Repower MC9 Conversion from 8V71

[RoyJ]

John, like you pointed out yourself, we're talking about a 400hp tune ISB here.

There's a HUGE difference between 190hp and 400hp. The school bus I drive is also pretty slow once loaded, and that's low 200's hp. Low torque can always be made up with gearing, low hp is low hp, cannot be made up with any simple machinery, or you'd get free energy.

There are some 40 foot hybrid transits out there with ISBs, but that's with a big electric motor assisting.

[RoyJ]

BTW, I am at about 46K with the 9.6K service truck.

I don't have any information to say that the ISB will not do a reasonable job in a lighter bus.  As has been pointed out, it is/has been used in some motorhomes.  However, when we start talking about 40 foot buses, they are often over 35K and some well over that.  Then you add a toad.  The Series 60 and other class 8 truck engines are very heavy duty and are designed to run all day under heavy load for 500K or more miles.  The have very strong blocks, cranks, and cylinder liners.  I don't think the ISB is that kind of engine.  Yes, you can modify them to get some pretty good HP and Torque, but in an RPM range that probably requires some unique gearing that is not readily available for buses.

Jim

Jim, with a bus at 46k lbs, I wouldn't even remotely think about an ISB, regardless of duty cycle. My assumption of a 34,000 lbs converted MC9 would be the absolute max I'd put an ISB in, simply because that's what hot shotter gross with Dodge Rams. The ISB plan was origionally for my 25,000 lbs bus, which can go up to 30,000 with a toad and heavy gear.

I never doubted that a Class 8 engine, bigblock (ISX, S60) or smallblock (ISM, C13) would be much more durable than an ISB, hp for hp. But that's the exact reason why I wouldn't want one in an RV bus - they're too durable. You pay for the durability even though you'd never use it.

I drive my bus no more than 6k miles a year (and probably most people here as well). At that rate, I'd never wear out a 500hp S60 engine, or even the ISB.

[RoyJ]

Cummins ISB 6.7 liter for motorhomes is currently rated at 360hp @ 800lb/ft torque.  Considering the 8V-71N with N65 injectors is rated at 304hp @ 800lb/ft torque, the hastle of changing the engine over is just not worth it.  Granted, you might get 1-2mpg better, but that improvement in fuel mileage would take a long time to see any advantage.  Better you either turbocharge the 8V-71N (I know personally that that works extremely well) or go with the larger ISC or ISL (same block) for a maximum of 450hp @ 1200lb/ft torque.  THEN you'll have some performance.  Good Luck, TomC

Tom, I definitely wouldn't pull out a perfectly running 8V71 and put in an ISB. But in the OP's case, where the engine is not running so well, and it's a choice between a rebuild or engine swap, then it makes sense.

I'm also not implying the ISB would run circles around the 8V71, but rather, that it's adequate as a replcement. At high elevations however, the ISB would shine.

Yes, I have read your past experience on turboing your 8V71, and it has inspired me to design a (very) low pressure turbo setup for my little 6V71 4V N70. I'm thinking 3 - 5 psi, with no engine internal changes, using two HX35 turbos. I'm satisfied with my power at sea level, but it falls flat above 4000'. The ISB is for my engine wears out.

[HighTechRedneck]

I like to see discussions of out of the box thinking, they sometimes lead to something innovative.  Thomas Edison was a big believer in that.  He once said "I can tell you 10,000 things that don't work."

However I do believe that the life span of an ISB in a MC-9 would be severely limited.  I am not a diesel engine expert nor am I an engineer, but there is one point to consider while talking about duty cycle and RV use of a highway coach such as the MC-9 that I haven't seen in this discussion.  In my opinion, the more important duty cycle consideration is about hours/miles of continous operation in a steady run than hours/miles per year.  That is where a heavy duty engine shines.

A school bus in school service will typically operate about 2-4 hours in the morning, rest for a few hours and then 2-4 hours in the afternoon.  During that time it will typically be ranging through its RPM/Power range frequently.  On occaision they may travel 4-6 hours to an out of town game.

There are quite a few folks here that take cross country trips in their buses, driving 8 or more hours per day using over 220-250HP sustained output.  There are some that push 12 hour driving days.  And there are at least a couple that team drive their bus 24 hours or longer virtually continous including up and over the Rockies.  I believe that kind of continous high output use pushing a 34,000 or more load would result in an early death for the ISB.  I do know that in a lot of factory RV's they often end up needing overhauls in 50,000-70,000 miles.  I don't know how many of those are ISB's.

I think most MC-9 conversions end up weighing 35,000+ and they will often pull a toad that weighs 3500-5000. The GVWR for a MC-9 is 38,000 I believe.  My RTS currently weighs 32,000 and my toad weighs 4100.  And my RTS doesn't have the large cargo bays, extra large tanks, generator or large house battery bank.

[kyle4501]

Neither is ignoring or failing to understand or investigate the reasoning behind current standards

Again, current standards are all designed for commercial duty cycle. Name one OEM that design for busnuts?

RV manufactures seem to agree with me, if they tune an emissions choked ISB to 360hp (easy 400hp without emmissions).

About those RV manufacturers, most use the minimum they can get by with in order to cut cost & last past the return period. Isn't that why most of us are here? To have something well above 'minimum'.

Dad has an Airstream MH built on a Freightliner chassis with a 330HP CAT (all as it left the factory & no mods at all). He can't use full power for anything except acceleration (& that is time limited too) because of overheating - they didn't install a radiator big enough to handle the engine's installed HP. Hmm, what does that say for one of the most respected RV manufacturers design intent?

The 460 in Dad's van has ~200k miles on it, ~100k pulling a 8,000# Airstream trailer. The same 460 in a motorhome seldom lasts past 75k miles before a rebuild is needed. I propose the reason is duty cycle - the van has periods of 'rest' where the MH is in constant duty.

While your math may show it will work, the preponderance of real world evidence leads to a different conclusion.

For long term considerations of time & $$, my bet is with a used heavy duty engine of similar type that is currently in the bus. While not guaranteed, history indicates a higher success rate or put another way, more bang for buck. 

But, feel free to "roll your own".

[robertglines1]

Roy J.    First of all I object!    Don't knock steam power..still the most bang for the buck..also my son is a engineer and works on drive systems for ships..in the end still steam.power plants still steam.no matter fuel source..still steam---we have two antique steam engines a 1905 Huber and a 1925 KeckGonnerman 19hp. we run the Huber 16hp( this boiler hp) .regularly 105 yrs old.we take scrap from the saw mill and burn in the boiler..recycle--Enjoyed your post!! and be prepared to get any point challenged..And by the way the three trucks my cousins run are not week end toys..to put 60,000 in a little cummins you got to get some of that back..Both John and Tammara are engineers one Mechanical and one Electrical .Later 20's brother and sister and their old Dad still helps with the work..They think outside box also! keep it up!

[bevans6]

I enjoyed this thread immensely.  I've had many conversations with people who confuse the relationship between torque and power, which are two sides of the exact same coin separated only by time (RPM).  And out-of-the-box thinking is always a challenge to wrap your head around.  On the "other" side of my travel effort I run a Dodge 2500 pickup with a Hemi at 18,000 gross weight, and so I know that power with appropriate gearing can work wonders - it's a ton faster at that load than my bus is, in any circumstance, and my bus is only around 26K lbs. 

Anyway, good to consider another way to kick the can...

Brian

[cody]

Yes, I removed some of my posts, some wern't appropriate and some wern't relevant, and some should take note of the action.  I'd like to welcome roy to the board, I'm pleased to see somebody that can write a mathamatical equation that I can read and understand instead of just saying something can or can't be done, here are the numbers, prove them right or wrong, everything starts with numbers regardless of what a person feels comfortable with, it all begins with numbers. I've always said that I don't understand metal, it confuses me, but equations I do understand and it's nice to see somebodies thoughts backed up by the math.  People have to wake up and realize that our beloved 2 strokes are doomed, if anyone has read the drivel that our leaders have signed onto in the international 'green' world, our 2 strokes are doomed.  We have to start to think about what is coming next and the smaller lighter duty engines may be all that will be allowed in our private rigs in a short time, Don Fairchild is already seeing what is being forced on us and is working to provide a remedy but the next wave is already been signed and is waiting in the wings, and the wave after that.  I know that many feel comfortable in their greasemonkey clothes but take a moment and climb out from under your beloved 2 stroke and do some reading, read what obama has signed onto for us in the international market, read up on exactly what a carbon footprint is and then take a good look at your engine compartment and don't expect to be grandfathered in, has anyone seen the required fuel mileage figures for the next few years?  We need a few more actual engineers on this board.

[TomC]

At least for now in California, RV's are exempt from smog laws.  But-when that time comes to switch over, I will do the engine swap on my truck's Caterpillar 3406B to probably a Cummins ISL with 450hp and 1250lb/ft torque.  Hopefully by that time there will be an assortment of crashed trucks with 2010 engines available.  At least for commercial trucks and buses-the law reads for California: that by 2023, all trucks and buses in or coming into California must have 2010 certified engines (ones running with Urea, or DEF [Diesel Exhaust Fluid], or BlueTec {by 2023 International will have a similar system}).  Still-RV's have not been mentioned.  Good Luck, TomC

[luvrbus]

What do need with more engineers on the board Cody Cummins Engine has 1000's that designed that engine, check the Cummins sites they will tell you what the souped up 5.9 changed to a 6.7 EGR is capable of doing or if that doesn't work just go to some of the Dodge sites.
I have a friend in Houston VP of Southern Plains Cummins read this post he said go for it and he will see you in about 30,000 miles and bring plastic or your check book it will only cost you 15,000 without the Bosch fuel pump



good luck

[cody]

What we need are more actual engineers on the board and not just people that would like us to think they are, whether you like it or not our 2 strokes are going to be history in the not too distant future, we all have friends we can quote, thats nothing new, what we need are fresh ideas to cope with what is being discussed in circles that we can't access.  Some engines won't be appropriate for weight classes that are extreme like a 46K bus pulling a 10K vehicle up a verticle wall but for many of the buses in use now that range between 25 and 35K there are choices that might be well concidered. Anyone that thinks that the emmissions rulings are going to just go away are in for a huge wakeup, several states are looking at what california is doing and thinking beyond that.  Bush set the stage and obama is bringing out a whole host of players, look at what he's signed onto in the international settings, and he's not afraid to use his pen to bypass congress thru executive orders just as bush did. It's your choice if you want to ignore whats going on around you but at some point we will all have to realize that there is a movement going on that we will have to cope with or at least adapt too and some new ideas arn't a threat to any of us.

[luvrbus]

Cody, I  know of 6 engineers here on the board you do battle with 2 all the time lol so they don't waste their time on posting the facts, knowing Jim he just reads a shakes his head he is not going to waste his time he has tried for years only to have it turn into pissing contest.


good luck

[cody]

Can you post the names of the 6 engineers and their PE registry numbers please?

[kyle4501]

No doubt that possible future restrictions should also be considered. Environmental impact awareness should also be a part of any action.

That is easier said than done sometimes.
Which will have a smaller carbon footprint will only be a guess based on past history - which we should all know "past performance does not guarantee future results".

In the past, we weren't a disposable society. We used to be able to buy brushes & bushings (off the shelf at any parts store) to rebuild a starter, now it is difficult to even find a listing for those items at most parts stores.

Even if the 2 strokes will be mandated out of use (by law or code) in 12 years, is it better for the environment to scrap them all out now & fave the impact of having to build new replacements? I don't know, but I think it is something that has to be determined on a case by case basis.

I have a feeling that the next 10 years will bring about some great innovations that will be of great benefit. Some will also be of great burden with nothing good.

The original poster was looking for re-power suggestions & he got several. One can't make an informed decision without seeing all sides. As was pointed out, changing from 2 stroke to 4 stroke takes more time than he wanted to spend & would cost much more than "fixing what he has".

Changing to a custom gear ratio isn't for the faint of heart either. . .

Sometimes, a little better understanding of the bigger picture makes it easier to live with the shortcomings of our less than optimum toys. 

[kyle4501]

Can you post the names of the 6 engineers and their PE registry numbers please?

A PE registration number does not make one an engineer.

Passing the test wasn't difficult. 
Earning a masters degree in engineering is much more mentally taxing. 

Staying out of pissing contests is another thing entirely.