Have any of you guys who run extended periods of full throttle ever experimented with reduced spark lead time as a method of reducing heat. 28 degrees is usually too much if the squish band is tight enough to do any good. I know that ignition timing and CHT are directly related on larger displacement cylinders, with heat climbing much faster than power once full rpm is reached. I reduced the spark lead to 19 degrees on my G62 for starting purposes, it cost 100rpm at 6100. I don't know if it made any temperature difference but I have since ran this new engine leaned to peak (and then some) for over 30 minutes, over-propped, with no sign of distress.

I did a little work with throttle position on a g-62. I think they are at 28 deg which is about tops for thise motors. Our 5.8 I had up to 32 and it just got hot and vibrated a lot. so 28-30 was the range. I wasn't able to change the spark timing on the G-62 but by playing with the mixture and a cylinder head and exhaust gas temp I was able to get it to make maximum power and live at full throttle. What really was interesting was that just throttling backa little say about 500 rpm the temps dropped dramatically. I did the same thing with the 5.8 in the Mustang. If I ran it with a small high pitch prop at about 8000 rpm it would get very hot and the mixture was critical. But if I loaded it down with a larger diameter and less pitch to about 7200 it ran much cooler. EGT ran about 900 F as I recall. I can't remember the CHT but I think it was less than 300 F. If you run slightly rich it seems to be a little cooler but the power actually drops off a bit too. Oil % made a difference too. the Amzoil at 50:1 actually ran hot untill I convinced myself to run 75:1. I never got to 100:1 as they claim. But it seems like it would work. An ounce and a half of oil in a gallon of gas just doesn't sound healthy in our models.

If you could retard the timing some within limits, it might help reduce the heat. I don't know. In the race cars every time we tried retarding the timing it got hot and the EGT got high. power went down. If it was advanced too far about the same thing. You had to stay with in the range.

We are knocking on the door of some endurance flying with the B-25 and G-45's . I'll be looking at fuel consumption EGT and CHT. I hope we can monitor them in real time along with airspeed and rpm. We'll be doing some bench testing in the spring.

ignition timing is a strange thing. Sometimes retarded timing suits higher rpm, and vise versa. Vlach ignitions advance the timing by 21 degrees when the engine speeds up, with standard start timing at 3 degrees. more retarded timing hurts idle and low rpm operation.

The Evolutions all seem to have fixed timing (fixed position pickups) so that the customer simply bolts on and goes - so far -here at 4350 ft - there are no signs of timing being too high-or low
On the ZDZ's we can set start point at higher or lower positions - but for all practical purposes - the 6-8 mm magnet to pickup advance works.
The actual curves they use is a variable from engine to engine type
on latest engines ZDZ and the Evolutions - the throttle smoothness at even extremely low rpms is smooth as silk
I have tested for reliable lowest usable speeds on std props - down to 800rpm -on the Evolution 116 the ZDZ80J and 160 J
The new FAI ignition a fellow in Czech Republic is using is also reported to be very good at killing the3000 rpm "vibe" on the singles .
I found on my tuned pipe ZDZ's , top power increases when basic setting is retarded a little -which is understandable if the pipe is really pumping hard.
on fourcycle engines - the camshaft timing affected total advance settings -
Some engines needed up to 52 degrees total advance - others about35 degrees
The extreme lead setups had a lot of overlap in cam timing
On two stroke the overlap is also variable -sort of - by changing the exhaust setup and increasing cylinder pressures
more cylinder pressure needs less advance. all within reason---
If the engine design has a longer rod to stroke ratio - the timing can also be advanced a bit more . even with increased compression