I have a client who wants a full system for his race ready rx8. I have no idea how to start doing the equations to get all the measurements, because I don't know what numbers to plug in.

The motor has 3 exhaust ports, 2 for each rotor and 1 that both rotors share. I am having a hard time figuring out what size pipes to use how long and such (since there is no over lap in this motor).

If anyone can brain storm this with me it would help a lot.

Thanks!

EDIT: rotary not rotory

 

http://www.nopistons.com
http://www.rx7club.com
http://www.ausrotary.com
http://www.kiwi-re.co.nz

 

After doing much much reading and looking around, this is what I came up with.



The header on the left is the original one, the one on the right is my design. This is going in to an open wheeled car which uses an RX8 motor so I had a lot of room to work with.

There is going to be an engine dyno done shortly, so I will know if all this was a waste of time or not.

Oh and don't mind the welds too much, this is a prototype the final one will have most of the bends programmed on my bender :

 

well the only thing that really limits the rotary's RPM and output is the amount of air moving threw the motor.

I think that the bigger diameter piping u could use, the better.


Nice work though, post up some pics of the car and all that good stuff.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 93supercoupe &raquo;</TD></TR><TR><TD CLASS="quote">well the only thing that really limits the rotary's RPM and output is the amount of air moving threw the motor.

I think that the bigger diameter piping u could use, the better.


Nice work though, post up some pics of the car and all that good stuff.</TD></TR></TABLE>

true.. with a rotary you have what i call sound pulses for the exhaust which the rotary is high for it RPM abilities

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 93supercoupe &raquo;</TD></TR><TR><TD CLASS="quote">well the only thing that really limits the rotary's RPM and output is the amount of air moving threw the motor.

I think that the bigger diameter piping u could use, the better.


Nice work though, post up some pics of the car and all that good stuff.</TD></TR></TABLE>

I did a lot of reading on various header designs for the rotary motors and it seems like everyone has tried big pipes, some even as big as 2" runners (the original design on the left uses 1.75" on the left and right side, and 2" on the middle) and the most people gain is like 4 5 hp. It's just very hard trying to figure out the numbers exactly without cams, bore stroke and all that good stuff.

I wanted to try something different and went with my experience and gut on this one. Will see

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danielm3 &raquo;</TD></TR><TR><TD CLASS="quote">I did a lot of reading on various header designs for the rotary motors and it seems like everyone has tried big pipes, some even as big as 2" runners (the original design on the left uses 1.75" on the left and right side, and 2" on the middle) and the most people gain is like 4 5 hp. It's just very hard trying to figure out the numbers exactly without cams, bore stroke and all that good stuff.

I wanted to try something different and went with my experience and gut on this one. Will see </TD></TR></TABLE>

4 or 5 hp can be a lot when you are making an open wheel car..... especially if you are racing.

 

remember Rotaries like to BREATHE

 

Had the dyno done today and my design lost 7 hp, which they said was very impressive considering how much smaller I went on the runners.

Anyway, on to design number 2

 

I have found that the sooner that you can get all of them together the better.And never make it smaller than the size of the port.

 

Why not try a stepped primary design similar to the original?
Yours definately looked nicer.
Maybe talk to Burns Stainless. You can get a collector designed just for the car,
maybe they have dealt with rotary before?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 9bells &raquo;</TD></TR><TR><TD CLASS="quote">Why not try a stepped primary design similar to the original?
Yours definately looked nicer.
Maybe talk to Burns Stainless. You can get a collector designed just for the car,
maybe they have dealt with rotary before?</TD></TR></TABLE>

Original looked nicer and simpler (for flow) to my eyes. Rotaries want air in and air out as simple and as fast as possible. Total air pump. I am not surprised the latter design lost power. But don't take that as a negative - glad to see experimentation happening.

 

http://ausrotary.dntinternet.c...ifold
^ forced induction specific - but should leave you down some useful avenues.

 

My suggestion, since you have an open wheeled car and alot of room to work with, is to make a prototype that allows you to change the runner length on the dyno...

Your design, using the true merged collector, and the expansion past the the collector, are good points...I would most definately keep those two..

All in all, I like your work, Just shorten the runners, IMHO...

 

Thanks for the links and advice, very good info.

Now that I know the engine likes to get the air out as soon as possible I have an interesting idea on how to make the manifold, I should have it done some time next week. I will be posting some pictures as soon as it's done.

Here is a quick drawing of my next idea, I was thinking what would be the best and fastest way to get the air out and this seemed like the best way, what do you guys think..

 

do you have dyno plots from both headers. I would like to see them...

Your problem could the the size of the choke on your collector...

 

I don't have the plots, I had to signs 300 papers to even be in the dyno room, but the curves looked 100% the same, just mine was 7hp less and like 5 tq less.

 

Nice work got to love R and D eh lol.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danielm3 &raquo;</TD></TR><TR><TD CLASS="quote">Thanks for the links and advice, very good info.
</TD></TR></TABLE>

this in theory would work well...expelling gases to a bigger area increase the pressure differential....but it would also kill exh gas velocity which helps the motor scavenge naturally.....

id stay w/ the standard merge collector & reverse megaphone...and work on the primaries sizing and step ups...also some good articles on anti-revision are kickin around on some sae papers...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDMCRX &raquo;</TD></TR><TR><TD CLASS="quote">Nice work got to love R and D eh lol.</TD></TR></TABLE>

Yeah haha.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drumking15 &raquo;</TD></TR><TR><TD CLASS="quote">

this in theory would work well...expelling gases to a bigger area increase the pressure differential....but it would also kill exh gas velocity which helps the motor scavenge naturally.....

id stay w/ the standard merge collector & reverse megaphone...and work on the primaries sizing and step ups...also some good articles on anti-revision are kickin around on some sae papers...</TD></TR></TABLE>

If this was before I had the dyno done of my 1st design, I would have agreed 100% with you, but I believe with the Rotary motors all conventional thinking of how to design a header goes right out the window. I came up with that design thinking what would be the best and fastest way for the gases to get out of the engine and after coming up with that design I happen to see a stock RX8 header which has the same concept.

I am really trying to think outside the box and trying to do what i think hasn't been done before (I may be wrong).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danielm3 &raquo;</TD></TR><TR><TD CLASS="quote">
</TD></TR></TABLE>

Isn't the middle exhaust port shared? should it maybe be larger than the 2 outside ones? I don't know, i'm just tossing some ideas out there.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 9bells &raquo;</TD></TR><TR><TD CLASS="quote">
Maybe talk to Burns Stainless. </TD></TR></TABLE>

2nd this. Their tech guys are pretty good. If they have done any work on a rotary engine before, they may have some useful data for you. Also, their header software may be able to be tweaked to work with your situation (although that is a bit of a long shot).

Best of luck with your project.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jweller &raquo;</TD></TR><TR><TD CLASS="quote">

Isn't the middle exhaust port shared? should it maybe be larger than the 2 outside ones? I don't know, i'm just tossing some ideas out there.</TD></TR></TABLE>

You are correct in that the 2 rotors share the middle port, but at the same time it's almost half the size of the other 2 (the outside two are about 1.3" across, where the middle one is a little over .7".

 

On one of the RX7 GTUs that I work with we use a 96in primary. The collector is right under the rear axle. This is for a peripheral port 13B engine, so it will be a little different. The other best option for that engine is a very short 16in Primary. According to Downing that is one of the best setups. Bigger is better.

Your final setup needs to be made of heavy wall stainless tubing. Rotaries have VERY high egts. They will burn out mild steel in short order.