Calculations for compression
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From: paintsville ky
Calculations for compression Hey guys just needing someone smart like Predator-Z or someone to chime in and let me know if this is correct. I'm buying a set of 243 heads to swap over with this MS4 cam. Wanting to flycut the pistons 0.070, mill heads 0.020, drop to a .35 Head gasket (-0.015). Stock 243s are 64.45cc @ 10.5:1, after milling and gasket should put me at 57.45cc then +2 cc for flycutting putting me at 59.44cc @ around an 11.1:1 cr. Does this seem correct, safe, and is there room for more to be done here besides porting the 243s bc this will also be done but with no valve job at this moment. ( I am aware that most valve jobs increase cc's from material being taken from the chamber)
If the stock chamber is 64.45cc, then a .020" mill equates to about 3cc reduction (0.007" per 1cc is typical), yielding 61.45cc new chamber size.
chamber 61.45cc
gasket thickness .035"
gasket bore 4.02"
desk clearance .10" above deck
stock deck height
piston volume flat tops w/ 2cc valve reliefs
With the above numbers I come up with 11.3 static compression. I wouldn't worry about that ratio, but if those numbers are right your quench is very tight (.025").
chamber 61.45cc
gasket thickness .035"
gasket bore 4.02"
desk clearance .10" above deck
stock deck height
piston volume flat tops w/ 2cc valve reliefs
With the above numbers I come up with 11.3 static compression. I wouldn't worry about that ratio, but if those numbers are right your quench is very tight (.025").
Thread Starter
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From: paintsville ky
Ahh see this is why I ask, its better to have second and third views on this, thank you for your response btw. So a .045 gasket is needed for the .035 quench Im trying for, correct?
It depends upon how far your piston is above the deck. If your piston is above the deck surface, or out of the hole, you subtract that from the compressed gasket thickness to get your quench. If the piston is below the deck surface, add it to the gasket thickness to get your quench. Aluminum will expand a little as it heats up which will increase the quench just a tiny bit more.
So if you measure the piston at 0.010" out of the hole with a 0.045" gasket, your quench is 0.035"; if it is in the hole 0.010", the quench would be 0.055"; not taking into account any metal expansion of course.
So if you measure the piston at 0.010" out of the hole with a 0.045" gasket, your quench is 0.035"; if it is in the hole 0.010", the quench would be 0.055"; not taking into account any metal expansion of course.
Thread Starter
12 Second Club
Joined: May 2009
Posts: 184
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From: paintsville ky
oh yea, I remember that now haha. Well sir thank you for time, I just needed to make sure that this wasn't too much milling of the heads and gasket size and such. I always feel better getting second opinions on my numbers before I start ordering the parts.
