Factory Turbo: 2005 Mazda MX-5 MazdaSpeed

The Mazda MX-5 Miata isn’t a car for everybody. If you are too large or if your family is too large, fuggedaboutit– you’re not gonna fit. But for all the people who want a convertible with a driving experience that is sublime, you need to at least consider a Miata. Obviously, the latest generation (ND) has the best combination of styling, performance, etc…but if you want the best bang for your buck — look to the NB generation Mazdaspeed MX-5. It was a limited production version that added a small turbocharger, Bilstein shocks, and a limited slip diff to 5428 versions equipped with the 6-speed manual for the 2004-2005 model years. Expect them to be collectible in the future, but for now, they are affordable. Find this 2005 Mazda MX-5 MazdaSpeed offered for $7,800 in Temple City, CA via craigslist.

From the seller:
2005 MazdaSpeed
VIN: JM1NB354250414532
condition: excellent
cylinders: 4 cylinders
drive: rwd
fuel: gas
odometer: 105270
paint color: grey
size: compact
title status: clean
transmission: manual
type: convertible
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Miata MazdaSpeed MX-5 Run good, did full maintenant on this car. Clean Title. Pure sale.

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I don’t understand the high resale of these turbo models as they were not great to drive. A buddy had one and I got some seat time. The turbo engine was not tuned very well from the factory and most importantly the gearing was horrible. It was a non stop mess of turbo lag, thin power band, and non stop shifting.
Over active WASTEGATE in the Driver’s seat !
So, I had one of these a few years ago. I knew the car’s shortcomings before buying it, so by the time arrived at my door from Ft. Myers, FL, I had a whole slew of aftermarket parts ready to go. Wheels, tires, suspension, FM Little Enchilada kit, etc. In stock form, they’re still quite fun to drive and handle very well. The 17″ wheels and tiny tires detract from the experience a bit, and to your point, the gearing is truly awful.
The real flaw of this car is this: It has the worst engine management I’ve ever seen for a modern turbocharged car. This car is not tuned via Speed Density, meaning while it HAS a Manifold Absolute Pressure sensor onboard, it uses only TPS, RPM, and MAF voltage to determine how to fuel when in closed loop operation. Now, it’s actually not that laggy of a turbo; it uses a ball-bearing GT25 Garrett.
The issue is 1) The tuning and 2) The crazy short gearing. Having said that, you can get much faster spool with a downpipe and exhaust, BUT HERE’S THE RUB: You now have the turbo spooling faster and making peak boost sooner, but because there’s no MAP sensor being used for fueling, the engine just keeps fueling at 14.7 AFR even if you’re in boost. The only way to trigger this car into Open Loop operation (where the ECU runs off of predetermined maps, not sensor feedback) is to jab the throttle and get the TPS reading over (something like) 85%.
Early in my ownership I installed an AEM Uego wideband, and was shocked to see an AFR of 14.7 at 8psi. I nearly vomited, gingerly drove home, parked the car, and contemplated my life. Now, there are effectively no OBDII compliant tuning solutions for this car; you cannot flash the ECU. You can tinker with piggybacks, or go full standalone if you’re state is cool with that. My bandaid was a Voltage Clamp for the O2 sensor. It intercepts the 0-1v signal from the O2 sensor, and using a adjustable potentiometer and pressure switch, you essentially trick the O2 sensor into experiencing a very lean event at ~1psi or so, and the ECU responds with more fuel. As crude as this is, it worked reliably for me, and the AFR richened as I entered and built boost.
Apologies for the grammatical errors. It’s pretty early to be ranting about cars.
No problem – very helpful comment. Thank you.