I'm looking at ripping the tired old 305 TPI out of my 90 Trans Am and replacing it with a blown 383. I've already figured which kit to get as far as the internals go. I'm looking at a compression ratio of 7.69:1 right now so that I can safely get around 8 psi. That should put the new compression ratio at 11.88:1 (boost / 14.7 + 1 x compression ratio). What I'm wondering is what ignition to use. Will an HEI distributor fit? Also what is the max RPM that these units? I don't want to base my decisions on a calculation that the blower won't spin to. I've heard the engine can spin around 5500-6000 with no problem but is that with the full 8.4 psi pulleys or the little 1.95 drive ratio pulleys that come with the kit? I know it's a lot of questions but I plan on sinking 10k easliy into this engine and want to catch any possible mistakes before the purchases are made and...yeah...boom. Any help would be greatly appreciated.

 

You'll never get 8 PSI shoved in the snoot of a 383 with that little blower. I'm running a very mild 383 with the nearly-identical 142 blower on top. I'm one step from maxed-out on the pulley selection and I'm only getting 5 PSI. Hosepower checks in at 390 to the rear wheels, so it works pretty well, but you're asking too much of that little blower.

A 350 would be a better starting point- very hard to get compression down in the 7s on a 383 and the blower really doesn't have the lungs to feed an engine with much more than 350 cubes. Don't worry, you won't lose any torque or power by going with a 350- the pulley ratio on the blower has a LOT more to do with that than does the number of cubes it's feeding. If I had it to do over again I'd just build a 350- the hassle and expense of building a 383 just isn't worth it with these little blowers.

I've got 76cc heads (older AFRs) and -31cc dished pistons and I'm right at 8:1 compression now in my 383. My cam, by the way, is a cheap little Summit K1103 with 214/224* @ .050 on a 112* LSA. Yes, an HEI distributor will fit- that's what I've got on mine.

You don't want to overdo it with the cam or the size of the engine when you're considering one of these little mini blowers. They can't flow much air (500HP at the flywheel is about the lid) so it's CRITICAL that you use what airflow they are capable of EFFICIENTLY. If you overdo it there's just not a wide enough range of pulleys available to make up for it (like there is for a big 'ol 6-71 blower).