so why did the engine loose power and then recover?

Been mulling this over . I notice there is carbon in behind the corner seal . This implies there is also combustion gas behind the seal as well . So we have gas at extremely high pressures (much higher than an NA engine) pushing the corner seal (like a piston) into the side iron . Then it passes over this overheated , underlubricated and small surface area land at the exhaust port .
It's a pretty bad recipe .....

Totally stumped on that one . I originally (before tearing the engine apart ) thought it was the apex seals wobbling around in the groove and getting stuck .

I think this is why so much attention needs to be taken when cutting the seals. Did you use precut seals on this engine when it was rebuilt last time or were they cut by the builder?

No - this one has the deeper RX7 ALS brand seals . Knowing what I know now - I think i should have saved my $ and stuck with the esmerils

Don't actually remember if he cut them or not - I suspect not .
I don't see a connection to this issue though?

Well it seems to me if they were not cut to tight tolerances then carbon could build up where you don't want it and then cause the side seals to stick and cause damage and wear out prematurely. :dunno:

I actually meant to say 'corner seal' above (now corrected) but yeah I see what you are getting at now .

The factory pre-cut side seals have very loose tolerances, the side seals shrink slightly as well which contributes to compression loss.

"I think you may have more turbo back pressure than you think? Maybe? Pressure/expansion under the seals could cause the seal to catch on the exhaust port."

Ahem..........cough, cough, cough")

Don't dismiss the hot spots around the plugs. That has to be addressed if you want longevity. There are specific things that you can do to increase the cooling to those areas.
Omp has to be used to get the max out of the side seals--pre mix doesnt fix the lack of omp injection---i feel like I am preaching to the choir here....bret knows these things already--sorry man.

I hear ya OD .But the pressure I was alluding to is the combustion pressure not the back pressure from the turbo.

Do you have details of what can be done around the spark plug holes and the exhaust port to improve cooling?

I havn't done it myself. But I will get what details I can to you. My engine rebuild has had it done.
I will Pm you Brett.

You can grind out little slots in the coolant jacked around the plug holes. The theory is that this causes turbulence around the plug area so the water cools a touch longer.

I'll take pics of it for you tomorrow if I remember. Pineapple does this, mazmart does a variation as well. Shoot even the factory casts have some cut out that dip on an angle to slow water flow... Basically we just improve on what the factory was going for.

I have pics of the exhaust ports as well if you want to see them ill try and upload them.

if i can make a recommendation, its to tap a fitting into the exhaust manifold and look at preturbo backpressure.

you don't need anything fancy to do monitor it, a boost gauge works fine.

i did it on the last car i really went after methodically, and its very informative.

The only problem with all of this is if he wasn't to reduce manifold pressure he will need to get a larger turbine which will increase spool times.

The 20G greddy turbine wheel is almost perfect, as far as size spool times goes.

The only other opportunity to gain more flow would be to convert the downpipe to a true 3" setup. I am still working on that but wont have anything done till the end of the year.

well the point is to find out what the preturbo backpressure actually is before you guess about having to change stuff

Yea I get the point, I'm just saying if there is an issue he wont wanna fix it.

I already know there is a LOT of backpressure due to the lengths i had to go to to get decent boost at high rpm . I'm not 100% convinced that this issue is caused by the backpressure or whether it is just a factor that exacerbates it . The main factor could be high pressure in behind the corner seal - IE from boost. We need a high mileage teardown from a SCd car to verify that they don't have it as well.

Gunna just throw this out there

The blurb from pettit suggests that they see this a LOT . They also say the cause is from turbos set to run at much higher boost than the stock 'assume Greddy' system was designed to run therefore backpressure blah blah blah.
I will put it like this - very few Greddy kits ever ran anywhere near the boost level (particularly at high rpm) that I ran on my car or got the miles i did for that matter . I wonder how many of the engines they see saw track time ? Maybe that was a big factor in the failure rates ?

I was holding 10psi from 4k to 8500 at fuel cut. That seemed decent enough for me, but then my engine went boom LOL.

Sounds like you had a very quick car on your hands :) Are there any signs of the kind of wear I have on your ex. ports ?

I still am not sure what wear you were talking about, on my end everything looked the same as my previous NA tear down. Identical wear minus the chunks of apex, I'll get some pictures for you to compare.

This -notice the big gouge at the outer edge of the exhaust port . Is there any sign on yours of scuffing or abnormal pressure from the corner seal ?

https://www.rx8club.com/attachments/...s-p1010172-jpg

Yea mine didn't have anything close to that...

But then again most of its career was NA.

Pettit has seen a LOT of turbo renesis engines. Not high mileage ones, but the ones from the Diaso track cars. Pettit is the supplier of engines to this model. He identified this issue back in 2008? Maybe?
I know my engines were not high mileage under boost engines (25000miles max)--but none of mine had any markings like that. My engines were ran pretty hard due to multiple track sessions--even in 105F ambient weather. SWEAT:)
Cam even recommends to not wrap or ceramic coat your header ( oem or aftermarket). He told me that the rear rotary exhaust port has more trouble cooling and a coating or wrap would make the exhaust ports run hotter.
Pettit does cooling mods for the lead/trail sparkplug area through an access they drill between the two sparkplugs. I now have a sealant plug between those two areas. like a water jacket plug.

Did you actually inspect the irons yourself ?