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Ok, I think that I asked a similar question about a
year ago here. I'm starting to work on my bus againg
and I have forgotten everything I learned a year ago. So, forgive me for asking twice. :)
My bus is a '71 Chevy C/50 with a 2 speed rear end.
At 65mph my 350 turns at about 4000rpm and sucks 5mpg.
Is it easier (possible) to replace the 2 speed with
another 2 speed with different ratios or should I just
go to a single speed rear end.
Is there a standard ratio that is good for highway driving?
I saw someone mention that they were looking for 4:10 gears.
I realize that by changing the ratio I may loose some power,
wont be able to accelerate as well. So, my next project would
be to ditch the 350 for either a better 350 or a big block.
If anyone has a similar bus with a different gear ratio or engine,
I would be interested in hearing what you get for gas milage and what
your top speed is.
Thank you,
Brent
Unfortunately, there isn't any simple quick fix to improve MPG. Basically, an internal combustion engine is a thermodynamic device for turning heat energy(combustion) into mechanical energy(rotary motion). How efficiently that is done depends on the engine design, ideally, the higher the compression ratio, the better. However, you reach the point where oxides of nitrogen are formed and must be dealt with before the exhaust enters the atomosphere. The high ratios demand a high octane fuel to control detonation so that knocking caused by multiple flame fronts doesn't occur. All that said,your MPG is going to depend on how much "work" the engine must do. All things being equal, a smaller engine is going to burn the same amount of fuel to produce the same power output as a larger engine. It's like removing a 100 watt light bulb fixture and replacing it with a two 50 watt bulb fixture, the energy use remains the same. There is no way to trick or lie to your engine to increase your MPG, it is, regardless of size, going to have to produce the same power to move the same weight against frictional loses and wind resistance. In light of this, you'd have to A reduce the weight of the vehicle, and B streamline it. This is just what the auto industry has done. I'm assuming your two speed is an under and direct unit, a good combination. The ratios have been worked out by engineers, so they're pretty good for all-around use. Unless you live in one of the plains states and always have a tailwind, I'd stick with it. |
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