question about middle exhaust port
 

Exhaust ports from either rotor merge into a single exhaust port at the intermediate housing... I know this sandwich has been visited before on this forum. However, is it feasible to design an intermediate housing that separates these two into separate and more flow-friendly and tuning-friendly exhaust ports. This new intermediate housing would necessarily require a different exhaust header, but people will have to do that anyway for turbocharging.

Would such a housing yield gains enough to be cost-effective to produce? Is there something specific about the 13b-msp intermediate housing construction that will make a new unit difficult to fabricate?

there's been lots of talk of modifying the existing housing to better suit tuning reqiurements (which would obviously be unbelievably cheaper and easier than having to redesign the whole engine, which is what you'd end up doing if you tried to change the intermediate plate beyond what you can do with modification).

well, it's made of cast iron. it's dimensions are extremely specific and has many features (like water jacket design, the drain to the sump) which would prove incredibly difficult to replicate with very much similarity to mazda's design.

racing beat has for a long time been making aluminum housings, but i don't think they've gotten to the rx-8 housings yet. the performance gains would be nil for the street considering the level of build even the most avid enthusiasts go to, and cost inhibitions that exist for street rides. it'll be done, for sure, but for owners who have the car for personal use (and aren't in high-level professional racing with the car or motor) this is way out of reach, and even the most hardcore and talented (or rich) would really want to try and change the way the siamesed exhaust port functions.

The only thing preventing the center port from being 2 seperate ports is the exhaust sleeve. The siamesed section is not affected by the casting of the housing and no new housing would need to be developed. There is an exhaust insert. If this sleeve were removed and a new one machined, it would be possible. It would necessarily help flow but it would keep the exhaust pulses seperate from each rotor to allow better exhaust tuning. This will only be beneficial once the engine is ported and has some overlap.

Racing Beat built and tested a header that had 4 equal length exhaust runners and an isert that entered into the factory housing to keep the ports separate. They also built a conventional 3 runner header. What they found is that both designs made the same power. The lack of port overlap in the Renesis and therefore lack of scavenging really makes the siamesed exhaust port irrelevant on the stock engine. Let's do some porting though and have some fun with it.

Here is a picture of the cast iron sleeve in the center housing. Just envision it removed and a new one made with dual outlets.

you're sure it's cast iron? that kinda sucks. but it's good that it's only a sleeve.

funny though, how you "aren't" able to tune a header when there's no overlap...
anyways, good info.

has anyone talked about going periport on the intake side at all yet?

That's what they were on the older engines so I am just assuming they are the same. I always called the material unobtainium. It is pretty damn hard.

Yeah that no overlap no tunability thing really threw me for a loop too. It makes me realize that my header idea will not work any better on a stock engine than any other ones attempted. Oh well.

If you were to port and polish the engine, would your header design help to produce more power? I think I remember hearing that Ito's port caused overlap? I'm too lazy to go look, but either way, would it and the catback be a lot more effective after a port job? Thanks

The inserts are made of Inconell

That explains why they are so damn hard.

you've got to be shitting me...

Inconell is machineable. It has between 8-12% machineability rating (depending on the alloy) which is in grinding territory but if you use carbide tools and plenty of coolant you can cut it. The trick is to have a stiff tool. :p and get the chipload per tooth around .001 per rev so you cut underneath the work hardened layer.

i take it inconell=unobtanium?

Inconel is damn hard to work with. It is very hard to cut or grind but by no means impossible. It is also very hard to weld unless you are very experienced.

a megaconducting steel (hard alloy, i can't remember if it's a ferrous base or not), it's perfect for cost-is-no-object exhausts because you can make the walls of your header or whatever so thin. unbelievably resistant to heat (hence unbelievably tricky to weld), and obviously expensive to boot. it's the kinda thing that F1 makes their headers out of.

edit: for more info, see http://www.micronmetals.com/inconel.htm. there's a little iron in it, but mostly nickel, as you can see here.
for non-engineers, here's a little thingy with pictures http://www.burnsstainless.com/TechAr...l_article.html

Inconell is used extensively in aerospace hight temperature applications such as hot gaspath sections of jet engines. If you need something to have strength at high temp this is your stuff. Other than that it's pretty heavy relative to say titanium or aluminum.