Im getting a donor head that i plan on building!!! Im going to get headwork done and i need to know what to tell the mechanic at the machine shop, like how much i want it milled down and what port and polishing i want done! Does anyone have any experience with this?? If you do i would appreciate some good info!
Im not too familar with the subject!

"Scars are tatoos with better stories"
10.17 @ 70mph 1/8th Mile

I don't know a lot, but I do know this. Port and Polish your exhaust side, but only port your intake side. Don't polish the intake side at all. You need the rough surface to help atomize the air-fuel mixture. If you polish it there won't be enough turbulance and the air-fuel mixture may remain slightly seperate. This results in fuel pooling and or fuel charge washing the cylinder wall. That would wash your lubrication from the sidewall and cause much bigger problems.

Kool, I think ive heard that before somewhere! What about milling the head down, how much is safe?

"Scars are tatoos with better stories"
10.17 @ 70mph 1/8th Mile

I've never heard of a smoothe surface pooling the fuel. That usually happens on a rough surface, where the fuel droplets stick to the rough spots. If anything, the smoothe surface will promote air flow, and help increase its velocity from less surface restriction. Currently, my head is being ported out, both intake and exaust, and also gasket matched in size openings. I'll let you know the results.

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Some of that is true. You should get the exhaust port matched and polished mirror smooth and maybe get a smoothed port to head intersection. For the intake Ive heard the best texture is 300 grit or so for best low rpm running and fuel mixing, look this up it shouldnt be hard, and dont get it just ported evenly on all sides. Since the air gets moved about 90* the top of the ports are where most of the air is gonna be at high rpm's, so you want to have that area ported out and the bottom either left stock or ported just a wee bit so the port cross section looks like an egg to keep the low rpm velocity fine and so the high rpm breaths a little better then even porting, do this where it starts bending, that egg shape should be blended to the port matched opening and to the valve opening. Also look into maybe a 5 angle valve job or anything that smooths that port valve transition. Also make sure you get the combustion chamber mirror polished for better detonation resistance and Ive heard about welding the outside of the chamber area to push the fuel in but I dont know if its needed, again do some quick research. Wow, long post, if anyone has something to add or subtract from this do so.
Brent

Yeah I haven't heard of the not polish intake side...

On the exhaust side though, don't do a full port match, leave a small lip so the exhaust gas won't pulse back into thehead disurupting air flow into the cylinders.

*edit*

I believe the max milling on the head is .090, but that seems extreme to me. a mill of .030" should raise approximately 1:1 Compression ratio.



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