Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Engine timing

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Old 02-16-2007, 03:55 PM
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SSGSPEEDMAN
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Default Engine timing

Well just read the thread about the os.55 on the f-20. I remeber asking myself sometime back how do you tell if the porting/timing is made for torque or for high rpms? Well I dunno. Maybe someone could let me in on how to tell. I mean would the timing ports be closer togther or spaced out more? Would the ports be bigger or smaller? Would you have a small intake and a large exhaust port or visverse?

Kevin
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Old 02-16-2007, 04:09 PM
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Default RE: Engine timing

The port timing is controlled by how TALL the ports are. You'll find the bottom of the port is even with the piston at BDC, it's the top that changes the tuning, taller more rpm, lower less rpms, that's the rule as my thumbs told me it.
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Old 02-16-2007, 04:52 PM
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Default RE: Engine timing

Exhaust timing is largely responsible for the rpm range an engine performs best in. Low rpm torquers don't need big (wide) ports, they may even benefit from smallish ports to keep the gas speed up during transfer. On a 30K screamer on the other hand, wide ports are necessary for an adequate gas exchange in a very short time.

The only way you can really tell is putting a degree wheel on it, and measuring the timing. It is nearly impossible to tell anything, just by eyeballing it.
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