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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
The last guy had some good advice. See how your engine pulls (i.e. using the vacuum guage. I would take it a bit further. If you engine pulls well, you are in great shape because you have a two speed rear-end. There are hundreds or thousands of Motorhome users out there who would kill to have the ability to split gear ratios with a 2 spd.
Basically it comes down to this:
Does your unit pull well on hills etc. I would guess that by using your 2 spd in combination with your trans. that you can find a gear that pulls almost any size hill. If the jump between most gears isn't too large, i.e. most shifts give you a 3-500 rpm change without great power loss then you should seriously look at putting higher ratio gears and dropping you rpm's when cruising. Turning 4000 rpm's at 65 mph has got to the be main reason you're down to 5mpg. My motorhome turns 3000 @ 55 mph. It's got a 4.10 with a 3 spd automatic. I'm looking to find a gear vendors overdrive unit to it. The main reason is to get a gear in between 2nd and 3rd (to pull hills) and to have an overdrive (cut the engine rpms at cruising). The 3rd Overdrive gear would equal a ratio of 3.20. Perfect for cruising @ 65mph around 2700 rpm.I have a 440 engine and my unit weighs about 11,000 1bs. dry so I think it would handle it power-wise).
You already have the two speed so you need to match up your ratio with the horsepower you have. You might be overgeared right now. Buses were designed to go slow - it may have more highway stretch available to it. I would check with a used truck shop or auto wrecker to see what ratios can be put in your specific rear-end. If you feel you have the power and you can extend your splits between gears then you can handle higher ratios. You'd notice a lot of difference in reduced noise). Less wear on your engine and alternators, a/c pumps etc because of lower rpm's. You'd also be perfectly set up for when you get to that bigger engine. It sure won't need the high rpm's to pull you around.
Good Luck! |
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