JMortensen Posted July 25, 2007 Share Posted July 25, 2007 Pictured below is one such flat top L-28 currently in our shop that we degreed in the cam and now are machining valve relief’s in the piston tops. Really??? This is interesting... When I assembled my engine I did not cut valve reliefs in the pistons and thought that I had missed out on that opportunity. Is a machinist able to cut the reliefs without diassembling the bottom end? That would open up a lot of possibilities for a larger cam for me... So with a .023†negative deck height, and a .045†compressed head gasket, piston to head deck clearance for this particular flat top L-28 and MN-47 combo is .022†I have ran this combo on more than a few engines and it will leave the imprint of the pistons oversize on the squish portion of the head, but there is NO evidence of actual contact. Compressed stock gasket thickness is .052". That means with my standard pistons and the stock gasket, I should be in the .029" range. Does that sound right? I realize now I should have measured when I was assembling, but I was in a bit of a hurry at the time... Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted July 25, 2007 Administrators Share Posted July 25, 2007 Really??? This is interesting... When I assembled my engine I did not cut valve reliefs in the pistons and thought that I had missed out on that opportunity. Is a machinist able to cut the reliefs without diassembling the bottom end? That would open up a lot of possibilities for a larger cam for me......... Uh, well… yeah, "Shhhhh…" it can be done. I was planning to include that in the CAM thread. I already have 95% of the piston notching info already written up for that thread, (If I ever finally buckle down to finish the cam thread...) I’ll PM you the piston notching portion within the next couple hours. BRAAAP...BRAAAAAAAAAAP.......BRAAAAaaaaaaa........ Quote Link to comment Share on other sites More sharing options...
1 fast z Posted July 26, 2007 Share Posted July 26, 2007 Ill ad some imput on piston valve relifes. I run a .585, 286 duration cam, on my NA car, with shaved P90, yada, yada. I measured piston to valve clearence on my last install, which was with a 270, 280 duration .475 lift cam, and had .215" EX valve clearnce, and .115" intake. I had then installed the BIG .585 cam about a year later and had .120" on the EX, and .050" on the intake, and have run it this way for about 5 months now. 8000RPM plus and no tapping. I do run titanium retainers, light valves, etc. Just some imput. This is on a DIRECT flat top, NO dish, and .022" piston to head clearnce also. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 26, 2007 Share Posted July 26, 2007 Ill ad some imput on piston valve relifes. I run a .585, 286 duration cam, on my NA car, with shaved P90, yada, yada. I measured piston to valve clearence on my last install, which was with a 270, 280 duration .475 lift cam, and had .215" EX valve clearnce, and .115" intake. I had then installed the BIG .585 cam about a year later and had .120" on the EX, and .050" on the intake, and have run it this way for about 5 months now. 8000RPM plus and no tapping. I do run titanium retainers, light valves, etc. Just some imput. This is on a DIRECT flat top, NO dish, and .022" piston to head clearnce also. That is interesting. I guess I need to buy the cam I want and then test it for clearance. Quote Link to comment Share on other sites More sharing options...
Daeron Posted July 28, 2007 Share Posted July 28, 2007 BRAAAP...BRAAAAAAAAAAP.......BRAAAAaaaaaaa........ I don't wanna sound.. funny, er nuthin...... ..but it always gives me chills when you do that. Don't tell anyone, I think you and I like the same sounds coming from the exhaust Quote Link to comment Share on other sites More sharing options...
HizAndHerz Posted July 30, 2007 Author Share Posted July 30, 2007 Here's another interesting tidbit I found from Bryan (1_fast_z): You want to run about .025" piston to head clearence, for maximum quench. WIth your current setup you are at .040" and that extra .015" actually makes a difference in detonation resistance and power. So you need to pop those pistons out of the bore .015". Thats the setup I have been running for a couple years now. Technically you should get your pistons to have a PERFECT mirror image of YOUR p90 head for maximum quench. This is done by assembling your engine for mockup, and inserting each piston in one at a time and then put your head on, and "bump" each piston to the head with prussian blue on it then scribe your combustion chamber and mill out ONLY that area and NEVER go outside that line, THEN you will have the MAXIMUM quench you can optain. Most people skip this step and mess up, P90 heads are worthless without all of these steps. http://forums.hybridz.org/showpost.php?p=736826&postcount=3 Bryan, can you provide a little more detail? Are you saying that material should be removed from the combustion chamber to make clearance for the piston? If so, how would you determine how deep to go? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 30, 2007 Share Posted July 30, 2007 I think he's saying that with a dished piston the quench is lost. So if you wanted dished pistons you really want the dish to match the combustion chamber. There are lots of V8 pistons done this way, but they have a more generic 1/2 dish. Quote Link to comment Share on other sites More sharing options...
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