Volume-testing for CR question

[Gunter]

How exactly is it done?
Can someone post details for equipment, formula. etc?
Thanx

[JeremyD]

Originally posted by Gunter
How exactly is it done?
Can someone post details for equipment, formula. etc?
Thanx

Try here

[JeremyD]

Here's a good resource too

http://www.rbracing-rsr.com/compstaticcalc.html

[cgarr]

This one too, just enter 2 then your in mm, if your cc'ing the cumpustion changer with the engine togeather then you can leave out all the other measurements, all you need is the bore, stroke and what your chamber cc'd at http://www.csgnetwork.com/compcalc.html

Craig

[randywebb]

I posted on your other thread ...

BTW - a formula can be used if you have flat top pistons.

[Jeff Alton]

Lets see some pics of your tools for measuring.....

Jeff

[cgarr]

When I did my 912 engine, rolled it on the stand so the plug hole was up, set it at tdc, filled the combustion chanber with water to the plug hole which was 51cc The bore is 86mm stroke is 74mm that gave me a cr of 9.4 to 1 very easy and accurate..

[Gunter]

Thanks Craig: A burette is necessary in any case. Water is not my favorite because of rust concerns; but one could use a thin oil.
Interesting; TDC, fill with.........thru plug hole, ??cc's, bore & stroke.
Sounds easy enough. I am a long way from doing it but it's good to know how CR is confirmed.

[randywebb]

use ATF

[Jim Williams]

Here's another, if you want to wade though it... I didn't post the graphics, but they're in the Oct 97 Porsche Panorama magazine if you can find a copy. Or if there's any interest, I think I can find the graphics on my computer and post them.

http://members.rennlist.com/jimwms/Tech/comp_ratio.html

[JeremyD]

Bruce anderson has a pretty good description with pictures too.

[ChrisBennet]

Originally posted by Jim Williams
Here's another, if you want to wade though it... I didn't post the graphics, but they're in the Oct 97 Porsche Panorama magazine if you can find a copy. Or if there's any interest, I think I can find the graphics on my computer and post them.

http://members.rennlist.com/jimwms/Tech/comp_ratio.html

It's not the method I use but I like it.
The advantages I see are that you don't need expensive Jo blocks (Bruce Anderson's method) and you don't need to measure deck height (my method) directly.
Disadvantages would be the amount of fluid necessary (multiple fillings of the burette) and the possibility of fluid getting into the motor.
-Chris

[Jim Williams]

Chris,

I came up with this trying to find a little easier to understand method. Deck height is handy to know for other reasons, but I couldn't see where it was necessary for C/R.

The volume around the piston dome can be determined with the piston and cylinder out on the workbench before they are installed on the engine, so you don't have to worry about fluids in the engine. It's also easier to level the p/c when they're on the workbench. This makes the cc'ing easier and more accurate. The top of the piston dome is adjusted to be level with the top edge of the cylinder, resting in contact with the plexiglass cover, so the only fluid used is that actually around the piston dome.

Only two burette fillings are necessary. One complete fill for the combustion chamber volume (under 100 cc) and one for the volume around the piston dome (well under 100 cc).

The only measurement needed on the engine is distance from the top of the cylinder down to the top of the piston dome, with the piston at bottom dead center.

[ChrisBennet]

Aha! Even better! I misread your article. I see now that you only measure the depth down to the piston when the engine is assembled, no fluid involved. I like it so much I think I'll try it on the next motor I do.
Sometimes I'm jealous of you guys with the big brains...
-Chris