I would be less concerned about the differential and more concerned with the
driveshaft. The drivetrain is essentially the same between the Spitfire and
GT6. The GT6 is 98 HP and 108 ft.lb of torque. I have seen GT6's bend
driveshafts during Autocross events.
You state that your electric motor is 100 HP but do not list the maximum
torque values, it would be easier to answer your questions if we had this
During the past autocrosses I have participated in with various spitfires, I
never needed to leave second gear. I used 1st gear to started shifted to 2nd
before the first turn and kept it there. I never exceded the 6000 RPM
redline on the engine. The spitfire engine produces enough torque in 2nd
gear to break the tires free on acceleration in an autocross course.
Remember, Autocross courses are almost all turns and the longest straight is
usually only about 100 to 300 ft long. This prevents you from placing the
maximum amount of tractive effort to the ground (with an open diffenential).
I think during autocross my motor runs in the range of 2000 to as high as
6000 RPM. Will your Motor be capible of spinning at that high rate of
speed? Tell us a little more about your configuration. I worked on
developing electric cars while in college and others on the list have other
various backgrounds and may be able to help with further information.
BTW, I was unable to link to the website you referenced. Is the address
correct or the server down? Please let me know. Thanks.
Ralph Goodwin wrote:
> I am working with a local high school to convert a 1980 Triumph Spitfire
> to electric power. Part of the competition includes an autocross
> competition. The web site used by event organizers for last years
> competition is linked below.
> The finished project should be at or near original weight and weight
> distribution. Peak HP of the installed motor will be around 100 hp.
> Torque will be significantly more!
> We are planning to use the stock drive train from the bell housing back,
> including clutch. It may be possible to run the car in a autocross
> event without shifting gears, but we aren't sure, so we went with the
> clutch. It will also help absorb the torque from the motor, protecting
> the rear end. The transmission in the car has an overdrive.
> Can you advise on any drive train mods that will help ensure
> durability. We don't plan on drag racing the car, but we suspect the
> rear end is our weak link. Rules will allow us to make substantial
> modification. Someone suggested a Datsun 510 differential, but they
> hadn't seen it done and didn't know if it is a valid suggestion.
> We would also appreciate any suspension mods, suggestions etc. Have
> thought some about coil-over shocks on the rear.
> Please don't come back and tell us how we are ruining a classic! This
> car was DEAD!
> Any suggestion would be appreciated! Thanks for your help!
Patrick Barber, Allen Park, MI
70 Spitfire MkIII FDU89984L
Visit My Triumph Website at