Thanks Supernaught!
I was toying around with the calculator to find the resulting compression ratio with the current piston configuration and possible crankshaft combinations.
I found this page with common m20 stroker configurations and information about each.
I wanted to see how each different crank would affect the compression ratio if I used the pistons and rods that are already installed. It required me to calculate and double check the piston compression height. By figuring this out with the known information and the ross configuration I could use the same piston compression height to compare the compression ratios without actually measuring the piston compression height.
Using the formula
Piston Compression Height = Total Block Height - (0.5*Crankshaft Stroke) - Rod Length
= 206.7mm - (0.5*89.6mm) - 135mm = 26.9 mm from wristpin to piston crown
I plugged that into the calculator with the other stroke lengths and compared them. It seems just about right and matched the information Ross sent to me.
Ross Racing m20
I then compared that to stock.
stock m20
and to a 84 mm crank from an m52
Ross Racing pistons with 84mm crank
and the m50b30 crank (85.8 mm)
As you can see the displacement goes up but the Compression Ratio keeps dropping on smaller cranks. That makes sense with what was mentioned previously about the low compression numbers I was seeing.
I have been doing some research to see how compatible different crankshafts are in the m20 and it looks like the 84 mm and larger cranks need a front seal as well as possibly longer crank bolt and intermediate shaft.
I am considering turbo down the road so a lower compression ratio is ideal, but with higher octane and proper tuning the 89.6 mm crank or 85mm crank are optimal compromize between cost, displacement, and compression ratio.
Feel free to let me know if you see i made a mistake somewhere, but right now I am leaning toward the s54 crank if I can get it at an ok price, eventhough the CR is higher than a stock m20 that people usually turbocharge.
I read about the Dynamic Compression Ratio and Rod/Stroke ratio and want to consider those as well for the build. It is important to note the head is stock and I live at an alititude of about 6500 feet.
I was toying around with the calculator to find the resulting compression ratio with the current piston configuration and possible crankshaft combinations.
I found this page with common m20 stroker configurations and information about each.
I wanted to see how each different crank would affect the compression ratio if I used the pistons and rods that are already installed. It required me to calculate and double check the piston compression height. By figuring this out with the known information and the ross configuration I could use the same piston compression height to compare the compression ratios without actually measuring the piston compression height.
Using the formula
Piston Compression Height = Total Block Height - (0.5*Crankshaft Stroke) - Rod Length
= 206.7mm - (0.5*89.6mm) - 135mm = 26.9 mm from wristpin to piston crown
I plugged that into the calculator with the other stroke lengths and compared them. It seems just about right and matched the information Ross sent to me.
Ross Racing m20
I then compared that to stock.
stock m20
and to a 84 mm crank from an m52
Ross Racing pistons with 84mm crank
and the m50b30 crank (85.8 mm)
As you can see the displacement goes up but the Compression Ratio keeps dropping on smaller cranks. That makes sense with what was mentioned previously about the low compression numbers I was seeing.
I have been doing some research to see how compatible different crankshafts are in the m20 and it looks like the 84 mm and larger cranks need a front seal as well as possibly longer crank bolt and intermediate shaft.
I am considering turbo down the road so a lower compression ratio is ideal, but with higher octane and proper tuning the 89.6 mm crank or 85mm crank are optimal compromize between cost, displacement, and compression ratio.
Feel free to let me know if you see i made a mistake somewhere, but right now I am leaning toward the s54 crank if I can get it at an ok price, eventhough the CR is higher than a stock m20 that people usually turbocharge.
I read about the Dynamic Compression Ratio and Rod/Stroke ratio and want to consider those as well for the build. It is important to note the head is stock and I live at an alititude of about 6500 feet.
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