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Old 01-12-2008, 12:41 AM   #21
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Re: Get my bus moving!

If you really want more speed, you need to change the rear end gears. It is not cheap on a big bus. I looked into it on my bus and it's about $1,500. Probably not a job you want to take on yourself either.
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Old 01-12-2008, 05:04 AM   #22
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Re: Get my bus moving!

Originally Posted by reprobate

Did you see much of a decrease in your fuel economy when you upped your rpms? I'm looking to do something similar to my 360.
i didn't drive it a whole lot before i turned up the rpm's, so i really can't say. i turned up the hp after about 15K miles and didn't get any worse fuel economy, but i didn't have to hold the pedal as close to the floor to cruise at my target speed of 60 mph. She was a lot more thirsty at 64 or 65 mph.
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Old 01-12-2008, 07:23 AM   #23
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Re: Get my bus moving!

I'm a little confused here. Ok, I'm very confused. Does the governor limit rpm or does it limit fuel delivery? Can you turn up the hp, without turning up max speed?

I can't imagine that another 200 rpm could raise engine efficiency enough to counteract the increase in wind drag, unless it involved getting to a higher gear. I ain't smart enough to remember the formula for wind drag other than to remember that it raises a bunch with speed.

I remember back a few hundred years ago when they dropped the speed limit to 55 for fuel economy reasons. The truckers bitched that it lowered their fuel economy because it meant that they couldn't make that last shift to 23rd gear.

I might buy this arguement, but, last I checked (actually, I never really checked), there aren't too many skoolies with 15 speed eatons. Are there any skoolie trannies that shift to high gear anywhere past 50 mph? I doubt it. Don't some of the new skoolies have 6 speeds? Maybe they might. But, how many of them have found their way into the clutches of this group?

Elliot, your ramblings uhhh, I mean valued opinion on this would be appreciated.
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Old 01-12-2008, 10:04 AM   #24
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Re: Get my bus moving!

The governor limits RPM -- by shutting off the fuel (gradually) at a certain RPM.
Yes, you can turn up the HP without touching the governor.
The two are two different adjustments.
Yes, wind drag is a major force and climbs like a rocket the faster you go.

The truckers complained because it took them longer to get where they needed to go. But the "optimal RPM" argument does have merit. Lots of variables.

Millicent shifts to high gear around... gosh... I think 35 or some such.

I'll happily ramble som more -- in three weeks. Gotta go hit 23rd gear.
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Old 01-12-2008, 11:42 AM   #25
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Re: Get my bus moving!

Have a safe ride Elliot, this string has jogged my memory some. Back in the 80's a buddy of mine own a 1 ton "hotshot" truck and was faced with simular challenges concerning gear ratios. He went to the junkyard and bought another transmission and installed it in the gear train behind his existing transmission. It worked great he had 2 shift levers and more gears than he needed for ultra low hard pulling to extra high for any speed and rpm that he had the hp for. I rarely drive mine more than 50 or 60 miles so it would take the rest of my life to justify that kind of time and money investment but if I used my bus more that is what I would look at.
Elliot, I have 2 names because my grandkids named the bus buster. I'm dave
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Old 01-12-2008, 06:16 PM   #26
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Re: Get my bus moving!

ok here is a question for the gassers has anyone done the usual mods with your small block or big block chevys fords or dodges? ie i have heard that a 350 under load will get better milage with a 4 barrell than a 2 barrell garb how about headers? cam change? i have not been out on the highway with our bus yet but with a clarke 5 speed and a 7.20 axle im not expecting much in fuel milage or cruising speed.i know when i do these things with my cars they make the power but the thirst......
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Old 01-12-2008, 10:55 PM   #27
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Re: Get my bus moving!

I would think that some of the usualy mods could probably help out a small block Chevy, but they could make things worse too just because a driver might get after it a little more. Wide open throttle is still wide open throttle and the gearing is going to dictate the top speed, but if you are able to flow more air and fuel in the process of getting know.

I might focus my attention on making the engine more efficient with what it has. If you can reduce the amount of energy per gallon needed to just spin the thing you can help the mileage out a lot.

I think a swap to a full roller valvetrain like you might find in a later model block and then some Vortec heads (I know, they flow more potentially, but they're great heads) might really net you some mileage. The valvetrain on a small block Chevy is a terribly inefficient design.

I think EFI would be the way to go as well for both mileage and power. I'm going to be undertaking a Megasquirt build for my truck here shortly and I will document it on the site here for posterity. With a smart fuel injection system like that it could be constantly advancing the timing and leaning the mixture until it gets a knock at which point it will back off a little. At the same time, if you get on it and drop the manifold vacuum it's going to be able to dump a lot of fuel in there to get some power. It's the best of what both a 2 barrel and a 4 barrel carb have to offer without any of the headaches...AND you have electronic spark control.

Just some thoughts....
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Old 08-18-2008, 08:08 PM   #28
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Re: Get my bus moving!

Sorry to dig up an old thread.
I guess I need to explain a little. The 8.2 Detroit was a mistake on my part. Turns out that screw is the buffer screw, and actually isnt anything worthwile to adjust, as one of you already found out. I will remove that section from the Low Buck Fuel Rate site.
As mentioned already, upping the fuel rate doesnt always mean economy will drop to nothing. Many times it will be the same, or even slightly better. RPM kills economy. As far as how much you can wind em up, it depends on each engine. The DT360 and Cummins 5.9 would be fine going 3k all day long. Whereas a DT466, Cummins 8.3, or Cat 3208 can actually go to 3200, but they really arent very happy at much over 2800(nor very efficient). In my how to sections, it says you can adjust the rpm on the DTs, Cummins, and 3208s. This really helps if you have an Allison when you need to get up to speed. I've talked with many people reguarding safe rpm limits, and there's a lot of cushion to work with. The little CumminsB, and the DT360-466 can actually run up to 4500 rpm and not scatter. The Cummins C and 3208 cant quite go that high, I would limit them at 3600, but valve float on all listed is right around 3200. Now we go to fuel economy. The best thing you can do with a mechanically injected diesel is advance the timing about 2-6*(depending on where it was set at the factory).
I'll be doing some fuel adjusting & timing in a couple weeks to CrazyCal's DT466. I'll let him report the end result. I'm not going hog wild, but just enuf to feel it & notice better mpg.

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