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Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 1:28 pm
by NewbVetteGuy
I've read a good number of the thermal coatings and particularly thermal barrier threads on here and what I'm interested in understanding is if there are any rules-of-thumb for the CR increase equivalent that you gain from coated combustion chambers and pistons?

(Thermal Barrier coatings are increasing the combustion temp, much like a CR increase, it would make sense that the easiest way to understand the change, in terms of torque, HP, mpg, & detonation sensitivity would be to just model your combo with an equivalent increase in static CR.)



Adam

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 1:37 pm
by ptuomov
Power gain or knock resistance? Keeping the heat in the chamber can sometimes help one and hurt another.

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 4:45 pm
by NewbVetteGuy
ptuomov wrote:
Wed Nov 01, 2017 1:37 pm
Power gain or knock resistance? Keeping the heat in the chamber can sometimes help one and hurt another.
For sure. More heat = more power but brings knock knocking at your door. That's why I'd like to understand HOW MUCH change it makes.


Adam

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 5:12 pm
by MadBill
I believe part of the intent of TBCs is to reduce heat transfer from the surrounding surfaces to the mixture during the compression stroke, thereby reducing the likelihood of detonation...

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 5:23 pm
by ptuomov
MadBill wrote:
Wed Nov 01, 2017 5:12 pm
I believe part of the intent of TBCs is to reduce heat transfer from the surrounding surfaces to the mixture during the compression stroke, thereby reducing the likelihood of detonation...
The intent or the effect? How far into the compression stroke do you have to be before the charge temperature exceeds the cylinder head temperature? I think someone smarter than me could compute the energy balance there, will less heat transfer lead to higher or lower end gas temperature.

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 5:28 pm
by MadBill
Good question; I think there's way more theory than data out there... :-k

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 5:35 pm
by ptuomov
MadBill wrote:
Wed Nov 01, 2017 5:28 pm
Good question; I think there's way more theory than data out there... :-k
What I’ve heard is that if you can feed the engine high octane gas and run it rich, the coatings seem to help power. On pump gas and with some limits on enrichment, it’s not so obvious which way it’s going to go. Also, turbo diesels (which don’t have knock issues) by my reading all seem to like coated chambers and pistons without any reservations. No first hand experience personally, the parts we tbc coat are external and the coating is there to protect components in a packed engine bay.

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 8:14 pm
by racear2865
Played with this a couple years ago. coated piston top, combustion chamber and face of valves. Was a SBC. Found it to be sensitive to timing to control detonation. Had a 6 inch rod. Changed to 5.7 to try to keep piston from being on top dead center too long. Finally decided that would do just like any motor to control detonation. Closed deck clearance from .041 to .o35. All worked to help but had a customer that wanted engine so couldnt play any more. Hope one day to try again and make more changes. Oh I also was going to change to Ceramic coated headers but didnt get to try. One thing I did notice was that oil temp droped but did not get to run any a/b/a test,. Wanted to coat intake bottom and top and wanted to insulate carb but------
reed

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 8:38 pm
by jsgarage
I remember a write-up of Smokey Yunick playing with ceramic coatings eons ago. He managed to coat a set of pistons so well, the underlying aluminum melted from retained combustion heat. So the unsupported coating eventually cracked. Maybe the melting point of aluminum is one limit?

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Wed Nov 01, 2017 9:24 pm
by 4sfed
jsgarage wrote:
Wed Nov 01, 2017 8:38 pm
I remember a write-up of Smokey Yunick playing with ceramic coatings eons ago. He managed to coat a set of pistons so well, the underlying aluminum melted from retained combustion heat. So the unsupported coating eventually cracked. Maybe the melting point of aluminum is one limit?
That doesn't make sense ... the combustion chamber is the only heat source capable of melting aluminum. Unless the bottom of the pistons were also coated, the coating could only reduce the temperature of the pistons.

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Sat Nov 04, 2017 9:20 am
by CharlieB53
The coating will only reduce the speed of the heat transfer from combustion into the piston.

It may be argued the incoming mixture does provide a % of piston cooling prior to the next combustion cycle. However, I seriously doubt that any insulation could function as a one-way heat valve, allowing the piston to accumulate temps and melt without other contributing factors causing elevated combustion temps.

I suspect if the underlying piston material was melting that Smokey was playing with leaning out the mixture on the big end, increasing power. The rise in combustion temps and the sustained heat transfer through the coating finally melted the underlying aluminum. This could easily have been prevented watching exhaust temp or possibly O2.

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Sat Nov 04, 2017 10:26 am
by John Wallace
He managed to coat a set of pistons so well, the underlying aluminum melted from retained combustion heat. So the unsupported coating eventually cracked.
If it let heat get to the piston, it wasn't really a heat barrier?

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Sat Nov 04, 2017 11:43 am
by In-Tech
In the mid 90's I was spraying and baking my own piston tops and never did an a-b-a test but also never noticed any gains. What dawned on me one day is how do I know I have the EXACT same thickness barrier on the top of the piston and if it isn't exact isn't the thinner part of the barrier going to have to take the most abuse just like the thinnest part of the piston and/or the exhaust side? So I quit doing it :?

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Sat Nov 04, 2017 6:21 pm
by MadBill
CharlieB53 wrote:
Sat Nov 04, 2017 9:20 am
.. I seriously doubt that any insulation could function as a one-way heat valve, allowing the piston to accumulate temps and melt without other contributing factors causing elevated combustion temps...
A heat diode! The ramifications are huge... :-k

Re: Chamber & Piston Thermal Barrier: CR Improvement Equivalent?

Posted: Sat Nov 04, 2017 8:32 pm
by modok
I have not seen any real evidence coating pistons reduces or promotes knock.
I have seen evidence a rough surface on the piston may reduce tendency to knock.

There have read a few back to back tests but they test plain piston VS blasted and coated.
They need to test blasted VS blasted and coated.