Engine timing for speed?
01-21-2004, 08:15 PM
#1
Engine timing for speed?
I m running a super tiger 45 in a W.M. dago red. With a apc 10/7. rpm is about 15,000. I have a nelson muffler and a 60 carb, and using 10% nitro and the plane is quick, no radar as of yet.. I recently ran up the exhaust time to 165 and the intake to 125 also on the crank intake i drilled out the crank and open the port, to open at 45 bdc and close at 45 atdc.. it now tacks to 16,200 on 30 nitro. on the test stand.. cant wait to fly it.. My question is am i at my time limits before i have to go to a full pipe set up or can i go higher... appreciate some input..
rich b..[
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rich b..[
]
01-23-2004, 10:40 AM
#2
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RE: Engine timing for speed?
I have seen as high as 188 exhaust duration on boat engines, but you will need a tuned pipe for that. I have gone as far as 168 with a stock muffler with good results.
As you increase RPM and nitro content you may start to get detonation (pre-ignition) and must increase head clearance to get rid of it. If you start to see pitting on top of the piston or the underside of the head you have this problem and need to start adding head shims. If your tach readings start to jump around eratically you have a pre-ignition problem.
I also have the W.M. Dago red with a .91 4-stroke on it, does about 105 MPH with a 12x10 prop and 20% fuel.
As you increase RPM and nitro content you may start to get detonation (pre-ignition) and must increase head clearance to get rid of it. If you start to see pitting on top of the piston or the underside of the head you have this problem and need to start adding head shims. If your tach readings start to jump around eratically you have a pre-ignition problem.
I also have the W.M. Dago red with a .91 4-stroke on it, does about 105 MPH with a 12x10 prop and 20% fuel.
01-23-2004, 07:59 PM
#3
RE: Engine timing for speed?
Appreciate the input on the timing. Your saying with a stock muffler up to 168..seems high, or do you mean with a jet or nelson muffler..I think there timing the nelson and jett motors in the 180s with there mufflers for plyon. so you timing is correct?
thanks rich b.
thanks rich b.
01-23-2004, 11:13 PM
#4
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RE: Engine timing for speed?
Sure, those QM40 engines are timed high, but they only use that muffler because they have to... if it weren't for the rules they would use a pipe too...
If you go past 170° exhaust timing, a pipe will start to bring a lot of benefits...
Also, if you rise the timing of a sport engine, you will have to find a way to rise the compression too... or you have to go to insane amounts of nitro...
When you raise the exhaust timing, compression goes down...
If you go past 170° exhaust timing, a pipe will start to bring a lot of benefits...
Also, if you rise the timing of a sport engine, you will have to find a way to rise the compression too... or you have to go to insane amounts of nitro...
When you raise the exhaust timing, compression goes down...
01-24-2004, 08:23 PM
#5
RE: Engine timing for speed?
Rudeboy, Ive run boats (riggers mostly) which are more of a motor thing
your right about the compression as timing goes up the volume is less and head volume decreases. Since the aero motor is not cooled whats a max nitro i can run with some consistantency.. 30-40.. with the boat engines being water cooled 50 to 60 nitro is common.. Since i up the timing to 165/125 bench run on 30% heli fuel my increase was 1000 rpm with the same prop. and had no plug problems.. infact i reduce the head clearance by .010 and it ran 200rpm less. need more head shim, maybe becauses i up the intake to 125. What ya think?
rich b.
/
your right about the compression as timing goes up the volume is less and head volume decreases. Since the aero motor is not cooled whats a max nitro i can run with some consistantency.. 30-40.. with the boat engines being water cooled 50 to 60 nitro is common.. Since i up the timing to 165/125 bench run on 30% heli fuel my increase was 1000 rpm with the same prop. and had no plug problems.. infact i reduce the head clearance by .010 and it ran 200rpm less. need more head shim, maybe becauses i up the intake to 125. What ya think?
rich b.
/
