With the success of the boosted LS2's I was wondering what everyone thinks about putting a blower on a larger cubic inch (383-402) forged motor with compression in the 10.8 range. What types of limits would it have? Would you have to run race gas all the time, or run low boost only?

 

Assuming you have a good intercooler... I think 7psi is about as much as I'd try to push with pump gas. You could probably get by with 10 psi with alky injection. Of course with race gas you could run a lot more boost, but that would get pretty damn expensive.

The engine would be very responsive and still pull nice with 7-10 psi of boost on top of it. Changing the heads might allow you do drop your SCR a point or so (depending on what you have now for heads), if you did this you could run even more boost.

 

What type compression would be needed to run about 15lbs of boost with a large ci motor ?

 

I'd keep it under 9.5:1. IMO, 8.5:1 to 9.2:1 would be about ideal for 15 psi.

 

We've run 16 psi with the compression ratio at 9.5/1 with an ATI ProCharger and a front mount intercooler, on 93 octane. Bob

 

The heads are 5.3's that have been milled about .015, I can't remember the chamber size though. How large of a chamber can you get with an ET head?

 

I don't think you'd need race gas all the time. You only need the octane when cylinder pressure goes up... as in during times of boost.
I would look into a very healthy methanol injection system.

 

You should be able to get a 72cc head from several of the aftermarket companies... that will drop your CR a good amount.

 

With stock heads and forged internals how much boost could be run safely on pump gas and still make descent power?

 

Can you run any boost with 11.25 comp?

 

Your total compression will be way up if you try to make a lot of boost on pump gas. My guess is that 6psi intercooled would be safe, but you'd have to really watch the IAT's, and try to keep them at or below 125F to be on the safe side.

 

I would also say 6psi intercooled should be pretty good, if you want to go farther than that new pistons are not too big of a investment in the grand scheme of things when your doing a full F/I setup, or you can always do big chamber aftermarket heads &/ cometic .7x head gaskets.

 

I can tell you what happes on 10:1 with 18psi.

Detonation is a big concern, and temp plays a big factor. At that CR it is very hard to control.

 

I'm running 5-6 psi on a 10.8-1 346 with ls6 stage 2 heads.

 

How much power put down with this setup?

 

602rwhp and 495rwtq!

 

A tuner friend of mine in Oz runs 10.8:1 on a forged H/C 383 at 14-15 Lb w/alky spray with the same blower as mine. Around 700 RWHP on a daily driver. He obviously keeps timing on a very short leash, but get excellent mileage and efficiency out of boost. Gas is very expensive downunder.

 

Keep in mind that if you are going to be adding forged pistons, you can lower the compression ratio with the right set of pistons, allowing you to keep the stock heads. Bob

 

Which blower is this? and how much boost is he able to run?

 

He's running the Starr/Whipple 2.3 L intercooled blower at about 14 Lb.