What's my compression ratio?
Thread Starter
Joined: Nov 2001
Posts: 8,246
Likes: 34
From: Victoria, TX
What's my compression ratio? I've got milled LS1 heads. The combustion chamber cc's out to 61cc (stock is 67cc). I have a stock shortblock (read stock pistons and stock head gasket thickness). Some of you compression gurus should know this. I think the compression height of a stock LS1 is .005" positive, but I could be mistaken.
Thanks,
Patrick
Thanks,
Patrick
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
TECH Regular
Joined: Nov 2001
Posts: 450
Likes: 0
From: Tullahoma TN
Re: What's my compression ratio? According to GM, the stock compressed head gasket thickness is 1.33mm or 0.0523". If you use 4" diameter for head gasket hole, then the volume of the compressed open space between piston and head is roughly .657 cid or 10.77cc. Of course the LS1 piston actually sticks up above the block by about 0.007" stock, so you will need to subtract this 'piston above deck' volume. Using a 3.9" diameter piston and a negative piston deck height of 0.007", you get -.084cid or -1.37cc for the piston above deck volume. 10.77cc-1.37cc=9.40cc. But then you have to add back the volume around the top piston ring which is approx. 1.2 cc. So 9.4 + 1.2 = 10.6cc.
So with a 61cc combustion chamber:
61cc+10.6cc=71.6cc. (709cc+71.6cc)/71.6cc = 10.90
So with a 61cc combustion chamber:
61cc+10.6cc=71.6cc. (709cc+71.6cc)/71.6cc = 10.90
Thread Starter
Joined: Nov 2001
Posts: 8,246
Likes: 34
From: Victoria, TX
Re: What's my compression ratio? Wow, what a fast and informative post John. Thanks! Everyone else concur?
__________________
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
TECH Regular
Joined: Nov 2001
Posts: 450
Likes: 0
From: Tullahoma TN
Re: What's my compression ratio? FYI:
Some stock LS1 dimensions per GM:
Stroke: 3.622"
rod length: 6.098"
block deck height: 9.240"
piston comp. height: 1.338"
piston to deck ht.= block deck ht. - [(stroke/2)+ rod lenght + piston comp. ht.]
9.240" - [(3.622"/2) + 6.098" + 1.338"] = -.007"
So the piston sticks up .007" above the block. The negative sign denotes the piston is above the block. Most conventional engines have the piston slightly below the block deck and would have positive piston to deck heights.
Some stock LS1 dimensions per GM:
Stroke: 3.622"
rod length: 6.098"
block deck height: 9.240"
piston comp. height: 1.338"
piston to deck ht.= block deck ht. - [(stroke/2)+ rod lenght + piston comp. ht.]
9.240" - [(3.622"/2) + 6.098" + 1.338"] = -.007"
So the piston sticks up .007" above the block. The negative sign denotes the piston is above the block. Most conventional engines have the piston slightly below the block deck and would have positive piston to deck heights.
