jay28 Posted May 23, 2009 Share Posted May 23, 2009 Hi all, When I started my car last weekend I seen some blue smoke from the exhaust.......I havent noticed any before when starting although there could have been.........It cleared after a few seconds, when the engine is warm and I rev it it also smokes slightly. I have only 5k miles on the engine so I was surprised.......I bought a compression tester today and looks like there is a problem. 1 183psi 2 183 3 185 4 186 5 185 6 191 Whats up with this? The engine is running perfect nice and smooth with no knocks or bangs. The car did overheat on me once when running it in after a frost plug came out, maybe the oil stem seals have hardened? although I dont think this would have anything todo with the high reading on cylinder 6. I was expecting a low reading on a cylinder not a high one Jay __________________ Quote Link to comment Share on other sites More sharing options...
jt1 Posted May 23, 2009 Share Posted May 23, 2009 Those are very nice comp test results, nothing wrong there at all. Smoke on startup is most likely the valve stem seals or guides. If it bothers you try replacing the seals and see if there is much wear in the guides while you have it apart. jt Quote Link to comment Share on other sites More sharing options...
jay28 Posted May 23, 2009 Author Share Posted May 23, 2009 Oh ok well thats good news, I thought there was something wrong with cylinder 6 as the comp was higher than the rest. Yeah I think ill take the head off, replace the seals and guides and maybe port and polish while am at it. Thanks Quote Link to comment Share on other sites More sharing options...
adamhoud Posted May 23, 2009 Share Posted May 23, 2009 wow those numbers are amazing! Quote Link to comment Share on other sites More sharing options...
Spooler Posted May 24, 2009 Share Posted May 24, 2009 Yeap, those numbers look good and are not too far off from each other. Quote Link to comment Share on other sites More sharing options...
ozconnection Posted May 24, 2009 Share Posted May 24, 2009 Yeah I think ill take the head off, replace the seals and guides and maybe port and polish while am at it. With a 5K old engine and with such good compression and the machine running smoothly, what else do you want? I wouldn't take the head off just yet. Have you tried a different oil, perhaps one with a slightly different viscosity or an additive and see if that has any effect. Valve stem seals if the culprit are easy to replace with the right tools and some compressed air. If you really want to port the head, go for it, seems such a shame to pull the head off to do something that perhaps you should've done before screwing it together 5K ago. Just my 2 cents worth. Quote Link to comment Share on other sites More sharing options...
Kash Posted May 24, 2009 Share Posted May 24, 2009 Hey Jay, what compression ratio are you running? Is that a turbo or a NA motor? Quote Link to comment Share on other sites More sharing options...
jay28 Posted May 24, 2009 Author Share Posted May 24, 2009 well the engine was put together a year and a half ago now, only done 5k in that time. And yes I probably should have done the port and polish back then I just dont like the smoke on startup............compression is "roughly"10.1 Its a f54 block, p90 head shaved 2mm, flattop pistons, stage 4 cam and triple dellortos, and its an NA motor I thought there was something wrong with cylinder 6 as the reading was much higher than the rest I'm using 20w 50 oil at the moment. Jay Quote Link to comment Share on other sites More sharing options...
Kash Posted May 24, 2009 Share Posted May 24, 2009 I would expect a little higher compression for a 10:1 CR. I was getting 180 across all six when I shaved my p90a head 2mm with 10cc dish pistons (1mm felpro gasket). Quote Link to comment Share on other sites More sharing options...
jay28 Posted May 24, 2009 Author Share Posted May 24, 2009 Well im not 100% sure on the 10:1 CR ratio as none of the calculators allowed for the 2mm shaved off the head. I used a standard head gasket. Jay Quote Link to comment Share on other sites More sharing options...
Kash Posted May 25, 2009 Share Posted May 25, 2009 10:1 is about right for your set-up, a 2mm shaved p90 head will give you a combustion cahamber of approximately 45cc. Quote Link to comment Share on other sites More sharing options...
Daeron Posted May 26, 2009 Share Posted May 26, 2009 bah, specific numbers change hourly. I wouldn't consider a gap of 6-7 psi to be that significant; roughly 3% isn't that big a deal. Quote Link to comment Share on other sites More sharing options...
kvansic162 Posted May 28, 2009 Share Posted May 28, 2009 Want some compression numbers? Try 250 per cylinder. I have a 77 motor using the comp pistons and a stage 2 cam and a 2mm gasket. I about craped myself when I read those numbers.. Anyways I put a nissmo cam sprocket on and retarted the cam 6 degrees. Brought the compression down to 225 per cylinder. I run hi test and methanol injection....mega squirt....runs awsome. Quote Link to comment Share on other sites More sharing options...
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