Project RX-7: Shifting into a new transmission

Image by Philip Royle

Project RX-7: Shifting into a new transmission

SCCA / SportsCar Magazine

Project RX-7: Shifting into a new transmission

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In 2011, when SportsCar magazine’s project RX-7 SCCA road racing car was just a glimmer in our eye, we built a glorious spreadsheet listing the budget of what we thought the build would cost. Once everything was thoroughly mapped out, we rescued a 1990 Mazda RX-7 from the junkyard and began to thrash, ultimately building the car for SCCA’s E Production class for a hair over our modest budget. Unfortunately, the project’s funding petered out before we touched the transmission.

Fast-forward to December 2013 and we picked up a used transmission that had Hewland dog-engagement internal components in a stock RX-7 housing. This hybrid setup is used by numerous racers in the SCCA road racing community as, with some cajoling, the magic internals will fit in pretty much any rear-drive Mazda housing ranging from the RX-3 to the NC Miata, and does so relatively affordably. Hewland offers a variety of gear ratios, and you get the speed benefits of shifting without the use of the clutch.

The used transmission did well in our project RX-7 from the moment it was installed, but because this setup is a mixture of race parts and street components, things break. Consequently, while prepping for the 2018 SCCA National Championship Runoffs we discovered the transmission had been abused enough that we were facing a $4,000 repair bill – close to what we paid for the transmission itself. It was time to explore our options.

Shopping for a new box

The secret to speed is a transmission that best utilizes your engine’s power band – and can handle racing conditions. Since the rotary engine produces all horsepower and virtually no torque, rotary-powered racecars seem to benefit greatly from very short gearing splits. Over the years, we’ve tried to find close gear ratios in a variety of transmissions (Miata gears in a stock RX-7 transmission, RX-8 transmission, syncro-based gears from companies like Quaife) but none of these options offered gearing splits as tight as we wanted – and, in most cases, they were using parts designed for street driving, not racing.

Rewind about a year and Mazda Motorsports had just introduced a new line of parts for its aging-but-still-popular PBS dog-engagement transmission; Mazda Motorsports was also finalizing its new EGMT dog-engagement transmission. At the time, we daydreamed about fitting the Mazda Motorsports EGMT setup into our project RX-7, but with a price tag just shy of $10,000, it was out of our reach – or was it? Now facing a $4,000 bill to bring our current transmission back to life (and knowing our current setup may face a similar rebuild cost in another four years) we began to look deeper.

The internal components of the Mazda Motorsports EGMT transmission are built to handle the torture of SCCA road racing competition. Image by Richard S. James

What’s in the box

At first glance, the EGMT 5-speed, dog-engagement transmission produced by EMCO Gears for Mazda Motorsports looked like everything we wanted, plus more. For example, like the older PBS, the EGMT is designed to use all five of its forward gears for racing, with drop gears in the back to allow for easy gearing changes. Our old transmission didn’t come with drop gears, so our experience on this topic was limited.

“This transmission has all of the advantages of the PBS, but with a modern twist,” says Jesse Prather of Jesse Prather Motorsports, who helped Mazda Motorsports and EMCO in the development of the EGMT transmission. “One of the things I always liked about the PBS is you have a drop gear in the back so that you can change the rear differential ratio to one that was never possible – that is a huge advantage. For a guy running a Mazda, you have final drive options of 3.9, 4.1, 4.3, 4.4, and so on, with three drop-gears, you can come up with a ratio that was never made – that’s a big advantage.”

The EGMT comes equipped with a 24/24 drop gear – that means it offers a 1:1 ratio for the internal gears. Swap the drop gear to something like a 22/26, and the drop gear multiplies all of the internal gear ratios by 0.846 before spinning the output shaft. Flop those drop gears so they’re a 26/22, and now you’re multiplying the gear ratios by 1.182.

“Between Indianapolis Motor Speedway, running around here [in the Midwest], and Sonoma Raceway, I have three different drop gears,” Prather explains. “At Indy, my top speed was about 140 mph, around here my top speed is about 125 mph, and then out at Sonoma [for the 2018 Runoffs] I geared for 117 mph. And it’s all just a drop gear change.”

Mazda Motorsports’ EGMT transmission uses a shifter turret near the bell housing. Image by Philip Royle

Notably, the drop gears can be swapped with the transmission still in the car. “You pull the shifter off of the tail housing, pull the driveshaft off and the transmission mount, and then there are eight nuts for the tail housing to slide off,” Prather says. “There’s one nut for one drop gear and a circlip for the other drop gear. You put your new drop gears on and re-install everything – piece of cake.”

Prather points out that this is also made possible by the design of the EGMT – it doesn’t seal with gaskets or silicone. “Everything in the EGMT is O-ringed, which is not the case in the PBS,” he says. “I did one gear change at the Runoffs in 2017 – I yanked the transmission out of the car, stuck it on my bench, pulled the housings, replaced the gear, put everything back together – there was no cleaning, no silicone, nothing.”

Jesse Prather Motorsports offers a shifter designed specifically for the EGMT transmission. Image by Philip Royle

For gearing options, Mazda Motorsports offers a slew of gears for the EGMT, but you may find the supplied gear ratios, which Prather helped calculate, are ample as they offer five racing gears with minimal drop between each gear – and the gearing drop gets shorter as you climb through the gears, offering a mechanical advantage to aid in pushing through the air.

Doubled with the drop gears, we were quickly scratching our heads when it came to potential options should we choose to install the EGMT in our RX-7. But as Prather points out, “You want options, that way you can really optimize the setup.”

Durability and drivability

Honestly, it didn’t take much to sell us on this being the project car’s next transmission – but we needed to justify the cost. It turns out, when you consider the EGMT’s construction, that’s easy to do.

“You can probably take this transmission apart about half as often,” Prather says when comparing the EGMT to a PBS. When we spoke, Prather had just opened an EGMT transmission to inspect the wear on the internals. According to Prather, that transmission had a couple of test days, the Runoffs, and six Majors races on it and, “It looked brand-new,” he says. “I would normally run two race seasons and then freshen up the PBS before that second Runoffs, but as good as the EGMT looks, I’d clean up the transmission, put it back together, and leave it for four years.”

This durability, Prather explains, is due to the intrinsic design of the EGMT. “Normally you’ll see some wear on the dog rings and the gears, but this one is just like new,” he says. “That’s a combination of the proper Rockwell hardness between the gears and the dog rings, and just a superior shifting ratio that helps everything engage quickly and smoothly.”

Speaking of gear engagement, Prather notes that the EGMT shifts better than many other transmissions. “The EGMT uses a six-dog setup, and the fewer dogs you have, the easier it is to shift,” Prather points out. “Not only that, but the dog rings have a slightly different angle on them, which EMCO says makes them engage easier. Having driven a lot of PBSs and now having driven the EGMT, I can definitely tell you it shifts smoother.”

Truly, the only downside we could find is that the EGMT weighs 27 lbs more than the Hewland-geared transmission we were using (16 lbs more than a stock RX-7 transmission). But if you’re upgrading from a PBS, you’ll find that the EGMT is 12 lbs lighter.

With that, we broke out our calculator and discovered the EGMT transmission would cost about $6,000 more than repairing our existing transmission – but considering repair costs of the EGMT are potentially less than half that of our existing setup, the EGMT should pay for itself in four to six years of racing.

So, yeah, we called Mazda.

We’re in

The EGMT is designed to bolt up to a 13B with a stock-style FC RX-7 driveshaft. If you’re installing this in any Miata then you’ll need to have the bell housing modified, and if you’re not using a stock 13B driveshaft, you may need to order a custom shaft. That said, installation in our RX-7 with a 13B was straightforward, but it was not plug-and-play.

For installation of the EGMT transmission, a portion of the car’s transmission tunnel must be removed. Image by Philip Royle

For starters, the transmission doesn’t come with a shifter. Luckily, Jesse Prather Motorsports offers a shifter that, with minimal welding, allows you to place the shifter nearly anywhere in the cockpit. Before you install anything, however, you’ll need to cut much of the car’s transmission tunnel in order to accommodate the EGMT’s shifter turret. We also found that the rear-most transmission mount on the EGMT didn’t line up with the stock location, as the drop gears require the mounting point shift back about an inch. Despite that, installation wasn’t difficult – although it is nerve racking when you first take the angle grinder to the transmission tunnel. While you can pay a shop to do the installation, it isn’t necessary; we did it in our home garage.

The task of installing the EGMT transmission may appear daunting, but this was accomplished with hand tools in a home garage. Image by Philip Royle

So, how does the EGMT drive? For that, unfortunately, we’ll have to wait to find out. You see, in order to install the EMGT we ended up removing the car’s dashboard and various other interior components, so we’re now taking the opportunity to jump on other much-needed projects, like rewiring the car. Once we’re done with that, we’ll build an aluminum box to cover the transmission tunnel hole and hit the track. Indeed, this transmission upgrade is a major undertaking, but the end result is promising to be a game changer for our E Production RX-7.

 

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