[ausev] VW FOX CONVERSION, GEAR RATIO QUESTION

[Chris Robison]

Did you plug in these gear ratio numbers directly, or did you multiply 
them by the final drive ratio (the gearing at the differential) first? 
Uve's calculator does not provide a separate spot for the final drive 
ratio, so you have to do the math yourself as you input each number. A 
quick google search reveals that the Fox 4-speed transmission had a 3.89 
final drive ratio, and the 5-speed was 4.11.  Multiply 3.89 by each of 
your gear ratios to get the full ratio for each gear in Uve's 
calculator. Remember that your redline with this big motor is going to 
be somewhere in the neighborhood of 5000rpm.

Beyond that, I'll just say this -- given your design goals as you've 
stated in the past, you haven't solved your primary issue. You still 
have *way* too much motor for your car. Although it may physically fit 
within the Fox's engine bay, you've actually made this fundamental 
problem worse in that the Fox was not intended even as a diminutive 
sportscar like the NX was. In gasoline terms, you're effectively 
cramming a 350 small block into an economy car, which generally 
speaking, is something people do if they're aiming to race. What comes 
along with that intent are the modifications to the driveline -- bigger 
transmission, custom hardened gears, multi-disk racing clutch, enlarged 
axles and CV joints, wider and softer tires etc, that are necessary for 
a small car to withstand the input from a big powerplant. Without these 
modifications, your car is going to be undergoing regular repair.  With 
the stock transmission, don't be surprised if you end up needing a 
rebuild every 5 or 6 months. The stock clutch will slip under the torque 
and will definitely need upgrading and the performance aftermarket for 
Foxes may be limited (I don't know).

Operating the motor at lower RPMs is actually something to avoid, as 
torque will be higher placing higher mechanical stresses on your 
transmission, current draw will be higher, cooling less effective, and 
generally the motor will run hotter and a bit less efficiently.

The way to make this motor work and not tear up your car would be to 
keep RPMs high, drive gently and limit the motor current from your 
controller, to limit the motor's output torque. Doing so will render 
unusable all the extra power the motor is capable of, which means you're 
carrying around a lot of extra mass that you won't be using. Worse yet, 
much of this will be rotating mass, which reduces efficiency during 
acceleration.

This motor really belongs in a full-size pickup, van or SUV, in a 
direct-drive configuration in a light truck or RWD sportscar, or in a 
small vehicle if high performance is desired (and planned for). It will 
work in your application, but I think it is far from ideal.

   --chris





loopcat wrote:
> Hello All,
>  After my 1st failed attemped at converting a '91 Nissan NX (motor too big for car) We had to make a decision, keep the motor or keep the car. So we decided on another donor car, a 1993 vw fox. 
> 
> Putting the cart before the horse, last year I purchased a rather large GE DC motor. The demensions/weight are very similar to the famed Warp-11. The motor tag states 16hp at 70v, 214amps, 1822rpm, ~210lbs. From what I have heard, The motor was designed for an air-craft-tug. So it should have a ton of torque. By most accounts the motor will function well in an EV.
> 
> The major reason for buying the vw fox was that the engine is latitudinally mounted so my GE-11" motor will fit into the car. 
> 
> After buying the fox, I did a bit of research and found some interesting facts on the transmission. The gear ratios are very low numerically speaking. 1st-3.450, 2nd-1.790, 3rd-1.130, 4th-0.830 R+P-4.110. So I was curious how this would perform with the motor. So I went to Uve's EV Calculator and added these transmission ratios to a vw rabbitt, zilla lv, and trojan t-105. The closest motor on the list was a Kostov. I then lowered the volts (120 t-105) and the motor rpm's (3600)  The results are interesting, the motor rpm's were low, but the speed/distance was very repectable, 1st gear was the best with a range of 30 miles between 40-60mph. Top speed ~70mph. At first, I thought the ratio info was bad. Most of the cars on the list have a 2nd gear ratio of about 8.0. But then I saw that the Fiat Palio also had lower gear ratios. So for kicks-and grins, I lowered the volts to 96v. In 2nd gear the rpm's were below 1700 at 50-60mph. 
> 
> And this leads me to my question. I have sometimes heard that these old GE-11" spin too slow at lower volts, "tons of torque, but no top-end speed". But if the transmission has lower gear ratios then it should produce the mph's, right? Any insights would be appeciated.
> Thanks, John Stuart in San Antonio tx..
> 
> 
>       
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