Patrick G

iTrader: (14)

No, it's the same as an LS1 head. You just heard wrong.

bww3588

iTrader: (49)

The only reason I questioned it is because I seen it in a post from Richard@wcch

I in no way shape or form doubt either of you, just explaining my questioning.

Zbinkley

I have a stock lq4 with L92's milled to a 64cc chamber. My cam is tsp 233/239 .595/.605 114 LSA and IIRC my ptv was around .120 at TDC. I put the number 1 cylinder on TDC and put a dial indicator on the end of the valve stem, and with a checker spring on the valve pushed the valve down until it hit the piston and read the indicator.

3pedals

iTrader: (3)

what about at ~5*- 10* ATDC? that is usully where the intake is closest
Its a good idea to check between 15* before, and 15* after TDC, on both valves

LS6

Now the case I have:

• Engine Bore: 4.0845"
• Engine Stroke: 3.622"
• Gasket Thickness: 0.051" (data from http://www.fbparts.com/ls_general_charts.htm)
• Gasket Bore: 4.100" (Assuming it is 4.100", since I couldn't find this value)
• L92 Cylinder Head Combustion Chamber volume: 70cc (data from http://www.fbparts.com/ls_general_charts.htm)
• Clearance Volume (Distance between the top of piston cylinder to block deck): -0.007" (Many thank to SAMER for his valuable information he provided, Negative value mean the piston is out of or above the block by 0.007" for stock LS block if the deck is not milled)

1. Cylinder Swept Volume: 0.7853982 X Bore X Bore X Stroke = 0.7853982 X 4.0845 X 4.0845 X 3.622 = 47.5 ci
2. Clearance Volume: 0.7853982 X Bore X Bore X Deck Height = 0.7853982 X 4.0845 X 4.0845 X -0.007 = -0.0917"
3. Piston Compression Volume: Assuming it is 0cc since it is flat piston.
4. Head-Gasket Volume: 0.7853982 X Gasket Bore X Gasket Bore X Compressed Gasket Thickness = 0.7853982 X 4.1 X 4.1 X 0.051 = 0.673"
5. Chamber Volume: cc's X 0.0610237 = 70 X 0.0610237 = 4.272"

Compression Ratio (CR) = (Cylinder Swept Volume + Clearance Volume + Piston Compression Volume + Head Gasket Volume + Chamber Volume) / (Clearance Volume + Piston Compression Volume + Head Gasket Volume + Chamber Volume) = (47.5 -0.0917 + 0 + 0.673 + 4.272) / (-0.0917 + 0 + 0.673 + 4.272) = 52.353 / 4.853 = 10.8

The Compression Ratio (CR) is 10.8

Please correct me if I'm wrong...
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Now to get 11.0 : 1

Keeping the item no. 1, 2, 3, 4 the same as above calculation, but changing the item no. 5 from 70cc to 68cc, this will yield the following:

1. Cylinder Swept Volume: 0.7853982 X Bore X Bore X Stroke = 0.7853982 X 4.0845 X 4.0845 X 3.622 = 47.5 ci
2. Clearance Volume: 0.7853982 X Bore X Bore X Deck Height = 0.7853982 X 4.0845 X 4.0845 X -0.007 = -0.0917"
3. Piston Compression Volume: Assuming it is 0cc since it is flat piston.
4. Head-Gasket Volume: 0.7853982 X Gasket Bore X Gasket Bore X Compressed Gasket Thickness = 0.7853982 X 4.1 X 4.1 X 0.051 = 0.673"
5. Chamber Volume: cc's X 0.0610237 = 68 X 0.0610237 = 4.1496"

Compression Ratio (CR) = (Cylinder Swept Volume + Clearance Volume + Piston Compression Volume + Head Gasket Volume + Chamber Volume) / (Clearance Volume + Piston Compression Volume + Head Gasket Volume + Chamber Volume) = (47.5 -0.0917 + 0 + 0.673 + 4.1496) / (-0.0917 + 0 + 0.673 + 4.1496) = 52.2309 / 4.7309 = 11.04



The Compression Ratio (CR) is 11.04
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Now to get 11.6 : 1

Keeping the item no. 1, 2, 3, 4 the same as above calculation, but changing the item no. 5 from 70cc to 64cc, this will yield the following:

1. Cylinder Swept Volume: 0.7853982 X Bore X Bore X Stroke = 0.7853982 X 4.0845 X 4.0845 X 3.622 = 47.5 ci
2. Clearance Volume: 0.7853982 X Bore X Bore X Deck Height = 0.7853982 X 4.0845 X 4.0845 X -0.007 = -0.0917"
3. Piston Compression Volume: Assuming it is 0cc since it is flat piston.
4. Head-Gasket Volume: 0.7853982 X Gasket Bore X Gasket Bore X Compressed Gasket Thickness = 0.7853982 X 4.1 X 4.1 X 0.051 = 0.673"
5. Chamber Volume: cc's X 0.0610237 = 64 X 0.0610237 = 3.90552"

Compression Ratio (CR) = (Cylinder Swept Volume + Clearance Volume + Piston Compression Volume + Head Gasket Volume + Chamber Volume) / (Clearance Volume + Piston Compression Volume + Head Gasket Volume + Chamber Volume) = (47.5 -0.0917 + 0 + 0.673 + 3.90552) / (-0.0917 + 0 + 0.673 + 3.90552) = 51.9868 / 4.4868 = 11.6



The Compression Ratio (CR) is 11.6



Now milling the head by a 0.006" is equal to 1cc.
Thus to get 64cc from the 70cc, it require to remove 6cc.
Thus 6cc is equal to 0.036" (0.9144mm) to be removed.
It would be fine to make it 0.0315" (0.8001mm) to make it 11.5 : 1 CR

72VenturaII

iTrader: (32)

Those are the correct calculations, but the issue I see is you are using theoretical numbers, ie. piston height and combustion chamber. Before I had the heads milled I would preassemble the motor and check the actual piston height and have the combustion chambers cc'd. I have read L92 chamber volume go all the way from 65 to 70 cc's depending on who you read.