Do you performance guys "tootsie roll" your pistons before installing them? I took my BRC's and radiused all of the sharp edges around the dome and in the valve relief pocket. Is this a common practice for squeezing out every last bit of power or have I been hanging around the Super Stock guys too often?

Here is a pic of before (as they come out of the box) on the left and after I cleaned up the edges on the right. I just have to do a little fine polising and they will all be done.

http://www.chevelles.com/showroom/Epistuff/piston.JPG

The guy that built mine had the domes ceramic coated, not sure about radiusing, I guess it helps spread the heat across the dome more evenly and retains the heat a little better. I can see where the radiusing and smoothing would remove any sharp edges where you could get hotspots which would lead to detonation.

Jim,
Nice job ! I have been using cross buffs. They really do a nice job of breaking sharp edges etc. Nice for polishing combustion chambers, especially in aluminum heads.
http://billkoustenis.home.mindspring.com/crossbuff.jpg

Very nice, how did you do that and why do you need to fine polish them??

gspan,
I did it using a dremel plugged into a variac so I could run it at real low speed. I had a "tootsie roll" sanding bit on it. This was used to radius all of the rough sharp edges, then I finished it off by hand in 3 stages with emery cloth, super fine, then ultra fine. After that I hand rubbed them with polishing compound. Then they get a complete dunk in laquer thinner parts washer to clean them up. Sounds like a lot of work, but it only took about 10 minutes/piston. I polish them smooth not for looks, but the smoother and shinier they are, the more heat they reflect back into the chamber. Like Robert said when there are no sharp edges they are less prone to detonation due to hot spots. The radius around the valve pocket also helps promote better flow (theoretically).

Bill K.,
What material are those little cross buff polishers made of?

Jim - Nice job. We make an effort to round over all the sharp edges, primarily to eliminate hot spots. It may have other advantages, but I don't have any data to prove that. You can see them here. (http://home.att.net/~rhcopeland/engine2.htm)

Bill - Who makes and who distributes those cross buffs?

Nice job cleaning those up graemlins/thumbsup.gif

Chris,
Yea, I figured for the 1.5 hours of labor, it would be worth the effort.

Roger, those domes look huge! You even have the spark plug dimple. What are you running.....13:1?

The cross buffs are the same material as scuff pads at different grades of coarseness like steel wool. Just like the scuff pads your wife uses in the kitchen. :D

Rod

Originally posted by Epistuff:
Roger, those domes look huge! You even have the spark plug dimple. What are you running.....13:1? Actually, 14.92:1

There are many suppliers. Do a "google" search on "cross buffs" Standard Abrasives, Cylinder Head Abrasives, Mondello, Snap On etc.

Ah ha, here they are>> Cross Buffs (http://www.sa-motorsports.com/cat/p15.htm)

Thanks Bill


Roger, 14.92:1 !! Yikes :eek: