High Manifold pressure during climb out...?

[hughfi]

Hi there,

I have an RV6 with an 032-E3D with Millenium cylinders on it. I also have a CATTO two blad prop that works well.

I have begun to experience some oil leaks in unusual places due to what I believe is high manifold pressure during takeoff. Could this be?

When I am climbing out of my home airfield which is 600ft MSL, I read 2300 RPM and 28inches of manifold pressure. Please bear in mind that this is a fixed pitch propeller. Can anyone tell me why I have such a high manifold pressure setting?

The oil leaks I am experiencing are at the bottom of the magneto housing and from around one of the bolts on the very top of the case.

I have checked to make sure that my oil overflow is clear and not obstructed.

Any thoughts would be greatly appreciated.

Thanks,

Hugh.

[Kevin Horton]

Originally Posted by hughfi

When I am climbing out of my home airfield which is 600ft MSL, I read 2300 RPM and 28inches of manifold pressure. Please bear in mind that this is a fixed pitch propeller. Can anyone tell me why I have such a high manifold pressure setting?

You have 28 inches of manifold pressure because your throttle is full open, and thus there is only a small pressure reduction between the ambient pressure of 29.3 inches of Hg (the ambient pressure at 600 ft on a standard day) and the intake manifold.

[Russ McCutcheon]

Hi Hugh

Your manifold pressure is just atmospheric pressure, when you partly close the throttle there is suction in the intake causing the pressure to be lowered but when the throttle is open you read full atmospheric pressure so depending on the calibration of the gauge you should see 28 to 30 at full throttle at sea level, totally normal.

As for the oil leak, I can?t say if your specific leak is serious or not, I can say they seem to leak if you use them and they have oil.

Russ

[AlexPeterson]

Originally Posted by Russ McCutcheon

Hi Hugh

snip

As for the oil leak, I can?t say if your specific leak is serious or not, I can say they seem to leak if you use them and they have oil.

Russ

Oh, that is classic! And true...

[DanH]

<<I have begun to experience some oil leaks in unusual places due to what I believe is high manifold pressure during takeoff. Could this be? >>

No. Manifold pressure and case pressure are related only through compression ring leakage, and case pressure is small. I think a decent engine with an open breather hose would have a case pressure less than 1" of water (about 0.036 psi), and the highest case pressure values would probably be at idle anyway (lack of dynamic ring sealing).

[Yukon]

Dan,

While I agree that maniforld pressure has nothing to do with oil leaks.......I've just got to ask how you come by the opinion that crankcase pressures are higher at idle than at high power settings? Did you read this somewhere,
or did you hear about it during your stay at the "Holiday Inn"?

Sure the rings seat tighter at higher power settings, but the ring end gap will remain the same, passing more combustion gases into the crankcase.

[DanH]

<<I've just got to ask how you come by the opinion that crankcase pressures are higher at idle than at high power settings?>>

An instrumented dynamometer.

[Yukon]

Where? On what type of engine???

[asav8tor]

Hugh, here is a great review on MP


http://www.warmkessel.com/jr/flying/td/jd/15.jsp

[hughfi]

Its certainly very enlightening. Greatly appreciated. Now to chase down those **** leaks!...:-)