i have a brand new set of stock pistons, wondering if there is an advantage to polishing the pistons?
polished pistons?
- Thread starter MKIII TURBO60-1
- Start date
No, total waste of time 3 minutes after the first start they will have a coating of carbon.
Having them coated is worthwhile.
Having them coated is worthwhile.
Firstly by polishing the surface of the piston to a mirror finish you will reduce the surface area of the piston top by remove all the tiny dimples left in the surface after casting. The effect of this is to improve the thermal efficiency of the combustion by reducing surface area(ever so slightly) this reduces the amount of heat transfered from the combustion chamber hence making your piston run cooler.
Secondly the polished surface will result in less carbon build up on the surface.
Thirdly the polished surface will reflect a small amount of heat back into the combustion chamber again improving thermal efficiency and lower piston temps.
Even with these three effects combined it would be completely un noticable in a DD. However would be worth doing in a racing engine.
Secondly the polished surface will result in less carbon build up on the surface.
Thirdly the polished surface will reflect a small amount of heat back into the combustion chamber again improving thermal efficiency and lower piston temps.
Even with these three effects combined it would be completely un noticable in a DD. However would be worth doing in a racing engine.
Agreed although I'm not sure how much a highly polished piston would resist carbon buildup. Certainly not as much as a thermal coating would.
Good point about the transfer of height, this is one of my questions about the popularity of polished radiators and intercoolers. Shiny, metallic surfacess will transfer less heat than flat, dark surfaces (talking convection, not conduction) I guess it's just a finish preference and is neglible when you figure most are increasing the physical size anyway? (slight increase in surface area would outweigh the surface finish)
Brian
Good point about the transfer of height, this is one of my questions about the popularity of polished radiators and intercoolers. Shiny, metallic surfacess will transfer less heat than flat, dark surfaces (talking convection, not conduction) I guess it's just a finish preference and is neglible when you figure most are increasing the physical size anyway? (slight increase in surface area would outweigh the surface finish)
Brian
When we assembled this:
We did not polish the pistons.
It ran for one and a half race seasons at 1,400+ RWHP and set two world records in it's class.
You'd be better off investing your efforts into shot peening and then beam polishing the rods.
We did not polish the pistons.
It ran for one and a half race seasons at 1,400+ RWHP and set two world records in it's class.
You'd be better off investing your efforts into shot peening and then beam polishing the rods.
I'm actually in the process of deburring the valve cutouts/edges on my NPR pistons with 600 grit sandpaper and I came on to see if it's worth it to continue lol.
I'm using 600grit and it's just enough to notice a difference when running your fingers over the tops of the pistons.
What do you guys think?
I'm using 600grit and it's just enough to notice a difference when running your fingers over the tops of the pistons.
What do you guys think?
streetracer_258;1507994 said:
i completely agree, this is done on most engines we (Nolden Motors) build.
-shane
On my son's kart engine, I would put on a layer of artificial carbon.
Rules forbid coatings, but they did not say anything about carbon.
Did it for 2 reasons:
First, it help insulate the piston, which is critical on a 2-stroke.
Second, if I did the bake time correctly, it would burn off durring the event, and increase head volume.
We were always teched after an event if we won, and had a minimum chamber cc that we had to meet.
So the end result was we had a higher compression ratio at the start of an event, and were legal by the time the event was over.
Helped qualifying a bunch !
Totally irrelevent, but fun to show what it takes to be competitive, and not get busted for cheating.
More to the point, I have known a lot of old school oval track guys that in the days before ceramic coatings, would spray piston domes with high heat header paint.
And if they were freshening up an engine, they would not decarbonize the domes, just to keep the insulating effects.
Rules forbid coatings, but they did not say anything about carbon.
Did it for 2 reasons:
First, it help insulate the piston, which is critical on a 2-stroke.
Second, if I did the bake time correctly, it would burn off durring the event, and increase head volume.
We were always teched after an event if we won, and had a minimum chamber cc that we had to meet.
So the end result was we had a higher compression ratio at the start of an event, and were legal by the time the event was over.
Helped qualifying a bunch !
Totally irrelevent, but fun to show what it takes to be competitive, and not get busted for cheating.
More to the point, I have known a lot of old school oval track guys that in the days before ceramic coatings, would spray piston domes with high heat header paint.
And if they were freshening up an engine, they would not decarbonize the domes, just to keep the insulating effects.
Adjuster
Supramania Contributor
Intresting stuff. I've found the piston crown coatings to work very well in helping to control detonation, and piston damage from excessive heat. (I have both my crowns, and the combustion chambers on the head coated with the same thermal barrier, and it works.)
I do the valves also.
Just the tops on the intake, and tops & undersides on the exhaust.
I would like to do the ID of the exhaust ports, but as yet have not figured how to get a good abrasive blast finish on them.
Does anyone make a miniature blast gun with a 90 degree head on it ?
It sure would take a lot of heat out of the head........
Just the tops on the intake, and tops & undersides on the exhaust.
I would like to do the ID of the exhaust ports, but as yet have not figured how to get a good abrasive blast finish on them.
Does anyone make a miniature blast gun with a 90 degree head on it ?
It sure would take a lot of heat out of the head........
It's harder for heavy carbon to stick to a well polished surface. I've taken engines apart with polished vs unpolished combustion chambers and pistons and in the polished engines the deposits are always thinner and usually flake off very easily (usually just by rubbing with my fingertip). I'd also say that preventing carbon buildup is more important on a street car than on a race car. Most of the carbon accumulation is from extended low load driving, race engines don't see a whole lot of that.
polishing gains nothing.
Coating at least attempts to maintain the heat in the gas instead of letting it easily transfer to the aluminum pistons. So a gain of thermal efficency. How much? No objective numbers measured.
Coating at least attempts to maintain the heat in the gas instead of letting it easily transfer to the aluminum pistons. So a gain of thermal efficency. How much? No objective numbers measured.