TreoWayne New Reader
Aug. 11, 2009 8:21 a.m.

My boss is working on a project to make a Miata into an electric drag racer. He has the batteries and the motors and many other parts. He has adapted a Nissan 350Z rear subframe into the car complete with the pumpkin.

He wants to run a higher rear end ratio. He heard something about 4.9 ratio parts from a non-SC 2002-2004 Nissan Xterra working in the 350Z rear pumpkin but was lacking in specifics.

Would he be looking for the rear pumpkin or the front? Front makes sense since the front end of the Xterra is independent and the rear is a solid axle, but he would like to KNOW before ordering heavy parts.

mad_machine SuperDork
Aug. 11, 2009 8:48 a.m.

Why does he want to go for such a ratio in the differential? Electric Motors make all there torque at ZERO RPMs. the faster you spin them, the less torque and less efficent they get.

I would stick with the stock ratio on the miata, or use an RX7/8 rear and put the biggest, most torquey motor you can hook up to it in the car

CarKid1989 Reader
Aug. 11, 2009 8:49 a.m.


TreoWayne New Reader
Aug. 11, 2009 10:34 a.m.

He said something about reduced back-EMF from having the motors spin faster. I also wondered why he wants such a high ratio, but he is sure it is beneficial.

I myself wondered why he didn't just use a Ford solid rear and call it a day. He also wants the car to handle.

I'm trying to convince him to bring it to the $2009 Challenge for the exhibition class since the budget is quite a bit more than $2000.

MrJoshua SuperDork
Aug. 11, 2009 12:53 p.m.

Electric motors do make max torque at 0 rpm, but gear multiplication is still a must. Think of a stock miata with 90 or so ft/lbs of torque. A 3/1 first gear and a 4/1 rear end allow over 1000 ft lbs of torque to turn the wheels. To get 1000ft/lbs of torque from an electric motor would take a 250lb motor running at least 2000 amps. Not something any current batteries, controller, or motor can sustain for any length of time. The other problem is you would only be turning 1000rpm or so at 100mph. A motor that big would easily have at least a 3000 rpm or so useful range. You would be missing out on at least 3 times the available torque with a 1/1 diff compared to a 3/1. Closer to 5/1 is considered a decent trade off in efficiency vs. acceleration for the commonly used motors.

mad_machine SuperDork
Aug. 11, 2009 2:46 p.m.

In that case.. I would look into the IRS set ups the Hotrodders use.. Corvette and Jag setups. You could probably have some axles made to bolt up to the Vette diff and still run the stock 350z suspension. With GM parts from their factory supercar.. it should be strong and the ratios easily swapable

andrave Reader
Aug. 12, 2009 1:13 p.m.

I think the 350z's rear differential is supported through nismo and alternate ratios are available.

do you know what diff that uses? R230?

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