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WFO
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I have heard of people doing this on their pistons. What is the bennefit of this modification? How much do they mill out of the piston. (Depth)
By placing the dish directly over the combustion chamber of a wedge-type head, the quench area is maximized and the flame front may have less distance to travel than if a round dish piston were used. But this is generally only used if the compression ratio would be too high if flat top pistons were used. Also, instead of machining flat tops into an inverted dome piston, a D-shaped dished piston is usually used. Not quite as good as a true mirrored dish, but close.

The amount of the dish depends on the target compression ratio, so there's no magical number for depth.
 

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WFO
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Maybe I missed something but exactly how do you get the "mirorred" finish?
Polishing the chambers and piston tops is a waste of time on a street engine, the chambers and piston gets a carbon coating the first five minutes the engine runs.

The MAIN thing you want to do is remove any/all sharp edges or casting irregularities from the combustion chamber (including the exposed spark plug threads) that could cause preignition. This can be done w/a die grinder and sanding rolls. A Dremel will even work but takes longer.

Smoothing/polishing intake ports might help a little. But this is after you've done other far more important things- like smoothing the lip below the valve seat and port matching the intake and head (NOT gasket matching, port matching is a different thing).

Giving the valve reliefs of the piston a small radius (just enough to remove the sharp edges, nothing more!) can help a tiny bit, too. Do not mess w/the rest of the piston unless you know exactly what you're doing.
 

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WFO
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You polish the pistons with a bench grinder that has longer shafts for a large polishing cloth wheel. Heads can be done with a diegrinder/dremel but it will take forever.

Polishing on the street is not needed. But is not effected by carbon for two reasons. One the carbon does not stick to the polished surfaces, two the polished surface still reflects heat even if it cant be seen. This is way home insulation has reflective foil backing and is never going to see any light because its buried in the ceiling and under the roof of the house but still reflects heat back into the house.

This will help on any engine street or race but usally time consuming and if your not doing the work your self you will have to pay way to much to have it done. If you got the time it doesnt hurt.

Only forged pistons can be machined with little impact on the strength. This is only becasue they are way stronger than most apps can use. But if they are borderline in strength and they are cut they will fail for sure. Also cutting the piston head tends to allow the head to collapse and expand at different rates from heat and casues issues that buying pistons cast in the correct shape is always the way to go.

Hyper, and cast iron pistons can not be but they will fail. They are sometimes cut to reduce compression but this is done to engines that make 200hp not 500. So once you think about your goals and you will be buying the correct pistons and go no need to cut them at all.
I'm getting a bit tired of correcting you. Have you ever even opened up an engine?? There is carbon almost the second you start the engine the first time- polishing chambers is a total waste of time for him.

Maybe you don't believe me- but how about Larry Freaking Widmer??

It does NOT take "forever" to use sanding rolls, etc. to do the chambers w/a die grinder- that's how it's done by everyone who does this!

Son, I have hand machined cast pistons to work w/a set of Trick Flow Twisted Wedge heads to work w/a 0.640" lift solid roller that we ran on nitrous, I hogged the HELL outta those pistons- guess what? No failures of the pistons. Period. Do I recommend it? Of course not- that's why I added the comment above. But it's not like it cannot be done as easily as it can w/forged pistons. What do you think was done in the early days of turbocharging, before there were "turbo" pistons?

I have the distinct feeling you're shooting totally from the hip and have no actual experience w/ANY of this.
 

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Discussion Starter · #9 ·
Cobalt327 you might want to go scroll on some other forums, cause I believe there is some schooling needed to take place. Haha a few others are under the impression that a polish will resist carbon aswell.
 

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TAKE A KID TO A CAR SHOW
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When I pit crewed we polished pistons and used water injection on the supercharged gas engines and some normally aspirated among some of the benefits was keeping carbon from building up on the polished pistons (no carbon build up to hold heat) But even on some tear downs there would be some carbon here and there!

We didn't polish pistons to stop carbon build up we polished them so there would be no hot spots that could start the aluminum pistons melting!

Jester
 

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Discussion Starter · #12 · (Edited)
I was told to never polish after porting when fuel will pass through because a smooth finish will not let the fuel flow freely, in a sense. It will have a tendancy to stick to the polished walls. If this is true, does it apply with carbon aswell? i take it nobody polishes with iron heads?
 

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Discussion Starter · #15 ·
so basically this is machining is done to lower cr and only not so much for hp? (obviously a gain but not major), Is this done on any other heads besides wedge?
 

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WFO
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You just showed me everything I need to know when you said "Larry whoever". Larry Widmer is way smarter than you. Or me, even.:mwink:

But tell you what. You go on ahead and go against what I said, I could care less. Polish the whole thing, inside and out. REAL nice ans shiny. You cannot make a horse drink- you can only lead her to water.
 

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WFO
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That's OK, I'm pretty sure he's doing OK. I don't much care about his diet, and I almost wonder why you would. But not quite. You went to his site? Didn't know he had one. At least that's a start. Keep reading, you will learn something. Maybe. Or maybe bolt something together, I don't know. It's a thought.
 

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WFO
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Cobalt327 you might want to go scroll on some other forums, cause I believe there is some schooling needed to take place. Haha a few others are under the impression that a polish will resist carbon aswell.
A LOT of misinformation gets repeated by people w/no real experience. They google something, and then repeat it thinking that no one realizes they're not speaking from experience. But resisting carbon build up isn't the issue, anyway. The issue is whether there's any real benefit or not to YOU.

I do not expect you to blindly believe me. But besides Larry Widmer, how's about Joe Sherman? He won the Engine Masters deal a while back. I think he- like Widmer, et al- also knows a thing or two. The thread below gives his take on polishing. BTW the title of the thread is not mine, that's what comes up when the thread address is posted (referring to & bull):

Polishing Piston Top and Combustion Chamber • Speed Talk

I'm done w/trying to convince you that it is a waste of your time (and this wasn't even your original question) except to say there are other things too numerous to mention that would actually give you an improvement that should come first.

As far as Widmer's chambers being polished, or what is on his site, I didn't know he had a site, so I cannot speak to whatever is there or not there. If you provide a link I could give an opinion.

But on a Civic he did that made 490 hp w/a little blower (no big deal), the head looks like:



Smooth, yes. Polished? No. Same thing for the pistons.
 

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Discussion Starter · #19 ·
So the debate here is that it is just a waste of time? I'm getting mixed answers. It is obvious that it helps reduce carbon build up, and reflects heat. Correct? Just time and money.
 

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Discussion Starter · #20 ·
Regardless of street or track, would you do it. Techinspector has a good way of removing carbon on a polished chamber without taking heads off. In previous post.
 
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