MX5 Parts Stainless Exhaust

Technical Area Engine, Transmission, Exhaust etc
1

Hi all - have a hole in my cat (scrape) and behind in the exhaust, so thinking of replacing the entire system.

understand I have a later model with the longer cat, but wondering if I am swapping the cat out if I can change that to get more freedom - was thinking of getting the three in the links below with the 440mm cat. Has anyone already done this? Is it ok - how much louder is the system on the whole? I wouldnt mind being a bit louder, but dont want full cherrybomb anti-social spec or too much of a drone on any motorway journeys.

Any experience/advise super useful!

  1. My model of MX-5 is: NA 1997 Dakar Edition
  2. I’m based near: Worcester
  3. I’m looking for technical help or recommendations on: exhaust compatibility/loudness
2

The manifold, if anything, quietens down the car.

The only slight issue is that the later cars are missing a bracket for the mid pipe; its not needed. A MOT examiner seeing the unused hanger on the exhaust, might conclude the exhaust is improperly secured. I cut the bracket off the exhaust on my car (a 1996 Eunos Roadster).

My car is subject to the same emissions test as yours, which is a bit stricter than for the earlier cars. I have had the expensive misfortune of finding the aftermarket cats were marginal for later cars. It would pass with the original factory 375mm cat. When I fitted the MX5parts manifold, originally they supplied an adapter to allow me to continue to use the 375mm cat.

Then the cat failed, so I “upgraded” to a 440mm cat, and got rid of the adapter, which caused the caback to gouge the PPF.

I then swapped out the Mongoose catback for a MXparts twin exhaust. Then my trouble started. Every couple of years, the car started to fail on emissions, and a new (aftermarket) cat got the car through emissions. The specialist looking after the car was confounded. It has a very strong engine. Coilpacks, MAS all changed, and he was concluding that I was looking at a top end rebuild. The final hail Mary was to refurb the injectors, which improved things marginally. The car was starting like it had a brand new motor.

So we decided the aftermarket cats were junk. I got hold of a scrapyard factory UK 440mm cat, which cost three times as much as the aftermarket cats. The omens weren’t good. What I got looked 30 years old, with half the heatshield rusted away.

Put it on. Emissions were “perfect”, best the specialist had seen on a 1.8 Mk1.

My car, a 96 Roadster, is supposed to have the slightly higher compression later motor, like yours, but it was swapped years ago for a motor out of a 1994 RS-Limited, but its running off the 96 16-Bit ECU etc.

Based on looking at the MX5parts twin exhause compared to other systems I have fitted over the years, I would not say its the best quality system. My exhaust is louder than the previous Mongoose, but not overly so. But it does drone at motorway speeds.

1 Like
3

Thanks for that, useful to know. Did you try an aftermarket 440mm one before the OEM? Just wondering if I pick that instead of the shorter one, in my head somehow the longer the cat the more effective it should be… could be totally wrong though

4

I’ve been through about 4 aftermarket 440mm cats

1990-93 1.6 Eunos Roadster/Mazda MX5s had a 375mm cat
1993/4-95 1.8 Eunos Roadster had a 375mm cat (it might be 370mm, I think a different part)
94-95 UK and US cars had a 440mm cat; the MX5parts manifold is basically a copy of a US header, I think made in China. Mine cracked a bit after a few years, but has basically been on the car 20+ years now.
Late 95 Eunos Roadsters kept the same 370/375mm cat, UK cars went to 470mm.

For 1992- end July 1995 cars, all cars undergo a full cat test unless it doesn’t match a model in the book, in which case its a basic emissions test. This is the basis of 1.8 Roadsters not necessarily getting a cat test. Pre-August 1995 cars are tested to manufacturer limits, but after August 1995, then satutory limits apply.

From another thread where I compared an aftermarket 440mm cat with 3000kms with a skanky looking factory cat

Test Results

(new Aftermarket cat had been fitted 2938kms before

1st Fail:
Engine Oil Temp:80

Fast Idle
CO: 0.73% FAIL
HC: 60ppm PASS
Lambda: 1.010 PASS

Second Fast Idle
CO: 0.66%
HC: 41ppm
Lambda: 1.000

Natural Idle
CO: 0.34%

Second Test (Fuel Injectors removed, cleaned, refurbed, 279,274kms on them)
Engine Oil Temp: 60

Fast Idle
CO: 0.40% FAIL
HC: 37PPM PASS
Lambda: 1.020 PASS

Second Fast Idle
CO: 0.70% FAIL
HC: 62PPM
Lambda: 1:000

Natural Idle
CO: 1.73% (!!) Fail obviously

Third test; used factory 440mm cat fitted (unknown mileage, but the heatshield was rusted through)

Engine observed to be warm

Fast Idle
CO: 0.11% PASS
HC: 3ppm

Lambda: 1.0000

Natural Idle
CO: 0.48% PASS

This engine has “about” 100k miles on it, but all the peripherals are on 279k kms (engine was replaced at 200k kms, with replacement engine that had about 50k miles)

Now, prior to ~2007-2008, my 1996 Roadster had the factory 375mm cat, and made it through 7 UK full cat tests without issue. 375mm factory catalytic converters are more plentiful that 440 versions.