|Last updated: January 21, 1998|
I'll start out basic, and try to define everything. Note that this information will be from my point of view and experience, and info given to me by other 'netters. If you have any questions or corrections, please feel free to e-mail me.
The Miata exhaust system is in three pieces. The header(exhaust manifold), catalytic converter and muffler/tailpipe. These pieces are bolted together, and the system is hung with rubber hangers from underneath the car. An engine is really just a mechanism to get air from the atmosphere, through a combustion chamber and back to the atmosphere as quickly as possible. Bigger, freer flowing exhaust is the easiest way to get noticible performance. Likely due to having an audible portion in addition to the tactile senses. (i.e. sounds faster as well as feels faster)
Many say that the best way to increase the performance of your Miata is to replace the exhaust system. This change can get you 4-18 HP, depending on what you do, who you believe, and other intake modifications on the vehicle. Most people say that the engine feels 'free-er' at the top end, when higher exhaust flows get the most advantage of the less restrictive exhaust.
It is difficult to describe the various sounds. I have not heard them all, and what one person finds melodious, another can find deafening. That said, I'll give my subjective opinions on the systems I have heard.
The muffler is the most commonly replaced item, often with a 'catback' system from one of many aftermarket vendors. Borla ($300), Jackson Racing ($460), Walker ($200), Genie ($378), Peter Farrell ($395) and Candoo ($250-$400) (see also Spare Relocation) all make Miata catback systems. The catbacks have an advantage over simple mufflers in that the pipe from the catalytic converter is larger than stock, and fitted to the system. Some come in normally aspirated and turbo (s/c) models. JR is reportedly high quality, early Borla systems had reported fitment problems (but mine fit fine), Candoo has gotten mixed reviews.
Many have used cheaper mufflers and had a shop build a custom system for far less than catback systems. Examples are Walker Dynamax Mini-turbo Flow ($85) (also see Spare Relocation), Millen (Liestritz) and Flowmaster 3 ($136.72)
Subjective sound ratings
Headers replace the exhaust manifold and are the second most popular exhaust change. Some people say the header is more effective than exhaust, others have said the header didn't make much difference. I've never done one so I can't say from personal experience. Performance claims range from 7-10HP (at high end.) What I can say is that many people believe in them and they do 'open up' the engine more. Offerings on the market are Jackson Racing ($379), Racing Beat ($275), Millen (HKS?)
Several Miatae owners have found renewed trunk space by relocating their spare tire underneath the car. The Candoo system was the first commercially available system with a kit to do this. It has undergone many revisions and is now available in several versions. An enterprising Dan Smith in CA found a cheaper mousetrap and designed a similar system using a Dynamax TurboFlow or Camaro Turbo muffler and a few pieces of locally acquired hardware and a custom shop to do a similar (some say better) system for under $100. E-mail me for details. Drake Daum also wrote a brief instruction on How to relocate your Miata Spare.
Nobody seems to know just how restrictive the 'cat' is in the system, but since headers and exhaust systems free things up, it can't be all that restrictive. I've heard of only one replacement cat, from Rod Millen. It's $169 and is said to be less restrictive, as they don't have quite as much 'catalyst material' as stock. A Millen rep said that it is meant to be a replacement part vs. a performance upgrade. Given that info it probably isn't much more free flowing, but the price is right if you do need to get a new cat.
Again, if you have any comments/corrections please contact me.