1997 Mazda MX-5 Miata Long Term Road Test

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1997 Mazda MX-5 Miata: Kraftwerks Supercharger Install, Pt. 2

December 13, 2010

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What you see above is a peek into Oscar Jackson's brain. That little restrictor pill is an example of the persnickety-ness built into the Kraftwerks supercharger kit in Project Miata, our longterm 1997 Mazda Miata.

I'll spare you an excruciating step by step installation process since Kraftwerks includes instructions far more comprehensive than I could (or would) write here. Instead, here are a few details that illustrate the gray matter behind the Kraftwerks kit.

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That pill lives in the vacuum line that links the supercharger's bypass valve to the intake manifold -- manifold vacuum is what provides the muscle to actuate the valve. As it turns out, sans restrictor, the muscle was too strong and the bypass valves in Kraftwerks' beta test cars would open and close abruptly when feathering the throttle. This in turn made the boost hit and release too quickly, upsetting the cars' driveability. Picture Oscar frowning.

Making the bypass valve actuator breathe through the restrictor's tiny little pee-hole forces it to move more gradually, eliminating the abruptness. An elegant solution. That's Oscar smiling.

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A few more examples -- this cylinder with the extrusions is the reservoir for the Rotrex's magic oil. It's a thing of a certain size, and the best location for it was already taken by the factory horn. The kit includes a lower-profile replacement (also shown here) for the factory hood latch bracket and relocates the horn to the other side of the latch. The lo-pro bracket also serves as the mounting point for the reservoir.

Same goes for the power steering reservoir, which gets a new mounting bracket -- supplied in the kit -- to make way for the intake plumbing. Also, the stock washer bottle of ABS-equipped cars is in the way of the intercooler hose, so Kraftwerks includes a new (factory NB) washer bottle and bracket that mounts near the brake master cylinder.

Suffice it to say that every bolt, clamp, ziptie, hose and bracket in the kit has been similarly scrutizined, and the company tells us they've accounted for every possible Miata build variation of a/c, power steering and ABS. It doesn't get any more 'bolt-on' than this.

It's Traction Fluid

Oh, and that magic juice is a key part of how the Rotrex works. It's a shear-thickening oil (like the stuff in a viscous coupling AWD system) which is critical for the planetary traction drive  to actually transmit torque. Don't go putting, say, gear oil in there else the supercharger will do a fine impression of a torque converter with an infinitely high stall speed.

This means that unlike a turbo, the Rotrex requires its own independent lubrication loop. The oil is fed via a pump in the supercharger's case, and then evacuated by a second integrated pump. In turn the internal planetry drive receives a fine mist of oil rather than being drowned in liquid. The oiling system uses a dedicated filter and cooler (shown adjacent to the reservoir above) and said oil & filter can go 50,000 miles before needing to be changed.

Engine Control

The kit includes a clip-in injector harness, a higher-flowing fuel pump and a black box that extends the pulsewidth of the stock injectors. An integral MAP sensor lets the box know when and how much to modify pulsewidth while an oxygen sensor clamp keeps the stock ecu happy at all times.

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This approach, combined with an auxiliary 8:1 fuel pressure regulator, is said to provide enough additional fuel to keep things rich and cool at full boost and revs. There is no ignition timing control in the black box, the thinking being that the boost is mild enough that the stock ignition curve allows ping-free motoring on premium fuel.

While tinkerers will prefer a unit that is user-adjustable, nonadjustable devices make CARB happy since the car runs exactly as stock during start-up, idle, cruise and many part-throttle conditions. It's a kit intended as a straightfoward and no-fuss way to get a modest but meaningful power bump. 

How much of a bump, exactly? Will let you know shortly.

Jason Kavanagh, Engineering Editor

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