At 01:41 PM 1/28/2002 -0600, you wrote:
> Carl..
> Minor problem here.. take 2.76 and multiply times .78 You will
> notice it gives you a really high top end gear, yes, but do you
> have enough motor to pull it... There is a point of diminished
> returns... That being if you have not enough motor to pull the
> weight of the auto then you must compensate by giving MORE gas,
> hence, lower mileage..
This turns out into a popular subject. An additional comment to Robb's
statement. This combination of 2.76 * 0.78 overdrive = 2.15 ratio would
result in about 1600-1700 rpm converter output at 65 (don't know your tire
size, so I am guessing). When you load the torque converter at these low
speeds climbing a hill, a lot of slippage will result which is nothing but
direct loss of energy converted to transmission heat. That's where you
need the lockup converter. The statement about higher engine load
resulting in poorer fuel economy needs to be a bit more
explained. Typically, spark ignition engines are more efficient at higher
loads, for two reasons, the most important of the two is that as the
throttle opens, the intake restriction diminishes, so the "pumping" losses
drop. However, if the load of the engine is increased to the point where
the mixture starts getting rich, then you might start loosing MPG. This
however happens fairly close to WOT, so it will have to be a very steep
hill, in which case you have the option to down shift to direct.. The
super low gear ratios like the 2.15 usually give better MPG's on the
highway but at the loss of low speed performance and economy. If I paid
the $ for an overdrive, I 'd rather use it for performance, but one could
rather choose to maintain a relatively high ratio and use it for
economy. If in the US though, it might take many years to pay back through
fuel savings.
D^2
Back to the Home of the Forward Look Network