LS2 10.9:1 compression?
Thread Starter
Drifting
Joined: Jan 2010
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From: Katy TX
LS2 10.9:1 compression?
I'm curious as to how GM came to 10.9:1 compression on the LS2. LS2 heads are the same 64cc chamber'd heads on the LS6, but the LS6 has a 10.5:1 compression. How did GM get 10.9:1 compression out of the LS2?
Le Mans Master
Joined: Jul 2005
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CR = (CV+CCV)/CCV
CR=compression ratio
CV=cylinder volume
CCV=combustion chamber volume
Easy to see when you look at the formula...the top number increases with an increase in displacement while the bottom number stays the same.
PS I left out the head gasket volume, piston deck height, and piston dish/valve relief/dome variables in the CR formula above in the interest of showing the affect of displacement on CR.
Melting Slicks
Joined: Sep 2007
Posts: 2,597
Likes: 3
From: READING PA
St. Jude Donor '08-'09-'10
Cr calculator
More displacement...for a given combustion chamber and all else being equal (head gasket volume, piston deck height, and piston dish/valve relief/dome), increasing engine displacement will cause an increase in compression ratio.
CR = (CV+CCV)/CCV
CR=compression ratio
CV=cylinder volume
CCV=combustion chamber volume
Easy to see when you look at the formula...the top number increases with an increase in displacement while the bottom number stays the same.
PS I left out the head gasket volume, piston deck height, and piston dish/valve relief/dome variables in the CR formula above in the interest of showing the affect of displacement on CR.
CR = (CV+CCV)/CCV
CR=compression ratio
CV=cylinder volume
CCV=combustion chamber volume
Easy to see when you look at the formula...the top number increases with an increase in displacement while the bottom number stays the same.
PS I left out the head gasket volume, piston deck height, and piston dish/valve relief/dome variables in the CR formula above in the interest of showing the affect of displacement on CR.
10.46 CR for the LS2. With the following assumptions.
1 4.007 BORE
2. 3.622 STROKE
3. .051 COMPRTESSED HEAD GASKET
4. 65 CC CHAMBER VOLUME
5. 0 DOME VOLUME
6. .016 PISTON TO DECK.
7. GASKET 4.060
used this CR CALCULATOR http://www.csgnetwork.com/compcalc.html
Le Mans Master
Joined: Jul 2005
Posts: 5,328
Likes: 405
I agree with everything you say but on this formula I come up with
10.46 CR for the LS2. With the following assumptions.
1 4.007 BORE
2. 3.622 STROKE
3. .051 COMPRTESSED HEAD GASKET
4. 65 CC CHAMBER VOLUME
5. 0 DOME VOLUME
6. .016 PISTON TO DECK.
7. GASKET 4.060
used this CR CALCULATOR http://www.csgnetwork.com/compcalc.html
10.46 CR for the LS2. With the following assumptions.
1 4.007 BORE
2. 3.622 STROKE
3. .051 COMPRTESSED HEAD GASKET
4. 65 CC CHAMBER VOLUME
5. 0 DOME VOLUME
6. .016 PISTON TO DECK.
7. GASKET 4.060
used this CR CALCULATOR http://www.csgnetwork.com/compcalc.html
1. The bore specification is 4.0007"-4.0017".
4. The OP says the chamber volume is 64 cc, which one is correct?
6. You entered the piston deck height as a positive number in the calculator, pistons above the deck have to be entered as a negative number. Having said that, are you sure .016" is the correct number for LS2s. I thought is was more in the range of .005"-.010".
Find the exact numbers for chamber volume and piston deck height along with the correct sign and recalculate. You should be closer to 10.9:1 with the correct entries.
Melting Slicks
Joined: Sep 2007
Posts: 2,597
Likes: 3
From: READING PA
St. Jude Donor '08-'09-'10
Let's review a few of your assumptions...
1. The bore specification is 4.0007"-4.0017".
4. The OP says the chamber volume is 64 cc, which one is correct?
6. You entered the piston deck height as a positive number in the calculator, pistons above the deck have to be entered as a negative number. Having said that, are you sure .016" is the correct number for LS2s. I thought is was more in the range of .005"-.010".
Find the exact numbers for chamber volume and piston deck height along with the correct sign and recalculate. You should be closer to 10.9:1 with the correct entries.
1. The bore specification is 4.0007"-4.0017".
4. The OP says the chamber volume is 64 cc, which one is correct?
6. You entered the piston deck height as a positive number in the calculator, pistons above the deck have to be entered as a negative number. Having said that, are you sure .016" is the correct number for LS2s. I thought is was more in the range of .005"-.010".
Find the exact numbers for chamber volume and piston deck height along with the correct sign and recalculate. You should be closer to 10.9:1 with the correct entries.
, Actiually the Chamber volume on the LS2 is 65CC.
Thread Starter
Drifting
Joined: Jan 2010
Posts: 1,447
Likes: 1
From: Katy TX
Melting Slicks
Joined: Sep 2007
Posts: 2,597
Likes: 3
From: READING PA
St. Jude Donor '08-'09-'10
