Guest iskone Posted March 29, 2005 Share Posted March 29, 2005 I have a N42/E88 combo. When I bought it the spec sheet had "Forged 11.5 to 1 Pistons" I've been trying to get an acurate measure of my compression. With my math the dome would have to be somthing like 16cc's. Sound right? Here's how I got the 16cc's 87mm bore (1mm overbore) 79mm stroke 53.5cc chamber (N42) 1.2mm head gasket 0.0 piston to deck clearnce Giving me 11.47cr I think the piston to deck clearance could be wrong. I used the specs from a 280 NOT my combo. My combo would be somthing around 14.76cr using the specs I came up with for the pistons. Something is wrong. I'm thinking maybe the 11.5 to 1 was a total not just the psitons. But I figured I'd explore all options. Oh, I almost forgot somthing very important the psitons DO have a dome, so how could that be overall CR? If they were flat tops with the above specs CR would be 8.54. Making me think it's the piston to deck clearnce I have wrong afterall. Help!? Isk Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 30, 2005 Share Posted March 30, 2005 According to the L engine calculator, your head stock should have a combustion chamber of 44.6 cc's. Since your head has been heavily modified, who knows what you have now, but it probably isn't 53.5. 53.6 is what is listed for a P90, just FYI. As for the dome, maybe you could take a mold of one of the pistons and measure the capacity of the mold??? Also stock pistons stick up above the deck just a hair. I want to say .003 or something like that. Quote Link to comment Share on other sites More sharing options...
Guest iskone Posted March 30, 2005 Share Posted March 30, 2005 Something screwed up is going on. I just got home to take alook at the pistons so I could compare them to this model I made. I got 18cc(I thought it was 18 at first) of clay put it on on a board and made what I thought the dome should look like. Not even close. The pistons have a much smaller dome. Big thing that is a problem is they do NOT stick up past the block. Now I could have turned the motor some since I pulled the head, but I don't think so. 1 & 6 are in the same position and there is a 1/4" carbon ring (just darkening not serious) at the top of all the bores. Since the pistons should peek out of the block there wouldn't be a carbon ring. I like the idea of making a mold. I'm gonna try it, but I left all my clay at work. I took some pics to show you, they are very bad since I use my cell phone. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 30, 2005 Share Posted March 30, 2005 The carbon ring is totally normal, and it only happens above the area where the top piston ring stops, not where the piston stops. Quote Link to comment Share on other sites More sharing options...
Guest iskone Posted March 30, 2005 Share Posted March 30, 2005 The carbon ring is totally normal, and it only happens above the area where the top piston ring stops, not where the piston stops. Quote Link to comment Share on other sites More sharing options...
Guest iskone Posted March 30, 2005 Share Posted March 30, 2005 I was thinking about the clay mold and I'm a little worried about going thropugh with it. I don't want any clay getting in the oil. I do have some Y2Klay that might not be a bad choice. How would I go about cleaning up the residue left behind? Isk Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 30, 2005 Share Posted March 30, 2005 I was thinking about the clay mold and I'm a little worried about going thropugh with it. I don't want any clay getting in the oil. I do have some Y2Klay that might not be a bad choice. How would I go about cleaning up the residue left behind? How about duct taping all the holes around the cylinder where you make the mold? Then you could make the mold without crap getting into the other holes. I would imagine the hardest part would be getting the clay to hold it's shape while you pulled it off of the piston. Maybe just put it on and let it dry for a day or something??? I don't think enough could get in between the piston and the bore to cause a problem since there is only a couple thousandths clearance there. Quote Link to comment Share on other sites More sharing options...
zcarnut Posted March 30, 2005 Share Posted March 30, 2005 To easily measure the volume of a piston dome just move the piston from TDC down into the cylinder a know amount, say A (in cm) just enough to cover the dome. Using a buret measure the volume on top of the piston up to the top of the cylinder. Call this B (in cc). Then the volume of the dome is then: A x PI x (D/2)^2 - B where D is the diameter of the cylinder (in cm) and PI is 3.14159.... (Fixed the units. Thanks Iskone!) Quote Link to comment Share on other sites More sharing options...
Guest iskone Posted March 30, 2005 Share Posted March 30, 2005 To easily measure the volume of a piston dome just move the piston from TDC down into the cylinder a know amount' date=' say A (in mm) just enough to cover the dome. Using a buret measure the volume on top of the piston up to the top of the cylinder. Call this B (in cc). Then the volume of the dome is then: A x PI x (D/4)^2 - B where D is the diameter of the cylinder (in mm) and PI is 3.14159....[/quote'] That's a great idea. I'll be working on it tonight if I get the time. For those who are reading and have to try somthing like this themselfs make sure to convert everything to CENTIMETERS before you start, if not you'll get some BS numbers. I'd did my calcs a little different though, easier for me. I verified this equation at the bottom. I used: Radius x Radius x PI x Height = Volume 4.3 x 4.3 x 3.14159 x 7.9 x 6 = 2753.3711cc Isk Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 31, 2005 Share Posted March 31, 2005 Maybe I'm being dense, but won't that only work with "gapless" rings. Because the ring gap would allow whatever liquid to pour through to the bottom, right??? Quote Link to comment Share on other sites More sharing options...
zcarnut Posted March 31, 2005 Share Posted March 31, 2005 Dab a little heavy grease around the perimeter of the piston top with a Q-tip to minimize any leaks. You can also use ATF for your volume measurement. It’s viscous enough not to leak. Lastly, make your volume measurement as quickly as possible. Quote Link to comment Share on other sites More sharing options...
Guest iskone Posted March 31, 2005 Share Posted March 31, 2005 Dab a little heavy grease around the perimeter of the piston top with a Q-tip to minimize any leaks. You can also use ATF for your volume measurement. It’s viscous enough not to leak. Lastly, make your volume measurement as quickly as possible. That's the game plan exactly. But I'll use ISP for for fluid. Biggest problem is I forgotthe Mic I was gonna use for the height and the small cylinder for the fluid. The cylinder I'll use is only 10cc and measure in .2cc incruments, it's all my work had lying around. I did buy the plexiglass and White Lithium Grease anyway. Isk Quote Link to comment Share on other sites More sharing options...
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