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Speedometer
Next up, the speedometer is a little more tricky. Our T56 Magnum transmission outputs a 17 pulse per revolution signal (or about 4,000 pulses per mile) but our Mazda expects 8,202 pulses per mile—a factor of about 2x. To correct this we turn to the Dakota Digital SGI-5 Universal Signal Interface Unit inherited from our previous swap.
This little $80 box takes just about any digital signal and converts it up or down to whatever ratio you need with the push of a few buttons and DIP switches as prescribed by the included lookup guide. Connect the unit between the bulkhead’s vehicle speed signal wire and your speedometer wire, give the unit some power and you’re good to go! We can’t test to see if our ratio is correct until the car drives, but even then there are buttons to manually fine tune the ratio up or down.
Oil Pressure
For the stock oil pressure and water temperature gauges we reused our stock Mazda sensors. Chevrolet puts a pre-threaded bolt-on “thingy” just above the oil filter that is the most common place to mount an oil pressure sender. Unfortunately, the pre-threaded portion is too large for our sending unit.
Rather than build an odd adaptor, Howard from Technosquare surprised us the next day when we came in with a beautiful new “thingy” he machined out of a hunk of aluminum!
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| On the left is the stock “thingy” that bolts up to the LS oil pan. On the right is Thingy 2.0 threaded for our oil pressure sender. |
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| The new “thingy” positions the sender close to the engine providing plenty of clearance for any future headers we may build and even has room to tap another hole for an oil temperature sender in the future. Thanks Howie! |
