Thread: What do you pros think??

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Help me test my app -

Oppps - posted before I saw tech's reply - let me try it with those numbers - great test case - thanks.

I was beta testing a java Compression Ratio applet I am developing and get these results, which is close very to the Crane advertised DCR of 9.5 for the cam.

What was your planned deck height and gasket thickness? With those numbers I could run it again. I assumed 0 deck height, .038 compressed gasket thickness (assume the same diameter as piston), flat top pistons and rod length of 6.8.

Also if those pistons have a valve relief, that volume should be added to the displacement volumes for a more accurate number.

Parameters:
Cylinders: 8
Bore: 4.39 in (.030 over)
Stroke: 3.85 in
Chamber: 75 cc
Deck Height: 0.0 in
Gasket Thickness: 0.038 in
Intake Closing ABDC: 68.0 degrees

Result:
Total Displacement: 466.20865373389995 ci
Cylinder Volume: 58.276081716737494 ci
Deck Volume: 0.0 ci
Gasket Volume: 0.5751924948664999 ci
Dynamic Stroke: 2.884533605675133
Static CR: 12.31140988142115
Dynamic CR: 9.4748420598766433

Using the numbers tech gave and a closing angle of 68 degrees ABDC for that cam -
My chamber needs to be adjusted for a floating point number - so I rounded to 79cc with valve relief added in.

Looks like that combo will take pump gas.

Cylinders: 8
Bore: 4.39 in
Stroke: 3.85 in
Chamber: 79 cc
Deck Height: 0.038 in
Gasket Thickness: 0.048 in
Intake Closing ABDC: 68.0 degrees

Total Displacement: 466.20865373389995 ci
Cylinder Volume: 58.276081716737494 ci
Deck Volume: 0.5751924948664999 ci
Gasket Volume: 0.7265589408839999 ci
Dynamic Stroke: 2.884533605675133
Static CR: 10.518149583509192
Dynamic CR: 8.131278529214296

Need to adjust my calculations for gasket diameter.

954.9 in the cylinder
95.0 in the chamber
4.2 in the piston
0.0 in the piston deck height
12.5 in the gasket

1066.6 total suckin'
111.7 total squeezin'
divide the larger by the smaller and find 9.548:1, rounded to 9.55

Ok - I have a couple of questions.
You guys have years experience - I'm just an engine theorist crunching numbers.

**************
With 95cc chamber,
4.2cc piston relief
0 deck
cam intake closing at 68 degrees ABDC

Dynamic stroke = 2.88 in
Dynamic CR = 7.4:1

**************
With the 75cc chamber
4.2cc piston relief
0 deck
cam intake closing at 68 degrees ABDC

Dynamic Stroke = 2.88 in
Dynamic CR = 8.8:1

***************
Isn't a dynamic CR of 8.8:1 well within the pump gas range?
Thanks for the info to determine the piston to deck height given overall deck height.