nightman06

iTrader: (1)

I'm putting my parts together to support my TT kit. I've got a stock bottom-end '98 C5 LS1 MN6. I'll be running Alky kit but would like to lower compression as well. This isn't going to be seeing track and I'm not too concerned with a little low end loss.

From what I can see on the summit racing calculator, 317 heads on stock bottom end with a GM 6.0 gasket will net me ~9.4:1.

Is that going to get me in a "safe" neighborhood or do I need to go lower?

If so, does anyone have a pn for a thicker gasket that will work?

Is there a set of heads that others are using that would offer a lower compression ratio with larger chamber volume?

Thanks guys, I usually post in C/F but the FI knowledge seems to be higher here.

SKULL

iTrader: (7)

I think the ls9 gasket is thicker. but 9.4 is fine. it just comes down to who is tuning it and youll be fine. I was running a d1 14psi at 10.5:1 no issues.

Meth Sled

iTrader: (1)

Like he said, it's all in the tune. The higher the compression, the more knock sensitive a motor will be, hence people running lower compression and higher boost.

JoeNova

Compression drop aside, I would still go with LS9 gaskets.

stevieturbo

You dont mention boost, power, type of fuel you use etc etc

So really, no idea if you need to go lower, or could quite happily remain high.

But a little lower will always add a safety margin for negligible loss

nightman06

iTrader: (1)

Thanks guys!

Yes, I realize I havent included ALL the details. My basic question was whether or not I'd be giving myself an adequate margin of safety with the thinking. I'll be on pump gas. Trying to run ~10 psi. I'm really trying to baby this stock bottom end as it's currently a daily driver and I'd like to get some mileage out of it before I re-open it for another project. From what I gather guys are having luck with that level of boost on a stock bottom end with a solid tune and meth. If I can get 600 rwhp on that amount of boost I'll hang there. If not, ill turn it up and if it goes......I'll have another garage project!

Orr89rocz

iTrader: (13)

With good intercooling and tune you should be fine to run that boost on pump gas. Guys run alot more than that on 93 lol Just watch the tune and take your time to see what it wants

oscs

iTrader: (19)

9.4:1 is a great median. I run a very similar compression and made great power on Pump gas.

Forcefed86

iTrader: (4)

Your splitting hairs IMO. 1/2 point of compression either way isn't going to make a huge difference. It's like a 2% gain/loss in power NA. Generally the less compression you run the more power potential you'll have with limited octane. Less CR also provides a broader tuning window. So IMO error on the low side, esp. if your new to the turbo game.

I don’t care how the engine acts out of boost personally. My 8.6:1 JY 5.3 went 8’s in the quarter mile and 0-60 in 1.3 seconds... not exactly a "low compression dog".

nightman06

iTrader: (1)

Sounds good. Yeah I'd like to get lower on the CR, but I think I'm out of options short of getting into piston dimension. I dont want to run a gasket any thicker than .060. I might be able to squeeze a little more out with a port/polish job on the 317's. I get that I am probably overthinking it, but I'm sure you guys can all remember back to your first FI diy, just want to get it right.