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Discussion Starter · #1 ·
Can someone tell me how to figure my comp ratio? It's a standard bore and stroke 427 BBC (It hasn't been bored out yet). TRW L-2300F forged pistons and 92cc iron heads. Thanks in advance. I believe it would be around 10.5 if it's .060 over, but it's not, so I'm guessing the comp ratio is lower with a smaller bore. I really don't know.....I'm just guessing the last part.

2,384 Posts
compression ratio

volume of one cylinder + volume of compression chamber+ volum of valve reliefs+ volume of head gasket+ deck relief of piston+ or - and dish or dome on piston, divided by the unswept area, which is all the area that is left when the piston is at top dead center.

volume of cylinder for a 427 = 878 CC
example combustion chamber =75 CC
example valve reliefs = 5 CC
example head gasket thickness of .040" X 4.3 " = 9.5CC
example piston relief from deck of block .030" X examp bore 4.25" = 7 CC Flat top pistons; no dish, no dome.

total CC volume= 974.5 CC

unswept area; 75 CC + 5 CC+ 9.5 CC + 7 CC= 96.5 CC

974.5 divided by 96.5 = 9.48:1 compression ratio

The combustion chamber, valve reliefs, gasket thickness, piston relief are examples only and not the actual figures.

The cylinder volume is also example, as I dont have your exact bore and stroke dimensions.

393 Posts
Heres the specs I found on them. You will have to refigure for your heads. With 92cc heads it will be higher

SDPC Part Number: L2300F
Manufacturer: Sealed Power
Bore : 4.250"
Stroke : 3.760"
Rod Length : 6.135"
Pin Height : 1.767"
Weight : 828
Ring Width : 5/64", 5/64", 3/16'
Compression Ratio : 9.5:1
Pin Type (P/F) : Pressed
Dome Volume : 16.8

*Compression ratio is figured with 107cc heads.
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