There's a few reasons why....

1) When I pulled the plugs out that came with this vette about 3 weeks ago they were split-fire and pretty much done with... with the #3 plug having somehow caked itself closed with carbon/oil deposit. Two others had the tips burnt with part of the electrode missing and all black in color.
2) The carb that was on this engine was totally erotic(backfires, idling up & down, fuel smells in the garage hours later)
3) I had never done it and needed to do it before I decided to do anything else.

So, I changed the carb(Holley 650) & the plugs to the stock R44TS's and decided to run them 300-400 miles to see what came of it. 200+ miles were highway miles and even a 1/4 mile run down the strip.

Now it's time for you all to give me some advice. Base your answers on the following. The engine has 95,300 original miles on it... 454CI matching #'s w/ 8.5:1 compression... rebuilt at 62,000 miles(as I was told)... does not burn oil and no smoke from the exhaust while starting or on heavy load.

So... to make a long story short. I pulled the plugs tonight after warming it up and found the following:

Driver's side: All were black colored on the outer electrode... no evidence of wet oil anywhere.
Passenger side: All slightly grey in color on the outer electrode... no oil

Compression test results:

#1 - 132
#3 - 130
#5 - 126
#7 - Did not pull(pain in the butt)

#2 - 136
#4 - 132
#6 - 130
#8 - 135

Concensous? I really don't know to think of those numbers. All consistent, but low. I've read some of the threads here that compression test results can vary based on the cam duration and pistons will give different #'s. And I've read that consistent #'s are what are important. Possibility that the engine was not rebuilt at all and the rings are all worn? Good question except that there is absolutely not one drop of grime or oil on this engine top to bottom. One of the few GM engines I have ever seen that does not leak something. I'm buffaloed. It runs great, but I was thinking about putting chambered exhaust on this thing and there's one set of ducks that needed to be looked at first.

 

Engine sounds good to me. Maybe if you pull #7 you'll see it doing something really awkward. Why not give that one a shot?

The only reason I'd go for a rebuild in that engine right now was if you really wanted to build some crazy motor.

I wanna say you might have a slight seal problem on the driver's side but don't quote me on that. I'm not a professional mech! Pass side sounds A-Ok.

-Steve

 

Well, let's see... Did you block the throttle wide open while doing the test? You can check rings by squirting some oil into the cylinder and repeat the test. If it comes up a lot the rings are bad.

The numbers are fairly consistent so I wouldn't worry too much. If it runs good and doesn't use oil you're ok.

 

The numbers are right around what I'd expect.

(8.5 compression)x(15 psi atmospheric pressure)=130 psi

Since your plugs looks different on each side of the engine, it sounds like you might have an exhaust problem (one side partially clogged or something). Or maybe its due to the intake, but that seems less likely.

 

I did not block the throttle wide open. What does that do?

And *aharte*....

Are these accepted principles or theoretical of 8.5 compression x 15 PSI = 127.5? This is the best forum ever at ripping at E-bay ads. Let's say someone put up that theory and the numbers I gave you as a note for their engine? Next year I may very well decide I want to go C-5 and if I should decide to I will sell this vette and would put up those numbers. A problem? I need honest answers here. I really don't know what I should be coming up with. Sometimes I think this board is not fair at all as no one wants to say the wrong thing. If the above are right then I thank you, but if not speak up. I want to know what I am working with.


[Modified by 71-LS5, 10:13 PM 11/17/2003]

 

On a simple compression test you want all the cylinders to be within ~5% of each other. I think your motor looks pretty healthy. You are right in that cam duration CAN have an effect on compression results, so I would not read too much into the fact they are ~130psi. I had a supercharged F*rd V8 that was ~8.75:1 CR and it was ~135-140psi.

But if the cam has some decent overlap in it, the #s could be lower than you might expect.

 

Can't help you, but I'd like to know how to get my hands on one of those erotic carburetors. :D

JB