Abnormal Compression on '86 4.3 Cobra

[eja]

Hello everyone! I am preparing to swap my 2-bbl setup to edelbrock intake and 600 cfm carb on my 1986 4.3 Cobra (600 hrs). I decided to prepare by verifying compression on the 6 cylinders. Uh-Oh.<br />> #1-152<br />> #2-160<br />> #3-155<br />> #4-115, 110 (verified 2nd time)<br />> #5-160<br />> #6-190, 192 (verified 2nd time)<br />><br />>Did a "wet" test, using ~1-oz of oil in each cylinder:<br />> #1-157 (up 5 psi)<br />> #2-165 (+5)<br />> #3-161 (+6)<br />> #4-120 (+5)<br />> #5-168 (+8)<br />> #6-202 (+12)<br /><br />I'm guessing that I have a burned valve on the #4, but it doesn't explain why #6 is so high! Any thoughts?? <br /><br />Planning to do a "Leak Down" test, pressurizing the cylinder and listening for leaks this evening.<br /><br />Anyone run into extremely high compression before?<br /><br />Erin

 

[Lou C]

Re: Abnormal Compression on '86 4.3 Cobra

Usually due to excess carbon build up, probably not uncommon in marine engines since they tend to run rich and cool compared to their car cousins.

 

[eja]

Re: Abnormal Compression on '86 4.3 Cobra

OK, a gearhead buddy of mine gave me some advice...<br /><br />Ran the engine until normal temp was reached. Then reperformed the compression test with the throttle wide-open (allowing more air to enter the cylinders.<br /><br />Results:<br />A improved range of 171 psi - 183 psi across all cylinders! <br />I am very happy (less than 10% variation)..<br /><br />Thanks everyone... Time to put on the 4-bbl!

 

[paulie0735]

Re: Abnormal Compression on '86 4.3 Cobra

great to see the good results after the 'correct' test procedure. how about keeping a tab on the cost and posting your final results?