globi

I agree with your statement regarding the 3-1 and 4-2-1 header.

(Actually I'm mainly questioning what maximum gains with any header can be reached and not necessarily what header concept should be applied and how they should be designed.)

Nemesis8

iTrader: (3)

So RE Amemiya's idea of splitting the siamese port is a good one?

TeamRX8

iTrader: (25)

they don't come with that plate, I have one

Nemesis8

iTrader: (3)

So whats up with that pic? Weird yours does not have this feature.

globi

If you want to keep it relatively simple from a modeling standpoint you should split the middle pipe into 2 pipes and then reconnect these 2 pipes with the corresponding pipe on the left and on the right shortly after the split (similar to what TeamRX8 suggested earlier).
Keep in mind the engine has only 2 exhaust chambers (and not 3, as a 3 pipe header design might suggest).

TeamRX8

iTrader: (25)

bump

I'm actually wondering now if the Renesis even responds much, if at all, by tube diameter and length like most 4 cycle engines. Maybe Mazda has it right and the best performance option might just be short pipes into a log collector built for maximum weight reduction, use 22 ga inconel 625 and it wouldn't hardly weigh anything at all, especially if you lightened the main flange up some more

rotarenvy

what about separating the centre port and running a dual exhaust?. A 2 into 1 with the individual ports and a separate pipe for the Siamesed ones.

tuj

With the center ports not seperated, they will cause interference with each other. The idea is to keep the branches that will be flowing at opposite times seperate initially. Interference is detrimental to flow.

Running a completely seperate center port header would double the weight of the exhaust, offsetting any gains that it wouldn't make anyway.

rotarygod

Separating the center port into 2 ports and making a 4-1 collector has already been tried by Racing Beat. They didn't get any more power out of it than the standard 3 pipe system.

rotarenvy

it dosn't need to weigh twice as much as you have smaller diameter pipes.

I was thinking that the centre ports are a basket case. Why bother tuning them just reduce their effect on the other ports by keeping them seperate and hopfully give them better flow.

tuj

Well, basic header theory says to eliminate interference first. Interference is eliminated by joining pipes that flow at the same times first, then join those pipes together. Hence, the typical 4->2->1 header on 4 cyl engines joins 1 and 4 together and 2 and 3 together, before merging into one pipe. If you joined 1 and 2 together and 3 and 4 together, you will create interference, meaning some of the exhaust gases from on cylinder will go into another, instead of out the tailpipe.

Of course, this is a rotary, and we have to deal with that siamesed port. My theory is to simply block off the center ports entirely, and have a 2->1 header. The siamesed port is going to have interference, but if its entirely blocked off, it doesn't really matter. The only issue then would be if the side ports could flow enough. I think the reason we haven't seen gains on the headers that divide the center ports with a little plate, is that the center port isn't flowing much anyway. Just my thoughts.

Asmoran

Holy cow. I was just about to ask what would happen if we plugged the center ports.

yay for a guy who doesn't know what he's talking about :D

On the off chance that the side ports can't flow enough, is it possible to widen them?

TeamRX8

iTrader: (25)

What I'm suggesting is that possibly all that theory is out the window on this engine. Making a tube header is no big deal for manufacturers now. In fact, it's quite common.

Why would Mazda not make a true tube header if it had something to offer? Maybe the question is the answer.

tuj

What do you mean by a tube header?

carbonRX8

iTrader: (1)

As opposed to sand cast.

Edit: I should note that the stock manifold is not cast but is a dual walled "tube" header. I hope I have not mislead.

Beodude123

I remember seeing something about this (center port topic) in another thread.... Basically, the ports won't flow enough exhaust gasses to really give any good gains. The exhaust has to go through two 90* bends before it gets to anything, or something to that effect. There was a guy that ported out the exhaust ports a little bit, and made the transition a lot smoother. I bet that setup would benefit from a good header a lot more than the stock situation.

globi

No that's not what it is. Since there's no overlap there's no scavenging and therefore any scavenging supporting measures such as headers won't do as much as they would normally do (just read the whole thread).
If the 90 degree bend was indeed a significant issue than pretty much all conventional engines with poppet valves (which are obviously even more restrictive) wouldn't gain anything from headers.

rotarygod

Flow through those ports definitely has a big effect on what an exhaust does. I don't see how any decent piston engine even with a valve in the way can flow much worse than the stock Renesis exhaust ports. It's that bad.

Philip_SA

The stock manifold is actually not to bad.
Some guys tried a few ways here,not exactly sure what,but no increase in power.I think it was still 3 pipes.The place said they will need a lot of time to try all the setups and dyno to see, but I dont think much will be saved / gained. AND

....Thats why I love a peripheral port - one hole in and one hole out, Cant be simpler he

globi

The point is that most piston engines have a 90 degree bend and a valve (with a very high friction coefficient at that) obstructing the flow and many of them still get about 10% or even more with a header.

So far no-one has come up with a header for the RX-8 that delivers 10% power increase.
One explanation for this phenomena is: The Renesis doesn't have overlap.
and another explanation is: All the guys that came up with RX-8 headers simply weren't the brightest bulbs. Even if this was true one has to admit that even a blind man may sometimes hit the mark. And so far many have tried already.

That still doesn't mean that a peripheral port won't flow better, it just means that headers don't lead to the gains that many people would like to see.

tuj

RG, have you flow-benched it?

Nemesis8

iTrader: (3)

What are you going to do?

rotarygod

Nope. Played with them apart and know someone who has flowed it but I personally haven't.

TeamRX8

iTrader: (25)

so what's the deal with the port openings in the gasket being so much larger than the actual ports?

rotarygod

That's ridiculous isn't it! No clue what the logic is there.