beezee
True Classic
Looking for some opinions...
I want to increase the compression ratio on my 1500cc FI engine, and to do this the easiest way seems to be milling the head. I have a spare head so I wanted to determine how much to shave off to achieve a 10:1 static CR. Here are my calculations:
Bore = 8.64 cm
Stroke = 6.39 cm
Cylinder Area = pi x rad squared = 58.63 square cm
Displacement = Area x stroke = 374.64 cc
Since the stock CR for this engine is 8.5:1, the combustion chamber volume is 374.64 cc / 8.5 = 44.08 cc
To achieve 10:1 the combustion chamber volume must be 17.46 cc, a reduction of 6.62 cc. To do this I need to shave down the combustion chamber circular recess. The recess measures 8.7 cm. The area of the recess is pi x rad squared = 59.45 square cm. To achieve 6.62 cc I need a depth of 0.111 cm (or 1.11 mm). In imperial this is 0.044" .
So to achieve 10:1 compression ratio I need to mill the head by 0.044". Does this seem reasonable? Most of the information I can find suggests milling the head to remove the recess, which is around 0.060" which would be too much by my calculations.
Is 10:1 a realistic compression ratio?
Brian
I want to increase the compression ratio on my 1500cc FI engine, and to do this the easiest way seems to be milling the head. I have a spare head so I wanted to determine how much to shave off to achieve a 10:1 static CR. Here are my calculations:
Bore = 8.64 cm
Stroke = 6.39 cm
Cylinder Area = pi x rad squared = 58.63 square cm
Displacement = Area x stroke = 374.64 cc
Since the stock CR for this engine is 8.5:1, the combustion chamber volume is 374.64 cc / 8.5 = 44.08 cc
To achieve 10:1 the combustion chamber volume must be 17.46 cc, a reduction of 6.62 cc. To do this I need to shave down the combustion chamber circular recess. The recess measures 8.7 cm. The area of the recess is pi x rad squared = 59.45 square cm. To achieve 6.62 cc I need a depth of 0.111 cm (or 1.11 mm). In imperial this is 0.044" .
So to achieve 10:1 compression ratio I need to mill the head by 0.044". Does this seem reasonable? Most of the information I can find suggests milling the head to remove the recess, which is around 0.060" which would be too much by my calculations.
Is 10:1 a realistic compression ratio?
Brian