Repower MC9 Conversion from 8V71

[RoyJ]

As you are a student of the ISB why don't you post a graph of the hp curve and torque curve of the ISB set at 400 hp for these guys compaired to the 8v71TA 350 hp set at 2500 rpm


good luck

I'm not a "student" of the ISB; I believe in innovation. If we keep thinking: this has worked for years, ain't broke, don't fix it. Then well, we'd still be driving steam locomotives.

Here's a dyno of a truck around 400hp, keep in mind this is at the WHEELS. For the sake of discussion, let's assume it's at the crank:



Look at the red curve. Keep in mind real torque does NOT drop off like that; it's the failure of a dyno to measure proper torque once transmission converter unlocks. Manual tranny dynos are flat till about 1400 rpm.

[RoyJ]

Before anyone says "torque is what matters", let's calculate the torque at the rear axle, since that's what really matters in the end. 68RE ratios are as follow:

1st 3.231
2nd 1.837
3rd 1.410
4th 1.0
5th 0.816
6th 0.625

Assume 5.88 rear end ratio, 40" tire, then at 60 mph:

6th: 1867rpm, 620 lb-ft at engine, 620 * 0.625 * 5.88 = 2278 lb-ft at axle  [Eco cruise]
5th: 2430rpm, 700 lb-ft, 700 * 0.816 * 5.88 = 3358 lb-ft  [Passing / small hill]
4th: 2964rpm, 650 lb-ft, 650 * 1 * 5.88 = 3822 lb-ft  [Hill climb]

We can do this for any speed, any gear. For example, steep hill @ 30 mph:

2nd: 2712rpm, 690 lb-ft, 690 * 1.837 * 5.88 = 7453 lb-ft

Can even back calculate this for 34,000 lb coach to find gradability:

7453 / (20" / 12) = 4472 lbs of thrust
4472 / 34000 = 13%

I don't know about you, but climbing a 13% steep hill at 30 mph, in a 34,000 lbs coach, seems like very decent performance to me. Something I wish my bus can do right now...



Now, let's compare that to some examples of 8V71N, TA, or 6V92. My guess is that the little ISB can hold its own!

[RickB]

Roy,

I feel the need to defend some of our proven experienced folks here. A friend told me once "Sometimes it's not what you say as much as how you say it" and you sure don't seem like you want or need our most experienced guys input so why don't you show us and quit telling us about your 400 HP no problem to install or modify, long life ISB. I'm betting $15-20k installed before you tighten the last bolt. Of course you could ask guys like Clifford or Brian Diehl or Jim who have actually done a repower too.

I think we'll all be singing your praises in about 250k miles of passing the best minds, two strokes and technology we have to offer like we're standing still.

Most of us that have been here awhile tend to find ourselves asking folks like Clifford and Tom C instead of telling them. I'm all for hearfelt discussion but these guys are our friends that help us with our ancient and out dated technology year in and year out.

No harm no foul just show some respect to our collective intelligence as well as your own.

Just my thoughts,

Rick

[cody]

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[luvrbus]

Rick, I finding the reading to be enjoyable not that I believe the bs but I really like the 13% grade at 30 mph he has the ISB out preforming a 625 hp C-15 or the 60s.
Even the larger ISL Cummins was junk in a bus Vanhool tried those without success for a few months, you need to buy a ISB then Eisenhower tunnel would be no problem for you  

 


good luck

[cody]

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[cody]

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[luvrbus]

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

[RickB]

Clifford,

Eisenhower tunnel isn't a problem I just go around it or I sit back and take about an hour and a half of people flipping me off wiyh a big fat smile on my face because I can't possibly go fast enough to make them happy!!

Cody,
I am not trying to discourage "new" thinking I'm trying to encourage a bit more dialogue here. I think it's pretty apparent that  "I'm set in my way, all telling, rarely listening" type discussions rarely end well in the long run here. Circusboy comes to mind. I for one would love an alternative to our current options horsepower wise bur there's talking and then there's doing and the too rarely run parallel. How many unforeseen problems have each of us encountered when doing any modifications to our rigs? How sure were we that we had it all figured out before we started?

Those encounters where reality makes a fool of our limited knowledge are the very things that temper the way we approach those that visit this place. Folks that speak in absolutes here based on anything other than hands on experience (either their own or collectively) tend to blow in here, cause a bunch of arguments and leave as fast as they came.

If I crossed a line I'm sorry but we have had quite enough drama this year for my liking I was just trying to keep another blowup from happening.

And I'm not joking Roy that if you find a realtime, where the rubber meets the road alternative to our low HP blues, I for one will get my checkbook out
Didn't mean any disrespect,
Rick

[cody]

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[RickB]

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 was encouraging Roy to show us not just tell us and it certainly didn't seem any more matter of fact than his passionate belief that it can be done and anyone who thinks it can't would still be driving steam locomotives. That is a quote from Roy in an earlier post BTW.

Cody, I'm surprised every time you voice a feeling that you feel we are the "new idea police" here, I just disagree that's all.
I am basing that disagreement on the very thing I am kindly asking Roy to provide. By experience.

This kind of discussion in the past has rarely if ever led to a good result. It usually ends up being locked by the moderators.

I do not know for a fact that the ISB is capable of Roy's claims but I'm pretty darn sure about how our board reacts as a group to monolgue type discussions and it's not very well

I am joining Clifford in the "I'm done with this" section
Rick

[bevans6]

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

[cody]

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[kyle4501]

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. . .

Simple minded wishfull thinking isn't usually the most successful way.
Neither is ignoring or failing to understand or investigate the reasoning behind current standards


Why not combine it with a "water to gas" system & really show the world how it's done?  

[TomC]

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