VinhZXT Posted March 10, 2007 Share Posted March 10, 2007 Hi guys, my stock turbo motor has a weak vacuum reading and today I did a compression check and all the readings were 175 PSI. The readings were 145 when I rebuilt this motor 2 years ago. I know my head gasket needed to be replaced but can someone explain why the compression readings are so high? Thanks Vinh Quote Link to comment Share on other sites More sharing options...
gjc5500 Posted March 10, 2007 Share Posted March 10, 2007 is it pinging durring acceleration? if not, i dont think id worry about it. but this is just me. ne one else Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted March 10, 2007 Share Posted March 10, 2007 Could be that when you rebuilt it you tested it before the rings had seated properly. Could be the last time you tested it you didn't have the throttle open and this time you did. Could be the head gasket that was replaced has a smaller crush thickness, though I kinda doubt that. Dave Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 11, 2007 Share Posted March 11, 2007 OOOOOR, you could have enough combustion chamber deposits that they are affecting the compression readings. Likely the rings seated better if it was a fresh engine. 145 is a bit low, 175 is a good (better) number... Quote Link to comment Share on other sites More sharing options...
wigenOut-S30 Posted March 11, 2007 Share Posted March 11, 2007 OOOOOR, you could have enough combustion chamber deposits that they are affecting the compression readings. Likely the rings seated better if it was a fresh engine. 145 is a bit low, 175 is a good (better) number... Isnt stock compression on a turbo motor 145? Quote Link to comment Share on other sites More sharing options...
Sparks280zt Posted March 11, 2007 Share Posted March 11, 2007 Isnt stock compression on a turbo motor 145? Yea thats what I thought. Quote Link to comment Share on other sites More sharing options...
VinhZXT Posted March 11, 2007 Author Share Posted March 11, 2007 Stock compression for turbo motor is 143 to be exact and I knew this. It was a long story leads to this problem so I leave it out for now. I am going to replace my head gasket and redo the compression to see what I get. I want to see any one in here can explain the high compression readings when you get a bad head gasket? Thanks for all the replies. PS. This time the compressions were the same regardless of my throttle open or close Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted March 11, 2007 Share Posted March 11, 2007 Is it possible for improper valve adjustment to do this? Or bad valve timing, like a worm timing chain? The other possiblity is maybe your compression gauge just aint what it use to be. At any rate puling the head will tell you if it is combustion chamber deposits. Just throwing out ideas. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 11, 2007 Share Posted March 11, 2007 Stock compression for turbo motor is 143 to be exact and I knew this. I want to see any one in here can explain the high compression readings when you get a bad head gasket? Thanks for all the replies.PS. This time the compressions were the same regardless of my throttle open or close In that case, I have to question your testing methodology, and the gauge itself. If your readings are moving around, and you are making comments regarding throttle position, you need to follow proper compression testing methodology---I simply thought we were beyond that point discussing it here, so apparently not. Test with standard methodology, or tell us the methodology you are using in your test for us to be of more help. Leaving things out makes for bad advice, and usless commentary. We may as well be grasping at hairs on a camel's back to solve the Mid-East troubles in that case.... Quote Link to comment Share on other sites More sharing options...
VinhZXT Posted March 13, 2007 Author Share Posted March 13, 2007 Thanks for all the replies. I don't think I did a compression test on this rebuilt motor. I must have mistaken it with my other turbo cars. Anyway I did the same test on very turbo ZX I have before and I got the correct readings. I guess the high compression is due to the fact the machine shop shaved the head and block. I replaced the head gasket with the correct one today and the compression was around 165. I am still using the stock HG BTW. In the process of replacing the HG I found my vacuum leak. It was the PCV pipe got burned by the exhaust manifold. I didn't have the shield there and being that close to the exhaust manifold it's just a matter of time. I put a shield there now. I got 18 mmHg reading now. Quote Link to comment Share on other sites More sharing options...
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