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Discussion Starter · #1 ·
Thought I'd ask now, while everyone is around. When summer time comes, I might have some tinker time.

Has anyone shaved the heads on the 500 fans or 583/670s before. Or maybe polished up the intake and exhaust? Maybe both?

What the maxium shave? And are there big gains to be found?

Just currious.
 

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i have done just that to a few engines i have always been happy with the results as an added bonus on the exhaust besides more flow is no carbon buildup on a mirror surface
 

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Havent cut my head yet. Did polish exhaust ports. I was told that I should not polish intake because fuel will puddle on a smooth surface.
 

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The intake is not suppose to be polished. An intake is to be ported hence port and polish motors. The intake is made to be rough for the fuel and air to enter slower and build more power before exit. And then the exhaust ports are polished so you get rid of the combustion fast. If you polished both, like mxzjunky said you will get puddles and the engine will load up because the engine cannot get rid of the fuel and air fast enough since it is entering to quick. If you cut your head you should see any where from 5-7 hp more. A port and polish job you will see 8-10 hp. This is also pending the size of the motor. Hope this helps you. Later.
 

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my cousin runs a machine shop and a yammie dealership (if that means anything)
I asked him about this a couple years ago he told me rotax has very good
casting and i would be better spending my money else where
 

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Discussion Starter · #7 ·
heslbay said:
I had my head cut on my 96 583 also carbs bored, it was worth it.
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I'm looking to give the 500 fans just a little more go power. If I was to guess, I'm thinking the Formula 500 sl's have somewhere around 55HP. A shave and some exhaust pollish might bring them up to 65-70HP. Certainly add some more torque with the compression bump. That about a 25% gain in power. Should put a bigger smile on the Kids faces.


Head shaving only costs about $30-$40 around here for something that small. Grinding out the exhaust a bit and pollishing is actually a lot of fun. Gaskets can't be very much. I don't understand why everyone doesn't do it to the older machines to even things up with the newer and bigger motors out there.
 
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