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polished piston tops

1K views 10 replies 7 participants last post by  clayewing 
#1 ·
In anybodys opinion should i polish my piston tops? heat coat piston tops?
zxt
 
#3 ·
A OK buddy , not looking for info on actual process but weather you have done it and (in your opinion is it a worth while investment).to Polish and then have heat treated???????? I appreciate the tip though (on using search ) why hadent I thought of that?



Post Edited (Mar 14, 6:59am)
 
#4 ·
i heard about using paint on top of the pistons? what kind of paint?
 
#6 ·
polishing piston tops gives you several benefits to flow, heat reflectance, and reduction of carbon buildup, and is definitely a worthwhile thing to do, and can be done when you have the head off, which can't be said for heat treating them...you gotta take em out, which is a bit more work. Don't paint them! While you are polishing piston tops, polish the combustion chamber too, and gently ease any sharp edges, as well as smoothing the little bits of thread exposed where the spark plug comes through; and you will reduce the likelihood of pinging, which is exacerbated by little sharp edges becoming hot spots. Heat treating a cast aluminum piston is gonna be a waste of time and money....what do ya think happens to heat treeating benefits when the part is re-heated? It works for steel parts, especially forged ones, which is of course why people who need lotsa power run forged......
 
#7 ·
Very little gain from polishing. (piston)

Could even argue pointless.

Do smooth semi finished dome pistons.
Do remove edges that burn away in chamber.

Coatings job is to prevent heat from dissipating as rapidly into piston.


Complete waste of time on previously run pistons

And I figure there are things neglected that would benefit you more.
Please no hate mail from all the profesional piston polishers
 
#8 ·
not hate mail....but...my dad built racing motors for years, including the motors for the Revellution funny car, and had his own dyno. He dynoed a MGB motor for my uncle's hill climber and then polished the pistons and chambers and dynoed it again. The only thing he changed was the polish, everything else was the same. He got 2-3% more power right off the blocks and then found he was able to tune more advance into the timing for a total of 5% improvement. That's free horsepower right there....all it cost was a couple hour's worth of elbow grease, and it most definitely is worth it to polish your piston tops up if you have the head off anyhow. The increase in heat reflectance on the pistons will allow you to tweak a little more advance in; if you don't do that, then no, you won't see as much of a power increase.
One thing my dad knew, was how to tweak out a motor. I had a 68 Firebird with a mildly worked 400 making 380 HP, and I thought I had it running great. I had to pull it for a blown rear seal, and my dad took it for a weekend. He tweaked it to 425 hp without replacing a single part. And apologized because he thought he coulda done more except his flow bench was broken. He did a lot of things you shouldn't try at home...., but he did a lot of things you can do at home, and when people asked him for advice all you ever heard was "polish polish polish blah blah blah"......
 
#9 ·
theghosttanker,

you said, "The increase in heat reflectance on the pistons will allow you to tweak a little more advance in."

This is all I know about timing advance: Initial + mechanical + vacuum advance = Total advance(full advance @ high rpm's). To do what your dad did, should one increase initial, mechanical, vacuum advance, or does it matter which? forgive me if seam uneducated in the subject (because I am:)]
 
#11 ·
Again I say polishing the piston top, very little gain.
Cutting the cumbustion chambers radially to the guide centerline will make a marked improvement on air flow and thus improve power.
SO a dyno test including polishing of both pistons and combustion chambers could yield a noticeable gain.
however care must be taken not to credit the prior modification when the latter is likely responsible for the % change.


And again I stress the obvious fact that other things NEGLECTED would benefit the engine more. To spell it out, spend anytime you have improving the flow through the intake,cylinder head, out the exhaust.
you will be rewarded with real gains in power.
On small displacement engines small % gains in power often fall under the resolution or repeatability of the dyno. (really apparent with manual load control due especially to inertia being loaded and unloaded due to less than perfect constant rate of acceleration).

I currently own two modern up to date dynos and plan to install the third during the coming year. so we have a" little" dyno experience.

Generally speaking, the "need " to run more timing is due to ineffcient cumbustion. the mixture needs more time to create expansion before the piston travels down the bore without being reacted upon by heat expansion of "spent" gas.

When building an engine, consider the goal and available resources,especially time. All I really was trying to say is spend the time working toward the 10% and 20% gains that are being neglected before concentrating efforts toward possible 2% to 3% gains.

When you polish the pistons Use the time to ponder why old timers preferred a light coat of carbon to insulate the piston from the heat in the chamber. I'm not saying they are correct, just that there may be merit to a coating dark, or light and reflective.

To clarify, I am in agreement with coatings once more important things are done.

I just can not see the expense when I don't even know if the pistons are new ,used....cast, forged...so I spoke out of turn .


I sincerly need to know if anyone can provide documentation of a controlled test where the ONLY CHANGE was polishing the piston with an improvement in power.
Doesn't count if the compression is lowered slightly thereby allowing more timing advance with the same quality fuel.
Or even the same advance, only now preignition is reduced and no longer "braking" the engine.
This could be an issue with borderline fuel.
fuel quality has upset many otherwise good dyno test.



Post Edited (Mar 15, 9:48pm)
 
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