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Baby Blue VVL
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Discussion Starter · #1 ·
I just ordered my 12:1 pistons and the person I spoke with (shop reseller) was bringing up an interesting point about piston coating. While he loves swaintech he doesn't recommend the tops of pistons be coated for heat emission.

More heat in the combustion chamber = detonation city.

This logically makes sense to me but do the piston top coatings really just insulate the pistons from heat? Or does it somehow absorb the heat to keep the pistons cooler and the Combustion Chamber more evenly tempered?

I didn't find my answer in searching so off to swaintech's website
 

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Baby Blue VVL
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Discussion Starter · #2 ·
"Thermal barrier" ceramic-metallic coatings for the tops of pistons are another type of coating that have been used on some diesel pistons and performance pistons. Improving heat retention in the combustion chamber improves thermal efficiency and makes more power. It also helps the piston run cooler. But too much heat in the combustion chamber also increases the risk of detonation and preignition, which is not a problem with diesels but is with gasoline engines. So when a coating is used, ignition timing must usually be retarded several degrees to reduce the risk of detonation.
http://www.aa1car.com/library/2003/eb40354.htm
 

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OnyxEros said:
I just ordered my 12:1 pistons and the person I spoke with (shop reseller) was bringing up an interesting point about piston coating. While he loves swaintech he doesn't recommend the tops of pistons be coated for heat emission.

More heat in the combustion chamber = detonation city.

This logically makes sense to me but do the piston top coatings really just insulate the pistons from heat? Or does it somehow absorb the heat to keep the pistons cooler and the Combustion Chamber more evenly tempered?

I didn't find my answer in searching so off to swaintech's website
Yes, the insulate the pistons, they do not absorb heat. Its piston hot spots that can cause detonation, so keeping heat out of them is a good thing. I think...
 

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"Gold Coat reduces heat transmission to the underlying metal by at 20-40 percent. This helps protect the piston from detonation-induced heat as well as reducing thermal expansion, allowing a tighter piston to wall clearance. Since pistons do not have the benefit of water jackets like those in cylinder heads, keeping heat out of them is a good thing. By reflecting this heat back into the combustion chamber, the coating helps promote a better burn, harnessing this bit of otherwise wasted heat."

from mike k.
 

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713 ways to be a dick!
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The heat is not introduced until combustion, excess heat becomes an issue if there are piston hot spots and the like. I have swain coatings on my cylinder head (exhaust ports, combustion chambers, valves) and I noticed higher EGT's at idle however they EGT's stay cooler under high boost conditions than other uncoated motors. Keeping the heat in the exhaust gas rather than soaking the engine components also helps with scavenging.
 

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some items I want to point out. Starting with the first post, the coating does not absorb heat, in fact this is the beauty of the coating. It is thermodynamically impossible for something to absorb heat without releasing it or doing work on the system.

I have to seriously disagree with any statement that a coating on the top of the piston will increase the potential for detonation. Detonation is casuse by 1 of 2 things, either extremely high pressures, or high temperatures on the combustion chamber's walls PRIOR to combustion.

As said before, hot spots on a piston can be a cause of detonation, the coating insulates the piston allowing the piston to run cooler, but in order to do so, it must be assumed that the coating does not absorb heat as efficiently as the metal piston. Thus, after the exhaust gases have exited the chamber the top of a coated piston will be cooler than the top of an uncoated piston.

Since heat is not absorbed into the piston, this means that the gasses inside the chamber will be hotter, but ONLY AFTER the spark plug has lit and the combustion process has begun, thus, it is not Pre-ignition. Those hot (or hotter) gasses are expelled on the exhaust stroke.

So why would they say that chances for detonation are INCREASED? I'll tell you why, if heat cannot be absorbed into the piston, the gas temperatures will go up. If the gas temperatures go up, the heat tries to find another way out (before it is expelled on the exhaust stroke). It does so in 2 different ways:
1. Less thermal loss (Q-out) means more work done (W-out).
2. Since the heat isn't absorbed into the piston, it absorbs into other parts, say the cylinder walls, the head, the valves, oh, and most importantly the spark plugs.

You should all know by now that spark plugs come in heat ratings. Hot plugs and Cold plugs. In boosted, nitrous, and racing applications, the plugs will get so hot they'll become glow plugs and detonation is a problem, well, same goes in this situation, the cylinder temperatures are higher and the plugs are getting hotter.

Don't quote me on this, but I'm almost positive that if you coat your pistons, AND you change to a colder plug (say a 7), you'll greatly DECREASE the chances of detonation.
 

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Always Different !
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Detonation:
Uncontrolled burn of the charge mixture; resulting from a rapid leading edge pressure wave that auto ignites the unburnt portion of the charge in the chamber. Occurs AFTER initial spark induced ignition.
Excessive boost, excessive CR, poor chamber design, rod length / stroke relationships also impact it being an issue.

Pre-Ignition:
Rapid pressure / temperature rise in the combustion chamber that auto ignites the charge PRIOR to initial spark induced ignition. OR hot spot ignition of the charge prior to spark induced ignition.
Glowing Carbon, excessively heated plug bridges, sharp edges, excessive chamber temperature, poor chaber design, excessive CR, excessive boost, etc.

The two are way, way different and very often described out of misunderstanding them.

If retained heat in the POST IGNITED CHARGE can be increased, efficiency will increase, however the fuel has to be able to sustain that increased efficiency / temperature. If the fuel is not up to it it will do one of either, detonate or pre-ignite.

Another clasic example of Tom, Dick and Harry running out and getting the "best thing since sliced bread" on the market and thinking, "it works for them, it will work for me".

The Plug comes in heat ranges for one reason and one reason only.
To maintain a tip(+) and insulator temperature that will deter carbon adherence to the insulator. If the carbon is allowed to build on the insulator it becomes a conductor and you get fouling of the plug from the tip (+) to ground. Hot or Cold fouling, same problem. The Bridge (-) on the plug is directly connected to the threaded portion and has the fastest heat discipation to the head. Hot plugs, Cold Plugs, once of the same brand/type have no difference in the heat discipation from the Bridge to the Head.

Can the coatings encourage this?
ABSOLUTELY.

Will the coatings do this?
APPLICATION SPECIFIC.
 

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Baby Blue VVL
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Discussion Starter · #13 ·
OK
12:1 90mm N/A VE Pistons from CP

Should I coat the top or not?
I will coat the walls and the bottom of the piston to help with oil sheding.

btw thanks guys ;)
 

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Honestly, I have no idea. 12:1 is insanely high compression in my book, 11:1 is the highest I would be comfortable with on the street. I think we're starting to go beyond the capabilities of 93 octane.
 

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Baby Blue VVL
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Discussion Starter · #15 ·
The VE head is much better than the DE head
Since it's a VE motor many have stated 12:1 is doable but the pistons have been ordered alread, i could lower compression with headwork but i would perfer not to. I just want to know that when i get the pistons back in 5 weeks if i should send them right back out to be thermal coated.
 

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oh, I figured the pistons were going in a DE.
 

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Theres is an SR20VE here in PR (his name is Payu on this forum), he uses SR16VE pistons. Try getting in contact with him. The car has ALOT of torque and top end as well. I know he did use a DET head gasket with an 87mm bore to lower the compression a little bit. Good luck.
 
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