RoadsterSport Helmholtz MX5 Midpipe 4 inch Converter - Suits 2.0 NC Models - GR-031 61-1738-4

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  • $1,439.00
  • Regular price $1,849.00
  • incl. GST


Unique Helmholtz MX5 Resonator is the Ultimate DRONE Prevention!

Comes standard with HIGH FLOW 4 INCH Catalytic Convertor.  Standard 4 inch converter is great for 2.0 motors normally aspirated, the big 5 inch is for boosted cars and 2.5 conversions and can be found on our product page. Five inch fits manual transmission only.!!

A revolution in exhaust technology finally in a MX5 application, this mid-pipe 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 MX5 cabin which is a common source of complaints with aftermarket exhausts on the MX5.

We outfitted our Project 2012 PRHT MX5 with a computer and sound spectrum analyser and microphones and drove it under varying conditions and loads with mufflers and without any muffler to measure the frequencies coming out the mid-pipe. 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 sounds to pass through. The result is 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 deceleration it is mild and quiet, yet when you push hard toward redline it sounds exotic and race-like. With the top down lots of throaty burble, but dramatically more tame when the top is up.

Designed as a bolt-on replacement for the factory mid-pipe 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.

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

All stainless steel construction for years of driving pleasure. This MX5 MX5 mid-pipe is larger diameter than stock for superior flow, particularly when matched to our headers. This mid-pipe will raise the final sound level because of the higher flow larger diameter tubing and because the Helmholtz is frequency specific in operation.

BRIAN'S APPLICATION NOTES: It's a serious revolution in MX5 exhausts, makes just about any muffler combination MUCH more exciting. I never seriously considered less than our RoadsterSport SuperQ as appropriate for the NC Generation MX5 AFTER adding any header but this mid-pipe makes ALL our choices MUCH more exciting, particularly after header install. NONETHELESS, this mid-pipe is NOT for the timid. Why? Because the nature of this style of resonator is that the targeted frequencies are much LOWER volume and other frequencies not targeted are much LOUDER than with our standard mid-pipe. This dual nature of the performance means when you are hard on the throttle it is LOUDER than with our standard mid-pipe, but on deceleration or running in the low rpm ranges where these cars tend to drone this setup is much quieter than our standard mid-pipe. You get all the sweet sounds, 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.


BRIAN'S INSTALLATION NOTES: This item is NOT an easy install FOR SOME, 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 hoist every time because two sets of hands and a hoist is just about required to get it done without a lot of frustration. Thus, we do NOT promise average Joe's 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 Joe's 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 hoist, and when they do they consistently report it got done easy once on a hoist 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. 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.


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: