DVITRX - Paul's 1974 Mazda RX-4 Sedan

 

Story and Photos: Ben Winstone

 

Ten-point-three-five seconds at one hundred and thirty-seven miles per hour. By the time you've read that first sentence, Paul Power's 'DVITRX' RX-4 sedan is probably 1/2 of the way down the drag strip. Yes this car has only one purpose, and that is to go fast, really fast...

 

Originally purchased from a female owner with a 12A Turbo motor sitting in the engine bay, Paul took the car to Vlad Berak, proprietor of Melbourne rotary specialists Rotorworx for a retune. The car then ran a best time of 12.6 @ 110mph. However, by then, the rotary bug had bitten so to speak, and Paul decided to ditch the 12A motor and go for the hugely popular Series 4 RX-7 13B Turbo motor.

 

Deciding to go with a full-house motor from the start, rather than just a standard 13B Turbo conversion, Paul had Vlad take a stock imported 13B Turbo motor and give it the full 'worx' in preparation for the power and times it was expected to produce.

 

A Series 4 motor was used because the rotors have a lower compression ratio than the later Series 5 motor, which is helpful when dealing with big power and turbocharging. From there, the block was dowelled, which is a process of adding several extra metal dowels into block in an attempt to add a lot more strength to the motor and prevent it from 'twisting' under heavy loads. The factory ports were also attacked with the die-grinder and are now larger 'turbo extend port' sized. The actual rotors were also clearance during this preparation, and the factory 2mm apex seals were also retained.

 

The standard 13B turbocharger was thrown away and in it's place is a large Garrett T04E unit with a 66mm front wheel, becoming what is more commonly known as a T04E/66 turbocharger. This is mounted on a custom exhaust manifold, with a 45mm PSR external wastegate handling boost levels and proceeds to pump 25psi of air through the custom-made large front-mounted intercooler, before entering the motor through a custom Rotorworx log-style plenum chamber which replaces the standard Mazda unit. These plenum chambers offer a lot more flow and allow a greater amount of air to enter the motor when compared with the standard manifold. A 3-inch exhaust dumps straight off the turbo and leads to a muffler at the rear of the car, the free-flowing system sounds great and allows the car to make all the right noises when its in action.

 

From there, a Microtech MTX-8 engine management system controls the ignition and fuelling needs, which are taken care of via a large fuel system setup comprising of a custom made surge tank mounted in the boot which then feeds two Bosch 909 fuel pumps before pumping the fuel through two 12A Turbo primary injectors and two Bosch 'Indy' 1700cc secondary injectors which come into action higher in the rev range.

 

This setup was good enough to reel off a massive 378kw (507hp) at the rear wheels on 25psi on a Dyno Dynamics chassis dyno.

 

Trying to put this much power through a standard RX-4 driveline setup designed to handle around 100kw would obviously not last very long, and it would only be a matter of time before the gearbox and diff internals were left scattered all over the road or racetrack. So Paul and Vlad decided to undergo a major upgrade of the driveline components.

 

The Toyota parts bin was raided, with a Supra 5-speed gearbox being fitted, which is a stronger box than the standard 13B Turbo unit, using a 3-inch heavy duty tail-shaft to transmit power to a Hi-Lux diff, which was used as an alternative to the heavy yet super-strong Ford 9-inch diff, because they are still able to handle large power loads, yet are a lot lighter than the Ford units. A 4.3:1 ratio is used in the diff.

However the strength of these parts may also be nearing a limit, with the car breaking a gearbox at a recent Heathcote event.

 

As for braking upgrades, well there are none! The car still uses the front disc/rear drum setup that RX-4's came standard with. Suspension-wise it is a similar story, with standard shocks being used with the standard coils up front and leaves on the back. A two-link setup is used on the rear to help avoid axle-tramp and assist the car in launching straighter.

 

The car rolls on 15-inch Performance Challenger wheels up front, with wider 15-inch steel 'stocky' wheels on the rear, like mentioned early, Paul's priority is on going fast, not looking flashy. However on the track, the car uses 26x8.5-inch slicks on a 15-inch wheel for much more grip.

 

The neat exterior of the car, resprayed in a bold red, may look plain compared to other rotors out there, except for the bonnet scoop, providing just a small hint at the fury that is present under the bonnet. The lack of exterior features, combined with the wheels, help to create a great 'sleeper' look, tempting other drivers at the traffic lights who may not be familiar with rotors into something they are going to regret.

 

Inside the comfort zone, the car is reasonably restrained with only a small boost gauge and shift light added, along with a turbo timer. The front seats have been replaced with bucket racing style seats trimmed in red vinyl, the rear seats have also been retrimmed to match the fronts, and suit the exterior of the car well. A sports steering wheel has also replaced the large factory tiller.

 

Above all however, is the fact that the car is still driven regularly on the street by Paul, where it uses 14psi of boost instead of 25, however it "hasn't lost a race yet" with this setup, and from the looks of it, doesn't look like it will for some time...

 

Contact:

Rotorworx - 4 Disney Avenue, East Keilor, (03) 9331 7756.

 

Model: 1974 Mazda RX-4 Sedan

Engine: 13B Twin Rotor Turbocharged

Engine Modifications: Fully prepared Series 4 13BT motor (including dowelling, clearanced rotors, and extend porting), Rotorworx custom inlet plenum chamber, Garrett T04E/66 turbocharger, custom-made front-mounted intercooler, two 12A Turbo injectors (primary) with two 1700cc Indy injectors (secondary), two Bosch 909 fuel pumps, PSR 45mm external wastegate, 3-inch Stainless-Steel exhaust from the turbo back, Microtech MTX-8 engine management system.

Driveline: Rotorworx steel flywheel and heavy-duty clutch package, Toyota Supra 5-speed gearbox, heavy-duty 3-inch tailshaft, Toyota Hi-Lux 4.3:1 differential.

Suspension & Brakes: Two-link rear suspension setup, standard coils (front) and leaf springs (rear), standard RX-4 disc brakes (front) and drums (rear).

Performance: 378kw (507hp) @ wheels (25psi), 10.35 @ 137mph.

Wheels & Tyres: 15-inch Performance Challengers (f), 15-inch Steel wheels (r), 26x8.5-inch slicks on a 15-inch wheel for the strip.