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Old 03-30-2011, 02:16 PM
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DaveC DaveC is offline
Motorized Bicycle Elite Member
Join Date: Jul 2010
Location: Boise, ID
Posts: 967
Default Re: How do you port and polish

Lowering or raising the port changes the timing. If you don't want to deal with that then widening the port is good just for more flow. Up to 2 mm from each side of the port really helps the flow. Now, I've seen some porting jobs that just make me cringe. They some how make it look like the port twists around several times on the way to the port opening. Be very careful with a Dremel. They spin so fast you are in trouble before you know it. I like useing the sanding rolls ment for a compressed air-powered die grinder. They are longer so you are less likely to overgrind a spot causing a dip. I use a pressure regulator to slow the grinder. The whole idea is a smooth transition from carb to intake pipe to port or exhaust port to header pipe.

What your looking for is a port that's as wide as possible and still be as straight and smooth as you can get it. Best is a straight line from one end to the other. If there's a taper then it needs to be a straight taper from port to port.

I first started porting when I was 17 or so with a set of mid-60's Pontiac cast iron heads. I used up two of my grandfather's old electric drills learning how to do porting on all 16 ports
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