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Old 08-16-2016, 01:26 PM   #1
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Possible engine swaps

I haven't bought a bus yet, but I've been checking a lot of websites weekly to see what aution prices are like and what's available. I'm looking for an FS-65 6 or 7 window bus, which should be short enough to go to most of the national parks in the US. The problem I keep seeing with these is their engines (mostly cat 3126, cummins 5.9L, or mbe 906 6.4l) are all around 210-250HP, which seems a little underpowered, especially since I will probably tow in the future. In comparison, my Dad's 93 f350 has a 195 hp 7.3L in it, and it was under powered with a slide in camper in the bed. Now to my question. Which engine type would be the easiest to swap out, maybe from a dumptruck that was in a wreck or another larger bus? I know that cat made the 3126 up to 330HP, with all of them being 7.2L, but I can't seem to find much on if the high HP blocks would bolt in or not. I've also read that cat engines are expensive to work on. I also know mercedes makes the MBE still. Does anyone know how hard of a job it would be to swap for a more modern 7.2L MBE to replace a 6.4? I know its not an easy job no matter what, but how bad is not easy? Whatever I get, I plan to replace the transmission with a more highway friendly one, so I will be tearing it down anyway. I just want to narrow down what engine I should be looking for when I'm looking at ads.
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Old 08-16-2016, 02:05 PM   #2
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get the engine trans combo you want in the first place. much easier than any swap. most fo the engines listed are under 210hp. 180-190 range imo. for 250 hp you meed a cummins 8.3, dt466.
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Old 08-16-2016, 04:18 PM   #3
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Its all about the torque. A 250 DT466 is pretty powerful.
My 190hp DT466 even does ok propelling a 40 foot, 18k lb machine. YMMV

If I were gonna go crazy and swap a semi engine and drivetrain in a bus I'd go for a Cat 3406. They're great.

http://www.truckpaper.com/listings/c...nu=CATERPILLAR
400 hp at 1800 rpm's.
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Old 08-16-2016, 05:47 PM   #4
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If I were going to go to all the trouble to repower a bus (Major project), I'd start with one that already had a dead engine (they can be picked up for practically nothing, and literally nothing in some cases). I wouldn't waste my time with a Mercedes engine (Last company I worked for had some and they needed more repairs, and cost more to fix). I'd skip the smaller big-truck engines and move up to at least an M-11 Cummins, or more likely see about dropping an ISX in it (somewhere around 550 HP, 1800 lbs of torque). Overkill, sure, but you'd go up any mountain like it was flat. Most of these engines already have engine brakes, and I'd most likely stick with the big truck transmission, too (often 10-speeds).

A big engine like that would likely need more room than some buses have, so cutting and welding the engine bay would be in order. And adapting a manual trans, you'd have to work in a clutch pedal, linkages (or the hydraulics) and of course the hole for the shifter.

*Edit* Almost forgot. Since these big engines turn lower RPM's, you'll want to consider needing to re-gear the rear-end as well. You may do well to pick up a wrecked truck to cannibalize for parts.
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Old 08-16-2016, 09:52 PM   #5
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What Turf said.
Get the bus with the drive train you want.
I swapped both engine and transmission but I am nuts.
That being said the ten speed overdrive transmission is the best thing I've done on our bus!!
Now it drives like it should!
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Old 08-16-2016, 10:35 PM   #6
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Turf makes a lot of sense. It's what I'm doing. However, I would really prefer a manual/overdrive tranny. That being said...

Realize that most skoolie drivetrains have been detuned for efficiency, reliability, durability and longevity. How much power does one really need for a bus that runs 60 miles a day, 180 days a year in the ultimate stop and go fashion? In addition to being less expensive, this is why the Cummins B5.9 & AT545 combination is so prevalent, even in 40' skoolies. Activity/trip buses are a bit different. These drivetrains don't make much sense in RVs however.

For a 40' skoolie, I look at 250-300 hp as being ideal. The DD 6v92, which powered tens of thousands of 40'/20 ton coaches, ran around 300 HP, albeit 1000ish lb-ft of torque. Cummins' 3rd gen B series engine (6.7 L ISBe) seems to fit the bill perfectly. It arguably has the best combination of performance, efficiency and durability. It should also drop into the same space as a 5.9 L with little hassle. The 5.9 L was released in Dodge trim as high as 325 HP and 600 lb-ft. Dodge tunes the 6.7 L to 350hp/600 lb-ft.

For a truly medium duty engine, the ISC (C 8.3 L) is wonderful. In fact, Cummins designed the ISC specifically for the urban bus market and recommends it for skoolies, motorhomes and firetrucks as well. The C-series and the DT466 variants, are probably the strongest engines actually installed in skoolies from the factories.

I understand the desire for mechanical engines over the electronically controlled. The mechanicals are simpler in design, easier and cheaper to fix and reliable almost to a fault (anyone actually see a runaway?). The mechanicals are also dirtier, less efficient, less powerful and need more regular maintenance. I also truly miss the days of the Chevy small block drivetrains. There was very little I couldn't fix.

Right now, a 15 year-old skoolie will have an electronically controlled engine. Unfortunately, that's reality. An ISB 6.7 out of a 7 or 8 year old junked vehicle is arguably the best choice for transplant. Out of general skoolie drivetrains, the B-series have the most third party/aftermarket support. There are also probably more competent B-series mechanics than any others.

As much as I'd love to dream about a DD 60-series or Cummins ISX, ISL or ISM, making them work or even fit in a skoolie sounds much more complicated and expensive than I'd want to consider.

You might be better off visiting Banks and picking up a PowerPack system for less than $3000. It adds 100 HP and 200 lb-ft to a 12/24V B-series. They're also easily tunable from the driver's seat. This means you can back off the power to increase efficiency, durability and longevity. Similar PowerPacks, at similar prices, are available for Navistar/Ford and GM diesels too.

Know that finding the "perfect" skoolie will be a fool's errand or at lest a long wait. Ask those here with experience. Compromises are made. Often the drivetrain is one of those compromises. By looking at shorties, based on Ford, GM or Dodge cutaways, you open yourself to much more affordable aftermarket options.

Just my 2.

Good luck!
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Old 08-18-2016, 09:59 AM   #7
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I agree finding a bus the size I want with the powertrain I want would be the best solution, but that's proving very difficult. I've seen one bus come up in almost 8 months of checking every week that came close, and I would still need to modify it some. They just didn't seem to put big engines in shorter buses, and it makes sense. The shorter ones were made mostly for special needs programs, so they didn't need to be able to go fast or pull anything. So, to get what I want, I either have to get something with the right powertrain and cut the frame down, or get the right frame and swap an engine/transmission/read-end, which the power train swap seems easier than cutting a frame. Just what I've been thinking. I know this will be a big job, but in the end, I will end up with what I want, and have it to use for years to come is the way I'm looking at it. I'm also planning on replacing a lot of the sheet meal on the front part with lexan to get a good view when driving through parks. Haven't figured out that part yet, but that's another topic.

I was already planning on trying to put a 13 speed in whatever I ended up with. I like shifting I guess, and I like the idea of having multiple overdrive gears. I know that will be a job. Its one of the big reasons I'm looking at the FS-65 series. They had a stick as an option, so at least the pedal rack and some other parts are available for them. I am a bigger fan of electronic engines. I'm still in school working on a doctorate in controls, and some of my professors work with engine controllers. That's why I was looking at some of the newer engines is I know what kind of performance you can get out of them if tuned correctly. I realize from the factory, its not practical to play with the parameters on every one, but I feel like a little bit of hacking might be in order for me. Its just a hobby of mine. I like the looks of the newer 6.7L and 8.3L cummins engines. Thanks for pointing those out. Did any buses come with the 6.7L? I can't seem to find any examples.
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Old 08-18-2016, 01:30 PM   #8
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Your best bet then is to ask your professors. Have you considered just getting a toterhome and calling it a day?

I narrowly missed a 5 window with 466 and 5 speed a month or two ago. Man was I bummed.
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Old 08-18-2016, 06:48 PM   #9
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The Cummins 6.7L is used starting in the model year 2008, I believe. It is Cummins' replacement for the 5.9. With CAT out of the business, there really is only Cummins and IH/Navistar left to power full-sized skoolies. Currently, Blue Bird offers the ISB 6.7 and ISL 8.9 in their Type Ds and the ISV 5.0 (8cyl) and ISB 6.7 in their type Cs.
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Old 10-27-2016, 11:41 PM   #10
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Big engines are thirstier and also weigh a lot more which throws of the suspension balance and braking ability. I'd get a bus that was designed from the factory so all components work in harmony. With a swap, you'll be spending thousands extra and end up with a mechanical nightmare. Putting lexan in place of sheet metal will seriously affect the integrity and safety of your bus (and you and your passengers) in a collision.
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