Static Compression Ratio calculator - TCCoA Forums

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post #1 of 1 (permalink) Old 01-16-2011, 11:43 PM Thread Starter
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Static Compression Ratio calculator

pertinent modular motor info

Stock: 3.552"
0.020-over: 3.572"
0.030-over: 3.582"
Big-Bore: 3.700"

Stock 4.6L: 3.543"
Stock 5.4L: 4.16"
Stroker "4.6L": 3.750"

HeadGasket: 0.036"

"Deck Height": 0.012-0.015" (0.120" for 5.4L)

Piston volume (dish):

10.49 cc's (romeo 2V NPI 4.6/5.4)
17 cc's (romeo/windsor PI 4.6/5.4)

4.5 cc's

2.8 cc's

Combustion chamber volume:

NPI 2V: 50cc's
PI: 42.5 cc's
SVO: 51 cc's
38 cc's (Trickflow Twisted Wedge TFS-51910001-M38, TFS-51910003-M38)
44 cc's (Trickflow Twisted Wedge TFS-51900002-M44, TFS-51900004-M44)

49.7 cc's



1. Now, this online calculator assumes the HG bore diameter is the same as the engine bore diameter, when in reality it is not the same. The bore on the HG is slightly larger, so when the number crunching is done, it calculates a smaller HG volume than there really is, so your actual CR will be just a smidge lower, but not by much. Also, combustion chamber volumes for OEM/FRPP heads are usually listed as ± 1.5 cc's, so there is generally some variance. The values I listed above are nominal values that can be used for a "starting point".

Most of these values I got from a list I had saved over the years, so if I made a mistake, feel free to correct me via PM.

2. There are NO negative numbers anywhere, EXCEPT if your pistons are going to ABOVE the block's deck surface, or if your pistons are domed upwards. I see a lot of online references to piston dish as "-10cc, -17cc", etc. The negative sign in these instances just refers to the fact that it is a downward dish. So do not use a negative sign in the "deck height" nor "piston top volume" entry field unless you truly are using pistons above-deck or they have an upward-dome.

Example (my current build-up):

Stock bore, stroke, HG thickness, pistons roughly 0.006" above the deck (hence why its a negative #), flat-tops with roughly 0.5cc due to the intake valve notch, and an estimate combustion chamber volume for PI heads shaved 0.030"

Last edited by guitar maestro; 01-17-2011 at 05:19 PM.
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