13 July 2012

Prius C: A sub-compact hybrid, at a non-hybrid price.

Prius C: A sub-compact hybrid, at a non-hybrid price.

by Bakari Kafele on July 13, 2012

The newest Prius, available for only 2 months now in the US, is a compact fuel-efficient hybrid.
One thing it is not, however, is a Prius.

09 July 2012

Adding an overdrive (BW T-19 to ZF-5 transmission swap)

(Just want tips for swapping a BW T-19 for a ZF S5? Skip to tips.  Not swapping a Ford truck transmission?  Skip to the end for the results.  Continue reading for all the gruesome details of my project.  Hopefully my trails and tribulations can at least provide you some entertainment.)

If you’ve never driven a vehicle more than a couple decades old, you probably take overdrive for granted.  You may not even have a clear idea what that term means.That 5th or 6thgear, with a ratio smaller than 1.0 (meaning the driveshaft is turning faster than the engine) lowers the engine RPM speed on the highway, and can make a huge difference in the fuel used to go the same distance at the same speed.Gears on a car are just like gears on a bicycle; imagine trying to ride a bike with only a small chainring and big cog, and having to spin your legs like crazy to get anywhere at a decent speed.  Lower RPMs means less internal friction, less internal reciprocal motion, and therefore less wasted energy.
If, like me, you don’t care to spend the money for a new – or even remotely new-ish – vehicle, you may have noticed that overdrive was once upon a time not always standard equipment, or even available as an option.

The Ford F-Series of trucks has been one of the most popular vehicles world-wide for decades, and though much has changed over the years, many of the internal design factors stayed the same from one generation to the next.  They were rather reliable, so a good many older ones are still on the road.  Those two factors mean that there is much interchangeability of parts among different generations, and those parts are easy to find.
The 7th generation F-series (1980-1986) had a couple of manual transmission options, all of them 4 speed. My own 1983 diesel F-250 ¾ ton truck came with a Borg-Warner T-19, in which the 1st gear was an extra-extra low granny gear (6.32) which is normally not used.  For all practical purposes it is a 3-speed.  No overdrive gear.  In fact, even 4th gear isn’t quite direct drive, at a 1.1 drive ratio.
This means shifting into top gear at 25mph, and 2400 RPMs at 55mph.
2400RPMs means each piston is going up and down 40 times every single second, which means the mass of the piston head has to stop, change direction, move a little, stop, change direction again, 80 times every second (once up, once down, for a full rotation).  This is bad enough is a small engine with light parts and a couple cylinders (like a motorcycle) but in a heavy V8 diesel engine, a lot of inertia is going to waste.
Not a terribly big deal in 1983, when the national speed limit was still 55, but post-embargo gas prices had dropped again; the lack of stock overdrive leaves a lot of potential for increasing highway fuel mileage.
The addition of an overdrive gear reduces engine speed from 40 cycles per second down to only 28, a 30% reduction.