If you want to know the truth about the condition of your engine do a leakdown test.
If your not ready to spend money on engine work do a compression test.
Just remember that many engine failures begin with valve problems, if the valve is not fully seated it will not tranfer heat properly. The excessive heat will cause the valve head to break off and rock the piston and crack your cylinder.
It is much cheaper to freshen a set of heads than to build a new engine.
Jeff

I heard that!

what is the # to look for for compression on a 500 hp carb motor mine has 370 hrs now and i did valve springs at 260hrs. and when doing a leak down does the motor need to be warmed up or not.

thanks

one other thing I thought of is you should do a leak down test when the motor is cold and hot there is a huge difference if the motor is tired.

Funny. My Merc 575SCi service manual even has a spec
for cold engine leak down test (30% by the way).

At 430 hours and 5 years one of my two 575SCi's was
at 33% so I'm re-doing the heads on that one. The
highest cylinder on the other one was 28%, it can wait
until winter.

Pesky Varmint

For a regular comp test, you would want to see 140 or so with less than 10% variance between the highest and lowest. It also should be done on a warm engine to get accurate results.

Your right, there is a spec listed for leakdown in the 575Sci service manual, I had not seen that before. They list 30% as the max cold leakdown, but then say it should be checked warm, and don't list a warm engine spec.

Dave

Anyone have the answer to this?

140 to 150 but you are more interested in the varience between cylinders. 10% max.

I've done leakdown warm and cold, with numbers pretty close. If you do it warm, by the time you get to the last cylinder, its not going to be very warm anymore.

Plus, the most accurate leakdown numbers that I've gotten have been with the rocker arms backed off. Then I KNOW that the valves are shut. you can rotate the engine all you want, but if its not something you do every day, it may take a while to get the valves closed 100%.

We did a leak down test and checked the valve spring pressure after each race. These two test combined will give you a good indication of the condition of your engine. Both these procedures are worth doing at least once per season.