Does anybody here have any 13B-MSP rebuilding experience?
Basically I want to know what is wearing out and failing on these engines. Like, could I get away with new seals on a low compression engine and it's good to go, or does the low compression come from housing and rotor failure like on the 12As?
I don’t have a clue but based on what I’ve seen/heard is the cat is the problem and just kills everything internally which kills the plugs which kills the coils which just kills everything else. That’s on top of being heavily covered in decorative plastic covers with no engine bay airflow....
In reply to Ranger50 :
That isn't very specific.
For example, on the FC RX-7 engines, the main point of failure is the rotor housings warp and cause compression loss, and separately the coolant seal lands fail. On the RX-7 12As, the chrome flakes off of the rotor housings and, separately, the slots in the rotor tips hammer wider which causes apex seal gas pressure to be lost, which also hammers the hell out of the chrome in the rotor housings at about the 2 o'clock mark.
If you get an engine with intact coolant seal lands, the FC can be rebuilt with a little smoothing of the rotor housings and new seals. The 12A engines usually yield usable bearings and eccentric shaft, with the rest unusuable garbage.
Caveat: I know nothing about rx8s specifically. But it sounds like the car's got a couple small catalytic converters right next to the motor and one downstream cat. That’s similar to the mr2 spyder and it’s a horrible setup. What happens is the small cat (one or both) breaks up, which clogs the downstream cat, then it builds backpressure in the exhaust which leads to ceramic bits being blown back into the motor. The ceramic wipes out everything in the motor that has tight tolerances. Cylinder walls, piston rings, etc. Rotaries run really hot right? I bet that would lead to even more likelihood of cat failure.
so what you are saying is that in a state with no emissions testing you could make an rx8 last quite a bit longer with very minimal work?
Subscribed for reasons.
I've now seen 2.5 different explanations.
1- the siamesed exhaust port gets too hot and causes the seals to fail (probably due to some sort of expansion/warping) because, well, its double the rotary exhaust trying to make an exit.
1.5- the siamesed exhaust port gets too hot because the catalytic converter fails as mentioned above (very good possibility)
2- in order to meet emissions standards, the oil injection rate was dropped, which causes the seals to fail (this would also be accelerated by extreme temps at the exhaust port). Premix would prevent this kind of failure, presumably.
As for preventing the siamese port of death, my thought was that if you rebuilt a renesis using a 13b housings (and, if possible, a 13b center iron, I haven't been able to get a straight answer about fitment) and renesis front and rear irons (and center if necessary), you could not only make more power because the exhaust is freer, but also make sure you don't have a failure due to a hot spot. This would require a custom header, but honestly *shouldn't* be too hard to achieve.
Renesis swapping my car is something I've seriously considered, double the HP without losing driveability and remaining N/A? Yes, please.
In reply to TheRX7Project :
I don't buy into the close coupled cat argument because RX-7s have had close coupled cats since 1981 and those old 12As would do 300k miles. The nonturbo FCs would do 200k+ too as long as you didn't overheat them and break a coolant land.
I can see the side seals taking a beating from the exhaust heat, and the reduced oiling as well as no oil getting to the center of the apex seal is also a known problem that is easily remedied.
You should be able to use a GSL-SE intermediate housing and GSL-SE rotor housings with RX-8 end housings, but at that point you're into some strange territory.... From my research, even the stock peripheral exhausts are almost too large but the geometry requires it, the MSP gets you the necessary port area without all the timing, so this is kind of the reason why I'm interested in playing with one. The highest power 13B-MSPs seem to make less power than the 13B in my car now but I want to see what I can do, you know?
I don't know. :) I haven't heard a common convincing narrative as in the past, although I haven't spent a lot of time post 8-year warranty trying to figure it out. Mine went due to bearings, or something along those lines because the engine seized. The FC turbo engines I had in the past went due to apex seal failure. My experience with the FCs and my general recollection of the typical failure was that the seals destroyed the affected rotor housing and the turbine housing if equipped. Side housing were usually okay.
The catalytic converter in the RX-8 is not super close, it's kind of medium distance. It's not quite as far back as the main cat in older cars (and most other 80s/90s cars), but it's not right near the engine as in the first cat in the older cars. It's definitely not as close as the main cat in new cars, eg. right in the exhaust manifold.
I wish there was a better answer to this because the RX8s are so cheap and the cooling/motor issues are what seems to hurt them as track cars.
And because LS swap all the things is not as easy as grannys speed shop for any of the other RX line
I don't know if there is just one smoking gun unfortunately, taking a shot in the dark I would put it between side seal's failing due to carbon issues or bearing issues due to keeping too much heat in the engine?
The internet is too full of speculation to really be able to determine one actual direction, unless you can find someone who works at a Mazda reman factory or just rebuilds RENESIS engines on the norm it seems hard to get a good consensus.
Mazda HAS to know though right?
The big question is though is, why could they not figure it out in testing?
Seems like pretty common failures at 80,000 in the real world would show up in testing. Maybe they did, and they just gone too far to back out, and they knew the rotarys future was dead.
TheRX7Project said:I've now seen 2.5 different explanations.
1- the siamesed exhaust port gets too hot and causes the seals to fail (probably due to some sort of expansion/warping) because, well, its double the rotary exhaust trying to make an exit.
1.5- the siamesed exhaust port gets too hot because the catalytic converter fails as mentioned above (very good possibility)2- in order to meet emissions standards, the oil injection rate was dropped, which causes the seals to fail (this would also be accelerated by extreme temps at the exhaust port). Premix would prevent this kind of failure, presumably.
As for preventing the siamese port of death, my thought was that if you rebuilt a renesis using a 13b housings (and, if possible, a 13b center iron, I haven't been able to get a straight answer about fitment) and renesis front and rear irons (and center if necessary), you could not only make more power because the exhaust is freer, but also make sure you don't have a failure due to a hot spot. This would require a custom header, but honestly *shouldn't* be too hard to achieve.
Renesis swapping my car is something I've seriously considered, double the HP without losing driveability and remaining N/A? Yes, please.
How about do a Renesis swap, then right away, like before starting the Renesis, do a LSx swap
I rebuilt a Renesis that a coolant seal had let go on and it more than likely had gotten hot. Just replaced all seals and put it back together. It lasted about 5 years/50k miles, track days and autocross, when compression was low enough to cause starting problems when hot. This engine never had very good compression after the rebuild. I don't know what I did wrong maybe should of bought new rotor housings, haven't pulled it apart yet to check.
I think if anybody outside of mazda knows the answer to your question it would be Kevin at RotaryResurrection.
It been years since I was in contact with him, but his webpage is still up.
Not sure how much help he will offer a non-customer, but I think in general he was good about sharing knowledge. I think he used to have info about failure modes on his website for 12A and 13B's, but looks like that's gone now.
In reply to DrBoost :
When I first got my 7, my dad kept insisting I swap in a small block Chrysler (we had one sitting on the rack). I'm a bit too much of a purist to piston swap my car.
At least for now.
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