Cylinder leak down?

#3 cylinder is leaking 18 percent, and #8 in leaking 14 percent. How much is too much.
All of the rest are under 5 percent.
Thanks

 

Listen where the air is coming from. Listen inside the blower hat for intake, header for exhaust. Then try tapping that valve Lightly!!! May be a little trash under a valve. If not probably a pinched ring land or stuck or collapsed ring. They all should leak about the same if all is ok.

 

cyl leak

What are you running?

Frankly, on our A/fueller, under 20% is fine...10% is worth having a beer over.

As mentioned earlier, give it a good tap to see if something is there.
and yes, listen for it.
When you do all of your leakdown testing, bring the piston up to about 10 deg before it's TDC, do the test & while holding it on, have someone bump it up another 5 - 8 deg to ensure an accurate reading.

If you get a wild variation in the top 30 deg of stroke, usually it's a ring or a scuffed piston.

Clif

 

If it's an exhaust valve it should be fine - the nitro guys always back the motor down at the end of a run to straighten the exhaust valves - they bend a little due to the heat - when I ran alky 25% or less on the exhaust side usually fixed itself on the next run - intake or ring leak we took it apart if 25% or more - was just our limit but each team has a different comfort level on leak down percent...

 

gapless 2nd rings

Hi Mike, re your last reply re leakdowns, I have just prepped a new set of pistons and rings for a blown alcohol BBC (532) running around 30-40psi boost. I am using Ross pistons with dykes rings and Total seal gapless 2nd rings. Are these OK to run as I seem to remember someone saying they werent a good idea in some applications? Your thoughts would be appreciated. Thanks Graham