Ceramic Coating and Upper Bore Temps.

[Reddog928]

I'm a big fan of TBC's, but lying awake in the wee small hours and contemplating the 4th dimension (as one does), I had these thoughts re ceramic coatings:

- once the piston crown, combustion chamber roof, and valve faces are all TB coated, so absorbing less combustion heat, the combustion gas temps will be higher than when these parts were uncoated.

- since the only remaining uncoated metal involved in combustion is around the top of the bore, it will be exposed to higher gas temps / heat loads not envisaged by engine designers in the pre-ceramic age.

Thinking out loud: consequences:

- faster upper cylinder oil film burn off ie less bore lubrication for the top ring on the next up stroke.

- greater differential expansion between the top and bottom of the bore:
-- piston running cooler + greater bore clearance = more piston rock and blow-by at the top of stroke ?
-- head gasket under greater shear c/- bore expanding more than cooler heads ?

Air/oil-cooled engines are probably the worse off in this regard:

- BMW's latest R1200GS 'liquid cooled' engine has a cooling jacket surrounding only the upper third of the bore. Verrrry Interrrestingggg.

- I'm rebuilding a 1971 Honda CB750 engine, trying to incorporate all benefits of the latest material science developments.

-- as I think "out loud" while writing this, I've concluded that "coating everything" in an air cooled engine may not be such a good approach. So:

-- -- piston crown: Yes.
-- -- combustion chamber roof: No
-- -- valve faces, stems etc: Yes.
-- -- intake port: No. (higher temp = better fuel evaporation).
-- -- exh. port: Yes. Lowers front to back cylinder head temperature difference + maintains exhaust gas temp into TBC headers.

I think this distribution of ceramic coatings produces an equalisation of top end temperatures ie lowering of the destructive temp peaks without causing undue thermal stress in adjoining cooler parts of the engine.


But back to my original thoughts re thermal overload of the upper bore walls c/- ceramic coating of 'everything':

While it seems possible theoretically, has it proved to be an issue in the everyday experience of Speedtalk members?

Cheers and thanks.

[groberts101]

Lots to talk about here but I have no definite answers based on scientific numbers and calculations to go off other than first hand experience using TBC's for just over 25 years. Easier to just reply in the message body(in red) to avoid confusion and help stay on point so here goes.

I'm a big fan of TBC's, but lying awake in the wee small hours and contemplating the 4th dimension (as one does), I had these thoughts re ceramic coatings:

- once the piston crown, combustion chamber roof, and valve faces are all TB coated, so absorbing less combustion heat, the combustion gas temps will be higher than when these parts were uncoated. Yes it will.. but I believe it's only at the peak temp spike and not overall temp's because the incoming charge is now cooler on all subsequent power strokes simply because there is less heat being exchanged from the now cooler running combustion space. So.. net losses on running temps BETWEEN POWER STROKES are available and can allow greater degree of tuning specificity for more idealized tunes. Now we don't have to run more fuel just for the sake of reducing EGt's to coincide with what's typically deemed as "safe". Also allows driving further into lean burn territory. This improves MBT while simultaneously improving BSFC and is what we really paid for in the first place, even if we didn't fully expect or realize that the second part would ever become available to us. Bonus.

- since the only remaining uncoated metal involved in combustion is around the top of the bore, it will be exposed to higher gas temps / heat loads not envisaged by engine designers in the pre-ceramic age. See above response. The very short period of time the walls are exposed to those peak temps is relatively low in the scheme of things and peak push period on the rod would not be right at the very top of the bore given the timing in crank degrees that it would normally occur anyways. Plus, keep in mind that the top ring will now be cooler and pass less heat into the bore and cooling system as a result of implementing full combustion space coating.

Thinking out loud: consequences:

- faster upper cylinder oil film burn off ie less bore lubrication for the top ring on the next up stroke. Possibly.. but me thinks the now lower temps of the piston/ring assembly and at least slightly lower overall reduced average bore temps will aid in oil temp reductions to further aid in barrier film thickness. I guess I can't say for sure oil temps go down because I've never monitored them in relation to coating usage alone, but I do know for fact that the cooling system temps are reduced on the gauge. Which then leads me to believe that oil will also follow that same trend based on that fact alone. I also typically run a slightly thinner viscosity oil on fully coated engines simply because I feel that the oils work loads and temp spikes have been reduced somewhat and work to capitalize on any bit of extra power through reductions in parasitic losses. I've yet to capitalize on the oil pumps contribution in parasitic loss though and there just might be some left in that area for additional anti-friction coatings too. I've seen plenty of hardcore types use teflon coated gears here and I try to use them in transmission pumps whenever I have the option. All the little stuff adds up and allows us to change other aspects for the better.

- greater differential expansion between the top and bottom of the bore: Not so sure about this one but would probably fall back on my previous thinking above.
-- piston running cooler + greater bore clearance = more piston rock and blow-by at the top of stroke ? I think this is a situation where we have the option of further capitalizing on gains and losses being seen elsewhere as a result of the coatings affect on various types of metallurgy. So, let's imagine, and this is exactly the way I build mine, that the coatings have an impact on piston expansion rates and the peak level of expansion being reached during sustained periods of peak power. The piston remains slightly smaller and ring gaps don't close up quite so much at typical running temps. Based on this assumption, and I haven't gotten in trouble for it yet, I will run my bores about half a thou smaller than rec'd for the piston being used and also shrink end gaps about 1/2 - 3/4 thou less per inch of bore size. Then in conjunction with those practices, I will also warm the engine for a slightly longer period of time before digging too deeply into the throttle and risking excessive piston rock(primarily when using forged materials). I run very cool 160° t-stats anyways so I'm used to this same drill and only extend it another 5 minutes or so for good measure and more piece of mind.
-- head gasket under greater shear c/- bore expanding more than cooler heads ? This happens as MBT increases anyways. So, par for the course and good bolts/studs along with premium head gaskets(preferably shim style for my particular taste) are just cheap insurance.

Air/oil-cooled engines are probably the worse off in this regard: Maybe so. But I'm still referring back to the ideologies listed above in that more is being used to push the crank around and less energy is being transferred into surrounding components. Exhaust side will be hotter of course but that too comes along with more power. Even though it's frowned upon my many, I prefer to run the pipe as hot as I can get it with coatings AND wraps. Sure the coatings will tend to fail and flake away if you ever need to pull the wrap off and you could even lose a few welds(which I try very hard to avoid on custom pieces) right up near the head port, but the temps are reduced for surrounding items and under-hood temps are also further improved upon as a result. Again, one change allows another for more cumulative gain.

- BMW's latest R1200GS 'liquid cooled' engine has a cooling jacket surrounding only the upper third of the bore. Verrrry Interrrestingggg. Dunno about that design but maybe they are "fixing" other inherent issues created by some additional wear or fragility created by or relating to reduced ring thickness and very short pin'heights/crowns? You have to remember that most OEM's will not jump on this TBC bandwagon because of the inherent issues that go along with coating failures. They will spend millions in revamping parts and engine designs, not to mention ECU calibration to improve safety margins, to avoid the necessity for their use. AFAIK, it's only more recently that they've finally adopted the usage of friction reducing skirt coatings.

- I'm rebuilding a 1971 Honda CB750 engine, trying to incorporate all benefits of the latest material science developments.

-- as I think "out loud" while writing this, I've concluded that "coating everything" in an air cooled engine may not be such a good approach. So:

-- -- piston crown: Yes. Very large surface area for maximum impact. Most definitely
-- -- combustion chamber roof: No Very large surface area for maximum impact. Most definitely
-- -- valve faces, stems etc: Yes. Smaller surface area but very high levels of heat retention between power strokes for higher than expected impact. Most definitely
-- -- intake port: No. (higher temp = better fuel evaporation). Could go either way here but certainly depends on power band expectations, port geometry and CSA, and carb tuning flexibility. Basically.. if you can run the mixture cooler is is best to do so for some of the same reasons listed above for overall power and efficiency.. BUT.. droplet size needs to be factored in and "tuned" for the what the motor likes overall. Coatings and cooler running engines with less heat transfer into the incoming mixtures can have the affect of increasing droplet size. So, sometimes we can allow that trend or even make them smaller for improving on other design/geometric deficiencies?.. and sometimes we allow some bigger droplets drizzling out of the boosters to promote more idealized scenarios further downstream in the induction tract.. or even affect "peak burn power" timing in crank degrees. No simple answer and the best way I've ever seen to do it is to copy what the other front runners are doing and run it on the dyno to measure what does what.
-- -- exh. port: Yes. Lowers front to back cylinder head temperature difference + maintains exhaust gas temp into TBC headers. Right on, brother!

I think this distribution of ceramic coatings produces an equalisation of top end temperatures ie lowering of the destructive temp peaks without causing undue thermal stress in adjoining cooler parts of the engine. I believe only part of this sentence is correct. As power increases.. peak temps will surely go up.. BUT.. this peak temp is obviously being exhibited well within the burn stage of the mixture where detonation would never have sufficient time to cause sudden pressure rise to counteract max power production potential. So, average temps between power strokes has now been reduced by the TBC's to allow a more precisely timed window for the higher pressure peaks and temp spikes to be capitalized upon. Hopefully I said that in a coherent enough way to get it across clearly and concisely enough.


But back to my original thoughts re thermal overload of the upper bore walls c/- ceramic coating of 'everything':

While it seems possible theoretically, has it proved to be an issue in the everyday experience of Speedtalk members? This might just be me here.. but I would think that there would be some signs of additional skirt, ring, land, and bore wear if things were getting out of control heat-wise. Not to mention the extra blow-by caused as a result of any combination of those issues. Which would be counter-intuitive to why we were using the coatings in the first place.

And I wouldn't be looking for ridges at the top of the bore to find increased bore wear either. I'd be looking for worn rings, lands, and barreled bores that would likely be the result of something you describe here. If anything, I have seen just the exact opposite on everything I've ever used extensive amounts of coatings on and the ring seal and wear characteristics is actually improved upon over the long run. In theory, you should be able to push the rings up higher and also make them thinner without all the typically accepted downsides.

Cheers and thanks.

I love TBC's and any other form of performance enhancing coatings that I can possibly afford to use it on. Lawnmowers, dirt bikes, snowmobiles, you name it and I've tried it, sometimes just because I had it on my shelf and said "what the hell, why not?" if the time and extra bit of cash was available while it was all pulled apart. Interesting subject and I hope that my time spent here helped you in any way.

[PackardV8]

- BMW's latest R1200GS 'liquid cooled' engine has a cooling jacket surrounding only the upper third of the bore. Verrrry Interrrestingggg.

Not exactly a technological breakthrough. See the Ford Model T/A/B/C for examples from the dawn of the IC era up into the late '30s.

[Leftcoaster]

I love TBC's and any other form of performance enhancing coatings that I can possibly afford to use it on. Lawnmowers, dirt bikes, snowmobiles, you name it and I've tried it, sometimes just because I had it on my shelf and said "what the hell, why not?" if the time and extra bit of cash was available while it was all pulled apart. Interesting subject and I hope that my time spent here helped you in any way.

Care to name the self applied coatings you had "on the shelf", what you used them on, and how effective you found them?

Thanks

[groberts101]

I love TBC's and any other form of performance enhancing coatings that I can possibly afford to use it on. Lawnmowers, dirt bikes, snowmobiles, you name it and I've tried it, sometimes just because I had it on my shelf and said "what the hell, why not?" if the time and extra bit of cash was available while it was all pulled apart. Interesting subject and I hope that my time spent here helped you in any way.

Care to name the self applied coatings you had "on the shelf", what you used them on, and how effective you found them?

Thanks

Been using Tech line coatings since they started advertising in one of the old mail order mag's years ago. Stuff has an excellent shelf life but needs to be shaken and stirred around every several months.

[Kevin Johnson]

groberts101 wrote: Lots to talk about here but I have no definite answers based on scientific numbers and calculations to go off other than first hand experience using TBC's for just over 25 years. Easier to just reply in the message body (in red) to avoid confusion and help stay on point so here goes.

I'm a big fan of TBC's, but lying awake in the wee small hours and contemplating the 4th dimension (as one does), I had these thoughts re ceramic coatings:

- once the piston crown, combustion chamber roof, and valve faces are all TB coated, so absorbing less combustion heat, the combustion gas temps will be higher than when these parts were uncoated. Yes it will.. but I believe it's only at the peak temp spike and not overall temp's because the incoming charge is now cooler on all subsequent power strokes simply because there is less heat being exchanged from the now cooler running combustion space. So.. net losses on running temps BETWEEN POWER STROKES are available and can allow greater degree of tuning specificity for more idealized tunes. Now we don't have to run more fuel just for the sake of reducing EGt's to coincide with what's typically deemed as "safe". Also allows driving further into lean burn territory. This improves MBT while simultaneously improving BSFC and is what we really paid for in the first place, even if we didn't fully expect or realize that the second part would ever become available to us. Bonus.

- since the only remaining uncoated metal involved in combustion is around the top of the bore, it will be exposed to higher gas temps / heat loads not envisaged by engine designers in the pre-ceramic age. [color=See above response. The very short period of time the walls are exposed to those peak temps is relatively low in the scheme of things and peak push period on the rod would not be right at the very top of the bore given the timing in crank degrees that it would normally occur anyways. Plus, keep in mind that the top ring will now be cooler and pass less heat into the bore and cooling system as a result of implementing full combustion space coating.

Thinking out loud: consequences:

- faster upper cylinder oil film burn off ie less bore lubrication for the top ring on the next up stroke. Possibly.. but me thinks the now lower temps of the piston/ring assembly and at least slightly lower overall reduced average bore temps will aid in oil temp reductions to further aid in barrier film thickness. I guess I can't say for sure oil temps go down because I've never monitored them in relation to coating usage alone, but I do know for fact that the cooling system temps are reduced on the gauge. Which then leads me to believe that oil will also follow that same trend based on that fact alone. I also typically run a slightly thinner viscosity oil on fully coated engines simply because I feel that the oils work loads and temp spikes have been reduced somewhat and work to capitalize on any bit of extra power through reductions in parasitic losses. I've yet to capitalize on the oil pumps contribution in parasitic loss though and there just might be some left in that area for additional anti-friction coatings too. I've seen plenty of hardcore types use teflon coated gears here and I try to use them in transmission pumps whenever I have the option. All the little stuff adds up and allows us to change other aspects for the better.

- greater differential expansion between the top and bottom of the bore: Not so sure about this one but would probably fall back on my previous thinking above.
-- piston running cooler + greater bore clearance = more piston rock and blow-by at the top of stroke ? I think this is a situation where we have the option of further capitalizing on gains and losses being seen elsewhere as a result of the coatings affect on various types of metallurgy. So, let's imagine, and this is exactly the way I build mine, that the coatings have an impact on piston expansion rates and the peak level of expansion being reached during sustained periods of peak power. The piston remains slightly smaller and ring gaps don't close up quite so much at typical running temps. Based on this assumption, and I haven't gotten in trouble for it yet, I will run my bores about half a thou smaller than rec'd for the piston being used and also shrink end gaps about 1/2 - 3/4 thou less per inch of bore size. Then in conjunction with those practices, I will also warm the engine for a slightly longer period of time before digging too deeply into the throttle and risking excessive piston rock(primarily when using forged materials). I run very cool 160° t-stats anyways so I'm used to this same drill and only extend it another 5 minutes or so for good measure and more piece of mind.
-- head gasket under greater shear c/- bore expanding more than cooler heads ? This happens as MBT increases anyways. So, par for the course and good bolts/studs along with premium head gaskets(preferably shim style for my particular taste) are just cheap insurance.

Air/oil-cooled engines are probably the worse off in this regard: Maybe so. But I'm still referring back to the ideologies listed above in that more is being used to push the crank around and less energy is being transferred into surrounding components. Exhaust side will be hotter of course but that too comes along with more power. Even though it's frowned upon my many, I prefer to run the pipe as hot as I can get it with coatings AND wraps. Sure the coatings will tend to fail and flake away if you ever need to pull the wrap off and you could even lose a few welds(which I try very hard to avoid on custom pieces) right up near the head port, but the temps are reduced for surrounding items and under-hood temps are also further improved upon as a result. Again, one change allows another for more cumulative gain.

- BMW's latest R1200GS 'liquid cooled' engine has a cooling jacket surrounding only the upper third of the bore. Verrrry Interrrestingggg. Dunno about that design but maybe they are "fixing" other inherent issues created by some additional wear or fragility created by or relating to reduced ring thickness and very short pin'heights/crowns? You have to remember that most OEM's will not jump on this TBC bandwagon because of the inherent issues that go along with coating failures. They will spend millions in revamping parts and engine designs, not to mention ECU calibration to improve safety margins, to avoid the necessity for their use. AFAIK, it's only more recently that they've finally adopted the usage of friction reducing skirt coatings.

- I'm rebuilding a 1971 Honda CB750 engine, trying to incorporate all benefits of the latest material science developments.

-- as I think "out loud" while writing this, I've concluded that "coating everything" in an air cooled engine may not be such a good approach. So:

-- -- piston crown: Yes. Very large surface area for maximum impact. Most definitely
-- -- combustion chamber roof: No Very large surface area for maximum impact. Most definitely
-- -- valve faces, stems etc: Yes. Smaller surface area but very high levels of heat retention between power strokes for higher than expected impact. Most definitely
-- -- intake port: No. (higher temp = better fuel evaporation). Could go either way here but certainly depends on power band expectations, port geometry and CSA, and carb tuning flexibility. Basically.. if you can run the mixture cooler is is best to do so for some of the same reasons listed above for overall power and efficiency.. BUT.. droplet size needs to be factored in and "tuned" for the what the motor likes overall. Coatings and cooler running engines with less heat transfer into the incoming mixtures can have the affect of increasing droplet size. So, sometimes we can allow that trend or even make them smaller for improving on other design/geometric deficiencies?.. and sometimes we allow some bigger droplets drizzling out of the boosters to promote more idealized scenarios further downstream in the induction tract.. or even affect "peak burn power" timing in crank degrees. No simple answer and the best way I've ever seen to do it is to copy what the other front runners are doing and run it on the dyno to measure what does what.
-- -- exh. port: Yes. Lowers front to back cylinder head temperature difference + maintains exhaust gas temp into TBC headers. Right on, brother!

I think this distribution of ceramic coatings produces an equalisation of top end temperatures ie lowering of the destructive temp peaks without causing undue thermal stress in adjoining cooler parts of the engine. I believe only part of this sentence is correct. As power increases.. peak temps will surely go up.. BUT.. this peak temp is obviously being exhibited well within the burn stage of the mixture where detonation would never have sufficient time to cause sudden pressure rise to counteract max power production potential. So, average temps between power strokes has now been reduced by the TBC's to allow a more precisely timed window for the higher pressure peaks and temp spikes to be capitalized upon. Hopefully I said that in a coherent enough way to get it across clearly and concisely enough.


But back to my original thoughts re thermal overload of the upper bore walls c/- ceramic coating of 'everything':

While it seems possible theoretically, has it proved to be an issue in the everyday experience of Speedtalk members? This might just be me here.. but I would think that there would be some signs of additional skirt, ring, land, and bore wear if things were getting out of control heat-wise. Not to mention the extra blow-by caused as a result of any combination of those issues. Which would be counter-intuitive to why we were using the coatings in the first place.

And I wouldn't be looking for ridges at the top of the bore to find increased bore wear either. I'd be looking for worn rings, lands, and barreled bores that would likely be the result of something you describe here. If anything, I have seen just the exact opposite on everything I've ever used extensive amounts of coatings on and the ring seal and wear characteristics is actually improved upon over the long run. In theory, you should be able to push the rings up higher and also make them thinner without all the typically accepted downsides.

Cheers and thanks.

groberts101 wrote: I love TBC's and any other form of performance enhancing coatings that I can possibly afford to use it on. Lawnmowers, dirt bikes, snowmobiles, you name it and I've tried it, sometimes just because I had it on my shelf and said "what the hell, why not?" if the time and extra bit of cash was available while it was all pulled apart. Interesting subject and I hope that my time spent here helped you in any way.

[Editor's note: the color codes previously used did not show up on my computer screen. Just looked at it using Chrome on another monitor -- original codes just visibly different there.]

[twl]

I run Thermal Barrier Coatings all the time on our air cooled 500cc single cylinder performance applications. We use Ceramic/Metallic(CerMet) coating in the chamber, piston crown, and valve faces. We use plain Ceramic inside the exhaust port.
We have an aluminum head, iron cylinder liner in an aluminum finned cylinder.
This has worked out very well for us, and we have almost 50 builds now which employ this strategy on street and track builds.

Essentially, my take is this:
We coat all the aluminum surfaces in the combustion area to limit the ingress of heat into the castings/forging, and keep the "flash" heat in during combustion for efficiency. We use the ceramic in the exhaust port to keep the exhaust temps up, and limit ingress of heat into the head casting in that area.
We don't do anything to the iron bore liner because it has a much lower thermal conductivity material, and this is keeping heat in already, as it is. And it can take heat because it's iron. So, we are just trying to keep the combustion heat from being too rapidly lost into the aluminum parts.

The heat on the iron bore liner is very hot for only an instant, and drops off as the piston descends. This happens in all engines, and I don't see this being any serious problem to handle a little extra flash heat during this time. It has not proven to be of any consequence that we have been able to determine, and no failures of barrels or rings or pistons have been showing up. In fact, they last longer than they did without the coatings.

We have seen no down sides to doing it, except maybe for the added cost of the coatings in the job. And we have not had any complaints about the costs from our customers. We also use Tech Line coatings primarily. On occasions, we have also used Swain Tech for some specialty products that they have for piston skirts.

[Reddog928]

Hi Guys.

Many many thanks for the time, effort and information that you've posted.

It's all too easy to start going around on a single train of thought inside One's head, hence the need for a mental 'circuit breaker', which you have kindly provided.

Back to full steam ahead.

Will keep you posted re developments.

Cheers.

[Roy]

Something I read once upon a time in the land of (mis?)information.."The perfect engine would be insulated, without any means to cool itself, indeed it would run as hot as it wanted. The only reason to cool it is because of the limitations of the materials used to build it." It was in some scientific paper about internal combustion engine efficiencies. As such I am of the opinion that all of the issues you are discussing would need to be remedied in some other way than to go without the use of a thermal coating if all out performance or even fuel efficiency is the end goal. Any heat that goes out of ANYTHING aside from the exhaust pipe is lost energy! In an ideal world even the exhaust temps coming out of the chamber would be room temperature. You probably know all of this already but sometimes the foundations are forgotten in the pursuit of other goals.

[GerryP]

Kind of like the vapor cycle engine, Roy. A theory that fascinates me to this day.