Friday, January 25, 2008

Watt-Hour/Mile ratings and Selling the Trannies

I dropped off the 914 with Alan at A&P today to upgrade the brake cylinder and do a front end alignment. Brett, a local guy, is going to purchase my two leftover transmissions and Curt from Salem is visiting today to see the car (hopefully back from the shop).

In the meantime, I took some approximate readings from my ammeter and voltmeter as I drove on flat roads this past week. Overall driving at 20mph tends to pull 30 amps at 140 volts. Driving at 60mph (flat road only) pulls 90 amps at 135 volts. This averages out to around 205 Watt-Hours per mile. Paul Jorg asked for this info, so hopefully this is what you were looking for. I suspect that the fluid resistance in the transmission consumes quite a bit of power.

Although I hate to admit it, there's still a faint screeching sound that comes from the transmission when I spin the input shaft with the electric motor. The sound goes away after I drive a block or so, which leads me to believe that the transmission fluid isn't getting into all the bearings it should. The rather frigid mornings probably aren't helping the situation either.


Mike Brown said...

Glad to hear you finally got your transmission problems solved. Also glad to hear that the problem was not in our adaptor. As for your concerns about the fluid friction, I have some synthetic trans fluid in the proper weight for 914s that I have used for years with good results. Let me know if you are interested and I'll send you some. Mike Brown

Ross Cunniff said...

Cool. I have the same problem with low-temperature starting up - the tranny groans for the first few minutes. I'll see if they go away when I replace the tranny fluid when I fix my mainseal.

Thanks for the watt-hour measurements. I've been meaning to get to that, but my ammeter only goes to 40A... I've got a digital multimeter that I've been toying with using.

Roger Daisley said...

In my little VW Cabbie, I use synthetic tranny lube that I bought a Schuck's Auto Supply ... Work's great.

I'm sure you've done it already, but make sure the tranny is actually filled to the proper level.


pjorg said...

Thanks for the info. I am happy that you are up and running again. It is going to be a while before I get my car finished and I was anxious to get this info. I am very surprised that it is more at 20 mph than at 60 mph. Wind resistance goes up as the cube so one would think that it would be much higher at 60. This tells me that there is a lot of rolling resistance and or motor losses at the lower speeds. This is about what the Prius is at 35 mph do I guess it is about right. More data at other speeds would also be interesting.

I would be very interested to know what the DC people have been getting. Any one got some data? We are all assuming that the AC system is more efficient.

It would be interesting to know if it changes much after the alignment and different transmission oil.

For any one interested, Firefly has finally published their new battery's performance data.