In a message dated 2/26/2005 11:22:01 PM Central Standard Time, lors01@msn.com writes:

<<  I'm currently flying on 87 Octane. Could this be impacting my ability to produce power this much? I'm working my way through the possible octanes to see how she behaves so as not to get caught out later. The next tankful will be 91, then 100LL. I've tried clean (not new) plugs. That's my next experiment. Any other thoughts or suggestions welcome.

  John (flying, but not climbing as fast as I'd like)

 >>

It sounds like you flaked an apex seal or broke a corner seal. Hot compression test without the prop should show it up. Apex or corner seals show up as two faces low (on each side of the failed seal) and failed side seal (rare) shows up as one rotor face low. The turbocharged engine is constantly changing its compression ratio. This gives me the willies. That means that the ignition timing must be altered constantly and accurately. Also there is the sad point that the rotary has little torque at lower RPM. The high HP numbers hoped for by everyone are a result of high RPM. Where the multiplier of RPM boosts the number. HP = Torque X RPM / 5252.

So if you want power at lower RPM (4,000 is low for a rotary) you then add more fuel and air via the turbo and then the engine gets to act as though it has a higher displacement then is true and a higher compression ratio that is true. The object of correct ignition timing is to light the fire at a point that will generate the maximum cylinder pressure at the ideal crank angle to produce the highest torque for that situation. That crank angle is a function of engine mechanics and does not change during operation. Everything else does change during operation however, and must be accounted for. In the NA race engine 20 degrees is plenty of advance for up to 9,000 RPM. Just stop thinking about this as you would a piston engine. The relationship of the crank and the piston is direct in the piston engine while it is diluted 3 to 1 in the rotary. So 20 degrees down around 4,000 is OK for the NA engine, but it could be way too much for a turbo. Because the rotor is moving slowly compared to a piston engine. So, the mixture can burn much faster and produce the highest pressure well before the ideal crank angle. Because the chamber is not getting bigger and reducing chamber pressure during the burn like a piston engine. More pressure = faster burn.

If the boost is high enough, it could be that ignition timing would all be after TDC.

So the point of all of this is to avoid detonation. Detonation in a piston engine at low throttle settings is no big deal. Mom starting out in the Chevy gets it to detonate right off idle from time to time. Dad going up a hill in the pickup leaves it in top gear and just adds throttle to maintain speed. That tinkling sound, like hard rice falling on the hood is detonation. The piston engine can do a bit of it and suffer little.

The rotary cannot. Detonation cracks apex seals and corner seals. Still OK if the pieces don't get loose from their slots or holes. But if they do, its over for the engine. Episodes of detonation over a long period, beat the apex seal grooves into a "V" shape. Cold starting seems OK but hot starts become difficult. Power goes down as compression goes down.

Detonation is the ignition of mixture remote from the spark plug(s) but AFTER the planned ignition event. It is totally charge temperature dependent. There are about 2,493 reasons for the charge temperature to be too high, but that is the only reason for detonation. In any one ignition event that results in a detonated mixture, the removal of a slight amount of excess heat will have prevented it.

So, the obvious things that could help you out of this problem are: reduce throttle=less fuel=less heat. Less timing advance lower cylinder pressure= less heat.
Richer mixture (number one protection device) = slower burn rate = less pressure= less heat. Bigger oil cooler = cooler oil = lower rotor face temps = cooler charge.
Bigger coolant radiator = lower chamber wall temps = lower charge temp. Higher octane fuel = slower burn rate = lower charge temp, and the anti knock stuff in the higher octane reduces sensitivity to pressure. Inject water at high boost levels = slower burn rate and direct cooling of the charge. And on it goes. If it was my engine I would have it off and apart checking that all is well, with a close check on the apex seal grooves. Detonation can overload the oil film strength, so if there is a shine on the bearings, I would press in a new set. Detonation also makes the rotor housings flex a bit near the plugs so look for the mating faces to be blackened a bit. This is the area where extra dowels are added to high output engines to make the housings stiffer. (Not so it can detonate, just not flex at high output.)

Lynn E. Hanover