to interject something--I hear you Harlan and in theory it is logical. With that , dont forget to keep the oil temps down. I dont know what happened to the suggestions Racing Beat and Rick E and a lot of other builders have advised concerning that the oil temps--RETURNING to the engine should never be over 205F. There are not many people paying enough attention to that. The oil temps go a long way in cooling the rotors.

 

if you ask Jim Mederer about oil temps in person, he says something about delta T....

people have done coated rotors before, the oil runs cooler, because the coating acts like an insulator.

the question is where does the heat go if it cannot go thru the rotors and into the oil?

 

Heat stays in the charge, can add power and can add knock. However, ceramic coating doesn't pick up carbon like bare metal so hot spots can be prevented. We'll see what happens.

 

The heat initially stays in the burning a/f mixture. This causes the pressure to be higher than before, meaning it can do more work on the piston/rotor. That's the main point after all. However since the stroke length (expansion) isn't increased, some of the extra heat ends up raising the EGTs. It also means relatively more heat going into the irons vs rotors, offloading what would be oil heat into the water cooling system.

That's my picture of what's going on anyway.

 

This...
The heat has to go somewhere. Some will go to the exhaust,but most will go into the water. If the water cooling isn't increased, then I could see your "hot spots" forming on the housing instead of the rotors, but it would have to be most, if not all of the oil heat being deflected for that to be a serious concern. Overall, I don't see it being a measurable difference. I just hope it doesn't flake off, and damage your motor.

 

Great experiment however, I am also concerned about the possibility of flaking. Rebuild is a time consuming and expensive exersice so why skimp on getting a proper coating.

If the coating fails then you would not have achieved any measurable result. Good luck

 

Rebuilding isn't that expensive although it is time consuming. Will probably want to try something else in a couple years and go through another rebuild. Direct injection looks fun....

 

may be also a time to consider evans coolant? but, one step at the time--right? You can increase the cooling around the exhaust port a little by some minor water jacket modifications.
IF I was going to run ceramic coated rotors i would also do some oil passage work to try and help the oil to shed a little more heat. A lighter weight oil will help. Redline 5w/30 has the hths of a good 40 wgt etc but the viscosity of a 30 wgt. It can make a 10f temp difference. Every little bit helps.

 

Currently running water free coolant. May experiment with the coolant jacket, I've seen some really nifty groves machined in to increase coolant area and may do that myself. Not worried about oil passages, most of the heat that needs to be shed is in the rotor and that oil goes straight into the pan. Could flow more oil but that would drop pressure, I'm not gonna mess with that balance. I'm currently running 0w20 with ZDDP added, but I tend to go against conventional wisdom. Also have a new water injection setup, we'll see if that works better at controlling engine heat.

 

ZDDP can be great stuff, but poisons cats. Check out the references in this article for more info: https://www.rx8club.com/general-auto...l-zddp-222999/

 

dont forget that the clearances within the engine is what really determines the oil viscosity requirements. Its my understanding that a 40 viscosity is the minimum? Watch for bearing wear etc--as you know.
I have been running a water methanol system for some years now and I can testify that it does help with carbon buildup--but I have not noticed any effect on any of the engines temperatures.
Granted I have not tested the EGT though. But on coolant and oil--nothing.
So you are already running a waterless coolant--you probably formulated it yourself?
When you have the engine apart--look at the exhaust port area. The restrictions are very obvious. Now cooling the sleeve MAY have some benefit on the area that the side seal touches--but I am not sure of the degree. If you look at what is cooling the iron at that depth ( where the side seal contacts) it is both oil and coolant. I THINK a better cooling of that side seal will be derived from keeping both the oil and coolant under control. So many people are allowing the oil temps to stay too high. Oil temps should never be above 200F on return to the engine. Without modifications the oem oil cooling system cannot do that--even during DD.
So --keeping the heat in the combustion chamber will increase efficiency -hope the coatings will show evidence of that and with effort the side seal will not be compromised any more than it already is?

 

The additive I'm running (STP oil treatment) should boost the weight up to around 30. The ZDDP would eventually poison my cat if I was running one, but it would also prevent bearing wear. The complaints of increased bearing wear that we attribute to the lighter weight oil in our engines corresponds to a similar increase in older engines which don't run lightweight oil. I may be wrong, but I believe the ZDDP is much more important than the weight. If I was running a cat I'd rather destroy it that the bearings anyway. Also lighter weight oil flows better and should cool better because of it.

I'm running straight EG coolant. Evans is an EG/PG mix that is slightly thinner. I was originaly going to mix my own, but straight EG works fine even in Texas heat. And has saved my butt from overheating twice now.

When I was running water injection it dropped water temps like a rock. I'm sure it did the same for oil temps, but I have no indication. EGTs could go either way depending on how much water.

Still learning as I go.

 

no doubt ZDDP is of benefit to bearing wear--look at all the evidence on the earlier recip models flat tappets/cams.
some use in rotary engines has been documented. another reason i like redline oil.
I thought you may have used a more measurable supply like Redline or ZDDP--but nothing wrong with good old STP.
The people I spoke with advise to only use 1 step lighter wgt viscosity. IE: if you need a 40 wgt--use a 30 wgt + the STP. But, I am not sure they base this on evidence.
i will probably use evans in the near future too

 

i was thinking about the side seal/side seal spring problem last night, and i think the big part of the problem isn't that the rotor is too hot, but that the side seal is in the exhaust directly.

in that light i think anything you can do to lower side seal temps would be good. i would also suggest that 2-3 small things would add up and have a better net result than one big one.

my one idea is actually to coat the side seal with a low friction coating, like they use on bearings, if it doesn't burn right off, lower friction between the side seal and the side housing is good, but i think the real benefit is lower friction between the side seal and spring.

Re: the ZDDP, i've seen a couple of SAE papers, and ZDDP won't hurt anything, but it doesn't seem to help much either

 

If you can find a low friction coating that will last on side seals let me know. The side seals must wear to break in, so any hope for a low friction coating must be impregnated in the metal. I believe mazda seals are made with moly for this reason.

People were screaming about the loss of ZDDP back in the eighties. At the time the first reduction took place. There were many studies that showed the sweet spot for wear reduction was still within the government limit. Then back in 2004 they reduced the allowed concentration again and a lot of people started seeing abnormal wear. There is a sweet spot for ZDDP, above it you get no real added benefit, below it you get accelerated wear. I'm too lazy to find links at the moment, but that's what I found when researching zddp.

Also I don't think the exhaust ports are the only major problem. Yes the side seals go right across them, but it's a quick contact hopefully separated by oil. I think it has more to do with moving the seals closer to the rotor face. The springs are now exposed to higher temperatures from all sides. Add that to the minimalistic oil injection mazda was using for a time and you have side seal/spring failure. The more I think about it the more I believe mazda fixed the S2s.

 

i have said the same thing--side seals closer to the rotory face has increased their heat exposure.
Also look at the paths of the oil flow within the irons............. there is a small area in which the oil nor coolant cools very well. This could possibly be an area in which waterless coolant may be of some help?

 

i think moving the side seal closer to the face of the rotor was a much smaller change than putting the side seal directly in the exhaust flow.

the peripheral exhaust engines have no trouble with side seals.

 

Well regardless, I'm not going to put the rotors in until my rebuild, and that's now on the back burner as I have summit fever with my turbo build. (and time and money to burn.) I'll keep yall posted.

 

 

Thanks team. At least I finally admitted to myself that engine failure is always an option with a turbo build.