I've seen a few pictures of peoples build and it looks as if the pistons have been 'scuffed' up a bit before install and i was wondering what this achieves and wether its worth doing? I've searched but not really sure what i'm looking for.

 

Some people will buff or sand piston tops to remove rough edges and smooth the piston top. It is done to help prevent hot spots and detonation.

 

i find it odd that some piston manufacturers swear that a shiny polished surface is ideal whereas other manufacturers swear that a "unfinished" finish is ideal...

maybe i havent paid enough attention, but does this have anything to do with the type of material the piston is made with or the type of engine it will be used in?

i really havent found much information supporting either side of the argument...wouldnt mind hearing what yall think.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Suck my DX &raquo;</TD></TR><TR><TD CLASS="quote">i find it odd that some piston manufacturers swear that a shiny polished surface is ideal whereas other manufacturers swear that a "unfinished" finish is ideal...

maybe i havent paid enough attention, but does this have anything to do with the type of material the piston is made with or the type of engine it will be used in?

i really havent found much information supporting either side of the argument...wouldnt mind hearing what yall think.</TD></TR></TABLE>

I can't find anything either tbh, not sure i'm searching for the right thing though.

I can see that rounding off thin edges of the valve reliefs would eliminate hot spots but as far as an unfinished surface all over the piston top i'm not sure off the benefits?

 

If you polish the crown of the piston you need to polish the conbustion chamber also. If you polish just the piston the heat is reflected toward the head and the head absorbs the heat. If both are polished then it reflects the heat back into the combustion chamber and increases thermal efficiency, which is why you're doing it in the first place.

 

^That has NOTHING to do with why we do it.

As B19 coupe stated, polishing the piston is only done to round off sharp edges AKA the dome and valve reliefs to eliminate hot spots from forming creating preignition.


This is before, notice all the mega sharp angles that will heat up MUCH faster than the thicker portions of the pistons surface.



And this is after some prep work, sorry for the shitty angles, wasn't planning on posting these, I just like to snap pics when I work on things.

 

All of the mahle hi comp pistons ive dealt with have some extremely sharp edges.

 

Myself as well, but they are a damn good piston when prepped properly.

 

Cheers for the feedback! Are there any guides or how to's on this?

Do i basically take a scotch pad to all the sharp edges?

 

We use a 90 degree sander with scotch brite (medium and then fine) to smooth out all the sharp edges.

 

I presume its not a good idea to catch the edges above the ringlands?

Do you just mask it up and go easy?

 

Scott wrapped his hand around it and went easy, when he felt pain, he knew he was too close lol.

 

That is a very good example for taking the edges off.

I have a question though, at the end of the day are you checking the weight to ensure they all are close to equal?

 

Marc, I honestly did not. I considered it but talking to Scott Sublett who assembled the short block for me (has credentials around 4.5 miles long and quite a few 6 second 1/4 mile motors to his name) that the actual amount of metal being removed is so minute once it's all been balanced that it won't affect it adversely at all.

Considering I DD the car 80% of the time and put around 1k a month on it since March and god knows how many 12 second motor passes, blasts of nitrous, and good god amount of dyno time just playing with things, I tend to agree with him lol. This engine has NOT had an easy life and she runs like stock around town at 180 degrees in traffic on pump gas, well, it speaks for itself.

 

That is the info, I was looking for.

Thanks