Reason for smoothing edges on a piston?

[Jay_Kay]

Just curious to why people smooth the edges off a piston.

From this

To this

 

[Fred@BTM]

because they like wasting their time?

 

[Dan@SJM]

And creating unbalanced pistons.

 

[Scrooge]

That's not particularly clever.

 

[mark123]

Trying to reduce hot spots maybe? Looks a bit excessive.

 

[Scrooge]

Looks like he got a few beavers and rasp file in to do it.

 

[...]

Surprised fred didnt answer this .... pocketed pistons (that ones extreme) for very lary cams ?
Thsts got four round cut outs for valve clearance

 

[...]

My race zetec used to look like that though not that extreme

 

[Scrooge]

^ That doesn't mean he then needs to attack the edges

 

[Laine_16v]

Nout to do with cleareances, Sand rolling the top pistons reduces chances of detonation, i had the same done to my pistons on my F7R build years ago.

This is what APD told me anyway, so make of that what you will lol. Probably a waste of time.

 

[...]

Nout to do with cleareances, Sand rolling the top pistons reduces chances of detonation, i had the same done to my pistons on my F7R build years ago.

This is what APD told me anyway, so make of that what you will lol. Probably a waste of time.

which bit are we looking/talking about here ? because i was looking on a phone earlier and i don't get which bit you mean ?



​the machining on the top ?



ok now on a pc and have looked at a normal f4r piston (never seen one and didn't know they had pockets in anyway) in which case , waste of time .

 

[NorthloopCup]

Any 'sharp' edge does indeed increase the possibilty of detonation.

 

[Mike@Rentech]

So they can post pictures of "Look what I've done today to my engine" on internet car forums ??

 

[Carlv8415]

But surely more flat edges make more surface area so would make greater power on ignition? Worded that badly but you get what I mean

 

[Gorms]

Stress raiser reduction? The only reason you would remove a sharpe edge.

 

[Dan519]

But surely more flat edges make more surface area so would make greater power on ignition? Worded that badly but you get what I mean

surface area of the piston crown doesn't really directly effect power.

softening the sharp edges is a worthwhile way to reduce detonation risk, det will always occur more easily on an edge, which is why you often see damaged squish zones on the head. The example above has gone a bit too far though, you don't want to change the shape overall, you just want to soften the edge

 

[Andyrg@ ClioTurbo]

Well said dan at a19

Im sure they must get a company to do this and then adjust weights so there the same normaly done from the pin area.

 

[Dan519]

You can see in this picture, the sharp edge of the squish has become a focus point for detonation

 

[Dan519]

Well said dan at a19

Im sure they must get a company to do this and then adjust weights so there the same normaly done from the pin area.

when i clean them up, I send the pistons to be weight matched with the rest of the rotating assembly. Usually a few minutes with some 1200 grit and some scotchbrite is more than enough though

 

[Yanoo]

As Dan said, sharp edges can cause hot spots in the combustion chamber.

 

[Chip-mk1]

When its an engine which is knock limited on power, its worth doing to try and squeeze an extra degree into the ignition table by removing sharp edges which can encourage detonation as they are invariably hot spots.

Gains will be minimal even on race applications, but if you are down to chasing every last BHP its worth the hassle.

If you go too far, you end up lowering the CR of course as you are removing material thats intruding into the unswept region.