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Polishing piston top

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Polishing piston top

Postby My427stang » Sun Feb 05, 2006 8:51 pm

Guys, I took down all the sharp edges on my new set of Diamonds, then went 320 grit wet, then 800, then 1500 (more work than probably necessary but they do look pretty)

Here is my question, any benefit to a mirror polish on a piston surface over what I have now? any downside?

Here is what I ended up with after knocking the sharp edges off and polishing, I could get it chrome-like without much effort at all if there is a benefit (The outside edges of the eyebrows arent sharp, I laid them back and tapered them into the relief, it doesnt show in the picture, nothing will get hot)

Its a street motor, 4.277 bore, 10.73:1 pump gas, alum heads. Thanks in advance

Image

Here is what they looked like as delivered, very nice and dimensionally PERFECT however every edge would cut a finger

Image
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Postby JBrady » Mon Feb 06, 2006 12:03 am

First of all nice work. Eliminating sharp edges is always a good idea. I haven't seen many advocate a polished piston top but at least in one theory it could help. Reflecting light rather than absorbing it should leave more energy to do work with.

BTW this picture is of some forgings that overheated in the outside valve relief areas suggesting a vunerable area due to heat. Only happened on 1 out of 8 and looks to be an injector problem but points to a weak link nonetheless.

http://www.lextreme.com/forums/attachme ... 2740&stc=1
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Postby Darin Morgan » Mon Feb 06, 2006 9:28 am

I have played with that for years and found nothing in it. On an engine that uses a little oil, it will actually hurt power. he piston will eventually get carbon on it and any benefits that could have been there will be gone rather quickly. It looks cool though.
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Pistons

Postby My427stang » Mon Feb 06, 2006 5:56 pm

Thanks guys, I certainly have other things that will better consume my time!

I appreciate the advice
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polished pistons

Postby Jerry ARNOLD » Mon Feb 06, 2006 8:50 pm

I have a story written by Asian engineers who tested the polished pistons on racing motorcycles and the found it was better than any heat coating on pistons.
more power even after carbon build up.
I couldn find the story tonight but will locate it sometime as i don't throw anything out.
when i find it i will post the info.
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PS

Postby Jerry ARNOLD » Mon Feb 06, 2006 8:55 pm

The story IS written in english!
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Pistons

Postby My427stang » Mon Feb 06, 2006 9:12 pm

LOL thats too funny, in Japanese it'd be a bit tougher to read.

If you can find it, I'd love to see it
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Postby femtnmax » Mon Feb 06, 2006 9:22 pm

KB-silvolite tech article suggests polishing the piston tops. Could not open their website tonight, so here is another route to same info: http://www.beckracing.com/page07.htm
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Postby Larry Widmer » Mon Feb 06, 2006 9:30 pm

In 1969, we spent a month at Holman & Moody doing dyno development work on our drag racing Boss 429 engine. One of the experiments included the removal of the heads followed by a thorough cleaning of the light carbon deposits in the chambers and on the pistons. After installing the heads again, the engine was down on power from where we'd been previously. As we accrued more run time on the engine, the power came back....as did the carbon-dusting on the pistons.
In the mid-70's we did some work with a laboratory here in Texas that was formulating additives that removed carbon from intake ports and combustion chambers. After over a year of testing, it was rather conclusive that "clean" chambers and pistons were less efficient than those with a base-layer of carbon. Less efficient, meaning higher BCSF's and less power.
I've never highly polished pistons or chambers since.....
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Postby bill jones » Mon Feb 06, 2006 10:38 pm

-I have never polished pistons other than maybe a set or two when I was young.
-I actually prefer to have the top of the piston precisionally roughed up with a 50grit sanding roll where the lines act as precise edges to rip up any liquid fuel particularly near the shroud wall of the intake.
-I sweep these striations from the intake eyebrow over towards the sparkplug and make gentle curvatures back in towards the exhaust pocket.
--------------------------------------------------------------
-On the dome or dish side it's a little harder to expain but each engine shows carbon and clean pattern areas---so when you start with one pattern and see how the above mentioned lines that changes the patterns---and how the engine reacts---then next time I would look at what the patterns are like and make a decision.
--------------------------------------------------------------
-We saw racers who had issues for several years where they were lifting the ring land above the ring right at deepest point of the intake valve notch---and thinking it was raw wet fuel getting into the crevices has got me to doing this roughness.
-And now piston companies are machining shallow circumferencial grooves on the top ring land supposedly to prevent this ring land lifting problem.
-I first started doing that same modification during the late 1970's and early 1980's becasue of what I was seeing for color patterns of those top ring lands.
-Can't say that we've ever had a ring land degragation problem now for 20 something years.
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Postby Shaun » Tue Feb 07, 2006 12:08 am

From the Beck Racing link above...

PUMP FUEL

8.5:1 - Quench head engine for tow service, motor home and truck.

9.0:1 - Street engine with proper .040" quench, 200° @ .050" lift cam, iron head, sea level operation.

9.5:1 - Same as 9:1 except aluminum head used Light vehicle and no towing.

10:1 - Used and built as the 9.5:1 engine with more than 220° @ .050" lift cam.
A knock sensor retard is recommended with 10:1 engines.

RACE GAS

12.5:1- Is the highest compression ratio suggested with unrestricted race gas engines.


Surely this is advice for THEIR pistons and not a general rule?
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Postby SchmidtMotorWorks » Tue Feb 07, 2006 1:48 am

Surely this is advice for THEIR pistons and not a general rule?


Your thinking the 12.5 is low too?
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Postby Unkl Ian » Tue Feb 07, 2006 2:09 am

Sounds out of date. :roll:
Just because you never studied the Laws of Physics,
doesn't mean they won't try to kick your ass.
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Postby Cobra » Tue Feb 07, 2006 8:32 am

Cobra
 

Postby Shaun » Tue Feb 07, 2006 12:02 pm

SchmidtMotorWorks wrote:Your thinking the 12.5 is low too?


Yes. Even their pump gas recommendations aren't entirely accurate I think.
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