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10:1 Compression. Ignition Timing.

Zero4Zulu

Well Known Member
My O320 has high compression pistons and the timing is set at 20 degrees. It doesn’t seem to be making the horse power expected. Low static rpm and slow climb rate. What ignition timing are others using with 10:1 pistons?
 
Timing sounds right

20 BTDC sounds right for 10:1 compression. It sounds like you are running a fixed pitch prop. What is the pitch of the prop? Low static and less climb rate than expected might just be you are running a cruise prop. What is the RPM and speed wide open throttle and 8000 feet?
 
I have a Catto 3 blade 67” 72”pitch. We only have a couple flights so far but we’ll get more data soon. Double checked with Catto and they think it is an appropriate pitch for my engine. This plane has to climb better than it does right now... especially with a hopped up engine.
 
What is your RPM, IAS, OAT and weight? The Vans numbers are at Vy which is slower than most ever climb. I had 10 to 1 pistons in a IO360 and we ran the base timing at 22. Currently I have a IO540 with 9.5 pistons that we run with fixed timing at 23.
 
Compressiom

I have an 0 320 with 10-1 pistons, carb engine, balanced, no other mods. I set the timing for break in at 22 degrees on recommendation from one of the bettr known engine builders. After the engine was broken in I reset the timing to 25 degrees. In the super hot AZ weather I climb at 130 knots which keeps the CHT well below 400. High altitude cruise in summer CHT is quite low.
I think the 10-1 increases the power less than 10 hp.
Unless there are runway considerations the best performance is obtained with a prop that will run 2700 r/m or a bit more full throttle at 8,000'.
I don't think I would do the 10-1 again because of the uncertain future of 100LL.
The engine is in a Wittman Tailwind with very tight cowl, much smaller intake and outlet than typical RV.
Whirlwind GA prop, I have to reduce power slightly to stay within the 2700 r/m limit. If I increase the pitch the climb will get pretty dismal in the extreme high temperatures. Temps in the 125 range for several days in mid Sep.
 
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