc's in the .625 range, its a fact the roots motor is using 10-20% MORE fuel to make same crankshaft hp, if its NOT from hp required to turn the blower then what is it from? We got a 1200 hp centrifugal motor using 1300 hp worth of fuel to make 1200 at crank, and on the low side at only 10% more we have a old school roots motor using 1430 hp worth of fuel to make 1200 hp, for sake of discussion both tuned to same exact afr also. BTW, these BSFC's are from personal observations of dyno sessions I have been part of. I love a good technical discussion, this ISN'T a argument, Smitty
I thought about the comparison between the 2 drives, hard to compare one drive thats turning suprcharger 10 to 1 at 58,000 rpms vs 1-1 on a roots , I do know the impellor shaft in y M-3 is 20 mm in dia (less than 7/8ths of a inch), I dont think you could spin a old school roots with a shaft that small without shearing it off.

Ill add i have never seen anyone double keyway a crank snout on a marine centrifigal. Those heavy billet lobes are geared on a roots too,and swing some inertia ,but still ...

Yes.. 7.5" lower & 5.25" upper pulleys is what they suggested...

I'm only shooting for 8-10 PSI on a 555 cid engine..