5.9 vs. 6.7 vs. 8.3

[pengyou]

I am finally approaching the $$ goal that I need to buy a pusher...will be looking for a 36 to 40 ft bus with intention of making it full-time live in rv. The dream is to do cross country driving during the summer. I am a teacher, so that is more realistic. I am hoping to find a bus with an Allison 3xxx or switch out to one and be able to actively use the 6th gear without blowing up the engine. There is one model that has a granny first gear, of 6 to 1, which makes towing something more agreeable.



Survey says that the 5.9 would be a little underpowered. From what I have read, using an underpowered engine might result in lower mpg than using a bigger engine that is more suitable for the job, and would reduce the life expectancy of the engine.



Like all of you, I am hoping to maximize fuel efficiency, while having a drive train that will give me reliable service for more than 250K miles. I am also hoping to find an engine that will not break the bank every time I need a new injector or some other part. With those requirements in mind, how do the 6.7 and 8.3 rate? I am guessing that parts for the 6.7 will be higher because it is a newer engine and likely to have more electronic stuff on it. What about use in this application?


My neighbors used to do long haul with an 18 wheeler pulling 50K pounds and got 11 mpg. They did have a manual transmission. Greyhounds cruise up and down I5 in California get get 11 mpg doing highway speeds (per a bus technician). I am hoping to breach the 10 mph limit. Any comments or insights to my random thoughts would be appreciated. I am not committed to a Cummins...but it is the brand name that keeps coming up in my circle. I would like to have an auto tranny with the specs of the Allison 3xxx - I haven't seen another one like it.

 

[Brad_SwiftFur]

It's been said (and with much truth) that a small engine running at full throttle will get less economy than a larger engine running at half power. In a larger vehicle, the small engine will strain/work harder to ascend hills, while the larger engine will do it more easily.


I have no long term experience with the 6.7, but the 5.9 and 8.3 both have excellent reputations. Parts are widely available and they're said to be pretty easy to work on. The 8.3 will definitely provide plenty of torque.


You may find some IH offerings. The 6.0 (Ford) / VT365 (IH) has a bad reputation from the factory. The deficiencies in these engines can be corrected (at no small cost) but if the engine fails, it will be completely ruined. More than one forum member has had this happen, and replacement runs $25K or more. The 7.3 (Ford) /T444 (IH) has an excellent reputation but is not known as a powerful engine (I have one of these in my shorty). The DT466 also has an excellent reputation, wide parts availability, and good power. Avoid the '05 and up "MaxxForce" versions - the emissions hardware is a nightmare. IH abandoned this engine design because of this.

 

[magnakansas]

opinion

dt466 or 8.3

um i know of one guy selling a pusher 8.3 with 3060 on craigslist for about $7000 says has less than 100,000 miles it is a pusher rv chassis. it is work by no means just bolt up and go... but it is all there. I think he is in one of the western states, CA AZ UT

william

 

[aaronsb]

I have an 8.3 with an MD3060. 6th gear is locked out. I wouldn't need it anyway, the ring and pinion have much more bearing on top speed. We travel at 70 mph @ 1800 rpm and 8 mpg on flat highways. There's enough left over to get up to 80 mph.

Previous experience on other trucks with larger power packages tells me that unless the transmission and engine are "stepped up" significantly, for example Cummins L10 mated to a 4000 series Allison, you won't get enough reliable headroom in power and torque.

Even then, with that much power you really need to pay attention because the vehicle dynamics of a giant steel bread loaf lacking a tag axle are not the same as a tractor trailer combination.

 

[alpharv]

I have the DT530 300hp. with the 3060 and 4:10 gears, 6 speed it gets 14mpg empty and hauling my 5th wheel 17K lbs I get 11.5 mpg it pulls a 7% grade from a dead stop @ 45mph. I got real lucky when i found this truck for sale@$22K in mint condition I mean this truck is like bran new.

 

[EastCoastCB]

I have an 8.3 with an MD3060. 6th gear is locked out. I wouldn't need it anyway, the ring and pinion have much more bearing on top speed. We travel at 70 mph @ 1800 rpm and 8 mpg on flat highways. There's enough left over to get up to 80 mph.

Previous experience on other trucks with larger power packages tells me that unless the transmission and engine are "stepped up" significantly, for example Cummins L10 mated to a 4000 series Allison, you won't get enough reliable headroom in power and torque.

Even then, with that much power you really need to pay attention because the vehicle dynamics of a giant steel bread loaf lacking a tag axle are not the same as a tractor trailer combination.

It wasn't you who posted the vid of their 6th unlocked?

 

[Elliot Naess]

... ... ...

My neighbors used to do long haul with an 18 wheeler pulling 50K pounds and got 11 mpg.... ... ...

I drove 18-wheelers for 27 years and my fuel mileage was always in the top handful of drivers, among hundreds of drivers in the company.
And my best was around 7.6 or 7.7 mpg.

Just a friendly reminder that with statistics you can prove anything you want.

 

[cadillackid]

It's been said (and with much truth) that a small engine running at full throttle will get less economy than a larger engine running at half power. In a larger vehicle, the small engine will strain/work harder to ascend hills, while the larger engine will do it more easily.


I have no long term experience with the 6.7, but the 5.9 and 8.3 both have excellent reputations. Parts are widely available and they're said to be pretty easy to work on. The 8.3 will definitely provide plenty of torque.


You may find some IH offerings. The 6.0 (Ford) / VT365 (IH) has a bad reputation from the factory. The deficiencies in these engines can be corrected (at no small cost) but if the engine fails, it will be completely ruined. More than one forum member has had this happen, and replacement runs $25K or more. The 7.3 (Ford) /T444 (IH) has an excellent reputation but is not known as a powerful engine (I have one of these in my shorty). The DT466 also has an excellent reputation, wide parts availability, and good power. Avoid the '05 and up "MaxxForce" versions - the emissions hardware is a nightmare. IH abandoned this engine design because of this.

this is prettyy much on.. in general the inline 6 engines will net you better torque than the V-8s.. I have a shorty with a T-444E and even 'turned up' doesnt seem to produce the torque the DT series engines do..



the V-8's youll find out there in school busses are generally the CAT-3208, Navistar T-444E(ford 7.3), Navistar VT-365(ford 6.0), Navistar MaxxForce 7(ford 6.4)..



The inline 6's you see most still are CAT-3126, Cummins 5.9 (2 variants.. the older 6BT or 12-valve, and the newer electronic 24-valve), Cummins 8.3 (I-6), Navistar DTA-360 (mechanical I-6), navistar DT-466 (mechanical I-6), navistar DT-466E(electronic I-6), navistar DT-530(E) (electronic I-6), Navistar MaxxForce DT(full emission control version of DT-466E)..


im sure i missed a couple.. I put out there the most common ones.. we all have varying opinions on which engines to stay away from and which to not.. alot having to do with one's mechanical abilities to perform Preventative measures or make repairs if you do break one.. All engines have some type of achille heal..



when looking at numbers.. pay attention to Torque.. Torque Moves Metal down the highway(which is what you want to do).. Horsepower wow's consumers and sells engines...

-Christopher

 

[BlackJohn]

....and some of us have to drive around with our old smokey 3116's


Just to add another to your good inline six list, Chris:wink1:


They are all mighty machines, mostly finely built and designed, when you think about what's available.
It pays to study them to see if you are up to the task of upkeep.



John

 

[Ronnie-SKO]

Not trying to make a fuss but.. Horsepower is work done, torque is only twisting force applied. Must have torque applied over time and have actual movement. This is horsepower.

Granted an engine with more torque at a given rpm will have more HP at the same rpm then and engine with less torque at the same rpm. Torque X time = HP

 

[Tango-SKO]

"Horsepower sell cars...torque wins races".
--- Enzo Ferarri

 

[cadillackid]

while I totally see the math.. essentially horsepower is torque applied over a period of time.. ultimately you need both to win a race.. you need a certain amount of torque just to begin performing what I call "real-world work" on the object.. in the case of a car.. to make the wheel turn and the car begin to move.. I realize this deviates from the true definition of work in physics.. and ultimately horsepower essentially keeps it moving.. after all horsepower is measured with and time.. in the case of advertising engines they use torque X rpm / 5252. (that constant is one recorded from a definition for engine measuring purposes.. so one can see that lots of torque will increase horsepower.. or Lots of RPM will increase horsepower...



reality is that when we want to think about real-world engines and driving.. we are at a stop light and want to get things going when it turns green. so we can build engines (aka diesels) with gobs of torque at low RPM to get things going.. Horsepower may niot look so impressive because our RPM is low that we measure at.. in fact many engines list their max torque and max HP in different lines on the spec sheet because the RPMs are different.. max torque occurs at leass than peak HP generally.. esp on a diesel..



consumer HP wars are why we have diesel truck engines like ford / navistar powerstorkes revving to 3400 RPM vs 2600 in the biog truck.. because they could advertise higher HP. really due to the fact it can rev higher..



Tango has it right.. torque wins races.. horsepower sells engines...



in building up my T-444E.. by swapping my turbo / injectors / and reprogramming the computer.. im increasinfg my torque by huge amounts (think of that 5252 divisor).. and of course along with it increasing Horsepower.. but my RPM is staying the same.. im not revving above 2600.. no wonder im mid-way through this project and my bus haul's ass already..... I dont have to make fake HP via RPM.. I can make real HP via torque...



of course as ive mentioned before.. power-adding is most generally the easiest way to break things... you may never break something.. but the more torque you apply through the same pieces of metal the higher the chances of busting something..

the key is only powwer adding enough that you czan complete the tasks at hand with ease.. but not so much that you get stupid and go beyond the limits of the metal or the vehicle you are driving..

-Christopher

 

[cowlitzcoach]

I have said it before and I will say it again, purchase the bus with the best power package and best rear end gear ratio for your intended purposes. If you don't you will spend the equivalent amount you paid for you bus updating and swapping stuff to make the bus do what you want it to do.

I can tell you that frontal area has a lot more to do with top speed than gear ratios or HP.

Our buses are not very heavy, relatively speaking. Instead they have a HUGE frontal area. Yes you really do need highway gearing if you intend to put a LOT of miles traveling around the country. You don't want to be stuck in the slow lane the whole way across the country. But with the huge frontal area our buses have you will reach a point of diminishing returns where you won't have the HP to push/pull the bus through the air at anything close to highway speeds.

For all practical purposes you need a minimum of 250 HP. 300 HP would be even better.

If you look at the engine spe'c sheets for most of the medium duty engines used in school buses you will see an interesting development.

While the Cummins 6BT/ISB and 6CT/ISC might have similar HP ratings the 6CT/ISC will have 50% more to 2x as much more torque. On the flats you may not notice a difference but as soon as you hit a hill you will see a world of difference.

As the hot rodders say, there is no replacement for displacement!

 

[Ronnie-SKO]

while I totally see the math.. essentially horsepower is torque applied over a period of time.. ultimately you need both to win a race.. you need a certain amount of torque just to begin performing what I call "real-world work" on the object.. in the case of a car.. to make the wheel turn and the car begin to move.. I realize this deviates from the true definition of work in physics.. and ultimately horsepower essentially keeps it moving.. after all horsepower is measured with and time.. in the case of advertising engines they use torque X rpm / 5252. (that constant is one recorded from a definition for engine measuring purposes.. so one can see that lots of torque will increase horsepower.. or Lots of RPM will increase horsepower...



reality is that when we want to think about real-world engines and driving.. we are at a stop light and want to get things going when it turns green. so we can build engines (aka diesels) with gobs of torque at low RPM to get things going.. Horsepower may niot look so impressive because our RPM is low that we measure at.. in fact many engines list their max torque and max HP in different lines on the spec sheet because the RPMs are different.. max torque occurs at leass than peak HP generally.. esp on a diesel..



consumer HP wars are why we have diesel truck engines like ford / navistar powerstorkes revving to 3400 RPM vs 2600 in the biog truck.. because they could advertise higher HP. really due to the fact it can rev higher..



Tango has it right.. torque wins races.. horsepower sells engines...



in building up my T-444E.. by swapping my turbo / injectors / and reprogramming the computer.. im increasinfg my torque by huge amounts (think of that 5252 divisor).. and of course along with it increasing Horsepower.. but my RPM is staying the same.. im not revving above 2600.. no wonder im mid-way through this project and my bus haul's ass already..... I dont have to make fake HP via RPM.. I can make real HP via torque...



of course as ive mentioned before.. power-adding is most generally the easiest way to break things... you may never break something.. but the more torque you apply through the same pieces of metal the higher the chances of busting something..

the key is only power adding enough that you can complete the tasks at hand with ease.. but not so much that you get stupid and go beyond the limits of the metal or the vehicle you are driving..

-Christopher

Very good explanation. Although I still say it is a misnomer that torque wins races. More torque gives more HP and therefore more work done, so raising torque gives more HP. HP is simply the measure of useful work done.

By the way race car engines run at very high rpm's, dragsters 8000rpms, formula one way higher. If torque alone wins races why not a diesel out of a tractor trailer.

As for a Ferrari their engines scream like crazy...

 

[Napabavarian]

Interesting discussion, I always look at the ratio of torque to hp. Lots more torque indicates a low revving engine, equal number is a mid range engine, lots of horsepower is a high revving engine.

Torque gets you there, hp gets you there fast.

A high torque engine with more gears is more economical than a high hp engine to operate, but it may take a bit longer to get there in the hills.

It's all up to your preferences

 

[cadillackid]

Ratio ffor bore / stroke.. long stroke engine can work at much lower rpm. Slower piston speed at beginning of stroke is why lugging then hard at low RPM is bad, too fast flame spread and you blow the piston apart or blow by the rings..
nice long lever arm makes for nice torque eso in the mid part of the stroke,
High rpm isn’t possible due to piston speed and mass.. I’ve always known where V8s fit in the gas world, being able To short stroke and rev high, burn more fuel in the same amount of time and with a spark , compression ratio can vary greatly so to be able to maximize gearing through a wider rpm range than an I6. But in the diesel world they don’t rev much higher than the I6 counterparts.. some of the old ones did and some of the new ones do but in the medium duty world they don’t make use of the extended RPM range like they do in the consumer trucks with V8 diesels...
someone can probably teach me why a V8 with same operating range as an I6 is made.. or what advantage it has..

 

[Napabavarian]

I can understand large v8s for space saving reasons, old 8v91 for instance, other large v8s not so much. In pickups it is more marketing, Ford and dodge share the work truck range so pick your preference, gm is aimed more at consumers, they have similar torque with higher horsepower for faster acceleration, and more cylinders sell, it's too bad they didn't have isuzu refit an i6 but I doubt that would sell.

 

[cadillackid]

back in the day the Scout used a Nissan 3.3 I6, it was a workhorse but even turbo'd it wasnt real powerful... it was the standard Bosch systemn like every common VW at the time used... Dad's 2 scouts never had the engines opened up... both 1980 models.. one got 375K and started to smoke... the other scout got 175K but was rusting to nothing so he swapped engines... turns out the issue was the injectors on the original engine.. its compression was still in the "very good " range...


of course those scouts didnt stand a chance in the consumer horsepower world that came on later.... even the ford and dodge "HD" trucks were still being bought a lot by regular guys flexing muscle or "my truck is bigger than yours" types... and those guys wanted to shred tires, make noise, and roll coal.. that was in FULL SWING in the 90s and early 00's..


of course the general public car-guy hated diesels by then from all the screw ups by GM... Olds 350s, Doggy 6.2's, lethergic 6.5's, crankshaft issues, you name it.. GM did to deter the public from ever wanting a diesel again..

 

[Napabavarian]

There is always the group who wants performance but they are fairly small, and loud. I was considering the majority that keeps trucks stock and just drives them.

Gm diesels had some issues but mostly suffered from gas engine maintenance, and a bad head bolt pattern combined with torque to yield bolts, slap in some arp studs and use diesel rated oil and you are good to go. The crank issue came from failed harmonic dampeners, fix that and you're doing well.

 

[GaryTheRock]

Swap Engine and Transmission on 2001 Freightliner?

I bought a 2001 shuttle bus with a Freightliner chassis, it has a Cummins 5.9 engine with a 2400 series Allison transmission.
It is currently titled in Georgia as a, "House Car", the current Georgia designation for a motor home.
Although the engine runs, and it's derivable, it makes a noise like a jet engine starting up now and then. I suspect it's the turbo, but could be the transmission.
What I want to know are the possibilities of changing to a different Cummins engine, like the 6.7 or the 8.3 for power reasons since it isn't exactly going to win any races taking off from a light or going uphill.
Since my Cummins 5.9 has only 100k miles on it I'm not as concerned about replacing that engine as I am about swapping the transmission out. There is a motor home version, an Allison 2500MH.
The 2400 I have does not have the nice panel on it that shows the fluid level or other information the newer transmissions show.
Can anyone tell me if it would make sense to swap the transmission I now have, the Allison 2400 for a 2500MH?
Maybe swap both the engine and the transmission?