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More RPM's

Old 09-26-2002, 12:56 PM
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Default More RPM's

This is above and beyond the call of duty for you folks but what the heck, thought I would ask anyway.
I am on the new side of pylon racing using the .46FX. Using 15% Power Master, #8 plug, 9.5X7 prop and the baffel removed from the muffler I currently tune for 14.8-15k RPM on the ground. This is right on the edge of lean when the engine unloads in the air.
Question is how to get more RPM's without going lean (and still visually appearing stock), in other words no tuned pipe. More then willing to sacrifice on the low end to achieve this.
Second question. Using a compression gage (our latest toy) and testing a dozen or so engines the .46 tested right around 80 PSI on all of them except one. It was 90 PSI. All engines had around the same amount of time on them. We usually start the season out with all new engines. The 90 PSI engine was a winner in the air also. Any thought on where the extra 10 PSI came from ?. All are pretty much broken in the same way.. In the air. Owner claims it's stock out of the box...... All six of mine come in at 80PSI which IMHO is testimony to quality control.

PS No, I won't be sending these in for warrenty work :-]

Old 09-26-2002, 03:28 PM
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Default More RPM's


We'd not have any mods you could make to the engine. If you're not worried at all about idle and midrange running, then you can tap the crankcase and run case pressure to the fuel tank. This will help deliver a lot of fuel to the engine. Unfortunately, this also tends to ruin the midrange and idle because you can't depressureize the tank when you throttle down.

Without going to non-stock mods, such as a carburetor with a bigger bore (that one WOULD need case pressure!), this is about the only way you can get more fuel to the engine.

One thing about breakins. In the "olden days" (the 70's) a lot of pylon flyers would take their ABC-type engines, fire them up out of the box, and lean them to right peak and fly. No real breakin process. The engines developed max power early in their lives. Unfortunately, you also had to chang out the piston/cylinder assemblies after about 10-15 flights/races.

The pylon engines were also so tight that you would ruin them if you turned them over cold. They were started by snapping the spinner backwards against compression. With the 40% nitro fuels being used, the engines would take off running forwards.

Hope this helps some.

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