Hey Guys,







I thought I would share a few ideas I have had about the rotary exhaust port. A friend of mine works for a place that do a fair bit of performance work on V8’s and I was having a look at the shape of there exhaust ports and surprise surprise they are totally different looking. The whole shape etc of the rotary port seems to be totally wrong in comparison. The resons are you have the rapidly expanding port tunnel which goes straight out of the chamber horizontally so to speak. So my theory is the port tunnel should exit on an upward angle as that is the direction the exhaust gases want to flow and the tunnel shouldn’t expand so rapidly as this kills the velocity.



I had an old set of housings that were from a 13b Large extend port. So I thought I would have a play around with one to show you what I am trying to get at. I have used bog to fill in the port etc and get the shape I want. I haven’t changed the port timing etc I have left it as it was, the focus is on the port tunnel. So yeah have a look at the links to some pics below and let me know your thoughts on my idea, and if you don’t think it will work please give me your reasons as to why rather than a simple it won’t work https://www.nopistons.com/forums/pub...DIR#>/wink.png I am hopping to get a chance to put them both on the flow bench and see the results https://www.nopistons.com/forums/pub...IR#>/smile.png







http://home.iprimus.com.au/brap/exhport/1.jpg



http://home.iprimus.com.au/brap/exhport/2.jpg



http://home.iprimus.com.au/brap/exhport/3.jpg



http://home.iprimus.com.au/brap/exhport/4.jpg



http://home.iprimus.com.au/brap/exhport/5.jpg



http://home.iprimus.com.au/brap/exhport/6.jpg



http://home.iprimus.com.au/brap/exhport/7.jpg



http://home.iprimus.com.au/brap/exhport/8.jpg



http://home.iprimus.com.au/brap/exhport/9.jpg





Look forward to some replies



Cheers



Lance

seems more restrictive

Even if the design is no better than stock, the results will be cool to see.

Do you mean the tunnel looks restrictive? It is no more restrictive than the port in the rotor housing. The reasoning for this is by keeping it the same or only slightly larger, it keeps port felocity high, which is very important imho, most people think that making ports huge is the answer as it increases air flow, but they forget that velocity is also very important.



cheers



Lance

I may be wrong, but isn't port velocity only important on the intake side? It seems like you would want as little restriction on the exhaust as possible.

maybe???



though i think if the faster the exhaust gases are moving the quicker they are going to get away, if that makes sence. Also if you were to do a similar setup on a turbo engine (though bigger etc) , the higher veolicty would help reduce turbo lag



Lance

I like your D shaped port. I also like your '74-'75 rotor housing. I cut some D shaped ports in a set of '81-'83 J-spec 13B rotor housings, and I also have some unported '74-'75 rotor housings that I'm going to port soon. Your idea here is quite interesting.



Somebody had this idea a while ago and made some sleeves out of stainless steel. They had a very similar shape to yours.



I'm not sure how well your bog (bondo?) will hold up to the heat, but if it can withstand temperatures as high as aluminum can, it may prove interesting. Keep those pics comin'!

seems like that would increase your EGTs.



Might be effective on a N/A motor, but I think that it is probably too restrictive for a turbo motor.



The "D" shape I have seen before a few different places, but not carried through the entire housing.

This got debated in a very long and informative thread on RX-7 Club about a year and a half ago.



Essentially, you have the right idea. However, the exhaust gas temperatures resulting from that are incredible.



Read this. Exhaust Port Sleeve It's long, but it's worth it.

I would have to agree here. In a N/A engine the result might help, however in a turbo car think you would be choking the turbo at higher RPM

Thanks for the feed back guys https://www.nopistons.com/forums/pub...IR#>/smile.png



the bog definatly won't hold the heat. I just used it to get the sort of shape i was thinking of to get some opinions. I would have to make up a sort of sleeve, to handle the heat. The difference with my setup compared to the sleeves discused on the rx7 forum, is that my port tunnel, runs in an upward motion rather than straight out. Im not sure how much of a benifit this would have but you would think it would have to help. Also i only used the D shape as that is what shape the housings i had used. I think the theory could be applied to any shape



I think for a turbo setup, you would do the usual port on the rotor housing, and have the port tunnel going in the upward direction, though have the tunnel expand in an outward motion along the length of the tunnel say on like a 3 - 5 degree angle on all sides for example. Though Not at the rapid rate the factory does. If that makes sence. In regards to the added EGT's would the addition of water injection help keep the egt's down. Also could the tune be changed to help lower the temps?



keep the feedback comming guys https://www.nopistons.com/forums/pub...IR#>/smile.png



cheers



Lance

it'll definitely help port velocity, w/ minimal if any flow losses. the problem is the heat. not only do you need a sleeve to handle the heat, you need a manifold and turbine housing and wheel that can withstand it as well. wi won't help.

would this in any way effect tq? It seems that having a slightly more restrictive exhaust creates more back pressure which in turn creates more tq



David

Uh, backpressure is the devil. It always has been. You're porobably thinking of something else.

Backpressure is our enemy. Velocity is our friend.

Yes i know this but wont the port make more back pressure or will it still flow the same

How about removing the sleeves altogether and making an extension of the pipes at the flange that extends into the rotor housing? I have seen some pretty thick material pipe that I think would be up to the challenge. You could have this smaller diameter pipe feed into a larger one and then have the blowby from his pipe feed into the larger pipe on its way to the collector. Well it just sounds good enough for me so I'm gonna give it a shot. I'll have results in about a month.



BTW I'll post a drawing of what I mean later on tonight.



think thermal reactor... hint hint...

Oh man, to anybody that hasn't, READ THE RX7CLUB ARTICLE. Its seriously worth it. Basically, the factory ports have the extremely rapid expansion in order to purposely induce tumble in the port. This helps reduce the temps and sound, but kills power. The ports which have a minimal area gain as they travel away from the rotor actually flow a fair amount more. The guy that did most of the work in that thread was saying like 30% more, without changing the shape of the port opening at all. But BEWARE! When you do this you will be unleashing the true nature of the rotary exhaust. Ceramic coatings and Inconel turbine wheels are your friends. But, as the author of the other thread said, turbo spool is un-freaking-believable. There is no loss of top end, simply huge across the board gains. The smoother higher velocity flow which is the cause of the reduced lag also means the engine will react more strongly to header tuning. This helps NA's and turbos alike.



Additionally, backpressure is the DEVIL! What started the whole backpressure = torque thing is header tuning. Tube diameter specifically. As you go down in diameter the velocity increases as well as (unfortunately) backpressure. The increased velocity helps scavenging and thus increases torque, but the backpressure does nothing but decrease power. The trick is to find a balance which yields the most. People prolly measured the increase in backpressure at some point and thought it was the cause, thus giving birth to an annoying urban legend that has never quite died.

ArmyOfOne: That is a good idea about making the manifold go into the acutually port, this way if the idea didn't work then you can allways fit a normal manifold back on. I think i understand where your comming from with the one pipe inside the other, though im not sure if there will be enough room in the port tunnel to fit it all in. Nice to see you want to give it a try. What sort of setup are you planning on trying it on?



CypherNinja: Have to agree the read on the rx7 thread is very impressive, and certainly worth the read. Good point about the back pressure etc. I have thrown this idea up on another forum we have in Australia, there has been so SAE papers submitted that have some details behind mazdas thoughts on the whole exhaust port design etc. And i have added some more details etc on there as well. Check it out at the follwoing link



ausrotary discusion



You might have to register to view it, but is worth it as there is heaps of other good info and stuff, on the rotor scene over here.



cheers



Lance

great info on both links. basically geared toward the higher spectrum of power goals but still very interesting. i wouldn't mind reading the rest of that article from the ausrotary thread...

Its a wild 6 port bridgeport with a 650 Holley. I am going to install a butterfly valve on the 5/6 ports.



1984 GSL, 12A Tranny (for now) and LSD. Car is gutted out behind the seats.



The real trick is going to be figuring out how long the smaller pipe running inside the other needs to be.

Now that sounds like a pretty wild setup https://www.nopistons.com/forums/pub...IR#>/smile.png got any pics of the intake ports?



with the pipe inside the other pipe, woudln't you want to run the smaller pipe all the way to the exhaust port on the rotor housing face. That way it will be a smooth transition? Or am i missing something with the idea of the pipe inside the other pipe.



Also i would have the headers run for 3" straight out of the engine before the first bend, to help stop any turbulence etc.



cheers



Lance

The smaller pipe would actually mate up with the insert or the port. The larger pipe will cath the blowby. What I mean is how long will they need to be coming off the exhaust port itself, as opposed to the flange.

Dam that is a pretty wild looking port there https://www.nopistons.com/forums/pub...IR#>/smile.png



as for the distance, not sure exactly which distance you mean, so i will try and explain them all https://www.nopistons.com/forums/pub...IR#>/smile.png



in your case, the factory sleeve is revmoved, you have the 2 pipes 1 smaller and 1 larger, the smaller fits inside the larger, the smaller pipe is inserted so it is hard against the exhaust port on the rotor housing face. It then extends all the way through the tunnel and stops at the end of the rotor housing (as in where the header flange bolts) As for the larger pipe i would have that run the same, though i reckon you might have dramas with the larger pipe, as there might not be enough room for it due to the floor of the exhaust port tunnel being to high. Now for the headers, you want the headers to extend 3" from the header flange before the 1st bend. You also want the exhaust port on the rotor face to merge nice and smoothly into the smaller pipe, and then merge nicely to the larger pipe, and then merge nicely into the header pipe. The only problem i can see is how are you going to stop any blow by getting in between the larger outside pipe and the rotor housing? You may want to consider not running the larger outside pipe, and just run maybe a thicker inside pipe and be very thorough in that it meats up to the exhaust port on the rotor housing face, with out any leaks



cheers



Lance

Red------------Small pipe



Yellow---------Large pipe catches any excess pressure



Orange--------both pipes join back into one on the way to the collector