Hello everyone,

I've searched this before posting and I have a few ideas already, but nothing will be like asking directly as I'm not sure it will fit.

I have a roughly 340-350hp single turbo FD running a custom 3" end to end exhaust. Now, I'm also tracking the car and it's already reaching 97db where most track are 95db max around here. Track days guys have been lenient so far, especially seeing a cute FD getting some track time, but at some point, I'll be rejected and this will hurt having driven a few hours for that :/

Also, the car has an awful droning between 3k to 4k rpm when the car is at temperature, and I'd like to make it all right as a daily drive too, without compromising much on the performance if possible.

What are the most silent exhaust for a tuned single turbo FD that would still allow a proper airflow through ?

Thanks

Kieran

 

Love my racing beat dual tip, really accents the rotary sound, second one ive owned after trading the last for an hks hi-power before making the switch back. 3" piping so itll still flow enough for your power levels.

 

Quitest exhaust I've heard on an FD was the Re amemiya dolphin tip. Specifically the muffler (not canister) subtype with the double sleeve tip. Quieter than the RB dual.

7
RE Amemiya New Dolphin Tail Muffler Mazda RX-7 1991-2003 - REA-M0-022036-030

 

Largest packed perf tube resonator with stainless then rockwool into a twin tube packed rear muffler.

AES in Australia is the Gold standard for high flow, low volume turbo and ported rotary/high power Japan turbo stuff. My FD has what was the spare 3.5 inch into twin rear muffler for Ric Shaw's old Nurberg 24 hour car.

If you are worried about cruise drone add a Helmholtz tube as well.

https://super-null.com/drone.html?fb...MARCanXDKRQpuw

 

Usual limit here is 95db at 30m, how close is the one in question to cause probs?

Even with empty cans, turbo rotaries don't seem to trouble the meters here, athough if you have a few miles on it, cutting it open and repacking may assist. Do you have a direct outlet pipe rather than a downturned tip........or maybe you're running a side exhaust!

 

Exhaust note isn't ALL reliant on just the catback. Tuning the sound is a collective effort starting post downpipe. Vibrant makes resonators that can be welded into the exhaust kind of anywhere. Kakimoto does this with their cat backs. Your noise level may not necessarily be an all cat back "issue".

To answer your question directly though, the re dolphin tail and the racing beat are the 2 quietest catbacks I've interacted with while using the same resonated midpipe.

Your droning is all harmonics and can be tuned out with either a (better) resonator, a different catback or adding a resonator in a different location.

Considering the cost of replacing the catback, I would recommend starting with adding a vibrant resonator somewhere in your exhaust post downpipe. I don't think it will matter a great deal where, just somewhere it fits cleanly.

 

This is very correct information.
I do not have any experience with the vibrant resonators/mufflers. I have been using the Magnaflow and recently switched to the Borla XR1. I highly recommend both. what has worked for me is the 5x8 oval resonators. the longest you can fit there the better. I currently have 2 x 24" resonators (one in the mid pipe and one as a tail pipe) and my exhaust is very quiet and i am running 4" diameter exhaust front to back

 

The magnaflow unit sold by banzai is what we default to on just about every car so absolutely, a magnaflow unit is great. It's convenient to be able to just buy it and bolt it in. For cars that are not FDs we use vibrant.

Size, shape and style are assessed based on application but I can say they are VERY good from all aspects. I think it would be safe to say any actual name brand resonator would be good.

For the fd, oval shape is a must if using it in the factory cat location. Anywhere else youll need a round one. You COULD use a round in the stock cat location but it wouldnt be an effective use of the real estate.

 

Hello,

First of all, thanks for all these answers, it makes me feel like I'm not alone, despite the fact that you guys are all around the globe

I think the regulation around here measures this at like 80cm of the exhaust, with a 45° angle from the ground or something, which is way harder to pass for a tuned car.

Most track have this 95db limitation, only bigger ones can go between 100db to 103db like Le Mans from what I recall.

I actually didn't mention any part of the exhaust to keep the question as opened as possible. And I agree with you, I think the mid pipe could actually be the source of my problem as it seems to be touching the transmission protective thingy.

I'll check Vibrant & Kakimoto, didn't know about these, thanks.

I'm having a hard time to find any reference of what you're proposing on the web, and the link you gave is down from my end :'( But Thanks anyway

Thanks. The RB & Re-Amemiya are actually always the one mentioned, and also by this Slip Angle guy :
He claims that the RB was actually too silent for him, and he went for the Re-Amemiya. Now I wonder if that's really true but he seems happy that the Re-Amemiya is turned downward to spit flames to the ground, and I agree too

Now one question, is the RB dual tip more silent than the RB single?

I also got the car quickly up to take a few pics and get measurements as even if I'm willing to buy some new cat back or mid pipe, I'm still afraid of the length of the custom elements the previous owner had done. From what I saw, and compared with Internet pics, I think only the down pipe is custom since it depends of where the single turbo was placed. Here are the dimensions of the rest in approximate length:

• Cat back : 139cm
• Mid pipe : 100cm

Does that look normal to you guys?

If so, I could definitely replace them with aftermarket parts without having to change everything, and even go progressively. As a good surprise, I could see that the previous owner had installed some RB exhaust flange.

Some pics now :

 

Hopefully this one works. They are real and they work for a target frequency. They are used on everything up to and including multi-megawatt mine ventilation fans pushing hundreds of cubic meters of air per second to mitigate resonance at specific frequencies.

https://strikeengine.com/helmholtz-r...j-pipe-length/

 

one of my home tracks is Laguna Seca, which does 92db on a normal day. since the sound meter is drivers right between turn 5 and 6
people add pipes on that point away from the sound meter, try searching Laguna Pipe

 

I'm running a race cat, one large resonator/straight through muffler, a second small resonator. and one of these: https://xforceusa.com/products/3-inc...inch-twin-tips. You can incrementally close it until its quiet enough but I wouldn't go full close in a race environment.

 

SP Mufflers out of Australia. They have one of the largest cans on the market (10×7” oval muffler that is 16” long) which is a fundamental acoustic property for reducing the exhaust volume. The quality of their mufflers is top notch and are an excellent price, especially with the current exchange rate:

https://spmufflers.com.au/collection...-dumpy-bolt-on

I used one of their 8x5" oval mufflers as a center resonator to further reduce the drone and overall exhaust volume:

https://motoiq.com/project-fd-rx7-re...d-sp-mufflers/

 

Tanabe Medallion Touring is pretty affordable and sub 95DB, huge muffler and pretty classy looking!

Dolphin tips are always a win on a rotary for me though, if you can afford the RE exhaust that's the sexiest thing out there.

 

Yes it does, thanks! The other one have dead DNS apparently.

It's beautiful that you can input your droning frequency for them to provide a pipe that will kill it.

Ah, I see, that's a fun anectode Poor cars though, the pics that I see on google image make my eyes bleed

It seems very good but at the same price, I have the midpipe as well with RB or Re :/

That's really interesting, it adds a lot of possibilities, and the finish seems really good.

What interest me is that you're running a race cat as well, do you have a tuned FD as well? If yes, how is it handling the amount of power?

I saw this Re-Amemiya cat while checking for their products and it seems interesting, just riding in the FD for 15min and you and your clothes stinks. If their cat could sustain a 350hp FD on track and some spirited street use, I could buy this instead. I'll probably have to re-tune the car though.

What are your thoughts on this?


Also, does anyone know the difference between these two Dolphin mufflers?
- https://reamemiya.us/products/fd3s-9...-mufiler-90sub
- https://reamemiya.us/products/fd3s-n...n-tail-muffler

Anyway, the previous owner confirmed that the exhaust is fully custom and that OEM might not fit directly but he suggested some exhaust braided pipes or exhaust compensators to fit the gap. He said that it's needed anyway with all the engine motion that will put some constraint on the pipes. I asked RB their exhaust an mid length just to have an idea.

 

I'm blown away at how quiet my RE-A TI dolphin tip (double sleeve tip) is with my Knightsports high-flow cat. I'm glad to see you say that, it confirms I'm not crazy. Also, I can show this to my wife....she doesn't believe me when I say the car is quiet hahaha

I believe the difference is the I.D. for the two. the "90sub" (first one) is a full 90mm piping with a 101mm tip (not double sleeved). The second would be a lower boost application 80mm piping and 90mm tip (double sleeved).

*Edit* I believe Quin (from your post earlier) has the 90sub version. This would explain the extra sound compared to the RE-A version ArmenMAxx is referring to.

 

So you own this one right? I thought at first reading your answer too quickly that you had the Titanium one, which is apparently not sold anymore Your wife might not kill you for the noise, but probably for the 1500$ spent



I actually like how it looks and if it's really silent, I could try this one first as I already have a resonated mid pipe. I don't have another option at RE-A anyway since:

• 90sub is not the good diameter anyway
• New Dolphin twin is only available on RHDJapan which is killing me on the delivery with a total price à 1130€-ish : https://www.rhdjapan.com/re-amemiya-...-fd3s-13b.html

The twin is just 100€ less but if nobody can vouch for the new one, I guess I might as well take the RE-A twin.

 

I re did my engine a bit ago but havent had it on the dyno. My last engine was at about 411whp with a race cat, I'm somewhere between that and 450. I have an Emtron standalone. The main thing with these race cats is that they don't really do much until you beat on it or have been on the highway for a bit. Any change I make I check my tune, but I do it on the street and its VE calculated so I don't really have to do a whole lot if anything.

 

Just throwing this out there: A well tuned street FD using a modern ECU, should not make your clothes stink even without a cat. These days relatively lean idle AFRs as well as proper stoich cruise AFRs using closed loop ignition and fueling strategies to combat the finnicky low torque/partial throttle and thirsty behavior of the rotary make for a pretty easy to live with car.

Making power and driving OK doesn't necessarily mean a car is tuned 'well' for street use.

 

Yes and no. There is always going to be the oil consumption aspect, whether it be from the OMP or premix or both. I personally would still tune on the side of caution and have it a little richer than perfect for an added safety net to help negate detrimental effects of possibly not as good quality of fuel, extreme temperatures etc. (which I know modern ECUs have a million sensors you can add to combat these.) This is me personally, not saying its the right way but maybe years of tuning these and seeing a fraction of a second of a lean condition destroy a $15K build, I would rather not chance it. Sensors go bad or get lazy, stuff happens and Murphy seems to be always around to lay down the law. Rob Dahm has proven that having all the correct sensors and tuning to the limit can be done. He's proven when the safeties in the ECU are properly setup, it can save engines......but its also $$$$ to obtain and properly install all the different sensors available to make this happen. So your general street build usually won't have everything available installed. I am starting to look into this for the future and quickly found that the sensors and supporting equipment can easily cost more than the standalone itself which most people won't want to do. You generally have people use the basic functionality and sensors to support it, but in order to really make it a "modern" setup, its going to be very pricey.

 

Almost everything you're speaking of is in relation to high load situations, which again will not make your clothes stink by being in the car for 15 minutes and have zero impact on tuning for the street. With regards to oil consumption - I premix all of my rotaries, my swapped MGB is side piped, running stoich on cruise and avoiding the old addage of 'more fuel better' when you have the opportunity to combat loss of torque by reasonably increasing timing outside of the main timing map makes for a very well behaved and (relatively) smelling car. Will it ever be as nice as if you're running a cat? No, not at all, but gone are the days and requirements of PFCs and other poorly tuned cars with no reasonable way to build in closed loop strategies that OEMs use to make the car livable.

 

When I had a car with the sunroof, that is when I would usually get the most smell at higher speeds like driving on the highway. With no sunroof its not nearly as bad. I definitely agree you can cut down on it but without a cat, but you will always get enough stink for people to complain. Even piston cars I build and tune at perfect stoich or even a little lean stink. With a Modern cat that can support your power goals, I don't see a reason not to run one......but I'm also getting old and have spent plenty of time with my non catted cars (not just rx7s.) The Wifes S14 is still catless and will probably stay that way because its more of a race car and she likes it that way. It doesn't get driven much so its not that big of a deal.

 

Again, running stoich with high ignition under low load you will not have that problem. I'd venture to guess that if you somehow have exhaust fumes being injested into the cabin on a relatively low pressure area IN FRONT of the standard exhaust exit you may want to look at a secondary source of your problem. The MGB I mentioned in my last post literally has no top, and has a 3" side exit in front of the rear passenger wheel - at cruise theres no issue, at highway theres no issue, at a stop sign I can smell a whiff every so often but again not enough to work its way into my clothes - which was the start of this conversation.

 

This has something to do with the low pressure behind the car allowing the exhaust to creep up through the sunroof when you have it open. Nothing special about the car, HKS hi power catback, stock twins etc. Had the same issue with a 2G eclipse, S13 and my FCs over the years. When the sunroof is stilted up, it must create some sort of low pressure to let this happen. Didn't happen if the sunroof was closed so it is 100% tied to that. People still complain about my current FD which is essentially stock. Still stock cat and air pump and running great. Its just something we have to deal with. Mine even stinks up the garage more than a standard piston engine when I have it running and again, totally stock emissions wise.

 

This is kinda true even just starting and running in the garage actually.
I just started tuning my huge streetport single turbo FD on id1050xds pri w/ elite on NSP. Ported polished XS LIM and Turblown UIM.

Almost zero stink, not much added fuel for cold start, can idle surprisingly close to stoich.

Much cleaner running than my old tuned single turbo FC with denso 720cc and E6k.