June 12-13, 2010

We started building our ITA Mazda Miata in 2007. Little did we know it would be more than three years later, on June 12, 2010, before the car would claim an SCCA Club Racing win. The following day, the car took home its second victory.

Neither race was easy. Local ITA competitor in a first gen Mazda RX-7 usually destroys our little Miata. In the past, we’ve been competitive in the braking zones and through the turns, but we always found the Miata’s acceleration a little lacking. The acceleration issue – or, more accurately, the lack thereof – is usually amplified at Auto Club Speedway in Fontana, Calif., due to the speedway’s long front straight. Ironically, Auto Club Speedway was the location of our Miata’s first two wins.

Did we add more power? Nope.

In a previous installment, we covered the addition of a front spoiler, under tray and the removal of the Miata’s side mirrors. Those all aided in making the Miata slip through the air with more efficiency, but we didn’t think that would be enough to get the job done. So with a week to go, we decided to re-gear the car.

Per the Improved Touring rules, cars may install any ring and pinion as long as the gears fit in the factory housing. Our 1996 Miata came with a 4.10, but we changed to a 4.30 when we installed a Torsen diff. At auto Club Speedway, however, the 4.30 would top out at between 116 mph and 118 mph, usually in fourth gear – fifth gear would result in a speed decrease. Swapping to a shorter final drive would lower the theoretical top speed, but increase the car’s ability to get there.

A popular gear set to use for Miatas is the Mazdaspeed 4.8 ring and pinion. The cost for that gear set is just under $400 through Mazdaspeed’s parts program. Unfortunately, the part was backordered. Then we got lucky.

While perusing a forum, we found someone selling a 4.77 ring and pinion out of a Kia Sportage. Apparently, a hot modification in the Honda S2000 world is to install the Kia gears into their Hondas. A little more research revealed that the 4.77 was also used in some Mazda RX-8s, and we knew from experience that the RX-8 ring and pinion was a direct bolt in to a first and second generation Miata. If “A” equals “B” and “B” equals “C,” then by our calculation the 4.77 should fit our ITA Miata. We bought the gear for $250 shipped and gave it a shot. And wouldn’t you know, the 4.77 fits perfectly.

While we haven’t tried them, we did discover that the Kia Sportage has a variety of aftermarket gears available to replace its 4.77, including a 4.87, 5.13 and a 5.38.

With the 4.77 installed, we could now hit 118 mph to 120 mph in fifth gear, spinning the motor to just over 7,000 rpm. The 4.87 gear might be usable in our Miata, but we know the 5.13 and 5.38 would be too short.

Because a weekend wouldn’t be complete without completely changing the car’s setup setup, we decided to test some new tires, so we ordered a set of new Goodyear RS R-compound tires. In fact we ordered two sets: 205/50-15 and 225/45-15. Not a lot of people are racing on these, but we’ve heard they’re as sticky as a Hoosier R6.

We also removed the Racing Beat rear swaybar and installed the 11mm stock rear swaybar.

By the end of the weekend, we’d won two races, one on the 205s and one on the 225s. As of this writing, we’re still sifting through the data to find the advantages and disadvantages of the two tire sizes – but the reality is, the car was fast, both races were won handily and we were very happy with the tires, the gearing, and the front splitter.

Our Miata is now going to sit dormant until the 2011 season, where it may reappear with “STL” decals rather than the familiar “ITA” ones.

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