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Old 07-15-2016, 04:23 PM   #1
Mini-Skoolie
 
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8.3 Cummins how fast do they go

I have a 93 Bluebird RE with the Allison Transmission what is the top speed I just found out I have bad fuel filters top speed before was only 65..
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Old 07-15-2016, 06:11 PM   #2
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Top speed is really going to be a formula determining what transmission you have and the differential gearing. The engine itself is simply there to provide all the power but at what speed that power hits the road is a little more involved than just the size of the engine.
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Old 07-15-2016, 07:53 PM   #3
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You have to remember that skoolies were not built for speed. 65-70 is about at the design limit of safety. The other half of going fast is stopping fast and 18-20K pounds is a lot to haul down. Even the new Greyhound interstate cruisers are not set up to go much more than that.

Can they be made to go faster? Absolutely. But not safely without upgrading just about everything on them.

Don't feel too bad. My '46 Chevy topped out at about 47. It will now go 65 comfortably but that took an all new turbo diesel engine, new springs, new shocks, a new 6-speed double OD transmission, a new rear axle with new gearing, new rims & tubeless tires and oversized hydro-boost disk brakes all around.
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Old 07-15-2016, 10:06 PM   #4
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my 32'bus is governed at 2300 rpm 63 mph, no problem in the mountains.
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Old 07-16-2016, 01:12 AM   #5
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Year: 1996
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Engine: C-8.3-300 Cummins MD3060
Rated Cap: 40 Prisoners
My 40 ft Bluebird rear engine pusher 8.3 with 3060 Allison transmission
and 5.38 rear gears and 1200R22.5 tires will do 85mph at 2400 governed
RPM in 5th gear as 6th gear has not been opened up.
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Old 07-16-2016, 02:47 AM   #6
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Quote:
Originally Posted by Dragonpop View Post
My 40 ft Bluebird rear engine pusher 8.3 with 3060 Allison transmission
and 5.38 rear gears and 1200R22.5 tires will do 85mph at 2400 governed
RPM in 5th gear as 6th gear has not been opened up.
Wonder what kind of mileage an 8.3 pusher gets at 85 mph.
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Old 07-16-2016, 06:30 AM   #7
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Quote:
Originally Posted by BusFiend View Post
Wonder what kind of mileage an 8.3 pusher gets at 85 mph.
1mpg! LOL

Of course the capability to do 85 and the routine habit of doing 85 are two very different things. Besides as mentioned above about the ability to stop a large vehicle traveling 85mph is the handling and comfort at that speed. For one thing, these buses are not in the furthest stretch of the imagination aerodynamically designed and the wind resistance at that speed is formidable. There's also cross wind which high profile vehicles are very susceptible... You haven't had a real come-to-jesus moment until you've been driving a large vehicle and encounter unexpected cross wind. If you're not being vigilant and just driving like many drive a car (10% attention) you'll end up rolled over in a ditch or worse. Plus the buffeting makes for a less than quiet and comfortable ride. Besides all of that, fuel economy does drop about an estimated 10% for every 5mph over 55 anyways so running that speed and rpm is probably not going to be the routine even if it is nice to know it's possible.
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Old 07-16-2016, 10:39 AM   #8
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Unlocking that 6th gear would certainly help the MPG.
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Old 07-16-2016, 11:33 AM   #9
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Yes the quest again on how to unlock the Allison transmission. Not sure
what the mileage at that speed was. we just happened to be on the freeway
in Utah where the speed limit is 80 mph for cars and trucks so we ran it up
against the governor to see what she would do. The bus does have full air
suspension and I added the Safety Plus steering stabilizer which improved
the steering about 80%. I also have a hydraulic retarder which improves
braking about 40% depending on where it is set. I felt rather safe at that
speed none the less.
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Old 07-16-2016, 01:55 PM   #10
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I don't doubt it. i chased my old boss across the desert, from LA to Vegas. He had just had the 8v71 in the buffalo rebuilt by a shop known for their screamers. The 6v71 in my MC7 topped out at a very stable 88. The buffalo went on to just break triple digits. We were empty, of course.

I think unlocking the double overdrive in your tranny will prove unnecessary, unless you you plan on cruising a lot at 75-80 mph. At 65, 6th gear will be too low in the rev range for peak efficiency. Not sure that spending the money on reprogramming the tranny is worth, unless you have the money for giggles.
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