i have been told by 3 people not to polish the combustion chamber, or the area next to the seat in the runner on the intake side. i was told to leave it rough for mixture purposes. also, does anyone have an old set of junk headers that they would be willing to cut the flange off of? or, if anyone just has a flange, i would like to purchase one for measuring. last thing....does anyone know if the stock 241 valve seats are nodular iron?

 

Yes what they told you is true. The turbulence helps for proper atomization. Most porters will hand finish the exhaust ports smooth but leave some material on the intake runners, w/ some being raw casting. CNC machines leave a bit more rough RMS (finish) on them purposely as well.

 

who told you not to polish the combustion chamber ? you can polish the combustion chamber to a mirror like finish, just do it with the valves in place and you should be fine.
the purpose of polishing the combustion chamber is to prevent knock.

 

Polish the chamber and exhaust port as much as you like. Leave the intake port with a 120 grit finish.

 

leave the entire intake port with 120 finish? or just the end of the runner near the seat? also, what diameter should the exhaust port be when i am finished?

 

oh yeah, anyone know about the valve seats?

 

is this your first time porting ? if it is don't install the head unit you get it flow tested.

 

no, not my first time....just don't want to make endless trips to the bench. looking to get as close to the final result as possible on the first pass. this is my first 241 head though. i am wanting to know how different people have done the intake runner, and what results they have had.

 

On the intake bowl area, just below the valve seat to the area around the valve guide, I use my round nose carbide burr FOR IRON/STEEL (not aluminum). I gently allow it to lightly skip/drag along the surface, but controlled-- not bouncing around (keeping it moving in circular motions, never letting it rest in one spot). It doesn't clog up with aluminum, since I am not actually trying to remove material. It kinda leaves a 'disco ball' look and has just enough roughness while still leaving an evenly distributed textured surface along the countours of the bowl/runner, without putting any bumps, gouges, or divets in the final port job. It works great for me.
I then polish the small amount of remaining/exposed iron seat material (throat area, not actual seat angle cut) to diminish any potential carbon build-up.
I also polish the runner from the intake side, in about as far as where I removed the excess rocker bolt boss material.
I polish the chambers as smooth as I can, and lightly round-off all sharp edges.

 

i used masking tape on the valve seat on the intake side and after porting to my likings i taped up everything but the intake runners and put them in my blasting cabinet and sand blasted the runners

 

would it be worth it to polish the chamber and exhaust runner, then have the intake cnc'd? would anyone do that for me? or, would they want to do the whole job? i want to try and keep from droping several hundred dollars when i know i can do it myself. i just think having the intake cnc'd would make more sense, then rest of it is easy.

 

I always polish the exhaust port fully to lessen carbon build up. It's not that difficult to do, so you may as well do it.