Project V8 RX-7: Part 11 – Finishing the Driveline

Project V8 RX-7: Part 11 – Finishing the Driveline

by Jeff Naeyaert

The end is in sight!  Only a couple of things left on the TO DO list and the most glaring is our driveshaft and rear end.  Ordinarily this wouldn’t be a really big deal; you just get up under the car, take a few measurements and head to your local driveline shop where they can either modify your old driveshaft or build a whole new one.  The first option only works if you need a shorter driveshaft than you had before, which happens to be the case for us!  Our T-56 Magnum is a few inches longer than the T-56 transmission we were using in the car when it was LS-1 powered, so the aluminum driveshaft we got with our old kit needs to be shortened.  And hey, while we’re cutting up our driveshaft we might as well slap on one of AEM Electronic’s new Dyno-Shaft on-vehicle dynamometers, right?

After years of development, we had a chance to check out the Dyno-Shaft first hand at the PRI show in Orlando last December…


…and a few months later we were able to get our hands on one of the first production units to try out on our RX-7!  The Dyno-Shaft is a simple to install 2-piece application specific unit consisting of a slip yoke with an incorporated sensing element containing a strain gauge (the black donut looking thing) and a controller housing (top left) that clamps to the tailshaft of the transmission with an optical sensor measuring the rpm of the shaft. 

Unlike an accelerometer based dynamometer whose results can be skewed by a host of environmental factors, the Dyno-Shaft measures a vehicle’s actual transmitted torque and speed at the driveshaft using a strain gauge and optical pickup, allowing it to record and output true horsepower and torque numbers.

You only have to stop and think a few moments to realize how useful a tool like this could be. Not only could it be useful for testing to see how changes made can affect power but also to see what those changes do real time, from anywhere, in real world conditions!

While an engine dyno is good for measuring pure engine power and a chassis dyno is good for measuring the whole package, the Dyno-Shaft isn’t meant to replace either.  Instead, it should be considered another tool for gaining visibility into how weather, chassis setup, driveline components, track surface and even aerodynamics are affecting the torque our vehicle is actually putting to the ground in a real time environment.  Say for instance we’re lifting a wheel in turns, our clutch is slipping, our LSD sucks or we’re getting wheelspin, we’ll be able to quantify the effect of those issues as a falloff in our torque numbers as they occur!  We can monitor that data in real time with any AEMnet compatible device or afterward in data logs collected by a similarly compatible data logger such as the AEM AQ-1 which we’ll be using in this project.

A closer look at one of the pickups within the controller housing of the Dyno-Shaft.

AEM offers 2 versions of the Dyno-Shaft—the Sportsman with a forged steel slip yoke and the stouter Pro Series that comes with a chrome-moly yoke from Strange Engineering.  Apart from the yokes the two units are identical and both capable of measuring up to 5,000 lb/ft torque providing nothing else breaks first!  A single AEMnet CAN communication line powers the Dyno-Shaft and transmits data to the host device or anything that can interpret the AEMnet protocol (such as a digital dash like Racepak, data logger or the yet to be released real time AEM Dyno-Shaft gauge).  No batteries are required to power the unit.

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