Steve Brown officially owns a monster. An RX7 13B turbo producing enough power to run a small town. Well, maybe not, but with 433hp at the rear wheels on a lossy Dyno Dynamics dyno, it will at least run an 11 sec quarter mile! That's right, 433 horses, or more Shetland ponies than you can poke a stick at! We take a look at Steve's RX7, it's buildup, and some of the problems Steve ran into along the way.
Steve Brown's rotary fixation began when he owned an RX2 with a mild ported 12A. He had some fun with the car, but rotary turbocharging was beckoning - then the opportunity arose in October of 1998 to buy a Series 3 RX7 13B Turbo. With a ported, dowelled Series 2 engine, 3000-rpm stall converter, and manual shift auto, it was a good entry to turbocharged performance.
The car looked nearly standard but packed a bit of punch, which was great for giving unsuspecting wannabe racers a scare at the traffic lights...
Back then Steve never dyno'd the car, but it did manage a run of 13.9 at 99 mph on about 9 psi boost. This level of performance kept Steve happy for a while, but once the modification bug bit him, it didn't take long for him to make some changes. And anyway, he didn't have much choice when the engine "let go" just before he was about to adorn it with a new turbo, wastegate and manual gearbox!
So, after much deliberation and consultation, Steve's further quest for lots more rotary turbo power began in March of 1999 with a full 13B Cosmo engine rebuild.
With the car off the road for three months, Steve had plenty of time to make sure everything was done properly. He chose a ported JC Cosmo Engine "because at the time it was a bit different." With porting, 3mm double spring seals, Series 4 rotors, and a T04 Turbo with .60 A/R front housing, P-trim exhaust wheel and a 1.0 exhaust housing, it was sure to pack a little more mumbo than the previous Series 2 engine.
Ambient air was sucked through a K&N filter, a huge front-mounted 3.5-inch thick Plasmaman intercooler, and Mazsport 3-inch stainless steel intake piping. A standard Series 3 radiator was used in conjunction with a Series 2 oil cooler to take care of other engine cooling requirements. Exhaust belched out through custom Mazsport 3-inch piping, with a 45mm Turbosmart external wastegate and custom-made exhaust manifold.
A Series 5 manual 'box was hooked up to through a modified Series 3 extension housing with a new Centerforce clutch and 1-tonne pressure plate. A standard 3.9 LSD was still being used at this stage, as were the standard 14-inch wheels that came with the car, making for "a lot of wheelspin, which was a big problem".
On completion, the car stormed out 321hp (on a Dyno Dynamics dyno) at 17 psi of boost. Happy with this configuration, Steve left the car as is for the time being. "It was making some pretty good power," and was great fun on the road.
In September 1999, a Haltech E6K fuel and ignition computer was installed and tuned by Mat the HITman, which resulted in improved throttle response, driveability and economy, and although Steve swears it produced a little more power, at the time it was never dyno'd.
As luck would have it though, the turbo seals were starting to wear out. Luck? Ah, that gave Steve the opportunity to upgrade the turbo with a larger front snail, a modified P-trim exhaust wheel, and a 1.0 housing, designed to make even more power.
The car's configuration was enough to strain out 289hp on only 10psi at those Australian Summernats, giving Steve a 4th place in the Rotary Horsepower category. But soon after the competition, it was discovered that the crank angle sensor had moved, retarding timing during the event. After this was fixed, AJC13B brapped to the tune of 320hp at 14 psi... ahhh, that's better! But with a bit more tinkering to come, Steve was confident the car would produce still more power.
By this stage Steve had decided it was really time to do something about those rims, and dressed the car up in a nice looking set of Simmons FR17s, treading the rear wheels with sticky Yokohama AO32Rs. The handling was vastly improved by Mazsport with King Springs and Koni Shocks installed all round, but brakes were still left in their standard set-up, with only Bendix Metal King pads at each corner to try to contain all that excitement...
But a cracked engine faceplate meant that it was soon time for rebuild Number Two.
Off the road for 6 months, Steve took the opportunity to fit the interior out with a quality Alpine sound system, comprising a CDM7861R head unit, 6.5-inch Alpines in custom door pods, 6.5-inch Alpine 2-ways in the rear, and a 10-inch sub in a custom box . Supplying juice is an Alpine V12 AMP, ensuring Steve has some decent sound (if you can hear it over the engine). More work on the interior included the addition of 45mm Omori gauges to monitor oil pressure and water temp. A 52mm boost gauge fits nicely in the driver's air vent, and a Haltech Haltuner A/F inspects fuel ratios. The only other changes made to the factory interior include a gearknob and Momo Race steering wheel.
A 4.11 LSD Borg Warner based diff was wedged under the rear of the car, with 31-spline billet axles and VR Commodore brakes. Calipers and brake rotors were left standard at the front. Mated to the diff was a 3.5-inch tailshaft fitted with a tailshaft loop for safety. The engine was rebuilt to the same specs, but this time dowelled for extra strength. A new TA45 turbo variant was bolted to the engine, and has remained on the car ever since. This turbo was designed for top-end power, rather than drivability, and "doesn't come on boost until 3500 rpm, and really hits hard at 5000 rpm".
With help from girlfriend Lang, the car was prepped for Summernats 2001, and on the dyno before the competition, the car pumped out 351hp using Elf 135 Octane racing fuel. Steve was disappointed with the Elf fuel as he expected it to help generate more power. He achieved his highest run of 344hp using 14.1 psi to net him 3rd in the Rotary Class competition.
But more engine trouble was looming - before long there was another engine destroying episode. It was "suspected that the engine ran too lean with the Elf in it", wrecking seals and melting an exhaust sleeve! Ouch. Damage enough, not to mention the piece of metal the size of a large coin found in the turbo inlet pipe...
Rebuild Number Three... Thankful that the turbocharger itself wasn't destroyed, the engine was rebuilt to similar specs. But then an R Amimiya twin plate clutch was installed as the previous one was slipping, but during Jamboree 2001 a a nagging fuel surging problem had developed. This limited Steve's quarter mile time to 13 seconds flat, which he says is "far too slow, man!"
With a new 3-litre surge tank, twin VL modified pickups feeding a Carter pump, and two Mercedes Bosch pumps up ahead of that, fuelling would no more be an issue. While this work was being done, liberty was taken to address the whole electrical system, as it had been through quite a lot! Justin Kearns from Haltech removed all the surplus wiring in the car. In case you are wondering, the little RX7 was carrying around 9kg of the stuff! After everything was rewired and running again, the car was looking great, ran fantastically, and was producing bigger numbers on the dyno - and smaller ones on the drag strip.
Reeling off a set of 11-second passes at Australian Supernats 2001 - with a best of 11.1 at 125 mph on slicks - the little Mazda showed its potential in good tune. Steve assures us that with a little more fine-tuning, "10s are on the cards soon".
So Steve went to the dyno competition at Summernats for the third time. With a steady show of strength during the qualifying rounds, he steadily upped the boost and horsepower output of the little rotary. Starting at 10 psi, Steve churned out 354 horses at the wheels. Another strong run, this time at 18 psi, saw a much healthier 427 neddies. This secured Steve a spot in the finals, and he duly took out took the 2002 competition with a meaty 433.4hp at the rear wheels on pump fuel.
They do say third time lucky, don't they? I guess in this case it is true!
AJC13B is a good example of a neat and tidy, well tuned rotary punching out some decent numbers, both on the street and the dyno. The only issues that remain are the spool-up time of the current turbo, and the near standard brakes. Currently, Steve is working on
fitting a smaller turbo to increase driveability, and fitting some larger 4-spot brakes to complete the package.
So, with the original carburetted 13B from the RX-4 producing about 127hp, and AJC13B producing about four times as much power at 618hp (assuming 30% loss to the wheels), can we confidently say that it is four times the car? Well, if you are measuring 'heart in mouth, balls out window' fun, then the answer is a resounding yes!
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