RX7Tuner.

If this has been covered before I apoligize for the redundancy.

What do you guys think about running an H-Pipe with true dual exhaust? I get a lot of pulsing in my exhaust flow (pushing out than sucking in) and I wonder if it would benefit from conjoining the pipes. Has anyone ever tried this? What do you think? My application would be for an RB setup.

Thanks.

Evil Aviator

H-pipes don't work on rotary engines. If you want the H-pipe type effect, then use a short (22-27") collected exhaust or long (120-125") collected exhaust. Pipe should be about 1.75" inside diameter. You can gradually increase the pipe size as it gets further to the rear if you like.

Yes, the RB headers collect at the wrong point. Why? I have no idea.

ramses666

iTrader: (1)

What about an x-pipe setup? Would this help with a ported NA application?

Ramses666

Evil Aviator

Mazda NA rotary engines: Endurance racing since 1969
Number of X or H pipes I have seen on competitive RX-7's: 0

While it may be possible to get a lot of power from an X or H pipe, I would assume that just about everything that could be thought of has already been tried by people smarter and wealthier than us.

GORacing

The H pipe design is for sound modification, it bleeds pressure off as the exhaust pulse travels past it and routes it down the other tube, the X-pipe is considered to be an improvment to the design by making the pressure bleed off more gradual and offering less restriction to over all flow, not really a power adder, just minimizes loss while reducing sound intensity...

ramses666

iTrader: (1)

um... ok... I was thinking that a true dual system tended to become less efficient as porting & rpm's increased over stock. Would collecting a true dual system at some particular length become more efficient?

Ramses666

GORacing

Understand there are differences between an true dual, dual and collected exhaust systems... but to answer you new question, yes benifits can be gained by going to a collected system... bottom end torque can be improved by collecting the head pipes relatively close to the engine around were EA suggested, while high RPM engines (typically 8500 +), benifit from the longer collected system...

Now, I can hear the question forming, so... the collected system differes from the X pipe design, as the collected brings both pipes together in to a single pipe with a larger volume, from there the collecter length has to be 'tuned' to an RPM range in the power band of the engine, now to explain futher, as an exhaust pulse exits one head pipe this tuning creates a lower pressure in the opposite head pipe which aids in removing the exhaust from that chamber (process is called exhaust scavanging).
Once tuned then the system can be opened into free air (really loud), one larger pipe or split back into multiple pipes as required to fit under and around the bottom of the car to carry it out past the passenger compartment.
Niether the H or X-pipe is designed to promote the scavenging effect and only serves to split the volume and pressure of the pulses... hope this helps to make more sense...

ramses666

iTrader: (1)

ok... let me get this straight... a long collected and then split exhaust will have better high rpm & larger port performance vs. a true dual setup? How long should the dual primaries be & how long should the collector be? Am I making any sense?

Ramses666

GORacing

True, however you will most likely not have any room for a split exhaust after the collector, you will be lucky to have room for a muffler and a turn down...

See EA's post #2, these are general starting ranges, now keep in mind that what you are doing with the car will determine which way to go, exhaust tuning is as critical to performance as the fuel, port and igntion timing, but the nice thing is that street cars tend to be a little more forgiving...
As for the collector size, off the top of my head without looking it up, a general rule of thumb for the diameter of the collector should be calculated out by 1.5 to 1.7 X the total inside area of your head pipes, and starting length should be around 10", the old school tuning trick is to mark a line down the length of the collector with a grease pencil or paint it with regular spray paint, make a hard WOT pass and cut the collector at the point were the paint or grease line is burnt off, then attach your muffler or splitter there...

certifiednut

i cant remember the guys name, but someone had a radass system on this forum that collecter about 6 inches before the muffler then used an apexi muffler,, i know he ordered it from a website too. it was awesome. it was in a HUGE exhaust thread from a while back. i'll have to see if i can find it, if i remember right it was around 15 pages long though.

ramses666

iTrader: (1)

ok.. I think I've got a handle on the concept, however I don't think I've got 120 inches of exhaust length. I'm looking at putting a collector at 64 inches about 10 inches long and 4 inch diameter then splitting into my two mufflers. Any idea if I would see any gains? A waste of time? Try it & see? Go back to the drawing board? Or should I just keep my true dual setup & forget about it all together?

Ramses666