The exhaust is split into 4 parts;

Header or tubular exhaust manifold

Downpipe from header to cat with lambda sensor in it

Catalytic converter

Cat back exhaust.

Most replacements are cat-back systems.

Headers normally replace the stock header and downpipe with one part

Roadster had a catalytic warning light to indicate whether the cat is overheating; this is an extra probe into the back of the cat ;The stuff written on your visor is very helpful here - it tells you to stop the car as soon as possible in an area where there isn't any inflammable material. Turn off the engine, wait for it to cool and get your dealer to inspect the car ASAP. The sensor just goes to earth when overheated to melt down… it is not connected to the ECU. Note that my ’94 1.8 Eunos had as standard a special down pipe which allowed a 1.6 cat (in US sizes) to be used – this cat has horizontal flanges front and back and is 13" long – the US 1.8 cat is 15" long and has a front flange bolt pattern that is tilted by 30 degrees (standard 1.6 pattern has the flange bolts horizontal – the flanges are all tilted) . So watch it if replacing cats on 1.8 Eunos cars.

After 1996 (OBD-ii) cars were fitted with a second O2 sensor so that cat failure could be reported . (US… so UK??)

Note that early 1.8 Roadsters have 1.6 cats fitted with longer front downpipes

Note that some UK cars have longer cats with shorter cat back exhausts 47.5cm long cats

Note 1.6 cat has straight bolt patterns front and back while the 1.8 has a 45 degree straight pattern at the front and is longer (even is std form).

There are a couple of high performance Cats out there.

Jackson Racing do a reasonable N/A one but they fall apart…

Flyin Miata do a higher flow one that holds together but is so high flow that it does not warm up enough for MOT tests in some cases.. so hold onto the old one.

Ilkeston, Derby 0115 9440366, stainless with lifetime guarantee made exhausts for Jackson Racing contact Phil Millington

exhaust costs A$351 including insurance plus A$43 for shipping by sea or A$113 by air. In real money, that’s approximately £154 by sea or £181 by air.

– cost form £270 to £500 and allows you to put the spare wheel under the car – what I have

The Toby Weir-Jones way; the config has a straight pipe coming back to the diff, a custom curved splitter assembly that goes around the diff and the subframe brace, then splits off to two glasspacks at 45-deg angles to the rear bumper line. The outlets are then angled again out the tail of the car.

Classic Exhaust Engineers in Egham.

Stainless cat back system all straight through 3 inch bore 4 inch silencer near cat, Y piece to split system in two
two rear 5 inch silencers joined and hung together as one in centre of car twin DTM 3 inch tailpipes
£425 inc VAT, Fitting and lifetime warranty. All hand made to fit the car and excellent quality.

Mk2 Borla from PBC $280, plus $160 UPS shipping plus £60 for import duty and VAT. Total: £335 approx.

Dealer Alternative singles, duals and turbos, Dealer Alternative duals; some have fitted Cherry Bomb DIVER fitted after cat for FM duals .. the new FM duals come with a box here as standard. (25" length, 58mm id, 89 od.)

Moss etc in UK do others..

Donutz do ILM dual SS exhaust for £350

Plus
Mild steel/aluminised systems

Remus: discussed recently. Black painted steel boxes with stainless innards? Only one to have square tailpipe (besides Power Flow, on which you can have anything you like...)

Timax: cheapy steel system. 80-90. Actually quite well finished with a chromed exhaust tip.
Bosal (sold by MX5parts). 109.
Peco: 150ish, 2 year warranty
Janspeed also do an aluminized steel version of their S1

"If my calculations are correct an FM turbo exhaust should flow at least 560 CFM (in other words as effective as a 2.5 straight pipe.) Also what is the flow rate of the High Flow Cat used in this system... I'm wondering how much power is lost in the exhaust. If it were an Ideal world a 300 HP miata would have about 660 CFM, a 250 HP miata would be at 550 CFM to minimize power loss from exhaust muffling to less than 1%." Mark Peugout

Hole in exhaust system before the Oxygen sensor. Because this in effect measures the combustion, i.e. Air/Fuel Ratio, because the sensor sees extra oxygen the ECU thinks the engine is running lean thus adds more fuel when in fact, within the combustion area (bore), combustion was actually O.K.

More fuel = explosion type things going on in around the cat area = melt down.

Holes are usually due to: rust, Cracked weld seams, leaking gaskets.

Custom tubular turbo exhaust manifold

"I can tell you some of the specifics on the manifold though. It is a non equal length 1.75 I.D. stainless steel manifold, and it cracked rather severely. The current one is closer to equal length and also is 1.75" I.D. piping with very short tubes. These headers are not easy to build and the last one had 5 expansion joints to combat cracking... only time will tell if it worked!!! Note that 304 SS for the manifold is difficult to do without intergranular corrosion due to heat and expansion. There are other forms of stainless that work well but may be very hard to find" Mark Peugeot

Are Carsound cats really the best ones out there? They look very well designed to me, with shallow flanges. Jason Cuadra

have flanges and gaskets for turbos etc for custom turbo systems

Also exhausts, intercoolers