I'm thinking of building a short block for an ATI P1SC blower. I want to run about 8 psi (max) and was thinking about good blower pistons with the stock crank and rods. Would the rods be strong enough if I had them shot peened and de-burred? How about the stock crank? I've seen some cars in GMHTP running low 11s with stock crank/rods. If this is feasable then what would the difference in power be if I were to use stock comp. ratio forged blower pistons and add the blower later. Is it better to have say 9.5:1 and 8lbs of boost or 10.4:1 and 8lbs?

Thanks for any help.

 

Stock rods and crank are pretty solid. Seen many cars with 700HP on them. The stock pistons are a weak point, but can still handle 600+ if the programming is there. The bearings are the weak part of the crank. They like to spin real easily when reved to high. If you are going to build for 8psi only, and put in forged pistons, I would go with the 10.4:1 compression ratio. 9.5:1 will be a nice power loss, and 8psi on 10.4 should be perfect with a good tune.

Mav

 

Stock crank & rods will take a good bit. Pistons will not! You will have to put in forged pistons. If you ever plan to up your boost, I would run low compression. I run 8.8-1. Its not a good idea to build a motor for a blower with high compression. Forged or not you'll have detonation issues. Running lower compression is definetly the way to go for a supercharged motor. In order to run high comp on a SC motor, you'll have to retard a good bit of timing. By doing this, you'll be losing power. If you drop the comp, you'll lose a little power, but the motor will live longer.

 

Thats why you go with forged components. So you can run more boost with higher compression. Quite a few people are running 8psi on the stock parts and stock compression. If you forge the internals, you have very little to worry about. Detonation because of high compression is not so much a problem with the LT1 as is improper tuning and heat. Intercoolers and a smart foot have all but solved this problem.


Mav

 

i'm running 8lbs of boost on a stock lower end and have had no problems to date. when the motor does finally kill over i'll go with lower compression forged internals.

 

Build that sucker low compression!!! After having 8# for a week, you'll want 12#, then 15#, etc. It doesn't end. No point spending all the cash for a blower and then not taking full advantage of it. Don't worry bout the 10-20 HP you'll loose NA doing this, the extra 100+ from the boost will more than make up for it.

 

Very good point. I really don't think anyone can stop at 8 PSI. If you can't, you will have to lower the compression.


Mav

 

I'm running 8# on stock compression. No problems to date. I have a P1SC with twin high flow intercoolers. I will not go any higher on the boost until I do forged internals.


If you're smart about it, you can run 8# of boost on your engine. Just don't go crazy...which I admit, is tough to do(just remember 1st gear is useless then and that usually does it for me)

 

I would go the lower compression route also, it makes more sense.

There have been a few catastrophic engine failures in some higher horse LT1's due to the connecting rods or connecting rod bolts. By the time you prep the stock LT1 rods, you could just buy a new set. You could get some really strong h-beam rods for around $400 a set nowadays. They are heavier than the stock rod, but much stronger. Most crankshafts and con rods are forged overseas and then machined hear in the USA, this keeps the cost down. The other american made stuff is expensive, ie Lunati and Cola, but of very high quality. The only failure of the stock crank I have heard of is the nose of the crank coming off. Scat makes some good stuff too.

About the stock main bearings: I ran 9 pounds of boost for a few years and then blew 3 pistons. Upon teardown, the main bearings looked perfect, could have reused them.

 

Since your all talking bottoms ends, I was wondering, will a blower cam in a stock bottom end help make the stock internals live longer/less or would it have zero effect. --just wondering?

 

A blower cam will put out more power, and put more stress on the stock bottem end. Probably wont last as long.

Mav