IanS

iTrader: (4)

OK so lately I have been helping out my friend work on his mustang GT (89). He was saying that an X-pipe would be very beneficial to his car. Now, since this mustang has dual exhaust and so soes mine (RB SP exhaust system), COULD this work for a rotary? I mean, isnt the x-pipe there for an increase in velocity as well as a type of equilibrium (maybe wrong word) for the exhaust? I understand that a 5.0 and a 12A are different engines, but exhaust still flows the same no matter what it is. I mean, put a straight pipe on a rx-7 and it does essentially the same thing as any other engine - its loud, has very little backpressure, and increases flow which equals more horsepower. Ideas? please discuss for NA ONLY.

Thanks,
IanS

Kenteth

X pipes (and H pipes) have been reserached pretty well on rotaries. The reason no one sells them is because they don't work as well as you would expect them too.

There is more power gain (hell probably even keeps resonance DOWN) by keeping the pipes straight and not crossing them.

You would get more power out of a full dual than you would an X or H system. It may not be true for piston engines, but for rotaries, it stands fast.

Its been tested. I don't know where the document is, but I believe it was wither by RP, REted (or Higgi), Kevin Landers, Mazdatrix, or RB. I can't remember who did the research, its been quite awhile...

EDIT: Amazing what I just learned in ten minutes of seraching, you should try it. Especially instead of bringing back this dead subject that will probably just cause people to get swifty and start swinging around what they think is best .

From how I understand it, crossover systems work well in piston engines such as v8s, because they are specifaly tuned for the v8 powerband (2k-4.5ishk rpm). Now... don't even try to tell me that a rotary has its peak power between 2 and 4.5k rpm. I think its at 4.6 or 5.6 or so actually, I can't remember now. Anyhow, what may work for a piston engine at its redline (5k) won't be working well at our 7k (not to mention our exhaust pulses are already far worse than a piston's).

take in effect how strong our exhaust pulses are, a crossover system probably couldn't be tuned much higher than 4krpm. this means Great low end power, but it will feel like soemoen shuts the power off at 4.1krpm. What would the point in that be when the powerband on a rotary barely even starts before 3800 whent the secondaries come and aux ports come online for the next 2.5-3k rpm,,,

sudseh

H-Pipes
H-Pipes are a good addition to dual exhaust systems. They help even out the velocity and back pressure between the two pipes which increases performance. An H-pipe should be no less then a half inch less then the two pipes it connects. Typically, ideal location for placing the H pipe is as close to the headers as possible.

X-Pipes
X-Pipes are yet another way to connect the two pipes. X-Pipes can sometimes make your exhaust note a little higher pitched.

~just a copy paste from a piston performance site~

i think the performance they are talking about is keeping the backpressure the same on both halves of the block thereby ensuring evenish power delivery.

~suds

Kenteth

In all seriousness, if you have a dyno, and good audio equipment, you could probably systematicaly tune an x or h pipe into the system. I think what you may hear though is that to tune it into the rotary powerband, you may have to ahve the x-pipe 8-10 feet behind the exuast stroke... Where does that put your fabrication, somewhere between you and the car behind you?

I suppose you could twist pipe like a pretzel under the car to get propper exaust runner length to get your hpipe in a properly tuned location,,, but seriously, is it worth it?

i personaly doubt its going to work all that well in the first place...

MPM

These two links are off the Austrailian Rotary Forum. Lots of good information. First link is specific for an N/A bridge ported engine

First exhaust info link

Second link is more for a N/A street port.
Second exhaust info link

Basically the same exhaust works for both types of porting. Long primary merged into a single muffler. Some of pros and cons for this setup. Good power but its loud. Thats true for most free flowing rotary exhaust.

Travelintrevor

is everyone forgetting that a V8 has cylinders on both sides..hence there are 2 headers running back to meet in a H or X or whatever...rotory has ONE side running back and then split into 2...why would ther ever be a need to conect them AFTER you just split the exhaust

RotaryAXer

iTrader: (4)

You are thinking of the second gen stock system only. On first gen and third gen they don't split into two at the back of the car.

On most aftermarket setups RB being the the most used there is a two pipe header out of the motor. The exhuast from each rotor is completely separate. On a good race setup these will stay separate all the way to the muffler or even never combine at all.

This my theory. I haven't really tested this:

The point of adding a X or H into a piston engine is to even out the flow and velocity. On a rotary this isn't as big of an issue becuase there is never an off cycle in the header tube. There is an exhaust pulse ever third of a revoltuion of the rotor in each pipe. So therefore the pressure is only off for a very short time. In a piston engine with six cylinders each cylinder has it's own header pipe. As the piston goes through its cycle there is a long time between exhaust strokes. The pressure within the header tube diminishes significantly between these exhaust strokes and therefore the gases in that pipe need to fight against the pipes that have just had an exhaust stroke b/c they are still at a high pressure. So if you add an X or H you are creating a more even pressure accross all of the header tubes which allow easier/better flow.

Travelintrevor

^^^ah..i see...very interesting indeed