cach22

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 I am hopping to get a chance to put them both on the flow bench and see the results







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

93 R1

seems more restrictive

Mazderati

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

cach22

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

CGeek2k

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.

cach22

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

Jeff20B

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'!

suganuma

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.

TYSON

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.

BigTone

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