Repower MC9 Conversion from 8V71

[Len Silva]

plus another 10,000 pounds of sand bags and a 10,000 lb trailer.

[kyle4501]

How happy do you think arl will be if his 'freshly tuned to 400 hp' takes a dump after just 40,000 miles?
I know there are no guarantees, but the light duty ISB is definitely more prone to failure than a heavier built engine.

Care to explain why the ISB would take a dump at 40k miles?

Didn't say it would, just asked how one would like it if it did.
I do feel it is likely the ISB at 400HP would have the lowest reliability of the engines mentioned.

As to why it would fail sooner:
Driving style for one thing. A lighter motor traditionally doesn't tolerate 'abuse' as well as a heavier built engine. This is purely cautious speculative opinion based on personal experience & education.
(edit to add) Or lack of education.

[blue_goose]

After reading all of the post I have to put in my part.
I come from the school of hard knocks and only repeat what I know for sure.  When you hear about a engine going bad like Jim's did it doesn't mean that all the series 60 are going to blow up at 650,000 miles.   For no reason that any of us know any engine can fail with a short life.
This is what I do know for sure, a friend has a coach with the ISB that has had two engines lock up in 180,000 miles. The second engine was rebuilt by Cummins in Mexico.
Another friend is in the process of rebuilding his 8v71 and has already spent over $6,000 on parts alone. He did have to buy two rebuilt heads, but most of the time you will find they have cracks when you need a rebuild.  The parts were not DD they were after market and cost about half of what DD charges.
I have rebuilt one 8v71 in my Eagle, replaced it with a 8v92 then a series 50.  Sure wish I had not done the 8v92, but love the series 50. I just make a big change in the series 50 that will more than likely shorten the life of the engine, but it sure runs good at 375 HP. Only time will tell, but if it goes bad I'll put another one back in for less than a rebuild on a 8v71.
Jack

[robertglines1]

back to the original post: $ wise it is less expensive to go with a engine currently being used in the bus transportation industry.Most Cummings and 4 stroke Detroit's would be the less expensive..50 and 60 series Detroit's are plentiful and have a pr oven tract record in the industry..If you want to be the one to experiment do what you want..let us know the results..My choice for present project was a 60series 12.7 liter with a 10 speed Eaton autoshift with the stock 4:56 rear end..36,000 lb coach. I had no drivetrain at all so got to select what I felt was best and most dependable for me..nice thing about this hobby do it your way!  Bob

[TomC]

Detroit Series 60 at a conservative 500hp @ 1650lb/ft torque with the 10spd Autoshift (with clutch pedal) makes for an excellent setup.  Granted the Autoshift is not as fast off the line as the Allison (not by a long shot), but your fuel mileage will be about .5-1.0 mpg better.  With the 4.56 rear end and 12R-22.5 rubber (485rpm), your overdrive cruise rpm will be- 1614 @ 60, 1749 @ 65, 1883 @ 70 & 2018 @ 75.  We gear the big trucks for 1600 @ 75, which I would lower to 1500 @ 75, which would translate into a rear end ratio of 3.38.  Then you'll get max fuel economy.  Good Luck, TomC

[Don Fairchild]

Roy,

If you don't mind my asking what year is the school bus you drive.

Thanks

Don

[rv_safetyman]

Wow, I see that Cody pulled all of his comments before I read them.  That kind of sucks and does not fit my image of good contribution.  Oh Well.

Wanted to add a couple of comments.  First about the loss of my first Series 60.  The engine did not blow.  It had a lot of damage (broken head bolt from heat, and some cam scoring (also heat related).  The "failure" was that the liners sank into the block and let the combustion pressure and gases/heat get into the wrong parts of the engine.  As I look back on it, my inspection of the truck it came out of and a couple of other things leads me to believe that it did not have great service towards the end of its life. I suspect they used automotive antifreeze as there was significant cavitation damage on the liners.  Even with all of the damage, the engine ran fine and got me home with no problem (other than blowing antifreeze out the surge tank).  I had no clue that there were some pretty drastic things going on.

Next, let me comment on HP and Torque.  My current engine is set at 470 HP and 1650 ft pounds.  Even with 10 speeds, it does not race up the hills of Kansas and Missouri (they have some pretty good hills).  In the Colorado mountains, I am in the slow lane with the trucks.  I can go faster than they can, but I don't have the power to pass them in a timely manner so that the folks who pay more taxes than I do can use the highway as their personal race track.  It does not bother me that I have to fall in behind the slower trucks, the scenery is great.  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.

Bottom line my big axx Series 60 is just about right and anything smaller would not be fun to drive with my weight.  

BTW, some Flxible folks use the ISB and that is probably a good fit.

Jim

[RoyJ]

Whoa, some of you guys take things way too seriously. So I'll try to clear up my intentions: in no way am I trying to disrespect any of the senior members here, I have my uttermost respect for these guys and their experiences.

That having been said, some of you also need to loose the attitude of "this guy's new, he must be an idiot and doesn't know what he's talking about".

Quote me where I said anyone (TomC or anyone else) is "wrong". I didn't. I simply defend my own opinions with calculations. I was disagreeing when others simply pointed out that I'm wrong, without any facts or scientific argument. If you feel that's rude, then well, I wouldn't know what to say.

[RoyJ]

Roy,

If you don't mind my asking what year is the school bus you drive.

Thanks

Don

Don, the one I've been referring to all the time is a 1996 Thomas MVP, with a 5.9 pusher. 12V, P7100 pump, so less than 250 probably.

It has a GVW of 18,500 kgs (40,000 lbs). But following US axle rules, probably no more than 36,000 lbs.

[RoyJ]

Cody,

Is it possible? I'm not sure but it isn't a fact either until it's proven in a chassis. So until we see it driving up a 13% grade at 30 mph it is a theory and that's why I was encouraging dialogue rather than monologue. I have to say once again that as a group I have never seen evidence that we are all closed to research and progress here in fact I've seen alot of forward thinking concepts become reality here. However, I have never seen an ISB even remotely considered for a serious repower here and I have also seen no evidence that it's ever been actually done to a 40 foot 34000 lb bus so until it's proven in the real world, saying that it's not a proven fact is not closed minded.

I am basing that disagreement on the very thing I am kindly asking Roy to provide. By experience.

First of all, Rick, I've stressed over and over again by now, about the tens of thousands 40 foot school busses, grossing mid 30k lbs, running around our nations. Do you not consider that "real world"?

Second, a little personal background here:

My main career is Mechanical Engineering, which means all my work is revolved around unproven facts, unknowns, and no experience. I'll stand by my origional quote: if everything has to be known by experience, we'd still be in steam trains, or worse, ox carts.

Why do you think the biggest advance in recent engineering is simulation? Everything from complex fluid dynamics to solid structures are simulated on computer generated mesh data. Why? Because no real world experience exists!

No, I do not have real experience with an ISB in an MC9, but what I did provide was cold, hard, basic calculations. Numbers don't lie. As busnut, we represent a very unique market - using commerical duty vehicles at a recreational duty cycle (a word I emphasis all the time). The reason no one puts an ISB in a coach, is that all coaches are designed for commerical service life. We're not after that.

[Van]

 Lol It's always fun on paper, til someone gets hurt  



Paper cuts suck

[RoyJ]

Cody, why waste the time I thought the guy maybe on to something till he got to end a 13% grade with a 34,000 lb bus at 30 mph my 5 year old grand child could figure that wasn't going to happen I am gone from this one   



good luck

So you ask for a real world dyno, I provide you with one, and even proceed to give some calculations based on it, and then you reply with this comeback?

Why don't you point out where I'm wrong instead?

Before you say numbers and calculations don't mean anything, consider this: my last job in engineering was fuel cell design. The larger stacks we designed were used for - you guessed it, buses.

How do you think we related a random output number from the fuel cell, say - 178 kw, to real life performance of the buses? All calculations, most on the good'ol Microsoft Excel. I was one of the main engineers responsible for performance simulations. Everything from uphill, downhill braking, passing manuver, to top speed, was pre-calculated before any trials were run.

[RoyJ]

I don't have a problem with the math at all.  I've known for many years that power is what does work, and gearing to allow power to be applied appropriately is what you do when to build a power train.  While I still don't think that an ISB is a great choice for an MC-9, it's not because I don't think it has appropriate power.  I think that the configuration above would out-perform an 8V-71NA in bus tune, no doubt in my mind at all.  I think that it would not out perform an 8V71TA, with 370 hp at a governed 2100 rpm, capable of well over 400 at 2500 rpm, and 243 hp and peak torque of 1064 ft lbs at 1200 rpm.  It may or may not get better fuel mileage, I would bet that the ISB fuel curve gets pretty stiff at 3000 rpm.  

Here is why I don't think it would be a great engine for a bus.  Transmission - probably not strong enough to push that amount of torque against that load reliably for hundreds of thousands of miles.  Engine - same thing, in a truck application it will be called upon to deliver max power, max torque far less often, and for far less time duration than the same engine in a bus.  For example, full throttle up a hill for 10 or 15 minutes, what will the engine and exhaust temps look like?  I have no idea, I don't think they will be great.  Gearing - postulating a 5.88 diff ratio in the rear axle of an MC-9 is one thing, actually getting one may well be another story.  I don't know,though.

I don't have a problem with the idea, I just wouldn't choose that route myself.  I continue to think the ISB is one of the great engines, though.

Brian

Brian, I don't disagree with what you say at all. I never claimed the ISB implant was perfect, or I'd be rich by now... Every solution has its share of problems, and transmission / gearing as you point out, was perhaps my biggest two worries.

Now, my own bus is a 25,000 lbs 35 footer, so the transmission would handle it without a problem. But even then, I'd beef it up with better converter and valve body, in addition to a huge fan blown cooler. The 5.88 is a big issue. I've considered axles from class 7 trucks, many of which have ratios of mid 5's. Coupled with low pro 22.5 tires, I might get close to 5.88 effective ratio.

The engine EGT and coolant temp shouldn't be an issue, as I'm not making internal changes such as huge injectors. In fact, the head load would reduce without the emmisions garbage. I also believe the cooling capacity of an MC9 is many times larger than a Dodge pickup.

About the continuous full power issue, this is what I was referring to by duty cycle. I highly doubt an MC9 would require constant 400 hp, considering the MC102 I drive at work (charter duty) gets by just fine at 290 rwhp (360 crank hp). Even then I'm not flooring it all the time.

But you make a good point. An ISB swap in a coach is definitely not for people that just want to step on it. Like any other modded hardware, it would require constant monitoring with proper gauges, and a restrained right foot.

[RoyJ]

The math needs to include inefficiencies & losses to be represenative of real world conditions.

The Caterpillar booklet "Understanding Coach / RV Performance" showed some interesting losses, like their 500 HP motor running at max rpm required 62 HP to drive the fan. Then there is the rolling resistance of the vehicle. Those are the biggest omissions.

In order for an experiment to produce usefull meaningful data, it needs to be well thought out. . .

To be fair, the dyno I showed is measure at the WHEELS, which is post losses (drivetrain, fan, alternator, and any other accessories).

The rolling resistance is a very good point though, and I admit, I forgot to include it. Typical tire rolling resistance is 0.015 for a bus, and aero forces for an MC9 size coach is almost negligible at 30 mph, it's only 35 lbs.

So, 34,000 lbs * 0.015 = 510 lbs, add 35 = 545 lbs.

From my origional numbers:

4472 lbs thrust, - 545 lbs = 3927 lbs net thrust.

3927 / 34000 = 11.5 % grade @ 30 mph

Still pretty respectable.


If anyone see any other error, please point them out to me. But don't just say your 5 year old grandson, or 200 year old great grand aunt knows better than an ISB pushing 34,000 lbs...

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).

[Iceni John]

I remember reading on CCJ a year or two ago of a front-engine Blue Bird (probably a TC2000) with an ISB  -  it completely stalled out while trying to climb one of the steeper climbs in the Sierras with a full load on board.   I'm assuming its engine was at the ISB's standard school bus 190 HP setting, and it probably was grossing in the low 30,000 pounds, but it literally could not get out of its own way climbing a grade that older Crowns and Gilligs could manage with no problem.   The difference of course is its torque (or lack thereof).

Yes, I know that more powerful settings of the ISB are being discussed here, but real world experience shows that small engines in heavy vehicles don't always work so well.   That's one reason why some school districts, especially those in the Sierras and Northern California, prefer keeping their thirty-year old Crowns with big-cam Cummins 855s instead of buying brand-new disposabuses with ISBs that CARB is forcing on them.

John