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Old 04-18-2012, 10:56 PM   #1
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Make sure my thinking is not flawed

Hey guys

I have a 83 GMC ward 66 passenger bus. Its kind of in mothballs for the moment till I pick up a job. So I am in planning mode for now.

Question 1: I have the floor plan thought out and I am going to assume there will be some additional weight added on to the bus. The engine is a 366 gasser so its not going to make a ton of power, which is fine, but with it running now it tachs very high at highway speeds. Not sure what the rear end ratio is but the plan is to put LP24.5's all the way around it to increase the diameter and slow revs.


My question is do I need to wait to change the rear end ratio when the bus is done or do it sooner? I am not in a rush or like to hammer the bus. Slow and low is fine so I dont think it needs to be as high of a ratio as it is.... Im thinking low 5's maybe mid 4's? Just wondering if someone has taken this on and would know what the ideal ratio would be.

I know you can get programs to calculate what rpm you want to run and make the adjustments to get there.

Any input would be appreciated.


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Old 04-19-2012, 10:04 AM   #2
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Re: Make sure my thinking is not flawed

Just go get a two speed rear axle from a similar era bus or small truck with highway gears that matches yours. You probably won't have to build a driveline or do anything else except hook up the brake lines etc. Bus is built on a truck chassis so they are the same.
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Old 04-21-2012, 10:17 PM   #3
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Re: Make sure my thinking is not flawed

That might work cause Im really wanting to get rid of the budd rims on the back. I would prefer to have hub pilot wheels on it if I can.
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Old 09-01-2012, 06:38 PM   #4
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Re: Make sure my thinking is not flawed

I know it has been a while since you posted this, but keep in mind that a reduction in RPM is not ALWAYS paired with increased MPG.
The gas V8, if it turns the same as a basic 454, should handle prolonged 3500 rpm quite easily.
(Usually, this sounds like the engine is screaming.)

In the old Ford 300/6 cylinders, you could drop the RPM's down to 1200 at 60 and it would get better and better MPG.
However, when we tried the same thing with the 4.3 Chevy V6's, much below 1700 and you started to go the other way.
The ford 300 had a 3600 redline, while the 4.3 was rated for 4500...but would take 5000 without trouble (as long as it was loaded at that RPM.)
The key is to find a chart of your engine and find where your optimum torque and HP crossover. In that few hundred RPM range, will be your best MPG.

If you already know this, sorry.
Just trying to help out.
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Old 09-01-2012, 06:48 PM   #5
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Re: Make sure my thinking is not flawed

Reminds me i have a ford truck 300 6cylinder that is rebuilt in a 1 ton dump truck that is going to the scrapyard...
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Old 09-01-2012, 07:32 PM   #6
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Re: Make sure my thinking is not flawed

Noooooooo, dont do THAT!

Those engines will pull a bus or a step van down the road with a 4 speed granny...better than a chevy 350 V8.
LOVE the torque ratings on those and the way they last...
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Old 10-06-2012, 06:46 PM   #7
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Re: Make sure my thinking is not flawed

My knowledge of 2 speed rear ends are slim.... does anyone think this would be a better option when or if I swap rear ends or do a gear change?

I have a friend who works on these types of rear ends so I wont fret about the work or advice but wanted to run it past everyone here.
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Old 10-06-2012, 07:21 PM   #8
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Re: Make sure my thinking is not flawed

The 2 speed rear is great!
Turns a 4 speed into an 8 speed........
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Old 10-07-2012, 12:17 PM   #9
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Re: Make sure my thinking is not flawed

sounds like that is the best money spent to me versus a gearing change? I assume no issues with a 545 tranny versus a stick?
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Old 10-10-2012, 01:39 PM   #10
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Re: Make sure my thinking is not flawed

There is a big difference in the way it pulls.
You can use a 2 spd axle behind either though.
With the auto, you would just lift off the throttle to let it shift.
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