gojo

I have an RX7 electric conversion, and with the electric motor I no longer have a working tach.

2500 rpm is the best speed to run the motor at.

The car is a 1983 GSL with a 5 speed transmission. If someone with a working tach would tell me what speed in each gear woud correspond with 2500 rpm, I would know what gear to use for different speeds.

Right now I leave it in third when I drive in town (the car has no clutch). For highway I start in second, and shift to forth at about 20mph. I leave the car in forth up to about 50 mph. I rarely drive over 50 because it increases amperage, and cuts down on range, but the car will do 65 in fifth gear, and that is the fastest I have tried to go.

So in other words. At 2500 RPM's, how fast would I be going in second, third, and fourth in an 83 RX7? First and fifth are rarely used.

DickGetty

with my '79, stock tranny, in 5th (.850:1), 3000 RPM = 60Mph
Assuming your transmission and rear-end are stock, and the tire diameter is stock,
they are the same ratios as mine.
So in 5th gear, every 500RPM = 10Mph

therefore, 2500RPM in 5th gear = 50Mph
65MPH in 5th would be 3750 RPM

4th gear is 1:1 so @ 2500RPM it would be 15% less, or 42.5Mph

AND, that's as far and as fast as my memory will take me. Look up the gear ratios in the FSM (on-line) or in the Haynes manual and do the rest of the math.

gojo

Found this site. It was just what I needed.

http://www.apexgarage.com/tech/gear_ratios.shtml

Buttwete

With direct connect to the tranny and the tourque of the electric motor, I wonder what the take-off would be like at WOT.

gojo

WOT=without Transmission?

I am using a DC motor, so I need the gears. As I stated earlier, 2500 RPM's is the best for the motor. Going much slower would tend to lug an electric DC motor over heat it, and use more electricity.

This is my poor man's tach. The motor redlines at 5000 (2X's 2500), and functions well between 2000, and 3500 RPM's.

@2500 RL X’s 2
1st 12 MPH
2nd 20 MPH
3rd 31 MPH
4th 44 MPH
5th 53 MPH

2nd 16 MPH to 28 MPH
3rd 25 MPH to 43 MPH
4th 35 MPH to 61 MPH

Pretty close to what you figured for 4th gear.

AC motors don't need transmissions, and they have regenerative braking. I have cheaper more reliable 100 year old technology. I started out with a brushless DC motor (they run like AC motors) but it burned out on me when I was driving into a strong head wind.

My take off is also limited by my controller. I have a 400 amp controller, and it has take off similar to an average gas engine. I can start in any gear, but 2nd works best. Then I shift to 3rd in town, or 4th on the highway. The motor can start good in 3 unless I am going up a hill, then it is a little slow, but starting in 3 is harder on the engine, and uses more electricity. I can burn rubber in 1, but not for long.

Guys with 1000 amp controllers can really burn up the road. If that is what you are into.