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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Wednesday, May 30, 2012 10:12 PM
Hey Team,
My name is Aimee - my Partner and I are from New Zealand and we have been following thie build with alot of interest and admiration! It is something we have been wanting to do for the past 2 years and finally we have gotten our hands on an amazing rolling body to work with...we are just in the second faze of figuring out 'what to keep and what to throw away'

This whole site has provided us with the inspiration to build up our RX7 (however due to cost it will more than likely be an LS2)
Needless to say we can't wait to here this thing fire up - love the exhaust work, its going to sound amazing!

Keep up the good work!

Thursday, May 31, 2012 1:29 AM
Awesome write-up, Jeff! I have been wondering how the Dyno-Shaft mounted up to the driveshaft in the real world.

Something that caught my attention was the use of the word "yolk". The actual term is "YOKE", and is named after the devices they use to tether a work animal (mule, ox, etc..) to whatever load or object they are pulling. The driveshaft yoke resembles the shape of the area used to hold the animals.
Jeff Naeyaert
Jeff Naeyaertlink
Thursday, May 31, 2012 1:41 AM
DOH!! good catch man, thanks! Globally changed :) ...I need to lay off that sweet berry wine!

Aimee, thanks for the kind words! Nothing wrong with an LS2, even the LS1 is super nice in the RX-7, you won't be disappointed!
Dusty Duster
Dusty Dusterlink
Thursday, May 31, 2012 4:27 AM
Aimee, we are expecting to see a build thread on this in our forums!
Dan DeRosia
Dan DeRosialink
Thursday, May 31, 2012 6:00 AM
So far so good! And damn I've been lusting after that dynoshaft gizmo since I first found out about it. It's funny; about 5-10 years ago, I saw a presentation at SAE World Congress by Sauber (of F-1 fame) I think it was about something similar. Now? Something you can just buy for reasonable bucks. In my dream world I'd like one on each halfshaft too to try to tell what the LSD is doing but... in my dream world I'd like my own wind tunnel too. ;)
Thursday, May 31, 2012 8:34 AM
Finally some data for us Instrumentation nerds.
Please don't hack up the stock harness too much for instrumentation to the AQ-1. Use the E-Rod's stock ECU for as much instrumentation as you can since it's actually VERY good. Too bad AEM doesn't have a CAN OBD-II reader to the AQ-1 that would be sweet.
If you get to tuning the ECU included with the E-Rod make sure you select good tuning software. I would hate to see you fumble with excel spreadsheets (Or MatLab) trying to figure out the 2nd order, non-linear, multivariate polynomial consisting of over 450 coefficients used to build the Virtual Volumetric Efficiency Tables. Welcome to the world of floating point processors..
Dusty Duster
Dusty Dusterlink
Thursday, May 31, 2012 10:18 AM
MatLAB brings back undesirable memories of engineering school. MAKE IT STOP!
Jeff Naeyaert
Jeff Naeyaertlink
Thursday, May 31, 2012 3:53 PM
Adam: Didn't have to hack up the stock harness at all! the E-ROD comes with a bulkhead connector that i used for engine speed, vehicle speed, throttle position and oil pressure! It also has the GMLAN CAN outputs in it as well. I asked them that very question--if I could log that info and not have to wire all those other sensors. The answer I got was that the hardware is there in the AQ-1 to do it, but the functionality hasn't been released yet.

from AEM's AQ-1 forum:

"We are adding OBD2 (J1979) and "universal" CAN logging capabilities in the coming months."

"The AQ-1 does, however, have a second CAN bus available on pins 33 and 34. This is completely separate from the AEMnet bus and will allow logging of custom/user defined messages and signals. Unfortunately, this functionality has not been released yet. I don't have a release date for this feature however I can say it won't be in 2011."

"J1979 will be supported as part of the OBD-II version of the AQ-1, available 2012 (most likely toward the end of the year). There are no current plans for J1939 support ."

HERE'S the link if you're interested..

Sooo, there's hope!!
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