Fudging Timing A Tad

[USCANAM]

In our -9A we have the following engine and details
IO-360-180hp Superior EX built by Penn Yan,
Vertical Fuel injection
Roller tappets
2 Slick Mags with dual impulse
100hrs total time.

When we first installed the brand new engine, we moved the timing ahead about 1.5' to be about 26.5 BTC, rather than 25' BTC. Penn Yan ran the engine for about 45 minutes on their test cell. Oil consumption was excellent when I first operated it.
Our reasoning being for advancing the timing;
: I've always felt that 25' was an arbitary, conservative number,
: the plane is light, so are the loads
: Once the wheels are off the ground, we pull power back to 25 square.
: Electronic ignitions in cruise operate close to 40' BTC as I understand.
After 100 hours of operation, while doing the Condition Inspection we found the following.
All cylinders are 78/80
Oil consumption is approx 1 quart per 15 hours (Aeroshell 80) (Aeroshell 100)
Cruising at 23 square we are burning 8 gallon/hour. Might even do better when the injector in #1 cylinder is enlarged to reduce EGT in this cylinder. It's about 35-40 degrees hotter than the other cylinders, so have to lean to this cylinder.

Has anyone else with standard mags advanced their timing slightly?
Jack

[Mel]

One thing you don't mention is the prop. If you're running F/P, take-off and climb is where you are most likely to get detonation. i.e. High MP with low RPM. With a C/S I think this would be a reasonably safe move.
Also only with 100LL.

[USCANAM]

Originally Posted by Mel

One thing you don't mention is the prop. If you're running F/P, take-off and climb is where you are most likely to get detonation. i.e. High MP with low RPM. With a C/S I think this would be a reasonably safe move.
Also only with 100LL.

Sorry Mel, how could I forget to mention the 3 blade MT prop. We only use 100LL
Most of my flying is done at sea level, and as mentioned before, power is reduced as soon as the wheels are off the ground, which is quite quick!!
Thanks
Jack

[Bob Martin]

Jack,
": Electronic ignitions in cruise operate close to 40' BTC as I understand."

If you go to electroair's site. http://www.electroair.net/technical.html
and read about spark advance. You will find the graph will show at 23" mp
there is about 2+ degrees added to the standard 25 degree advance for a total
of 27+ degrees of spark advance at 23"mp.
The 40 degrees is actually at a much lower mp.
Good Luck.

[Russ McCutcheon]

Hi jack,

Just because the plane is light has nothing to do with the power your engine makes or the Cylinder pressure it makes or it?s detonation margin, the engine makes the same pressure and power no matter what you bolt it to.

Keep an eye on the timing, if the points in the mags wear faster then the point cam the timing will advance, this is common, you could easily check it on you next oil change and find it at 28+.

Frankly I have run mine at 20 and 25 and could not tell any difference, you?re probably gaining nothing, probably not hurting anything either so long as you don?t let it advance on it?s own to far beyond where you have it set.

[osxuser]

Should be OK. I've run up to 32? on a racing O-200 before, and as long as you keep the CHT's under control (read no detonation) you should be OK.

[USCANAM]

Originally Posted by Russ McCutcheon

Hi jack,

Just because the plane is light has nothing to do with the power your engine makes or the Cylinder pressure it makes or it’s detonation margin, the engine makes the same pressure and power no matter what you bolt it to.

Russ
Thanks for your reply.
What I meant by "the plane is light", is that in a climb, it would not be necessary to run at higher power settings, therefore keeping cylinder pressures lower, and diminish the possibility of detonation.

Also when you said that you've run your engine at 20 and 25'BTC, and didn't notice any difference, I would have to believe that you should have gotten better fuel mileage in level cruise.
Jack