question about polishing the ports on heads
question about polishing the ports on heads i have a set of patriot cnc ported heads, and i have them completely disassembled. is it a good thing to polish all the runners and combustion chamber to a mirror finish? wouldnt this help with head flow? i just want to squeeze all the performance out of these heads that i can so does anyone have any advice about doing this? thanks for the help. P.S. i have already taken them to a machine shop and had them milled to 59cc chambers, and switched out the 2.02, and 1.57 vaves with 2.055 and 1.6 REV stainless vlaves.
I don't think you are suposed to polish the runners and chamber to a mirror finish because the fuel stays atomized better when there is a little texture to the surfaces of the runners and chamber .
they are still at the machine shop getting a valve job, milled, and the bigger valves installed. but i guess i wont mess with them once they get done, ill just install them and see what they do.
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I remember reading an article on head porting a few years ago and it covered everything from over porting and polishing and it said that slick smooth walls in the runners actually caused an uneven fuel burn because the fuel droplets did not stay suspended as well as they should have . Now that was for the intake runners , but I don't think it was as detrimental on the exhaust runners as I would think that the smoother the walls, the faster the exhaust gases could exit the cylinder. I beleive it also said that polishing the chambers to a certain extent promoted better flame travel and a reduction on carbon build-up . I'm sure someone who is versed in head porting will chime in with a better explanation than mine .
Last edited by Zitty'sZ; Apr 16, 2008 at 04:49 PM.
I did my heads a month ago. 241s + around 12% flow.
I am an engineer but not a head expert, that would involve application-specific flow testing and experimentation, measuring for cross-sectional area, etc... Most of the "porting" has been done for you, the design is already there "as cnc'd". Alot of the work I did was grinding rough edges around the valve boss, valve seat, etc. which, again, has already been done for you.
Polishing the chamber has the effect of letting the charge last a little longer without detonation. Kinda like putting a grain of salt in super critical carbonated water, absence of imperfections and rounded curves will delay preignition.
A turbulet boundary layer along the surfaces of the runner will actually decrease air resistance. However, increased runner cross-sectional area can be gained on the exhaust side by polishing the walls, preventing carbon build-up.
Use a 120 roll on a dremel to smooth up runners. I hand-sanded to finish with 240 grit. I had some callouses after.
Use those polishing wheels or gritted brushy wheels (like scotch brite) for the chamber. An old valve ground down to no thickness at the margin will aid polishing around the valve seat.
Oh, and don't let the Karma Karma Caution Club deter you with what you want to do. Just 1) do one task at a time to all the runners before starting another task, so that you have some consistency, and 2) to ensure flow as designed, follow existing curves and minimize depth of cut to as thin as possible (polishing only!)
Look up valve back-cuts and port-matching if you want to finish the job.
I am an engineer but not a head expert, that would involve application-specific flow testing and experimentation, measuring for cross-sectional area, etc... Most of the "porting" has been done for you, the design is already there "as cnc'd". Alot of the work I did was grinding rough edges around the valve boss, valve seat, etc. which, again, has already been done for you.
Polishing the chamber has the effect of letting the charge last a little longer without detonation. Kinda like putting a grain of salt in super critical carbonated water, absence of imperfections and rounded curves will delay preignition.
A turbulet boundary layer along the surfaces of the runner will actually decrease air resistance. However, increased runner cross-sectional area can be gained on the exhaust side by polishing the walls, preventing carbon build-up.
Use a 120 roll on a dremel to smooth up runners. I hand-sanded to finish with 240 grit. I had some callouses after.
Use those polishing wheels or gritted brushy wheels (like scotch brite) for the chamber. An old valve ground down to no thickness at the margin will aid polishing around the valve seat.
Oh, and don't let the Karma Karma Caution Club deter you with what you want to do. Just 1) do one task at a time to all the runners before starting another task, so that you have some consistency, and 2) to ensure flow as designed, follow existing curves and minimize depth of cut to as thin as possible (polishing only!)
Look up valve back-cuts and port-matching if you want to finish the job.
Ok, IM NO super head expert, but people got it right so far. only thing Id add is you can polish the chambers and it will help with detonation and flame travel. just DONT TAKE ANY MATERIAL OUT. you had them milled already, dont make them bigger again by opening them back up with the buffer. also, you run a HUGE risk of ruining the new valve job too. you'll need some scrap valves to put in the head chamber to protect the valve seats. I took some old stock vavles and grinded them down to a thin/sharp edge makeing sure they kept the seats covered, but allowed access all the way up to the seat for the buffer to do its thing. you want to use the polishing buff's, not a sand paper roll to get a smooth finish. also, take some tape and cover the head gasket surface cause its EASY for the buffer to take a trip all the way across the head surface. and it doesnt take much to mess up the perfect machined side of the head. I was soo freaked out about the gaskets sealing (since i used cometics) and not leaking. my buffer took a trip so I had to get them machined again. I learned from that though. and this is what its all about. luckily for me the guys at ET Performance hooked me up. but they are local to me.
DanF1000 had some very good info. In the old days we spent hours mirror polishing the ports only to find with modern technology that as far as the intake ports go you want a semi-rough surface to break up the surface tension hence better flow & greater volumetric efficiency. 
