safe compression ratio? - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

dragonsp600 · 12-10-2018, 03:23 PM

gonna be doing heads and an intake over this winter on my 2010 ss. looking at doing ls9 headgaskets, arp studs and livernois ported heads. was debating having livernois mill the heads .020, which would bump the compression up to 11:1. is that safe on 91 octane? not gonna run e85. that should leave plenty piston to valve clearance also I beleive? may be running nitrous down the road, would I be safe running it at 11:1, or stock compression better? thanks for any and all help!

zz430camaro · 12-10-2018, 03:36 PM

Is it an LS3?

Bo White · 12-10-2018, 04:06 PM

What cam?

zz430camaro · 12-10-2018, 04:29 PM

I know LS3 pistons stick out of the hole about .007 so make sure you consider that. 11 sounds high for .020 off and a LS9 gasket.

dragonsp600 · 12-10-2018, 07:28 PM

yes, ls3. Brian tooley night fury cam. I was just guessing the comp. might be like 10.9ish?

dragonsp600 · 12-10-2018, 07:37 PM

Cam specs are 233/242 .629"/.629" 113+3

zz430camaro · 12-10-2018, 07:43 PM

11 to 1 should be fine, especially with a larger cam like that. I would not worry about it.

sixty9fordkiller · 12-11-2018, 12:43 AM

my car is at 11.5:1 and runs on 91 octane. It runs perfect BUT, there is still power left on the table. Had to pull timing because 91 octane is not quite enough

GRNFLSH · 12-11-2018, 06:32 AM

I have GPI ported and polished heads milled 0.30 on an L99 with their SS1 VVT cam, tuned on 91. Their thought was that that milling will compensate for the material removed in the chamber and it should cc slightly less than stock.

We did have to update the tune to address some light KR at moderate cruise (I assume as the VVT cam phasing changes), and I’ve never picked up any KR at the track or WOT. The butt dyno and ear perceive that it’s happier when I have 93 in the tank, but it’s a rare find in my area. I’ve tried a few octane boosters and have had the best luck with Lucas, but there’s no substitute for 93.

Russell James · 12-11-2018, 07:40 AM

Just an opinion, but with a modded engine and putting that much money into heads, I'd leave a little meat for future clean up passes which are generally .005". Anytime a head is off it should get a clean up. So maybe take .010"ish off now. 93 would certainly be better for 11 to 1. 10.7 is about ideal for 91. If you end up pulling timing, there is no benefit to the hair extra compression.

Usually with cams, the cam manufacturer has dynod the combination and dialed in a grind to a compression and flow. I'd spend the $20 and send one of the pay per recommendation cam grinders all your specs and have them custom spec out a cam for your exact needs/wants. And the attention to details like - Johnson lifters, perfect length PRs, rockers, lobes, cam core material... that are easy on the valvetrain... will pay off in the reliability. Fast ramps and marginal parts will be a one summer experiment. It's no coincidence that most the peeling lobes come from the same cam grinder.

zz430camaro · 12-11-2018, 09:22 AM

I used thinner Cometic gaskets to raise compression and just milled a little off heads, so far it's worked great.

12-10-2018, 03:23 PM	#1
dragonsp600 Drives: 2010 ss Join Date: Feb 2018 Location: madison, wi Posts: 8	safe compression ratio? gonna be doing heads and an intake over this winter on my 2010 ss. looking at doing ls9 headgaskets, arp studs and livernois ported heads. was debating having livernois mill the heads .020, which would bump the compression up to 11:1. is that safe on 91 octane? not gonna run e85. that should leave plenty piston to valve clearance also I beleive? may be running nitrous down the road, would I be safe running it at 11:1, or stock compression better? thanks for any and all help!

12-11-2018, 12:43 AM	#8
sixty9fordkiller Donkey Dick Cam Camaro Drives: 2010 2SS/RS LS3 M6 Join Date: Oct 2009 Location: Los Angeles, CA Posts: 2,000	my car is at 11.5:1 and runs on 91 octane. It runs perfect BUT, there is still power left on the table. Had to pull timing because 91 octane is not quite enough __________________ Bone Stock

12-11-2018, 06:32 AM	#9
GRNFLSH Drives: 2015 Camaro 2SS Green Flash Edition Join Date: Dec 2015 Location: NW Arkansas Posts: 200	I have GPI ported and polished heads milled 0.30 on an L99 with their SS1 VVT cam, tuned on 91. Their thought was that that milling will compensate for the material removed in the chamber and it should cc slightly less than stock. We did have to update the tune to address some light KR at moderate cruise (I assume as the VVT cam phasing changes), and I’ve never picked up any KR at the track or WOT. The butt dyno and ear perceive that it’s happier when I have 93 in the tank, but it’s a rare find in my area. I’ve tried a few octane boosters and have had the best luck with Lucas, but there’s no substitute for 93. __________________ Kooks stepped headers & Solo XL Cat-back ADM CAI w/race scoop & Rotofab w/w relo GPI VVT SS1 cam and CNC ported heads milled .30 BTR .660 springs, Straub solid bushing trunions GPI rod-mod intake with I-M heat sheild Circle D 258mm Pro single disc 3700 rpm stall converter 169F thermostat & manual fan switch Tuned by Ryno at GPI - 455 RWHP / 416 lb-ft

12-10-2018, 03:36 PM	#2
zz430camaro Drives: 2015 1LE Join Date: Oct 2015 Location: Cleveland, OH Posts: 1,485	Is it an LS3?

12-10-2018, 04:06 PM	#3
Bo White Drives: 2015 Summit White 2SS 1LE Join Date: Feb 2012 Location: Vance Alabama Posts: 8,018	What cam?

12-10-2018, 04:29 PM	#4
zz430camaro Drives: 2015 1LE Join Date: Oct 2015 Location: Cleveland, OH Posts: 1,485	I know LS3 pistons stick out of the hole about .007 so make sure you consider that. 11 sounds high for .020 off and a LS9 gasket.

12-10-2018, 07:28 PM	#5
dragonsp600 Drives: 2010 ss Join Date: Feb 2018 Location: madison, wi Posts: 8	yes, ls3. Brian tooley night fury cam. I was just guessing the comp. might be like 10.9ish?

12-10-2018, 07:37 PM	#6
dragonsp600 Drives: 2010 ss Join Date: Feb 2018 Location: madison, wi Posts: 8	Cam specs are 233/242 .629"/.629" 113+3

12-10-2018, 07:43 PM	#7
zz430camaro Drives: 2015 1LE Join Date: Oct 2015 Location: Cleveland, OH Posts: 1,485	11 to 1 should be fine, especially with a larger cam like that. I would not worry about it.

12-11-2018, 07:40 AM	#10
Russell James Drives: '15 SS 1LE, '69 Z28 drag car Join Date: Dec 2009 Location: Mich Posts: 4,483	Just an opinion, but with a modded engine and putting that much money into heads, I'd leave a little meat for future clean up passes which are generally .005". Anytime a head is off it should get a clean up. So maybe take .010"ish off now. 93 would certainly be better for 11 to 1. 10.7 is about ideal for 91. If you end up pulling timing, there is no benefit to the hair extra compression. Usually with cams, the cam manufacturer has dynod the combination and dialed in a grind to a compression and flow. I'd spend the $20 and send one of the pay per recommendation cam grinders all your specs and have them custom spec out a cam for your exact needs/wants. And the attention to details like - Johnson lifters, perfect length PRs, rockers, lobes, cam core material... that are easy on the valvetrain... will pay off in the reliability. Fast ramps and marginal parts will be a one summer experiment. It's no coincidence that most the peeling lobes come from the same cam grinder.

12-11-2018, 09:22 AM	#11
zz430camaro Drives: 2015 1LE Join Date: Oct 2015 Location: Cleveland, OH Posts: 1,485	I used thinner Cometic gaskets to raise compression and just milled a little off heads, so far it's worked great.