[chironwsc]

Hi Guys

I am new to the forum and what a fantastic forum it is so much information on here!!

We would like to fit a 3 or 4 rotor engine into a road race car but I am worried about the noise problems associated with the rotary engines.
Not only would the engine be a 3or4 rotor but also peripheral port just to add to the noise issue!! Most of the championships in the UK now have noise limits, we would need run the engine to a 102dba noise limit. The noise test is done 20inch at 45deg away from the silencer exit.

Now my question is will this be possible to silence a non turbo 4 rotor race engine to 102dba without losing lots of power? Are there any tricks that people have found to help quieten rotary engines for racing?

We normally build our own silencers they are the typical race type re-packable straight perforated tube type fairly free flowing. Would 2off 7"x22" straight perforated tube type silencers do the job?
We did make a silencer a while ago for a customer which had an 80deg bend in the perforated tube this made a massive difference to the noise approx 12dba but we have not checked what power loss having the bend in the tube caused. Would a similar type of silencer with a bend in the perforated tube be too restrictive for a Rotary engine?

I would very much appreciate any thoughts and comments or just throw some ideas my way.

Kind Regards
Henry Nickless
Chiron WSC

This post has been edited by chironwsc: 30 August 2008 - 09:04 AM

[Lynn E. Hanover]

chironwsc, on Aug 30 2008, 07:02 AM, said:

Hi Guys

I am new to the forum and what a fantastic forum it is so much information on here!!

We would like to fit a 3 or 4 rotor engine into a road race car but I am worried about the noise problems associated with the rotary engines.
Not only would the engine be a 3or4 rotor but also peripheral port just to add to the noise issue!! Most of the championships in the UK now have noise limits, we would need run the engine to a 102dba noise limit. The noise test is done 20inch at 45deg away from the silencer exit.

Now my question is will this be possible to silence a non turbo 4 rotor race engine to 102dba without losing lots of power? Are there any tricks that people have found to help quieten rotary engines for racing?

We normally build our own silencers they are the typical race type re-packable straight perforated tube type fairly free flowing. Would 2off 7"x22" straight perforated tube type silencers do the job?
We did make a silencer a while ago for a customer which had an 80deg bend in the perforated tube this made a massive difference to the noise approx 12dba but we have not checked what power loss having the bend in the tube caused. Would a similar type of silencer with a bend in the perforated tube be too restrictive for a Rotary engine?

I would very much appreciate any thoughts and comments or just throw some ideas my way.

Kind Regards
Henry Nickless
Chiron WSC

In the US that requiement is at 50 feet from the track centerline on the outside of the track (where it would affect those folks on the next property) and at a place where full throttle is typical. And then the level is 103 Db.

So, is your measurement on a dyno at full throttle? at idle, or come other situation?

I have a big Borla 4" ID stainless packed perf tube muffler, with the outlet on the right side of the car to the inside of the track, and pointed at the ground. We make 103 easy with this setup with a 2 rotor 12A engine.

With a three rotor it would be a problem. At least another muffler beyond the perf tube job, perhaps one that breaks the stream into two elements and has them run into each other, along the lines of a Flowmaster. A big suitcase looking thing used on street V-8s. Would need to be at the very end of the system to keep the heat down, and the hammering of the supersonic pulses dropping to subsonic. The tip pointed at the ground is a big help as well. Possibly a copy made in stainless.

Use NA rotor housings and leave the splitter in the exhaust ports.

Lynn E. Hanover

[Lynn E. Hanover]

chironwsc, on Aug 30 2008, 07:02 AM, said:

Hi Guys

I am new to the forum and what a fantastic forum it is so much information on here!!

We would like to fit a 3 or 4 rotor engine into a road race car but I am worried about the noise problems associated with the rotary engines.
Not only would the engine be a 3or4 rotor but also peripheral port just to add to the noise issue!! Most of the championships in the UK now have noise limits, we would need run the engine to a 102dba noise limit. The noise test is done 20inch at 45deg away from the silencer exit.

Now my question is will this be possible to silence a non turbo 4 rotor race engine to 102dba without losing lots of power? Are there any tricks that people have found to help quieten rotary engines for racing?

We normally build our own silencers they are the typical race type re-packable straight perforated tube type fairly free flowing. Would 2off 7"x22" straight perforated tube type silencers do the job?
We did make a silencer a while ago for a customer which had an 80deg bend in the perforated tube this made a massive difference to the noise approx 12dba but we have not checked what power loss having the bend in the tube caused. Would a similar type of silencer with a bend in the perforated tube be too restrictive for a Rotary engine?

I would very much appreciate any thoughts and comments or just throw some ideas my way.

Kind Regards
Henry Nickless
Chiron WSC

In the US that requiement is at 50 feet from the track centerline on the outside of the track (where it would affect those folks on the next property) and at a place where full throttle is typical. And then the level is 103 Db.

So, is your measurement on a dyno at full throttle? at idle, or come other situation?

I have a big Borla 4" ID stainless packed perf tube muffler, with the outlet on the right side of the car to the inside of the track, and pointed at the ground. We make 103 easy with this setup with a 2 rotor 12A engine.

With a three rotor it would be a problem. At least another muffler beyond the perf tube job, perhaps one that breaks the stream into two elements and has them run into each other, along the lines of a Flowmaster. A big suitcase looking thing used on street V-8s. Would need to be at the very end of the system to keep the heat down, and the hammering of the supersonic pulses dropping to subsonic. The tip pointed at the ground is a big help as well. Possibly a copy made in stainless.

Use NA rotor housings and leave the splitter in the exhaust ports.

Lynn E. Hanover

[chironwsc]

Hi

Thank you for your reply.

The static noise test is at 3/4 revs so approx 7000rpm needs to be 102dba. We also have to meet the 102dba on drive by they don?t give a distance from the car for the noise meter.
What are the approx dimensions of your silencer, length and diameter?
Would a 13b make much more noise do you think than a 12A?
Also the exhaust port splitter is this part of the housing or a removable part we have very few non turbo 13b engines in the UK so don?t have any experience of the exhaust port splitter. Does the splitter affect engine power very much if used?

Thanks
Henry

[chironwsc]

Any one any experience of the Spin Tech mufflers for racing use? They seem to work ok on 20b engines used in aeroplanes.

Henry

[Maxt]

If you choke a p-port with to much muffler, power falls off like a cliff.. From playing with my own p-port car, the very end muffler and opening has the most effect on the overall noise. Adding presileners midway with perforated cores did nothing to the noise of the motor, absolutely nothing. I have a pop in silencer I drive with most of the time on the street, sometimes highway I take it out.
I think you may be wise to go 4 rotor, then muffle to meet track levels.Once you choke down the 3 rotor you may not be competitive power wise, if you read some of the older articles on the Mazda race cars in Gt and Imsa, they had a very difficult time meeting track noise levels, and making enough power to compete.
The scoot car runs cats, air injection, and met Japans street noise level, all corked up it did 370 rwps, it would probably do 425ish at track noise levels, figure on 100-115 rwhp per rotor with a muffled p-port.

[chironwsc]

Hi

Thank you for your reply.

Do you know what the IMSA /GT noise limit was in the day? What engines ran in the IMSA/GT cars are we talking 2,3or4 rotor?
That?s interesting what you say about the pre silencer. So for the 4 rotor maybe it would be an idea to split the 4 pipes in to 2 silencers not sure how this would affect power that?s something for the dyno I guess.
Are you talking about the Scoot 4 rotor car?

Thanks
Henry

[1962]

chironwsc, on Aug 30 2008, 10:01 AM, said:

Hi

Thank you for your reply.

The static noise test is at 3/4 revs so approx 7000rpm needs to be 102dba. We also have to meet the 102dba on drive by they don?t give a distance from the car for the noise meter.
What are the approx dimensions of your silencer, length and diameter?
Would a 13b make much more noise do you think than a 12A?
Also the exhaust port splitter is this part of the housing or a removable part we have very few non turbo 13b engines in the UK so don?t have any experience of the exhaust port splitter. Does the splitter affect engine power very much if used?

Thanks
Henry

Hi Henry,
Welcome to this forum as I'm from UK, what kind of model is your a FB,FC,FD or FE?
Mine's an FC with13Bpp motor( still building it up) as prevouis with13Bbp with 2" dual header/pipes all way from the engine to driveshaft then joining into one trumpet 3" to4"( aboot 12" long) then single muffer 24"x10" diam(95db to 105db depends on near building or in open area) and lynn 's right about tailpipe pointing to the ground to dump its sound
The splitter's better to leave it in the engine, very small number of hp's loss and it's aid to cut sharp sound.
your's best bet is go and see Pip from WGT or Carl from Haywardrotary.
REgards
Ian

[Lynn E. Hanover]

chironwsc, on Aug 30 2008, 11:01 AM, said:

Hi

Thank you for your reply.

The static noise test is at 3/4 revs so approx 7000rpm needs to be 102dba. We also have to meet the 102dba on drive by they don?t give a distance from the car for the noise meter.
What are the approx dimensions of your silencer, length and diameter?
Would a 13b make much more noise do you think than a 12A?
Also the exhaust port splitter is this part of the housing or a removable part we have very few non turbo 13b engines in the UK so don?t have any experience of the exhaust port splitter. Does the splitter affect engine power very much if used?

Thanks
Henry

The splitters take off about 3 HP per housing. They are removable with difficulty, as they are pinned in with a double roll pin. Removal from a junk housing is easy, as you just drill a groove down to the pin and drive the liner out with a punch. To install the liner in the race housing you would want to remove the roll pin from the nonsplitter liner, so as to protect the housing. You can also do both the same way, and the header flange will hold the liner in place. Or, once you have the roll pin out, you can replace it with a length of drill bit shank, that will be held in place with silicone, and after assembly the irons will prevent the pins from moving. You can sort of drill out the pins with a concrete drill that has a carbid tip.

It actually breaks the pin into tiny chunks, but the hole is empty when you finish. The splitter takes out about 3 Db right at the top, so it makes a big difference on the sound meter. The 102 figure is actually down quite a bit from our 103 and 105 Db. You are on a nearly vertical line on an exponential graph.

The Borla is 22" long and has a 4" perf tube in the center with 5 smaller perf tubes packed in the 4" tube. The car is making only 100 Db with the Borla and the exhaust outlet away from the sound meter.

Before the Borla we had a number of mufflers, and two tail pipes that we could switch, so the outlet could be out either side of the car depending on where the track had the sound meter set up.

Borla does not make this one any more, and deny that they ever made this one, maybe just the 4" pipe size.

The Flowmaster was very effective as long as it is at the end of a long system. We melted the first one when it was mounted about even with the driver location wise. It held up fine just behind the rear axle.
You can hammer one to death, and all of the baffles will end up in the rear of the shell blocking the outlet. The shell swells up like a giant pillow.

In this picture you can see the 4" outlet just ahead of the rear wheel.

Lynn E. Hanover

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[j9fd3s]

check out pix of the 787b. i'm not sure if its 102db, but it does have mufflers, and its not really loud

[Lynn E. Hanover]

chironwsc, on Aug 30 2008, 04:15 PM, said:

Hi

Thank you for your reply.

Do you know what the IMSA /GT noise limit was in the day? What engines ran in the IMSA/GT cars are we talking 2,3or4 rotor?
That?s interesting what you say about the pre silencer. So for the 4 rotor maybe it would be an idea to split the 4 pipes in to 2 silencers not sure how this would affect power that?s something for the dyno I guess.
Are you talking about the Scoot 4 rotor car?

Thanks
Henry

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.

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[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]

chironwsc, on Sep 4 2008, 04:10 AM, said:

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

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.

[1962]

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

[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]

http://www.rotaryeng.net/tuned-muff3.gif

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]

j9fd3s, on Sep 6 2008, 11:29 AM, said:

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.

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

[1962]

Lynn E. Hanover, on Sep 6 2008, 09:06 PM, said:

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

How about mazda furai which's got rotary shape muffer?
check it out!
http://www.youtube.c...h?v=oEOHn7rspsk

[1962]

Lynn E. Hanover, on Sep 6 2008, 09:06 PM, said:

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.

Lynn E. Hanover

belived that's system's suit to12APP, not quite sure about 13B

[j9fd3s]

Lynn E. Hanover, on Sep 6 2008, 10:06 PM, said:

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

now that you mention it we put a turbo shaped muffler in our race car, and it dropped the volume, but had to reassemble it after each race....

[heretic]

I am curious to see how long an A-RF style "Swirl Silencer" would last.
They seem to only muffle at full throttle, so it may not be of too much benefit on the street, but for the track it should be stellar. They got a huge drop in noise for less than one horsepower on a 300hp peripheral port.

[BLUE TII]

Yep, I have run my exhaust through a divided turbo without the exhaust wheel in place and it was just at "quiet" as with the exhaust wheel, No exhaust port diffusers, but still no harsh raspy noises like a header produces.

Well, that is exactly like the what Mazdaspeed7 posted :)