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LS-powered Mazda RX-7 gunning for mid-fours on 235 radials

26 Nov 2020 Features

LS-powered Mazda RX-7 gunning for mid-fours on 235 radials

Ash Mason's LS-powered Mazda RX-7 heads for mid-fours on a 235

THE 235 radial class has really exploded in Australia over the past few years – as has radial drag racing generally. With the 275 class requiring 2500-plus horsepower to be competitive, a bunch of highly refined and super-quick cars have changed to the smaller tyre to make a bigger impression rather than just making up the numbers elsewhere.

This article was first published in the November 2020 issue of Street Machine

One of the real standouts, not just of the 235 class but of the Queensland racing scene of the past decade (stretching back to the Modified Street days), is mechanic and electrical/tuning guru, Ash Mason.

Mazda RX-7

Ash is a car guy through and through, having earned his stripes swinging spanners before opening his own business, Wiring & Tuning Solutions, where he has forged a great name for himself.

At one time he was a rotary guy, which has a lot to do with his current car. It’s a Series II Mazda RX-7 that he owned, then sold, then bought back before making the decision to fit a turbo LS and head to the track.

Read next: VL Calais runs eighth-mile in four seconds on 235 radials

“I don’t know why I don’t see more of these cars as race cars,” Ash says of the little RX-7. “They have a huge engine bay; they are light, aerodynamic and have a good rear-end suspension set-up.

Mazda RX-7

“Back in the day, this was built as a Mod Street Blown car, and all I wanted to do was fit an LS and run eights,” Ash says. “I was working at Hi-Torque Performance at the time and they were pretty much the LS gurus, so it made sense to go down that path.”

The engine has been in the car for almost seven years now, having minor freshen-ups by Hi-Torque along the way. In its current trim, it’s making an impressive 1483rwhp on 31psi, and last year, Ash set an Aussie 235 record with an incredible 4.714sec pass (although that record has since been taken from him by George Josevski in an RB-powered VL, who bettered Ash’s time by just .005sec).

As far as LS engines go, it’s a pretty serious deal, with an LQ9 6.0-litre block with a steel forged crank, Oliver rods, JE pistons and L98 heads, sealed with copper gaskets and beryllium fire rings. The intake was fabricated by Spot On Performance. The mill rests in a mixture of mounts that include the original K-member, chassis rails and the factory rotary mounting points. It’s solid-mounted with a set of V-banded stock VE exhaust manifolds, one facing forward and one back.

Watch next: Eight-second RB-powered LC Torana on 235 radials - video

Mazda RX-7

The Mazda currently runs a single 91mm Garrett GT55 turbo, which is an older Gen 1 cast-wheel item. “We started with a journal-bearing GT42 eBay deal, then stepped it up to a Garrett 47 [before this one],” Ash says. Surprisingly, the old 47 pushed the car to 4.91sec with 25psi of boost on methanol, before the new 55 fell into Ash’s lap at the right time and price. It’s an impressive lump of go-fast, and Ash uses a converter dump valve to help get it in the erogenous zone.

The car went 4.85 straight off the trailer with the new turbo, and with a bit less boost. The team knew it wasn’t going to make the 2500hp required to take scalps in 275, so instead they headed to pointy end of 235.

“At that point Mick Arnold was first into the 4.7s, and I was about fourth on the list,” Ash recalls. “Once I worked out what the rear end wanted, I stepped the boost up 5psi and went from a 4.88 to a 4.74 on a 235. We were stoked; you need to consider that in the States at the time the quickest 235 cars were in the high .50s and bottom .60s.”

Mazda RX-7

Looking further into the set-up, the fuel system uses a front header tank with an Aeromotive Atomic Black Series fuel pump feeding 16 Bosch 2200cc injectors via an Aeromotive regulator. As the car doesn’t run an intercooler, the intake temperatures are off the charts, but the engine is getting massive amounts of fuel to cool the mix and is set up with EGTs and all the regular Haltech engine protection safeguards.

“I have recently fitted the new NEXUS R5 VCU by Haltech, which I would rate as the best experience ever. It’s frigging amazing; it’s incredibly fast and does so much so easily. I can’t wait to test its capabilities.”

Mazda RX-7 engine bay

At 2800lb race-ready, Ash’s RX-7 is light. The body and suspension haven’t received many mods. The rear end has been swapped out for a nine-inch with 35-spline axles, built to Mod Street rules, which stipulate factory locations for pick-up points with adjustable arms permitted. Other than that, it has a set of double-adjustable coil-over shocks and a wishbone track locator. The 235 tyres are stretched over a double-beadlock 10-inch rim, and they look every bit as impressive as a 275 from behind the car.

As I write this, Ash remains in the number two spot in the national 235 list, with the JW Automotive VL Commodore of George Josevski ahead of him by the tiniest of margins.

“When I started this deal, I dreamed of making 1000rwhp, and it made 7-800hp straight up,” Ash says. “It’s been an evolution of time, learning and money. The original plan was to run an eight-second pass on a 10.5in slick, and then I went to 275 and the car went quicker: 5.30 on a slick and straight to a 5.0 with a radial.

Mazda RX-7 engine bay

“You need to remember that the window where it works on a radial is narrow, so you have to find the sweet spot,” he continues.

“Some guys go out, smoke the tyres and say: ‘That’s junk’, but the reality is you need to spend more time than that. It’s been all about power management. When I first started with the car, the first year we won the Modified Street Championship. We weren’t the quickest by any means, but we were consistent.”

As for moving forward, Ash states: “We just have to wait for COVID to rack off so we can race! Hopefully Kenda will be on in Sydney if the track gets completed.”