300zxls1

iTrader: (13)

Just picked up a built LS6 today and I am tossing around the idea of putting it in my Procharged Sierra. The truck is driven almost every day and will only see the track a few times a year. Sense its street driven all the time I feel a engine with a higher compression ratio and lower boost psi, will give great low and wot driving. Sure in a all out race motor a 9.0-9.5:1 compression ratio is wanted if you will be running 15-25psi and low throttle driving is not a concern. But in my case I want out of boost perfomance as well. Below I will list the specs on the engine and some effective compression numbers for two different setups. I feel for my goals and being a 99% of the time street driven truck this motor could work out great.

It seems like most people jump right away and say you must have 8.5:1 compression for a supercharger or turbo and for a street vehicle the out of boost performance would be horrible. Plus you would have to run such high boost numbers to gain it back I would be out of the limits of the P1sc or stock 6-rib belt setup. I do plan to upgrade to the D1sc when I see one for the right price. But I see no reason to switch to a 8-rib belt if I am only going to run 10psi of boost and I have zero belt slip right now making 12psi with the Ls1 in the truck and stock heads. So with the better flowing warhawk heads the 3.7 pulley should make right around 10psi. Or I can just swap pullies.

I have always read and been told on a supercharged engine that has forged internals and supporting mods an effective compression ratio for 93 octane is 16.0:1-18.5:1. On all out race engines sometimes they will see 25:1 effective compression, but who wants to do the majority of there driving on the street with a 8.5:1 compression ratio out of boost.

9.5:1 compression engine running 14psi has effective compression of 18.55:1

I would feel safe running that amount of boost with a 9.5:1 compression Ratio. Below is the ratio for my engine. But as soon as I mention 10psi and 10.7:1 compression almost eveyone says it wont last. But why the effective compression ratio is less? Wouldnt the 10.7:1 engine make less top end power but tons more down low? And be a much better suited daily driver?

10:7.1 compression engine running 10psi has effective compression of 17.98:1

Here are the specs on my new engine:

LS6 Block, decked, honed
LS6 crank
Eagle Rods ARP2000's
Diamond Pistons
Steel Top ring/Napier second
Coated bearings
ARP head/main studs
Main Caps pinned
Cadillac Lifters
Yella Terra Rockers
Comp Cam custom grind 234-232 .593 lift
World Product Warhawk 235cc 64cc LS1 heads
Dual springs, stainless valves
Comp push rods
Pro-Flow intake and rails
TBSS 87mm throttle body
LTs, x-pipe, true duals
T-56 trans
P1SC w/custom FMIC
Tial 50mm BOV with 3psi supercharger spring

yessir

iTrader: (5)

just out of curiosity, if all else were equal in your example engines (heads, cam, rpms, displacement......will the motors with different static compression ratios make the same power if the are both boosted to reach the same effective comp ratio?

300zxls1

iTrader: (13)

Thats the general feeling. Effective compression is a good starting point for comparing two boosted setups.

BoostnTBSS

iTrader: (-1)

Goes good with E85 @18psi lol

Kory 88Iroc Lt1

iTrader: (7)

Subscribing. I am interested in this as well
Kory

1SlowHoe

iTrader: (27)

I don't see any real problem with your build and boost level goals. You are right about not needing to be 8.5:1 for what you are wanting.

Many people run 10-15psi on stock LS engines. The 6.0 GTO is 10.5:1 and with a good tune you can run 12-14psi all year long with no issues.

I have the same goal as you. I have already built my 10.4:1 408 and have a TVS2300 to go on it. I plan to run 12-14psi.
With my cam 231/239 .598 .610 116+1 I will see:
Static compression 10.4:1SCR
Dynamic compression 7.50:1DCR

I'm not sure how you calculated the effective compression.

That 408/2300 is going into my 2002 Tahoe by the way

Jax326

Out of curiosity what do you expect for hp numbers. I have been curious about the advantages of running a close to 10:1 compression ratio in a 6.0 turbo'd car that was 99%the street driven

madmax4499

iTrader: (3)

Wow your over thinking things! three types of CR's come on! your running a p1sc with a hell of a parts list. with the ls platform it seems no matter what you do it is going to make good power. it all depends on how you want to use the power you make. it looks like your building a DD car, the 10.7 will work but if your tune is questionable or you get a bad tank of gas, your going to break parts. 8.5 is old school and you rarely see it anymore, the norm seems to be 9.5 for most builds, you do see higher on e-85 builds.

my street build is 9.3 on 92 pumpgas, i have 4-link and 29-18.50-15 tires. the power is fun getting sideways at 100 mph just rolling into boost not so much fun! i always wanted a 1000 rwhp street car, now i find myself trying to keep it off the guardrail.

WheelsUp84z

iTrader: (14)

its all bout the lb/min thats flowing essentially more than the compression. Also efficiency. a P1 at 16 psi could flow less than a D1 at 12 psi (example only not real world). And as debatable as it seems, look at the GMHTP with the wastegate on the procharger. The larger pully at XXpsi, made less power than the small pulley limited to the same boost number.