Lynn E. Hanover

There were none that I remember. Very bad idea to be near a rotary with no muffling at all.



Does this exhaust port look too big? Not really. Its part of a flow bench rig for flowing intake ports. This is the exit into the bench.

j9fd3s

mazda like to bring all the old vintage race cars out to different events. by far the loudest noise ive ever heard is the c/d rx2, it sounds like the entire 20 car field by itself, 12A bridgeport into a megaphone



the next loudest is the 79 imsa factory car, its got a little muffler but you can still hear them start it and warm it up, across the paddock, during a race. it sounds wonderful for some reason...

BLUE TII

RX-7 by Jack yamaguchi chronicling the development of the 2nd gen RX-7 has some info in its race section.



Apparently, by 1980 17 of the 22 teams competing in the Grand Championships Series had converted to rotary power and the cumulative effect of all the screaming rotaries was fearful enough Mazda engineer Matsuura decided to act before the race officials did.



He developed an exhaust system called the IR-4A which remained in use on racing rotaries and offered to racers. It reduced the noise levels from 125 dBA to 115 as measured at Fuji speedways front straight. It reduced power output 3% or about 10hp.



Mazdamotorsports still sells a 40lb stainless steel contraption packed with lava rocks for race rotary exhausts- I don't know if it is the original IR-4A, but it is apparently one of the very few mufflers that can survive endurance events on a peripheral port engine. Part # 0000-06-9101-LR and it is 3" inlet and outlet $408.90



One user on the RX-7 club forum noted that it reduced his exhaust noise to 100 dB at idle :P

chironwsc

Thanks for all the great replies. Looks like the race pp rotaries are bloody loud!!!!

I think we will have a look and do some testing with the exhaust port splitters as mentioned in an earlier reply. We have some CFD software so I will see if we can keep good flow out of the exhaust ports and also keep the noise reduction that the splitter offers and maybe even improve on it. I will keep you posted on our findings.

I have heard that the Renesis engines are a lot quieter than the older engines. I know that as soon as you make the engines peripheral port or add big side ports that the noise increases. But I am wondering if the Renesis engine is so quiet because of the side port exhaust? This has got me thinking would a peripheral port Renesis engine keeping side port exhaust (ported out to improve flow) help reduce noise and still produce good power? Or would the side port exhaust still be too restrictive? Your thoughts please!!!



Henry

Lynn E. Hanover

Any time you change the speed or direction of a flowing media, you force it to give up energy. So, the Renesis turns the flow out through two 90 degree turns, with a total cross section larger than a peripheral exhaust port. So the velocity is lower than that in the periphery port, and has less energy.

The turn also drops some energy and that is shown in the coolant temperatures be higher.



You can also increase the diameter of the exhaust pipe as it nears the muffler, the hope here is to have much of the mass drop to subsonic before and inside the muffler. If the flow velocity is maintained and allowed to drop to subsonic outside the muffler, all is lost, and it will sound as though there is no muffler in use.



The exhaust pulses have dense fronts, and the splitter peels off a section of this front and shoots it out ahead of the front, removing some energy and filling in mass between the fronts. The perf tube muffler allows for a room of increased volume to allow the front to expand and leak through the perfs into the muffling media, and leak back into the flow behind the reduced front as it exits the muffler. With a 4" ID perf tube, it needs to be longer rather than shorter to give enough time for this activity at high throttle settings. It is possible to do it. It is done every day. Even on airplanes with very little room for the pieces.



Lynn E. Hanover

Maxt

Some of the tuned Rx-8's with racing style exhausts on them I have seen are as loud or louder than my p-port, I think the factory rear muffler design and the cats are doing most of the work on the noise in the renesis, an rx8 with a header and larger bore race pipe is ear splitting, its got a different pitch to it as well. Mazda did a alot of work on the rear muffler to appeal to new car buyers who expect a quiet car.

Research around the early to mid 90's on mazda's imsa and gt efforts, thats when the noise was an issue, I cant remember where I read the article, I know it was online, but it highlighted why Mazda was losing ground in racing with the rotary, and it was having to cork up the motors for noise. It detailed their noise reducing efforts and how they moved to adding more and more rotors to overcome it.

The scoot car is probably the quietest p-port car in existance, but as you can see it takes a power penalty.

The loudest car has to be Re amemiyas Gt300 car, I was in the pits with that thing with ears covered and it was still stupid loud. On the back straight it was still louder than the cars coming down the front straight near us in the pit area . Its about 30" header that just runs into a megaphoned dump pipe near the door off of a p-port 20b, I am not sure how long that car will be allowed to run for as they tighten down on noise in Japan.

scot62

Keep the post going as it's interesting topic! as wouldn't call it " Noise", just called "Rotary music"

Back in the late80's, talking to the driver,was sitting in the car at the pit awaiting prior to race(TWR Race car with 13BPP with magaphone)

a waste of time talking as I'm shouting " Hello" and he just smiling away

j9fd3s

so if i'm reading this right, in a long primary type system the muffling in the primary pipe isnt going to do as much as having the megaphone slow down the exhaust in a BIG main muffler?



i should add that a friend of mine ran a big bridgeport with 2x2.5" pipes, the muffling was 2 loooooong glasspacks (they went from the header to the rear axle)into 2 "turbo" style mufflers. because it never collected it should have been down on power, but it did 230rwhp. it was also quiet enough for the street.

mazdaspeed7

More good info here



Thats a very interesting design that leads me to another question. Why does a muffler core have to be round? The borla lynn mentioned is a good example, and some bike mufflers use triangular or square cores in their mufflers.

Lynn E. Hanover

The long system described in the Racing Beat catalogue is for 102 inches to the colector. Then into the Factory Mazda 3" race muffler. Lava rocks in a short perf tube with a short room at the front before the perf tube starts.



The picture is of a homoginizing muffler for an airplane very effective but costly from the power view.



The round muffler is used as the best shape to survive the high pressure pulses. Flat mufflers tend to be hammered to pieces. Flat muffler are sympathetic to so many frequencies, that life from metal fatigue is short.



Lynn E. Hanover