Re: How much compression can you go with a S/Charger?

88-406 · 01-19-2002, 10:13 PM

If boost is kept low, say around 3-5psi. How much compression can a 383 have without being at risk of detonation?

Thanks

KM

LPDesRoche · 01-20-2002, 01:19 AM

Well they are running 6lbs on LT1's with 10.2 CR. No real problems except when they get greedy. The cast pistons like to spit ringlands when the detonation gets bad from either poor tuning or higher boost levels.

norvalwilhelm · 01-21-2002, 02:43 PM

I have a boost vs static chart in front of me and 9.5 compression turns into 13.4 compression ratio under 6 pounds of boost. Start with 8 and 6 pounds of boost becomes 11.3. They don't recommend over 12 to 1 compression taking the boost into account for street use. I run 8 to 1 compression, o ringed the block and run 12 pounds for a compression of 14.5 under boost and get away with it so far.

Lohkay · 01-21-2002, 04:53 PM

What do you mean by you o-ringed the block? Everytime I see that I imagine an engine using o-rings instead of gaskets. its that what you did?

J Z06 · 01-21-2002, 05:22 PM

Not too sure If He's a member of the forum...there's a SUPER CLEAN Black Rippie/LaRocca 383 Blown LT-1 that comes to Englishtown a few times a year. He runs low 11's with 6PSI and runs a mix of race/pump gas. I think He tried more boost and it blew the head gasket(typical weak link, luckily). It does run HARD all day long. Pretty sure without the blower it does around what mine does which is respectable.

Good luck.

88-406 · 01-21-2002, 07:16 PM

Thanks for the info JD!

Norval, can you post a copy of that chart? or better yet, mimsk@megapathdsl.net

GTXgp · 01-21-2002, 08:50 PM

Here are two online calculators that I found for another project I was working on...
http://www.smokemup.com/utilities/calc/eff_cr.cfm

This one is a bit more in-depth (don't let the Turbo thing fool you, obviously it will work the same for SC). I haven't figured out which of these two is more accurate.
http://www.turbofast.com.au/TFcompB.html

Adam

norvalwilhelm · 01-22-2002, 12:26 PM

Lohkay. O ringing a block involves cutting a groove .032 deep around the cylinder, then a .040 stainless wire is carefully tapped into this groove leaving .008 of the wire sticking above the top of the cylinder, a copper gasket is used and the stainless wire bits into the copper gasket when the head is torqued on. I also use studs as they hold alot more then bolts. Copper gaskets can tend to weep oil so unless I needed them I would stay away from them. My compression can exceed 14 to 1 under 12 lbs of boost.
Boost is not everything. It measures how much resistance is in a motor. Have stock restrictive heads and exhaust and the boost is high. Install free flowing heads and exhaust and suddenly your boost is alot lower but the engine is making more power and using the boost. Also blown engines like alot of initial timming. Get it in fast but keep it low on top end. For light cruising I still run over 40 degrees but a boost computer pulls timming out as the boost increases

88-406 I don't have a scanner so I can't post the boost chart It does recommend not exceeding 12 to 1 with 92 octane fuel. So 8-1 with 8 lbs of boost is the limit.