Mazda Miata Project Car,1993 1.6L NA Miata at JSC Speed

The little 1.6L motor in the 1990-1993 Miata delivered about 110 BHP new, and many of these powerplants are well into the upper 100,000 mile area. Mine had over 160K on it so I had been looking into anything I could do to maximize the power output of this aging roadster. I already had the Jackson Racing CBE on the car, but I am old enough that I found it's loud tone too much after more than half an hour of driving. Since one of the primary uses for my Miata is competing in SCCA STS2 autocrossing, my search for more power started with my 2008 SCCA Solo rule book:

14.10

The air intake system up to, but not including, the engine inlet may be modified or replaced. The engine inlet is the throttle body, carburetor, compressor inlet, or intake manifold, whichever comes first. The existing structure of the car may not be modified for the passage of ducting from the air cleaner to the engine inlet. Holes may be drilled for mounting. Emissions or engine management components in the air intake system, such as a PCV valve, or mass airflow sensor, may not be removed, modified, or replaced, and must retain their original function along the flow path.

Exhaust manifolds and headers may be replaced with alternate units which are emissions-legal. Relocation of the oxygen sensor on the header is permitted. Alternate oxygen sensors, including heated types, are permitted. This allowance does not permit relocation of the catalytic converter (see 13.10.E). Exhaust heat shields may be modified the minimum amount necessary to accommodate allowed alternate exhaust components.

Catalytic converters may be replaced by aftermarket units. Replacements must:

Be certified for use in that vehicle application by the manufacturer or reconditioner,
Bear correct EPA-mandated labeling,
Be of the OE quantity and type (i.e. oxidation, three-way, etc.) and
Be used in the same location(s) as the OE converter(s). This does allow for high performance replacements, provided they meet all restrictions herein.

With these rules outlined it was evident I was clear to invest in a better intake, a freer breathing header, a high flow cat and another exhaust. First I picked up a cold air intake from SPX. While I didn't notice too much improvement in overall performance, the sound alone made it worthwhile as it helped tone down the exhaust noise. The original, 15 year old cat, was beginning to make sounds like it was a coffee can full of rocks, so a new Magna-Flow direct fit high flow catalytic converter was ordered. I had been investigating headers for a while and narrowed it down to what I wanted: Racing Beat 4-1 header. Once the header and cat arrived I dug into the installation of these new components.

Removing the OEM header was pretty easy, especially since I wasn't worried about keeping it to resell or reuse. I busted out my trusty cut-off wheel and hacked the OEM header off the cat and again at the downpipe joint. Having the parts in three manageable pieces made the job much easier. Dropping the RB 4-1 header into place was a little tricky, but after a few failed attempts I finally got the approach angle just right and got everything all lined up. The new cat required a little trimming of its heatsheild to clear the tunnel heatsheild, this was easy thanks again to my cut-off wheel. I had gotten myself a test pipe from MazdaSpeed competition parts bin and installed this straight pipe for a weekend at the track (leaving the cat sit in the garage until before the next autocross). The exhaust would have to wait a little while yet, but don't worry, it was not forgotten.

JSC Speed's 1993 Mazda Miata Project Car