Here's the sort of innovation that we love to see in our feature cars. But we didn't enjoy the action-packed photo shoot quite so much though.....
Any car with over three times factory power is going to be a bit of a handful.
So when we were out taking these shots of this creatively modified RX4, we asked the owner Darryl to get the car displaying some handling attitude. Some power oversteer for the Nikon, we thought. A couple of passes later everything was okay. "Just one more" called Julian to the buzzing Maz. A change in camera location caught the car at a good angle, but what we didn't expect to see was the car then screeching sideways and out of control towards the inside gutter. Some quick-thinking opposite lock from Darryl saved the day, as the car snapped in the other direction (still with its brakes locked up) and struck the curb with a considerable amount of force, coming to rest about less than six inches away from Julian's parked Skyline GT-R...
It wasn't Darryl's driving skills that caused the problem, rather he was a victim of circumstance. A relatively unfamiliar road, cool tyre temperatures and a 184kW (245hp) at the wheels monster turbo rotary all conspired to really spice things up!
Darryl is just the third owner of this immaculate RX4, having bought it complete with service records which spanned back to the car's release in 1974.
It came with no body rust and was therefore the perfect base for a gradual mechanical build-up. A 13B bridge-port engine was fitted before the turbo engine, and although the bridgey revved to 9500, Darryl's still happy he went the forced induction route. There's a clean idle, quiet exhaust, and better driveability to back his judgement.
He blew two of the 'lucky dip' Japanese import turbo motors before deciding to build a good one in the home shed. Wanting to retain driveability, he kept the gas ports standard, but machined the rotors and fitted two-piece 3mm steel apex seals which aren't as prone to blowing. Other than that, the engine is internally stock, but with particular attention paid to clearances. The standard RX4 oil cooling system also remains in position.
The turbo was also rebuilt (not by Darryl) to high-flow specifications using a bigger compressor wheel in a machined housing. This bolts to the stock cast exhaust manifold. The intake system uses a Maztech modified throttle body, an aftermarket blow-off valve and a custom alteration of the original Series 4 intercooler. Darryl has welded a box around the original core and fills this with water through a Mazda radiator cap mounted on top. The water is then recirculated by two 12 volt pumps (one a deckwash and one a bilge pump) which both push and pull the water through the core. Heated water is then fed into a front mounted Hyundai air con evaporator core before it makes its return journey.
Darryl says this system has reduced the maximum intake temperature down from around 90°
C to 46 degrees - nearly halving the intake temp! Although it hasn't been used yet, a reservoir on the passenger's side of the engine bay is able to be filled up with dry ice to further cool the water in the water-to-air intercooler system. This is ideal for only short spurts and so is strictly a one-shot intercooler.
As the engine was imported from Japan sans engine management, an aftermarket Microtech Digi1 Plus unit has been wired in. This has the potential to control fuel and ignition, but is currently dedicated to just fuelling. Because the previous EFI system used separate 'stand alone' systems, the ignition system was left in place as its spark timing was known to be correct. The electronic ignition uses a re-graphed Series 2 RX7 dizzy with a chopper system within its cover.
The Microtech unit controls fuel by taking inputs from throttle position, intake air temp, coolant temp and a MAP sensor. Standard Series 4 Turbo injectors are still in place, but are augmented by two 12A turbo 880cc extra injectors mounted on the intake. Firing these mirco-fuellers is performed sequentially by the ECU.
Converting from carby induction to EFI meant a high pressure fuel system needed to be installed. Darryl's system uses a Carter pre-pump supplying a Maztech surge tank, which acts as a supply reservoir to a pair of Pierburg pumps. These maintain separate lines right through to the engine bay where they feed the separate sets of injectors. Appropriate fuel pressures are attained with a Malpassi rising rate pressure regulator. One interesting feature of the car is its boot-mounted bilge blower. This sucks out fumes and also cools the fuel in the surge tank, as it gets super-heated from the muffler below. In the past a good quality leather jacket has been destroyed by the hot boot mat!
The exhaust system in disrepute is a 3 inch mandrel bent turbo-to-tip jobbie with a mid mounted straight-through resonator and an Exhaust Technology RotoFlow rear muffler. That last item works very well, according to Darryl who has tried various mufflers to keep the rotary bark down to a minimum while not trading off too much power.
In this mechanical configuration and with 13psi boost, the car has achieved a best quarter mile time of 13.06 at 110mph!
A bit surprisingly, a Mazda 121 5-speed gearbox (similar to an RX5's) has never had a spanner near it since the engine/drivetrain combo was installed back in 1993. Not bad considering the car has tackled racetracks and drag strips countless times! The clutch, Darryl says, is "marginal"; another 10 or so kilowatts and it'd be out the door. It does offer good pedal pressure and feel though, as it keeps a full face heavy-duty disc and a 3/4 tonne Centerforce pressure plate.
The differential uses a 13B housing and axles, a 4.44:1 CIG-locked (ie welded up!) SelectMaz centre and a custom modified tailshaft which achieves its goal of being vibration free.
Slowing the car down are Holden VL Commodore Turbo front calipers acting on Mazda 626 vented discs; a combination which came as a kit from SelectMaz. Three inch flexible ducts are fed by under-car scoops and cool the eyes of the front discs, allowing heated air to exit through the disc ventilation channels. The rear brakes remain drums, but use a custom ventilation duct to the back of their mounting plates. Pads are Metal Kings at the front and Competition Linings at the back.
Sitting low enough to avoid road damage, the 1½ inch dumped Selby front springs are damped by Tokico gas dampers, while the rear leaf springs now have an extra half leaf inserted. They are also damped by Tokicos. Body roll is lessened with the fitment of K-Mac sway-bars measuring 27mm and 18mm diameter at the front and rear respectively. All factory rubber suspension bits have been replaced with Nolathane. The problem of severe axle tramping off the line was also cured by sticking a big pair of slapper/tramp bars under the rear bodywork.
Inside the cabin there's an aftermarket steering wheel, re-trimmed seats, new carpet, velour headlining and an Alpine CD and Pioneer radio/cassette. A VDO 10,000prm tachometer is cleverly located in the factory gauge position plus there's an oil pressure and Autometer vacuum/boost gauge. A locally made air/fuel ratio meter sits atop of the steering column in company with a Fizz turbo timer. Darryl also installed switches to control boost pressure, intercooler pumps and the radiator thermo fans.
The home shed also became an 'in-house spray booth' which saw Darryl and a mate strip and then douse the car in numerous coats of the original Mazda duco. Looking around inside his shed revealed a couple of chairs which looked remarkably similar in colour to the Mazda!
Also in the shed is an LP gas-fuelled jet engine which he's made up using an ex-Mazda turbocharger. It runs an internal boost pressure of up to 21 psi! The neighbours don't like it - with the loud noise and all - but we love to see this guy building stuff that's just so damn tricky!
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