Took out plugs and ran compression test... have some questions

[SadbutTrue]

I went to re-gap the spark plugs and took them out. Five of them were oil-fouled. So we ran a compression test and the compression came out fine. So I guess the oil problem is with the valve stem seals?

Also, on our old engine (also a 351w, originally a 2 barrel and therefore a 9-9.5:1 engine) would usually show compression readings for 140-160 psi on all cylinders when healthy. This engine showed readings of 180-200 psi on all, which is more indicative of the 351 4 barrel (which I think was 11:1 stock) version... would you all agree? This would explain the ping I've been experiencing, and would also dictate what I should gap the plugs to.

Thoughts on both?

 

[D.Hearne]

Your pinging problem has NOTHING to do with plug gap. Colder plugs, higher octane gas, or retarding the timing will help.

 

[SadbutTrue]

actually, i was hoping for more confirmation of my guess as to the compression. Does my assumption of a higher-compression engine make sense? Either way, I'll be using 91 octane in my next fillup (I live in Cali).

and as far as the gap goes, I'm just going to set it at what MSD says to set it at and leave it be.

 

[Route666]

180 psi / 14.7 psi = 12.2 (12.2 atm of pressure in the cyl, or 12.2 : 1 CR)

This seems very high, although not really for a dynamic cylinder pressure (engine cranking over relatively quickly).

 

[68GEETEE]

http://www.mityvac.com/compression.html


http://www.geocities.com/dsmgrrrl/FAQs/leakdown.htm


I think your leak is valve guides and seals. I agree with D Hearne about the pinging, I think you need to see how much total timing advance you have, I have a feeling you are over 40btdc, and that is really too much. SHould be no higher than 36-38 total advance. If the timing isnt over advanced, a colder spark plug one heat range colder should help. Or try the highest octane you can buy.

http://www.gofastforless.com/ignition/advance.htm