I am porting and polishing the heads for a motor that I am installing in my 72 GMC truck. I will probably be using the truck to pull my 66 Chevelle back and forth to the track and carshows. The Standard Abrasives kit I just bought says to polish the combustion chamber. A friend of mine says that if I do it could lead to vapor lock and poor fuel atomization. Is he right? I am not trying to build a 1/4 mile drag truck. I am just trying to build a few extra ponies while I doing an engine rebuild. Thanks!!

I would do it. Personally, I think it's more important in an engine that sees a high load.

Vapor lock? Don't think that's possible, but I may be wrong. Poor fuel atomization is unlikely, but it more likely to happen if you polish the intake port. Maybe that's what he thought you were talking about?

Polishing the chambers serve a few valuable properties. The most valuable are the reduction in hot spots which reduce detonation; the second is the polished finish keeps heat within the chamber and can produce more power. And if you deshroud the valves while you are in there, that's another good benefit.

One of David Vizard's books has a good explaination of all of this.

A third good result is there will be less carbon buildup in the chamber. Polishing the exhaust ports will help with carbon control, too. The intake port should be somewhat rough to promote turbulance and keep the fuel suspended in the air column.

Digging up an old post.....

Could someone use a dremel to polish the chambers on a set of heads? If so, which stones should I buy?

If not a dremel, I have access to some air tools, what should I use to polish them out?

I know I need to put some old valves in the head chamber that's being polished to protect the seats, but is there anything else I should know?

Thanks guys!!

Dremel makes a larger tool, sold as a tile cutter. It will accept a 1/4" collet (optional). Then get an assortment of 3M Rolock disks and the proper arbour. It will make quick work of polishing the chambers. Make sure you put a set of old valves in the chamber, so that you don't frig the seats. Stones are useless imop. Get one or two good quality carbide burs with an extended shank. They are 25 to 35 bucks each, but will last along time on cast iron, and cut very well. You will need to go to a specialy tool supply for everything except the dremel, which you can get @ home depot.

Could someone use a dremel to polish the chambers on a set of heads? If so, which stones should I buy? I would just buy that standard abrasives kit. Good for polishing but you will need a carbide bit for real material removal.

Hey, I knew I recognized this post. I just used the Standard Abrasives kit that I purchased for around $35 or so. It came with everything plus instructions. I just used my air powered die grinder. It's easier to control the speed of too if you have an air adjustment on your air compressor.

He had to be thinking you meant polishing the intake port. Its good to have somewhat of an unfinished surface with some texture in the intake port. That way, around the edges of the port, against the port walls the air will tumble. This creates a boundary layer of air agains the walls of the port, and it allows the rest of the column of air and fuel to travel quickly and smoothly through the center of the port. If you polish, you lose that boundary layer of air. In turn, the air and fuel rides right agains the edge of the port which can cause fuel to "puddle" on the port walls and Id imagine that imperfections in the casting will disturb the flow moreso than if it were riding in the center of the port, away from the edges. I can see the logic behind vapor lock as well, cause if the fuel is right up agains the port walls and possibly puddling, it would not be strange for it to boil off easier than if it were away from the heated metal and in the center of the port.

However, polishing the chambers and exhaust port is a good idea. The idea behind detonation resistance is that a polished chamber will reflect heat into the center of the chamber and help to stop hot spots in the physical chamber. Plus, horsepower is heat energy, so its better to keep the heat suspended in the chamber where the combustion process occurs, rather than soaking into the materials and out through your cooling system and what not. Plus, if the surface is less textured, its much harder for things to stick to a smoothly polished finish(like carbon). So thats the idea(or part of it) behind the logic that a polished chamber will prevent carbon buildup. Also, carbon retains a lot of heat as well, so carbon buildup itself can create hot spots. For the same reasons, a polished exhaust port will not see as much carbon buildup as fast as an unpolished exhaust port would. Your buddy had good intentions, I think he may just have confused this area with that area.....know what I mean.

If you want to use your dremel, these would probably work well.

http://www.dremel.com/productdisplay/bit_template.asp?SKU=511&Color=660099

Originally posted by MarkM:
If you want to use your dremel, these would probably work well.

http://www.dremel.com/productdisplay/bit_template.asp?SKU=511&Color=660099 I wonder if there is anything that would work with my plain old power drill? I'd guess it prob doesn't turn fast enought right?

This is the tool I use. A drill doesn't spin fast enough, and the bits would just chatter on the surface. ( you remove the handle and the depth gauge )

http://www.dremel.com/html/images/products/tools/9000-04.jpg

I used a dremal and some air tools along with the Standard Abrasives kit to smooth the intake runners (rough finish), mirror polish the combustion chamber, and exhaust port. The polish turned out well. When I got a bigger air compressor I did more on some F*%d heads and it was easier. I did more bowl work on them. The BB heads I invested some serious time into an I hope it made things more efficient. The books I read said to do it for the reasons above. It took a lot of time. I wish I had CCd the heads while doing it to get a true 119cc but some milling might have needed to happen for that to.

Originally posted by Whittaker:
I wish I had CCd the heads while doing it to get a true 119cc but some milling might have needed to happen for that to. I doubt you removed more than 1 cc by just polishing the chambers.

Originally posted by greg_moreira:
He had to be thinking you meant polishing the intake port. Its good to have somewhat of an unfinished surface with some texture in the intake port. That way, around the edges of the port, against the port walls the air will tumble. This creates a boundary layer of air agains the walls of the port, and it allows the rest of the column of air and fuel to travel quickly and smoothly through the center of the port. If you polish, you lose that boundary layer of air. In turn, the air and fuel rides right agains the edge of the port which can cause fuel to "puddle" on the port walls and Id imagine that imperfections in the casting will disturb the flow moreso than if it were riding in the center of the port, away from the edges. I can see the logic behind vapor lock as well, cause if the fuel is right up agains the port walls and possibly puddling, it would not be strange for it to boil off easier than if it were away from the heated metal and in the center of the port.

All of that makes sense to me, but it also brings another question to mind. Every aftermarket SBC/BBC aluminum head I've seen has a smooth, almost polished finish on the intake runners, some are like glass because of the CNC machine. Why don't aluminum heads have the problems you stated that come with polishing the intake runner of iron heads?

Thanks!!

Originally posted by bluerebl:

All of that makes sense to me, but it also brings another question to mind. Every aftermarket SBC/BBC aluminum head I've seen has a smooth, almost polished finish on the intake runners, some are like glass because of the CNC machine. Why don't aluminum heads have the problems you stated that come with polishing the intake runner of iron heads?

Thanks!! =
Don't know what heads you are lookin at but I haven't seen a polished intake runner in 30 years unless it was something someone "improved" on at home :D

The CNC stuff is not smooth although the pictures you see make it look pretty shiny.

Yeah although they look it, they arent(or shouldnt be) polished. The only thing I can say is check online for some cylinder head companies that do custom port work. Usually they have pics of thier finished work to show off what they can do. Usually you can compare a finished iron runner to a finished aluminum runner cause they will have random pics of both. when you compare the aluminum port to the iron port, the aluminum looks as if it is polished mostly because it is a more "brilliant" or shiny material than iron. But, they both have the same finish in the end. Anyways, after that, compare a properly finished exhaust port in an aluminum head to the intake port in that same aluminum head. Now the difference becomes more obvious, because just as the intake port looks glossy or polished, the exhaust port definitely has a shine to it, moreso than the intake port does(cause the exhuast should be polished). It just looks as if it would be polished compared to an iron head cause of the two different types of metal and the way they reflect light.

Check out this link for some descent pics of various intake and exhaust ports and chambers in alumium and iron heads.

http://www.replikamaschinen.com/auto_chevy.html

Thanks for the replies guys.

I wasn't planning on polishing the intake runners, plus I don't have a collet long enough to get all the way down even if I wanted to.

Eastwood has the collets (short and long) that fit a std die grinder. After I was finished any shaping work, I used 80 grit tapered cartridge rolls to start and did intake & exhaust ports and brute work in chamber. Then switched to 120 Grit and went over exhasut ports and chambers. In the intake ports, don't get too hog wild, most benefit is the smoothing the bowls and blending in the seats. In the chambers I basically just tried to smooth al the casting pores but not drastically remove metal. My 290's finished at 104CC after polishing.

JMHO, but I doubt my 9.5/1 408BBC gained much from all this, but I intend to swap these same heads onto a much higher compression and bigger big block in the near future where the benefits of port and polish work should show up.

Enjoy guys!!

Here are the heads before polishing:

http://memimage.cardomain.net/member_images/1/web/685000-685999/685533_59_full.jpg

.......and after:

http://memimage.cardomain.net/member_images/1/web/685000-685999/685533_68_full.jpg

http://memimage.cardomain.net/member_images/1/web/685000-685999/685533_69_full.jpg