Porting tips?
10-15-2008 | 01:46 PM
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From: pilot mountain,
NC
Porting tips?
Can some of you engine guru's give me some tips on porting an engine? Not any particular engine, just some ideas and principles. I ruined a perfectly good echo by following some instructions I found on a thread somewhere in here (but I didn't know what I was doing anyway). Seems every post I've found on porting lists completely different timings. I'd like to better understand the principles before I start cutting my next engine.
Thanks.
Thanks.
10-16-2008 | 10:15 AM
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From: Riverton,
WY
RE: Porting tips?
One thing to remember, the more porting and port timing changing you do the narrower the power band width.
You can end up with max power but a power rpm range of 500 rpm or so. Thats why highly tuned racing motorcycle have 12 speed gearboxes.
You can end up with max power but a power rpm range of 500 rpm or so. Thats why highly tuned racing motorcycle have 12 speed gearboxes.
10-17-2008 | 06:28 PM
#7
RE: Porting tips?
Porting weedies is fun.
General rule of thumb on carbs:
Bigger carbs require you to run higher RPM's. Get a smaller prop or lower pitch.
Smaller carbs will flow the right fuel/air mixes at lower RPM's if you want to lug down with a big prop.
When the carb gets too big, it won't transition past 1/3 or 1/2 throttle no matter how much you crank the needles down.
Exhaust:
About 150* duration - MAX
Shave the insides of your case gaskets. It does no good to port match the cylinder and the case if your gasket is 1/4" into the crankcase. That will mess up your flow no matter how much you port it. I glue the gasket to the case and let it dry overnight. Then use a SHARP exacto knife to trim out all the excess gasket on the inside of the case. Shave the carb and intake gaskets too. Glue the gasket to the carb insulator block or the cylinder. Let it dry overnight and trim any excess out of the fuel/air stream with an exacto knife.
Get a Bowman ring for it. Frank Bowman lives in Farmington, New Mexico and he has thousands of rings. If he doesn't have your ring, send the engine to him and he'll make one.
Electronic ignition is up to you. I like it and won't run a gasser without it. Some guys do fine with magneto ignition.
General rule of thumb on carbs:
Bigger carbs require you to run higher RPM's. Get a smaller prop or lower pitch.
Smaller carbs will flow the right fuel/air mixes at lower RPM's if you want to lug down with a big prop.
When the carb gets too big, it won't transition past 1/3 or 1/2 throttle no matter how much you crank the needles down.
Exhaust:
About 150* duration - MAX
Shave the insides of your case gaskets. It does no good to port match the cylinder and the case if your gasket is 1/4" into the crankcase. That will mess up your flow no matter how much you port it. I glue the gasket to the case and let it dry overnight. Then use a SHARP exacto knife to trim out all the excess gasket on the inside of the case. Shave the carb and intake gaskets too. Glue the gasket to the carb insulator block or the cylinder. Let it dry overnight and trim any excess out of the fuel/air stream with an exacto knife.
Get a Bowman ring for it. Frank Bowman lives in Farmington, New Mexico and he has thousands of rings. If he doesn't have your ring, send the engine to him and he'll make one.
Electronic ignition is up to you. I like it and won't run a gasser without it. Some guys do fine with magneto ignition.
