Audiofn

My buddy has a 383 stroker motor in his Formula. It has stock risers and is putting out aprox 425-450hp. The guy took out the plugs today and two of the gaps were totally closed. He then noticed water on the plugs. He took out all the plugs and hit the starter and water came out. We then did a compresion test and he had on the starboard side 120,160,120,160 and on the port side 120,120,110,120. The compresion numbers seem low to me but I am not familiar with this type of motor at all. What can cause the gap to close like this? I am guessing water but could anything else do that? Do those compresion numbers look low to you guys?

Thanks
Jon

cuda

Sounds like it may be a head gasket problem to me.

mopower

A 383 making that kind of power should have 170 up to maybe 200lbs cranking. My buddies 408 blows 190/200.
Plus the 110 low and 160 high are way out of line.
The gaps closed and water in the cylinders doesn't sound too good. The only way gaps close is something hitting them.

Dennis Moore

Is he using the correct length thread spark plug for the cylinder head he has installed? Maybe he is using a plug that is too long. The different types of cylinder heads available for the small block Chevy come with different length plug requirements.

It is possible that he has created hot spots in the cylinders (with an incorrect plug) causing detonation or pre-ignition and burned the exhaust valves creating a loss of compression. The E valves aren't seating properly and sucking water into the cylinders at an idle. Add compressed air to a cylinder and listen at the exhaust ports for an air leak (remove the rocker arms so you know that both valves are closed).

More than likely he needs AC R43TS or Champion RV15YC4 plugs (after he replaces all of the exhaust valves).

Dennis Moore

Audiofn

We will do a leak down today or tomarrow. That will surely tell us more we just did not have the time last night. Thanks for all the info so far and I will get back with our findings.

Dennis thanks for the plug recommendations we were actually talking about what would be the proper plug.

Jon

TomZ

I agree with Mopower... I have one of these bad boys and it blows 190-200 PSI as well... though the wrong cam could bleed off a ton of pressure (and be totally wrong for the application).

Not to disagree with Dennis, but if an exhaust valve were bad, you probably would have a dead cylinder (or at least some very low numbers). Due to the way these things can be built (especially if using the short 400 rods), a tremendous amount of side-loading of the piston can cause extreme wear of the pistons and rings. When these are built for auto use, the engines rarely see extended high loads so the longevity of the engine isn't really a question. In a boat application, though, the engine speed is increased, and more wear is caused in a short amount of time (especially if the engine is just "thrown together"). That is why it is better to use a longer rod with a 400-based (3.75" stroke) engine in this application. So, the lower compression readings could be indicative of worn piston rings/pistons. If the heads are snatched, I would take a look at the cylinder walls to see if there's any evidence there.

I do agree with Dennis' plug theory. What cylinder heads are being used? Is he using (hope not) domed pistons?

And lastly the water could be indicative of leaking risers or manifolds or he could be sucking in water through the exhaust depending on the cam (water pouring out of the cylinders though? probably not).

Hope it all works out.