Engine operating techniques, Racing

[sailvi767]

I am curious how those who race operate their engines under race conditions set the mixture. If CHT's are not a factor do you normally lean to best power or do most feel detonation could be a problem at full throttle leaned to max power at low altitudes? I know most operate at 2700 RPM and some exceed that number with the prop control but I am wondering how mixture control ties into this. Leaning to best power would certainly be the fastest mixture setting but I am concerned about long term effects of leaning under full power operation at low altitude.

George

[hydroguy2]

depends on the race and the conditions also different racers have different limits.

For me I stay within the manufacturers suggested limitations. so that means 2600rpm prop limit from Whirlwind. Everything full forward, then lean for best power. I watch CHT's and EGT's. I have also ran at 2500rpm and lower depending on turbulence.

[sailvi767]

Thanks, It sounds like leaning to best power is acceptable even at low altitude as long as CHT's are reasonable. I have a whirlwind RV200 prop however the limit on it is listed as 2700 rpm.

George

[Bob Axsom]

I run the highest RPM I can get - usually 2720 rpm with a Hartzell blended airfoil prop using F7496 blades 72" diameter. I lean for what I hope is best power but it is strictly a gut thing, I have no instrument that indicates a direct power difference as I vary the mixture control in the normal operating range. I have come to find that an EGT of 1300 on cylinder #4 works very well so that is what I target. CHTs are never a problem on our airplane - the highest I ever see is in the 370s and typically in the 350s. I determine my altitude for each leg of the race based on plane old climb, descend, and cruise performance calculations and the head or tail wind component. I haven't found a need to go into cross wind component effects on speed yet.

Bob Axsom

[DanH]

http://www.vansairforce.com/communit...7&postcount=81

[edsong]

Just as I expected, more rpm's less detonation. Remember your racing, so 50 to 100 degrees rich of peak is max power. Lean of peak is for economy, not speed. Max power = max speed.

[mike newall]

Forward

Forward

Forward

Concentrate on the corners

Don't look at the wings when you turn

If it starts to smell - I guess you are probably winning........

[mike newall]

Schneider crew twice

City Livery Cup crew once

Piper Lance

Oh, boy - you really don't want to look at the wings in the turn......

Or the yachts, or the sheep ......

[hydroguy2]

Originally Posted by sailvi767

I have a whirlwind RV200 prop however the limit on it is listed as 2700 rpm.

George

George, when did you get your prop? the paperwork I got with mine bought in 2009 says 2600 max continuous.

[jetdriven]

All 3 knobs full forward, CHT 330-340. ~1280 EGT, or about 250 ROP. 18.8 GPH. 165-170 KIAS.

The last two races we experimented with leaning about 75-100 degrees from full rich, so that puts it about 150-175 ROP. 16 GPH. Picked up a knot or so. The CHT in that case rises to 360-380. That's as far as I was to go. This is summer time as well. You can detonate an angle-valve IO-360 with normal CHTs in very cold weather at sea level with not much leaning at all. Cylinder pressure is already pushing the maximum at full rich.

I dont think you could get to 80 ROP (remember, peak is going to be higher than cruise) without exceeding 420 or more on the CHT. I am not going there.