wicked_95z

A little info. The car is a 95 383 procharged LT1 running about 10 lbs so far with methanol. The reason I started this check was I am loosing coolant. I have looked for leaks and havent found any. No coolant in the oil. I think I may be burning it off, however none of the plugs are really clean. 6 are a tanish color and two are black. Im pretty sure due to spark plug wires arcing as I have had a problem with those plugs before. And for the results:

Cylinder
1 13%
3 6%
5 5%
7 13%

2 8%
4 3%
6 5%
8 10%

What do you guys think??

jonathan_abilene

where did you get yours? how much?
It looks like 1,7,and 8 are loosing compression.
but I havent used a tester before.
Did it not come with instructions?
It'll tell you whats wrong like: bad rings, bad valves, bad head gasket

1racerdude

Anything over 10% is rebuild time. If ya got molly rings there is your answer.
If ya rebuild go with a set of plain ductile iron rings or gapless top ring with NO moly, for the blower.

wicked_95z

Well the car has hit 220-230 degress because I forgot to turn the waterpump on so I was thinking head gasket at the wrost. The motor is built for the blower and only has a few thousand miles on it

1racerdude

If ya got molly rings they won't last very long period. They don't LIKE boost.
Why ya think ya got 10+% leak when 220 is NOT hot for these cars. That's too hot IMO but shouldn't HURT parts.

jonathan_abilene

So where is that 10% and 13%s leaking to? head gaskets? rings? or valves?

I hear that steel is the best kind of compression ring... I have them, from Total Seal

SABLT194

In my experience you have to be very carefull with leakdown tests. The technique is everything. For example, I found that I got substantialy different leakdown results depending on weather I positioned the piston on the upstroke or the down stroke. Positioning the piston in preparation for the test on the up stroke seems to seat the rings in the piston grooves better and gives a better leakdown number. I always make sure I come to close TDC on the piston upstroke, then lock the crank down so there can be no piston motion when the leakdown pressure is applied. A uniform test procedure on a cylinders must be used. Varying test procedures have yielded up to 25 psi difference in leakdown results on a given cylinder for me. Any of you big guys seen similar results? Again this is just my experience.

Steve

1racerdude

Well that's a given.
If ANY test is not done right it will not be valid.

Yes the piston should be at TDC.

WS6 TA

Um, at TDC both valves should be open and you’ll read 100% leakdown.

1racerdude

Don't think so. Not on the firing stroke.

rskrause

All of the valves better be closed at TDC on the compression stroke!!! For those who need a little primer, you can look here http://www.compcams.com/Technical/TimingTutorial/

This drawing may help. The first frame represents where you are measuring leakdown.

Rich

wicked_95z

On the exhaust stroke, yes. Not on the compression stroke.