8.3 Cummins how fast do they go

NguyenBus · 07-15-2016, 03:23 PM

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..

jake_blue · 07-15-2016, 05:11 PM

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.

Tango · 07-15-2016, 06:53 PM

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.

superdave · 07-15-2016, 09:06 PM

my 32'bus is governed at 2300 rpm 63 mph, no problem in the mountains.

Dragonpop · 07-16-2016, 12:12 AM

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.

BusFiend · 07-16-2016, 01:47 AM

Quote:

Originally Posted by Dragonpop

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.

jake_blue · 07-16-2016, 05:30 AM

Quote:

Originally Posted by BusFiend

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.

Tango · 07-16-2016, 09:39 AM

Unlocking that 6th gear would certainly help the MPG.

Dragonpop · 07-16-2016, 10:33 AM

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.

BusFiend · 07-16-2016, 12:55 PM

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.

Stu & Filo. T · 07-16-2016, 07:32 PM

Theres an old saying that goes,, "Speed cost money how fast do you want to go"

Carytowncat · 07-16-2016, 09:58 PM

Quote:

Originally Posted by jake_blue

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.

Come to Jesus moment; to this day (almost two months later) i still have a stomache drop when i think about the ride home when at about 50mph on a tight two lane road, i nearly went into the ditch. Oh goodness that wouldn't have been pretty. I am comfortable at 55. I know i can stop, react, and the great thing about a bus is drivers dont try and bully me out of the way lol.

superdave · 07-17-2016, 06:21 AM

63 is good with me. from what i read diesels have an rpm sweet spot. a front tire blowout would be disasterous at high speeds, enjoy the drive and be good to your drive train.

64crew4x4 · 01-31-2017, 11:56 AM

Hello, to you all....

Been a while.

So I have a 1997 Thomas 8.3 Cummins Allison 6 speed 6th is still locked.

I did 2 Trips in it of 350-450 miles last summer got an average of 11.5 mpg...

Pulling the Oregon Passes From Willamette Valley over to the East, it would only do 15-25 mph up the grades in 2-3rd gears.

We tweaked the Rail on the P-Pump after the last trip....I just did 1400 miles over to East Idaho and Back to recover a Car and Trailer....( different story there )

Bus hit the Passes and Never came down below 45 mph....I was Passing Semi's....

Also Stayed in 5th till near 45 mph, then dropped to 4th....Heat was Good, all things looked good

BUT it only got 6.5 mpg loaded or empty....lol

I was trying to average 60-65 mph the entire trip and it was running at 22-2500 rpm....

Curious as to what you guys are Running for averages...?

My dodge Truck with 5.9 24v cummins runs 72-77mph at 1900 rpm based on load and Climb on the hwy....

Does this 8.3 Rev limit out..? if so at what RPMs...? range
and What is the Happy range for Fuel economy , power, torque...?

Thanks Guys
John

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