Engine Question!

[steve5B]

Hello,

  Hope everyone had a nice Thanksgiving!  I have a friend that is thinking about buying a bus for a conversion project and he ask

  me about the 8V-71 engine.  I said I would would post some questions. 

1.  Would this be a first choice engine?

2.  Is there enough power for this heavy bus MC-8?

3. Is it low on up keep?


Any help would be great, as I will pass it on to him!

  Thanks,

  Steve 5B.....

 

[turbobrat930]

If I may, I would like to add to this... and pose another question.   

I would like to know the answer to the question posed above as well as the 6v92 T or NA... against the 8v71.. Which is the better motor? From my searching on this forum, I believe they are close to the same HP, but I would guess the 6v92 is better in the mountains because of the turbo. Does either lend itself to modifications better? I would also guess that the 6v would be more fuel efficient as well?

[Utahclaimjumper]

The 6V92TA makes more horsepower on less fuel and weighs less, no need to modify or "hot rod" it, will also fit all transmissions that the 8V71 will>>>Dan

[Utahclaimjumper]

The 6V92 is also more sensitive to overheating issues.>>>Dan

[quantum500]

All 92 series engines have wet liners all 71 series engines have dry liners.  All of them can and have been turboed.  Depending on what is available and how much work/money you want to invest anything can be a good starting point.  8v71n's are rated from 270 to 335, thats at sea level and altitude seems to really get to them.  6v92 are usually rated at 350 and can get up to 400, those ponies are good up to 10,000ft altitude.  A turboed 8v71 will be very similar.  The two engines are almost identical in displacement so performance wise they are very close.  The 8v weighs a little more and is physically bigger.  The biggest difference is the wet vs dry liner debate.  Dry is a little harder to rebuild but has the advantage of never leaking coolant in the oil.  Those are most of the facts you need to work with.

[TomC]

If you want more horsepower out of a 8V-71, it can be rebuilt into a turbocharged and air to air intercooled putting out 400hp and 1200lb/ft of torque with 80 injectors.  90 injectors can be used, but should also be used with a multi speed transmission for closer gear spacing-getting 450hp and 1350lb/ft of torque.  I turbo'd and air to air intercooled my bus with a 8V-71 and with 75 injectors, has 375hp and 1150lb/ft torque-a very big improvement in performance.
If you're going to change the engine, I highly recommend you changing to a 4 stroke engine-like the Cummins ISM that weighs the same as the 6V-92 (2,100lbs) and can be rebuilt up to 500hp and 1550lb/ft torque for RV use.  Then you'd have hill climbing and fuel mileage all in one.  The Cummins ISM with 10spd Ultra shift transmission (no clutch pedal) would afford you the best possible fuel mileage. 10mpg wouldn't be out of the spectrum.  God Luck, TomC

[Songman]

The 6V92TA makes more horsepower on less fuel and weighs less, no need to modify or "hot rod" it, will also fit all transmissions that the 8V71 will>>>Dan

This is the common belief. Personally, I am taking the 6V92 out of my Eagle and replacing it with a 8V71 Turbo because the 6V92 is underpowered. The 8V71, if built right, can go far beyond 400hp. The one that is going in my bus is already built and we will be 'de-tuning' it back down to around 450 just because that will make it more streetable. The 6V92 does weigh less though. The 8V71 Turbo is my engine of choice. When I first got into buses I talked to a lot of guys who have been doing this a long time and they all sang the praises of the 8V71.

[uncle ned]

Yes but you have don close   The rest of us do not

uncle ned
4104  1 "hot" 6v92&730
huggy bear

[turbobrat930]

here is a link that I ran across while searching thru the archives... I found this on google...

http://www.busconversions.com/bbs/index.php?topic=9931.0

from this forum no less !!

[buswarrior]

The best bus conversion engine is the one that is already in the bus and trouble free.

There is not nearly as much savings as already having a good power plant in the shell.

You do NOT have to re-power, the stock engine is quite capable of pushing you across the continent without spending any more money to reach the summit 30 seconds earlier.

That said, the early 6V92 were not as fast as you might like off the line, and many stock installs were at the 277 HP rating, not 350 HP. And when you get into the DDEC motors, you need a computer that is rated, not just the hardware.

For your comparison in east coast bump climbing:

I have an 8V71, stock 280HP, and it runs me around just fine.

I have driven a loaded MCI EL3 Renaissance with 400 HP Series 60 and Allison B500 up Fancy Gap in Virginia on I77 at 50 mph, same speed in both 4th and 5th gear.

My MC8 with 8V71 and Allison 740 will climb it at 44 mph in 3rd gear.

So, spend your cash as you see fit, that's what do-it-yourself is all about!

happy coaching!
buswarrior

[makemineatwostroke]

turbo;10 to 12 mpg is going to be the exception for a 450 or 500 hp Cummins if they have the gear ratio Cummins recommends 4.33 to 4.88 it is going to be a 5 mpg engine.That is the standard engine for a VanHool bus and having friends that use the ISM in their 40 and 45 ft Monocos, Foretravels and Van Hools they average about 5 mpg.Some of these guys get away with using the 3.73 and 3.36 gears for good fuel milage with 10 speeds.

I have friend in NM that has a new Dynaquest truck conversion that has a smaller 330 hp ISC Cummins with the Allison 3200TRV transmission with 4.88 rear gears he was told to expect 13 mpg his average is 8.4 when he ask the question about the low fuel milage he was told "that is what we got on our test tank at 60 mph" I have a  60 series in my bus and average about 5.5 at 70 mph so do your own research on mileage not what you read on these boards  FWIW my DDEC 8v92 got better mileage than the new 60 series it got 6.5 mph
have a great day

[turbobrat930]

well, since I have not even got a bus yet.. just trying to do some research first. Since I am familiar with turbo motors.. That is what I will probably stay with, Buswarrior, you are right.. Unles the coach I buy has no motor, or needs a rebuild, I will not be repowering anytime soon.  Just trying to do some research before committing on one bus.

[cody]

I've got a 6-92 and the biggest determining factor in my fuel mileage is how much my foot weighs on any particular day, I've never been one to try to beat a porsche off the line or crest a hill with a full head of steam, I'm just kinda relaxed and I get where I'm going when I arrive, to me thats the important thing lol.  As long as you are still looking for the perfect bus, pick one with the perfect engine/tranny combo, much cheaper to get the right set up to begin with than to repower later.

[quantum500]

I have a  60 series in my bus and average about 5.5 at 70 mph so do your own research on mileage not what you read on these boards  FWIW my DDEC 8v92 got better mileage than the new 60 series it got 6.5 mph
have a great day

That is very interesting!

[kyle4501]

If good fuel mileage is important, get the fuel curves for the engine & look at the gearing of the bus. This will guide you as to where you will find the optimum operating speed.

All engines will have a rpm range where they make the most HP per Lb of fuel. Operating in this range will yield the best fuel mileage. This is where more gear choices can come in handy. 

Ignoring this explains why there are such varied reports of fuel mileage . . . . .

My 4501s have the Greyhound spec'd drivetrain (8V71 @ ~270hp, 4 spd, & 3.7:1 ratio) still in 'em & I get ~10 mpg on the East coast. I ran about 65 mph & I wasn't interested in being the first one up the hill.

Be wary of buses that someone has changed out the power unit to something other than factory supplied, especially if they radically increased the HP. Many potential problems can arise from a non-engineered system. Cooling issues come to mind.



All that said, the 8V71 is a reliable engine that will soldier on long after it is due for a rest . . . . A 'smoke' turbo can be added (to a healthy engine) without replacing all the internal parts -IF- the boost is kept low enough. . . .