combatpigg
Posts: 9788
Joined: 11/22/2003
From: arlington,
WA, USA
Status: online
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I'm sure a company like OS with a good size budget for R&D would carefully select the venturi size to give the engine good all around behavior.
Mass produced performance engines share common rpm limiting features. Throttles with venturis sized for fuel draw & heavy pistons with no SPI sacrifice unloaded rpm.
Take as much weight out of the piston, rod and wrist pin as you can and see what happens to the redline. Oval shaping the rod beam works. Right now the engine is turning about 350 cycles per second, micro-grams add up, especially if the engine is to go faster.
The pathways into the transfer ports when the piston is at BDC are usually restrictive due to machining limitations, look to see where those passages can be opened and straightened.....hog out anything that is needed to accomplish that, including notching the piston skirt. I'll bet this engine can be made to pull a usable prop a little faster?
A few years ago I did this stuff to a K&B 6.5 and it responded nicely. Rebalancing the crank took 1 WAG to get right. Less reciprocating mass makes the balance less critical...but I realize I was lucky to get it on the first try.
The neat thing about these mods is that they can be done without fancy tools and they are safer to try than WAG timing mods.
Oh ya, another thought..... unshrouding the bottom of the transfer passages isn't needed in some engines I've looked at.....in fact those engines might have benefitted from having less crankcase volume to improve pumping action. A rear intake engine with a disk valve has less crankcase volume than a hollow crank engine, that should be an advantage....but the disk takes power to turn. The disk is something I've never messed with, it's always looked like something I could ruin.
< Message edited by combatpigg -- 5/19/2008 4:42:00 AM >
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All Forums >> RC Airplanes >> Extreme Speed Prop Planes >> RE: 8.8X9.75 @ 19,300+ ! 
RE: 8.8X9.75 @ 19,300+ ! - 
