pcakes55 Posted June 26, 2012 Share Posted June 26, 2012 Anyone know what compression ratio this will yield: - l28 bored over .040 - dished pistons - P90 head shaved .006 - OEM head gasket In addition, anyone know what compression ratio flat-top pistons would yield? I know these would be just rough figures; I tried using a calculator but I was unsure of the new combustion chamber CC after being shaved down. Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted June 26, 2012 Share Posted June 26, 2012 (edited) Yeah you'd have to know the CC if you want to calculate it using that online calculator. Why are you only shaving it that much? Normally people shave it .08" and use flattops to get a 10:1ish comp ratio. What is your reasoning for using dished? It will do nothing for the head you have except mess with the quench zone. Are you going with a high comp engine, or a turbo? This combo seems like it will yield similar to stock NA performance. IF you have the diameter of the cylinder head combustion chambers you could use math and calculate the area and subtract that from the stock CC for a good estimate. Edited June 26, 2012 by BluDestiny Quote Link to comment Share on other sites More sharing options...
Z Greek Posted June 26, 2012 Share Posted June 26, 2012 Milling a P90 head .006 is negligible as far as a change in chamber volume. Do you mean .060 by chance? I just milled a P79 .045, and ended up with chamber volumes of 49-49.5 cc. With .040 over FLAT top pistons milled to .010 negative deck height (protruding .010 out of deck) my compression ratio calculated at 9.65:1. Dished pistons will yield less static compression, but not knowing the volume of the dish, impossible to calculate. I have been using an online calculator that works really well. www.csgnetwork.com/compcalc.html Quote Link to comment Share on other sites More sharing options...
pcakes55 Posted June 26, 2012 Author Share Posted June 26, 2012 This is a turbo engine; Starting to consider ditching my turbo set-up for an mild NA build just to get it FINALLY running this year. Just wanted to see what comp ratio's i'd be looking at w/ flat tops vs dished. Also iirc, the head was shaved previously and .006 was the maximum they could go. Oy my memory is hazy (been 2 years since the machine shop), I'll have to measure the head height tonight I suppose. Quote Link to comment Share on other sites More sharing options...
roger280zx Posted July 1, 2012 Share Posted July 1, 2012 .006 does not change compression considerably. A flat top p90 is 8.8 shaved .006 woud be about 8.86-8.9. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.