RoadsterSport HELMHOLTZ MX5 Miata Midpipe with Converter for MX5
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RoadsterSport HELMHOLTZ MX5 Miata Midpipe with Converter


Unique Helmholtz Resonator Makes ANY Muffler Sound Better.

PART NUMBER: 61-1738


Reg. Price: $976.35

Sale Price: $849.00

Converter Size


Due to EPA restrictions, this product cannot be shipped to California.


Free shipping offers apply only to destinations within US Lower 48.

Reg. Price: $976.35

Sale Price: $849.00

Converter Size


Due to EPA restrictions, this product cannot be shipped to California.


Free shipping offers apply only to destinations within US Lower 48.


NOTE we have ended the polishing of the setup because costs have jumped so much and we didn't want to further increase the retail price. Polishing added no function, so we did away with it to keep the price more affordable.

A revolution in exhaust technology finally in a Miata application, this midpipe features an exclusive Helmholtz Resonator that massively reduces the standing wave 'boominess' inside the exhaust system BEFORE it gets to your muffler of choice! Cuts the 'booming' frequencies of 120-130hz by 48+db inside a top up Miata cabin which is a common source of complaints with aftermarket exhausts on the MX5. Bottom line: makes ANY exhaust system sound MUCH better!

Now with option for ultra flow FIVE inch converter. Standard 4 inch converter is great for 2.0 motors normally aspirated, the big 5 inch is for boosted cars and 2.5 conversions. Five inch fits manual transmission only.

We outfitted our Project 2012 PRHT Miata with a computer and sound spectrum analyzer and microphones and drove it under varying conditions and loads with mufflers and without any muffler to measure the frequencies coming out the midpipe. We then use that data and some special software to calculate the particulars of the Helmholtz chamber needed to precisely knock down the frequencies we do not want to hear while allowing the good throaty burble fun sounds to pass through. The result is all the fun, an almost exotic burble throaty result, without the drone! Note it is very dual personality because the effect of the Helmholtz is very frequency specific such that under decel it is mild and quiet, yet when you push hard toward redline it sounds exotic and racy. With the top down lots of fun throaty burble, but dramatically more tame when the top is up. In brief, FUN when you want it, and mild when just cruising.

Designed as a bolt-on replacement for the factory midpipe to carry higher flow all the way out any of our mufflers. Works with ANY of our muffler choices and customers report great results with everything from our RoadsterSport line to the original MazdaSpeed Mufflers. Simple Bolt on. Note you don't get much additional benefit running this Helmholtz with our Helmholtz Race muffler because both helmholtz chambers are tuned to attack same peak drone spike these cars tend to make.

INCLUDES TWO O2 SENSOR bungs which gives YOU the option to later add our RoadsterSport headers and avoid engine codes (by using our optional O2 plug and play extension cords to relocate the factory O2 sensors to before and after the converter in this midpipe).

All stainless steel construction for years of driving pleasure. This MX5 Miata midpipe is larger diameter than stock for superior flow, particularly when matched to our headers. Uses high quality SPUN catalytic converter with metal core (despite presence of converter this unit is not CARB approved...which makes it legal in California only for off-road/race track use). Note that there are states in addition to California that now follow the California model and require CARB compliance, please check the rules of your state before ordering, in some states this setup is legal only for race cars and may never be used on public highway.

This midpipe will raise the final sound level because of the higher flow larger diameter tubing and because the Helmholtz is frequency specific in operation.

SORRY, NOT CARB APPROVED, NOT LEGAL ON CALIFORNIA HIGHWAYS. Sorry, we will not ship these to residents of California.

Read full installation hints and notes in our forum Installation Instruction Section! (Click "Forum" at the top of our site, go to installation instruction section, and look for NC/ND Midpipe install thread).

STR LEGAL under Class Rules Update 2012. Pursuant to SCCA 14.10.E: our cat fits entirely in the space that the factory cat occupied pursuant to SCCA 14.10.E....and Magnaflow certifies the core for use in any application andlt;6.2L and 6000 pounds. Cat core has 2yr/25,000 mile manufacturing defect warranty (no core warranty for boosted or track cars), and the rest includes a lifetime warranty.

BRIAN'S APPLICATION NOTES: This is the ultimate Miata Midpipe and it's a serious revolution in Miata exhaust tech, the secret sauce to making a great sounding Miata exhaust system. I never seriously considered less than our RoadsterSport SuperQ as appropriate for the NC Generation Miata using any performance header upgrade but this midpipe makes ALL our choices MUCH more fun. The nature of this style of resonator is that the targeted frequencies are much LOWER volume and other frequencies not targeted are LOUDER than with our standard midpipe. This dual nature of the performance means when you are hard on the throttle it is LOUDER than with our standard midpipe, but on decel or running in the low rpm ranges where these cars tend to drone this setup is much quieter than our standard midpipe. You get all the racy fun, without the drone.

A little on the science, we targeted 120-130 hertz range which is where most folks report uncomfortable 'drone' or 'boominess' and got a total of 48 decibel max drop right at the 125 hertz level...which is a MASSIVE reduction. Nonetheless, looking at broader range we get an average 20 decibel drop from 115 to 138 hertz with reasonable 8 decibel drop in the ranges of 95 to 115 and 138 to 180 hertz. When used with our RoadsterSport Street header and SuperQ the result to my ears was so calm and collected that I think many would not realize the car was modified. When used with our RoadsterSport Max Power header and SuperQ the sound is certainly still louder than stock and almost exotic when on throttle, fun running through the gears and yet when you back off the throttle and just cruise down the freeway very controlled (no issues listening to music or your passenger, etc).

Video Sample:

Shot on our Project 2012 with our RoadsterSport Street Header, RoadsterSport Helmholtz Midpipe, RoadsterSport SuperQ Exhaust. In this first sample notice what you do NOT hear, I get on it briefly and then engine brake almost down to a stop and during that engine braking the system gets more and more quiet where normal systems would drone as you engine brake down through 3000 rpms to 2000 rpms.

Second Video Sample: Shot from the bumper this clip massively exaggerates the volume but notice again what you don't hear, lots or racy sound when on throttle but every time I close throttle it quickly gets quiet instead of drone like many systems.

And now a more complete driving sample with camera in the driver's space:INTERNATIONAL SHIPPING NOTES: We only ship to USA and Canada but we do have dealers outside the USA. CUSTOMERS IN EUROPE CAN GET THESE IN EUROPE AT THIS LINK!


BRIAN'S Installation Notes: This item is NOT an easy install, though I often install our RoadsterSport items at home on ramps or with jack stands to be closer to the average user experience and snags, with this item I drive to our shop and use the lift every time because two sets of hands and a lift is just about required to get it done without a lot of frustration. Thus, we do NOT promise average Joes can install this without a professional mechanic, does not matter if you have installed 20 other midpipes before, this is MUCH BIGGER than the factory ever planned in the center tunnel and precise fitment on a lift is pretty much required. May not clear some aftermarket braces such as Beatrush or ILM. Clears our own braces and factory braces. Again, this is MUCH bigger than factory midpipe and install needs careful attention to detail, some fiddle time with the slip joint with two people to get it adjusted just right is normal to get it hanging just right when you are stuffing something three times bigger in the available space. We have installed it hundreds of times, all the units are the same because they come from the same JIG, two sets of hands makes it go much faster. That means doing this one at home is going to be too hard for many average Joes to get right with just jack stands or ramps, get the call all the time that it is 'impossible' and we tell them to get the car on a lift, and when they do they consistently report it got done easy once on a lift with two sets of hands. Adjust it too long at slip joint and it will hang too low and bang braces, make it too short at the slip joint in the middle and it will sit too high and tap the differential housing. For these reasons, a professional muffler shop install may be required. Spray a little soap and water on the slip joint between two halves of the midpipe so you can smoothly play with that length and alignment of both ends. You can spend 20 minutes on the first try and not have it right, or spend more time and get it right, we suggest more time up front to make sure you have no points of contact (grab finished install and yank in all directions to see if hit taps anything, adjust again if it does). Note the Helmholtz valve is temperature sensitive, if you live in cold climate just understand it will not do much for you on cold morning starts UNTIL the system is up to normal operating temperature. Please don't make your Mechanic fly blind on the install, instead PRINT THIS PAGE for your mechanic so they know what to look for in doing the install.

Note a few customers have reported strange metal noises from helmholtz chamber, loud enough to hear while driving and from behind the car. No moving parts in the Helmholtz setup but it will capture and broadcast noise from upstream and in our experience this includes stuck open EGR valve, loose O2 sensors, bent valve in the motor, tiny 3 inch O2 sensor heatshield, etc. Also had a customer with busted off spark plug tip that somehow got into the helmholtz chamber and set to buzzing madly. Typical sources of rattle reported turn out to be midpipe set too long at slip joint clamp in the middle and hits X brace below only when car is running, answer is open the clamp nut and push midpipe straight up to make assembly shorter before your tighten that nut again and it will sit high enough to not hit the X Brace.

NOTE that to offset massively higher converter costs we are dropping the full polishing, will update picture soon.


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Customer Reviews

RoadsterSport HELMHOLTZ MX5 Miata Midpipe with Converter

Brian - Thanks for the rapid order fill and shipment. Your installation notes helped out tremendously. Mated this midpipe with the Super-Q muffler. Drone is now gone and nice reduction in nose in the cabin. Love the throaty burble. Wife also noted the difference and loves the results as well. A must buy for your Miata.

First of all customer service was amazing. My midpipe came exactly 1 week after i ordered it and it is such a high quality product. It completely changes the sound of the car so it sound much angrier. I paired this with the street single exit muffler and it sounds ridiculous. It pops on every single up shift and down shift and it burbles a ton on decel. I can't go through a tunnel without down shifting. It also completely gets rid of any drone which is especially good when i have the roof up. Overall the buying experience was incredible and I will absolutely be buying more parts from here, I think headers are next on the list.

I started out with installing the Roadster Sport II extended tip cat back exhaust, and immediately wanting more. The sound was improved but not much better than stock even with out the baffles. Step two was the Helmholtz mid-pipe. This was really a big improvement to the exhaust without sounding obnoxious. As Brian has stated this is the best setup for an automatic. This has been a well spent investment. I'm looking forward to adding headers if I can find a workable solution to an automatic.

I'm not sure why the website tries to scare everyone from DIYing the hemholtz mid pipe. It went on super easy and I did it solo. You need to raise the car high enough to get decent clearance. First thing is to remove the x-brace and remove the old mid pipe.

Next, I mounted the lower section with the hemholtz chamber on the hanger and then connected the upper section to the header and loosely put on the nuts. Laying on your back, you can use your feet to push the lower section towards the axel to give you enough room to slip on the upper section into the sleeve. I didn't have any issues with clearance so there wasn't any adjustment needed.

I installed this along with the RoadsterSport 2 muffler and the catted ceramic coated RoadsterSport street header. I had serious droning issues with a cat back exhaust in my NA that was annoying so this was a big concern for me in the NC with a RHT. There is virtually no drone from this setup and the exhaust note sounds great from outside the car. With the windows rolled up on the RHT, the exhaust is barely audible but still better than stock. I may go with a race or street single in the future in order to hear it from inside the cabin. Overall I'm very happy with this mid pipe.

Really got rid of the booming low frequency drone I have had since put on removable hard top. It was there when I had soft top up but hard top really traps it in cabin.
It was like I had the exhaust leaking into the cabin.
Now it feels like exhaust is finally outside the car.
I have had high quality sound padding in addition to stock carpet padding but still had the boom until this HH mid pipe.

Definitely get it, even if you don't have hard top. Save your ears from permanent hearing loss.

Not sure why Brian's installation notes stress this as not being an easy install - it was possibly one of the easiest parts I've ever installed while under the car on the garage floor.

My son and I just installed the ceramic RoadsterSport Max Power header (not so easy of an install) and the Helmholtz midpipe on his NC3. Took about 9 hours total, but once we had the O2 sensors in the midpipe and slid it under the car, it was a piece of cake to bolt-up and fit in place, assuming you're not doing it alone (even alone I think it would be easy).

Once everything was back together we started the car and went for a drive. Car sounds HORRIBLE with the RoadsterSport Street Single (loud tin can), but this was to be expected. We purchased the Single when we thought we were leaving the to exhaust stock, and the Single sounds amazing in that configuration. Being too embarrassed to drive the car down the street, I immediately ordered the Super Q and it should arrive in a few days. I have high expectations for the Super Q bringing everything together sound-wise, and combined with the first class quality construction of the Helmholtz, it gave it 5 stars.

I'd been running the RoadsterSport MAX POWER MX5 COMPLETE EXHAUST COMBO for about 5 years and although it got a little loud in the cabin between 2.5 to 4k rpm it was tolerable. I did a 2.5L engine swap and used the same system and that changed from tolerable to nearly unbearable. Swapping out the midpipe for the Helmholtz was the best thing I did other than the power gain from the 2.5L conversion. There is no discernible drone or boom at any stage of deceleration and the change in tone on hard acceleration is spine tingling.

I have noticed at start up from cold it 'sings', a kind of higher pitched whistle between 2 & 3k rpm for a minute or so but it disappears completely once up to normal running temp.

Installation is a breeze and anyone with a set of axle stands and metric spanners should be able to knock it over in under an hour.

Highly recommend the O2 sensor line extensions, particularly if replacing the stock header.

What a nice piece. I was running the RS race single with the stock header and mid.
I added the RS catted street header the same time I installed this Helmholtz mid, and there is LESS drone now with the full header system than just the muffler.
This pipe works.
It also sounds great, letting all the pops and burbles through.
And it looks good.
Absolutely worth the extra $$ over a normal midpipe.

Goodwin exhausts are amazing! I previously had purchased the RoadsterSport MX5 STREET Header, BRIGHT CERAMIC FINISH which is beautiful and definitely added some HP to my Miata. I also have a Cobalt Exhaust(sorry, I got it before I discovered the greatness of Goodwin!) So all I had left was to do the mid-pipe and was excited about the Helmholtz mid-pipe. I finally ordered it and was pleasantly surprised at how quickly it was shipped. This is also a beautiful piece of kit and was extremely easy to install. Again, my HP has increased and I am having a blast driving my car and love the sound I am getting out of my car. It is quieter (less drone) at cruising speed but also has an awesome burble on down shifts and great sound on acceleration. Goodwin is the best!! Next on the list is ECU Tuning and then maybe some suspension work, new radiator. I also had purchased the The smartTOP roof control unit from Goodwin. You have a loyal follower and customer for life!

You don't pay good money to make an exhaust loud. You spend money to make it quiet at the right times. That is exactly what this product has done. I installed this along with GWR 1.8 header and Street Single at the same time. This setup sounds like a swarm of bees rushing to attack when you lay into the throttle. Once you are off throttle its very mellow can hardly tell the car has a modified exhaust. No drone just as advertised But it is so much more than that. I'm absolutely in love with this setup who knew a 4 cylinder could sound so mean. I get all types of compliments not just from friends, from strangers who approach me as well at autox or track days ect.

This is a quality part. Even my mechanic commented on the build quality without having to be prompted. This resonator definitely knocks out the drone from my louder exhaust. I highly recommend it.

First off, this is my first Miata, and without a doubt the most fun I've ever had with an automobile! And the best part, my wife loves it, too! Second, I've NEVER done mods to a car but already spent more for fun/upgrades on this one than any I've owned before, and it's been great! Starting with a K&N cold air intake, then the Super-Q muffler, I was hooked on this, much to the chagrin of my savings...! But in a great show of support, my wife got me the Helmholtz midpipe for Christmas! We both liked the sound of the Super-Q and stock header/midpipe, but like others, there was that bit of drone/boom while slowing down that I knew would get annoying after a bit. So, enter the Helmholtz! I actually had some knowledge of the science behind it from some home theater sound mod experience, so it made immediate sense to me. After a bit of a learning curve on the muffle part (and one rounded off bolt later), the midpipe went on without a hitch! It was packaged very well, arrived in perfect shape. From GWR's "how to" forums, I wound just taking off the mid x-brace, assembling the mid-pipe based on the original mid-pipe's length, and was able to install it in one piece fairly quickly, with no followup adjustments! After a few weeks now, it sounds even better than ever, and definitely gives a little more "oomph" with acceleration, especially between 3-6 thousand RPM. I highly recommend this product, and I'm already saving up for the header from GWR!

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