pd_day

iTrader: (6)

Since everyone is saying that a true dual on a NA is loud and annoying, I was wondering if it's possible to build one that is tolerable without dropping power?

I had the idea dawn upon me but don't know if it will work, but here it goes.

Is it possible to use the pulses from the two exhaust ports to quiet the exhaust tone down? Since sound waves have trophes(spelling?) and crest(spelling?), can we time the pulses by manipulating the lenght of the primaries/piping so that every crest on the front exhaust port would meet a troph on the rear exhaust port (or vice versa) so that the extreme noise cancels out?

This exhaust in my mind would be like the 3rd gen's N1 dual where both piping and muffler would exit out the same side of car, piping running side by side. This way, the cancelling effect would be more efficent.

Do you guys think that this will work?

Can someone provide me with the exhaust port duration and timing?

Thanks.

Samps

Wouldn't the pulses vary in relation to RPM? If so then the exhaust would have to grow and shrink in relation to RPM.

mazdaspeed7

Its not that easy. Nothing ever is. First, true duals are quieted down A LOT by a crossover pipe, which also tunes the powerband. Heres a thread about the tuning effects of a crossover pipe

The pipes MUST converge to cancel out the noise of true duals, either an h-pipe, or an x-pipe.

pp13bnos

iTrader: (1)

My exuast is actually realy quite at idle. But once you get on it, or roll into the throttle is sounds so sweet. I have a dual outlet header, that i cut the flange off of, to get the RB pre-silencers as close the motor as possiable. This is very important! After that, i just had some mandral bent exuast to some RB mufflers. Sounds realy good...and remember to keep the pre-silencers as close to the motor as possiable

About the X and H pipes. I asked Rob about them, and he said they will produce more power...but it comes at a cost. On a rotary, you would need to have a X/H pipe that would be able to slide up and down the exaust system...to get beniefts over the entire power range. So its impossiable to do. Unless you have a race car, that is tuned to run in a certain RPM. Like a bridge/PP engine that spends most of its time between 7-11k rpms. You could in those cases, get a H/X pipe and have it put in there, and you would make more power.

Placement of the pipe is also very important. He said when he was doing some exuaust work on a bridge engine, with a H pipe, they just could'nt get the thing to run right. Until the motor hit it's "sweet spot", and the thing just came alive. They finally yanked the H pipe, and the thing ran great.

So basicaly, for overall driving the true duel is still the best. If you are racing, between a certain RPM range, then the H/X pipe will make more power...but will loose hp in anouther spot. Kinda a trade off. He talked about it quite a bit...but my head started spinning from info overload , and i could'nt hold any more information. CJ

peejay

Is that for the PP engine or a stock-port?

mazdaspeed7

How narrow was the powerband(the real "sweet spot") with a crossover pipe? Did Rob tell you that? I am really curious about the whole exhaust tuning issue. In the link I posted, someone(sorry, but I dont remember the name) was talking about water injection in the exhaust at low rpm's. It slows the exhaust pulses(and I would assume increases exhaust volume), and when a crossover pipe is set at a certain point, the slower exhaust pulses will effectively make the crossover point farther from the engine, increasing low end. Anybody not lost yet?

CJ, if Rob didnt tell you how narrow the sweet spot was, do you think you could ask him for me? I am seriously considering trying a crosover pipe, tuned for high rpm, and using water injection to help the low end.

pp13bnos

iTrader: (1)

I never asked him about how large the band was...he just said that he did'nt think that the gains warrented the $$ it would cost of finding the sweet spot of the engine, as every engine has slightly different demands. But if you're going to do your own exaust, you could realy cut down on cost. I could ask him for some general advice though. Like how far from the header it should be, and about water injection. I'll ask him this weekend.

The current duel exaust is on my mildly ported 6 port engine. The motor was ported as far as it could be while still having a stock idle (minimal over lap) and still pass emissions if it has to.

The peripheral port exaust was pretty much the same thing, but instead of having RB mufflers, i ran Turbo Walkers. They flow better, but are louder. This is my daily driver, and i'm buying a home in town, and don't want to **** off the neighbors just yet

The peripheral car was'nt realy loud (I've heard far louder Harleys, and Hon-du's) but the uneven exaust surging made it very unique sounding. I loved it when you would pull up to the gas station and the moron would say "Man your car has a realy bad miss!" Or when i would put the pre-mix in the tank, before the fill up the guys would allways yell at me "The oil does'nt go in there!" I would say in the straightest face possiable "IT DOES'NT?!? Where's it go then?" My friends would almost die laughing. Well anyways....sorry for rambling. CJ

mazdaspeed7

Let me know what he says. As far as I know, putting the crossover pipe closer to the engine will raise the powerband, and with the water injection, it should be wide enough to not be a problem.

I havent had anyone ask me about the oil for premixing, but I am seriously going to say that if someone does. That has to be one of the funniest situations you could possibly get into.