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Author Topic: looking for information on converting a 892 to cummins big cam in a 83 prevost  (Read 3141 times)
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« on: November 14, 2013, 08:59:43 PM »

new to this board is this possible? thanks.
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« Reply #1 on: November 14, 2013, 09:15:43 PM »

It can be done but it is a very big job. I installed a Cummins M11 in my 81 lemirage. The big cam is to long.
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« Reply #2 on: November 14, 2013, 10:08:47 PM »

thanks for the comeback  are you happy with your changover?
 did it fit in your engine compartment? how did you cool it?
   thanks jray.
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« Reply #3 on: November 15, 2013, 03:15:08 AM »

The tag axle is the big issue Ken installed a 14L 60 series in his Prevost he can tell you the in and outs it takes a while and a few bucks

 I looked at doing one for friend and decided it was too much work while the old 855 was a good engine doing that much work I would look into a more modern up to date engine JMO
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« Reply #4 on: November 15, 2013, 04:03:30 AM »

The issues are going to be the length and dealing with the tag axle. Even Prevost couldn't install a late model 6 cylinder until they had the availability of the 6 speed Allison transmission because the 5 speed used prior to that transmission in combination with the 6 cylinder engine was too long. When they did make the change in the mid 90s they had to modify the tag axle among other things.
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« Reply #5 on: November 15, 2013, 04:55:59 AM »

As stated, the length is the problem combined with the diameter of the Allison 6 speed. I used an Eaton Ultra Shift because it's more of an oval shape and would go over the top of the tag axle. I still had to notch the tag axle to provide clearance when all the air was dumped from the suspension. I had about 1000 hours in my swap and I have most every piece of equipment needed to do the swap. I think an ISM would a little easier but you're still in for a tremendous amount of work. Take a look at some of the things I made.  https://www.youtube.com/watch?v=oxAFFBcoTQI

Ken
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« Reply #6 on: November 15, 2013, 05:04:34 AM »

Prevost got together a lot quicker on the H models for some reason you run across 92 models of the H series with 60 series

 I was told Prevost never used a 11.1 but I bought a 92 model H that had a 11.1 series 60
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« Reply #7 on: November 15, 2013, 06:56:58 AM »

If you're converting from a 8V-92TA, cooling another engine will not be an issue since the 8V-92TA is probably the hardest engine to cool. The easiest would be a Cummins M11/ISM rebuilt to RV spec of 500hp @ 1550lb/ft torque with an Allison world transmission.
If you notice on Prevost (not sure of the model), you can easily tell when they switched from 8V-92TA to Series 60 since the rear overhang is noticeably more with the Series 60.
But-like the Cummins big cam/N14, ISX15 or Caterpillar 3406/C15/C16 or Series 60, these are all what is called a big block. Stick with a medium block engine (still more then enough power) like the Cummins M11/ISM/ISX12, Caterpillar C12. Don't use the Mercedes 4000-it is a warmed over Series 55 that never worked right. Good Luck, TomC
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« Reply #8 on: November 15, 2013, 08:37:49 AM »

new to this board, is this possible? thanks.

Anything's possible if you throw enough cash at it.

OTOH, if it ain't broke, why fix it?

FWIW & HTH. . .

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« Reply #9 on: November 15, 2013, 09:24:03 AM »

Have  to agree with RJ here even if it is broke; Clifford and others have managed to get over 7mpg out of the 8V92 with out the headaches of the swap. I know the challanges first hand.  you take care of the old beast and she will be there for the long haul.  You will have to go to the mid 90's prevost around 94-95 to get the independent  rear tag axle to have enough clearance for a 60 series or Cummings. I had a 89 now a 98 and both tags are different. One had 8v92 the newer 60 serries---Ken had the older tag and was a real challenge and mine required no mods at all for the autoshift.   Bob
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« Reply #10 on: November 15, 2013, 11:00:49 AM »

Some of the middle 90's with the Series 60 had a solid tag axle but it was over the top of the transmission like an upside down U. Before that they were like mine, solid axle that when under the transmission. I'm pretty the over hang on mine and a 45" entertainer chassis with a Series 60 is the same. Prevost made the wheel base slightly longer on the 45' entertainers for a better ride. A 45' motor home chassis has a slightly shorter wheel base causing the extra overhang which allowed a slightly shorter turning radius and a 40' motor home chassis with the Series 60 has the same over hang / wheel base has my 1988. I'm speaking of the XL chassis.

Ken
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« Reply #11 on: November 15, 2013, 01:10:02 PM »

another thing you need to think about is weight, an 855 cummins weight's 4400 lbs. and the 8V92 2300 lbs. My 8V92 DDECIII with overdrive Allison gets 8.4 towing and 8.9 with out towed.

Don
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« Reply #12 on: November 15, 2013, 03:11:27 PM »

I installed the12V-71 in the MC7 with the RT910, it proves you can do anything if you want.
My largest issue was a very special short driveshaft with slip joint of 9.5" center to center of u joint in mid position. A crazy looker due to very short splines, but about 8 " diameter, they gotta get the meat in it sonewhere as the splines were about 2.5" long.
With a welder, grinder, drill and some thought, you can make anything and have it work great.
By the way the 12V-71 is about 3450 lb, the 855 is about 2700 lb, then add options.
I would not do it again, with better choices, the ISM  Cummins Series is smaller, lighter and a lot more fuel efficient, Little less hp, but am not in such a rush now. Grin
Dave M
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« Reply #13 on: November 15, 2013, 07:13:54 PM »

Don's a bit high on the weight of the big cam/N14. They tipped the scale at 2,900lbs (without trans). The heaviest engine now is the Cummins ISX15 at 3,100lbs. The 12V-71 weighed in at 3,200lbs-3,500lbs with turbo and aftercooled. The Cat 3408 was 3,500lbs and the Cummins KTA 3,800lbs.

The Cummins ISM is right at 2,100lbs, or about the same as a 6V-92TA, with the Cat C12 a bit more.

Also, keep in mind, the 8V-92TA (along with 6V-53TI) are still being made for the military. Good Luck, TomC
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« Reply #14 on: November 15, 2013, 09:43:26 PM »

thanks all who comented to this post. I think I will go with the ims or the imx  I would like to stay mechanical as I am an old guy and like simple want the HP for fuel mi. thanks to you tom you helped me last
year when I converted the 6 speed to the 754. should have done this then but I don't do simple.thanks again. Jim.
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Jim& sherry Pagnotta
 83 prevost 92/754
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« Reply #15 on: November 16, 2013, 09:23:12 AM »

another thing you need to think about is weight, an 855 cummins weight's 4400 lbs. and the 8V92 2300 lbs. My 8V92 DDECIII with overdrive Allison gets 8.4 towing and 8.9 with out towed.

Don
DON, what else have you done to increase mpg to 8 besides overdrive. Mine with 3.58 rearend and 755 cr allison weighing in at 40,000 lbs, gets about 4 to 5 tops towing a ford f 150 4x4 supercrew. Probably as good as it gets.
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« Reply #16 on: November 16, 2013, 10:02:12 AM »

It is very hard to have accurate discussions about mileage because there are so many variables and in very few of the posts is enough information provided to assess if the information is accurate or applicable to your situation.

Over the years and approaching somewhere around 350,000 miles of driving my coaches I have recorded every gallon of fuel I put in the tanks. I have noted whether I was towing in my logs. I have mostly driven my coaches consistently, by that I mean at the same highway speeds depending on the coach. I have learned the factors that have the greatest influence on mileage. First is speed, or to put it another way, headwinds. The faster you drive the lower the mileage. Hills are a killer. You will never make up for the fuel burned climbing the hill as you do coasting down the hill. Nothing else comes close to the impact on mileage as those two and I have the thousands and thousands of gallons of fuel burned to document that. The weight of the coach obviously has an impact, but for most concerned about mileage it is with the coach that they own.

The toad has some influence, a greater influence as the toad weight increases, and using over the road whole bus AC systems has a modest impact.

My 41,300 pound 40 foot 8V92 powered Prevost got 5.6 MPG driven at 1800 RPM which was about 60 MPH. That was consistent from year to year to year.

My 46,600 pound 45 foot 12.7L Series 60 powered Prevost initially got 8.0, but once they tinkered with the fuel in the change in sulphur content and then ethanol it went to 7.5. I drove that at 62 MPH which was 1500 RPM

My current 53,000 pound 14.0 L Series 60 EGR powered Prevost has consistently gotten 5.9 MPG. I drive it at the same 62 MPH at 1500 RPM.

The numbers are based on annual calculations based on miles traveled and fuel burned.

The cheapest way to increase mileage is to take your foot off the gas. Electronic 4 stroke engines are going to be much more efficient than the 2 stroke engines, but regardless of what you have you only pay for the HP you use.

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« Reply #17 on: November 16, 2013, 11:30:20 AM »

The 855 Cummins is not going to be any better on fuel than a 8v92 if fuel mileage is what you are looking for if you don't get the hp to weight ratio with the proper  gearing neither will the ISM

I have friends with the ISM and the M11 electronic engine they are around 5 to 5-1/2 at 60 mph and around 6 to 6.5 at 55 mph

good luck
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« Reply #18 on: November 16, 2013, 11:34:55 AM »

I have friends with the ISM and the M11 electronic engine they are around 5 to 5-1/2 at 60 mph and around 6 to 6.5 at 55 mph

good luck

Ouch, I would sell at that point, if I didn't run over 55MPH.
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« Reply #19 on: November 16, 2013, 11:54:15 AM »

Love the expression "your results may vary". Oh boy, with the 12V-71 & RT910, 3.73, 11R24.5 at 480 rev/mile at 2100 @ 72 run to Fl & back 5.9 mpg,  8V-92 RTO910 same rear, tires, 7.6 mpg.A
 Now with the ISM500' 4000MHR Allison, 3.91, 275/80R22.5 at 520 rev per mile tires not towing, easy 8.8. Towing a F150 @ 4600 lb get 8.2+\-
The best part, it does not make a dern if it got 4 or 20 mpg, would not change how far it goes.
My normal is about 10,000 miles a year.  Not trying to save for the DW's next Buffalo, with luck, will leave him a lot of wore out junk.
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« Reply #20 on: November 16, 2013, 01:47:58 PM »

You should have had the RTOO9513 behind that 12V71.
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« Reply #21 on: November 16, 2013, 01:58:41 PM »

Yes, howsomever there was no room as the OD box made it too long. But sure gave it a thought, actually a 5 speed would be plenty with the 12V torque, never found a mountain it would not run 2100 in 10th.t   I was not planning on selling the 12V, but a guy kept throwing money at me, when he hit the magic #, I surrendered.  Was going to do the 13OD when I did the 92, but had the RT turned to the RTO WITH ALL NEW BEARINGS & seals, then ran the synthetic 50 wt, worked great and no leaks.
Still miss those days
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« Reply #22 on: November 16, 2013, 03:40:18 PM »

Go to Pittsburghfuelinjection.net which I think now is Pittsburghinjection.com but not sure.  I was told it was easy and fairly $cheap$ to use factory used parts to get an easy 600hp out of the Big Cam.  Seems the turbo was the key.  At one time I was toying with rebuilding the Big Cam in my old Crown Supercoach to an easy 500hp.  Long ago and far away now.  Oh well.  The Fuller overdrive 9 speed in the appropriate torque range would have worked with the V12 Detroit or Big Cam in a Bus Conversion application.  HB of CJ (old coot)
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« Reply #23 on: November 16, 2013, 04:17:50 PM »

The best fuel mileage non smog engine is the pre 2002 Series 60 (without EGR). The newer trucks are actually getting better fuel mileage then ever. We had a guy run 4 round trips to Bakersfield from L.A. weighing 80,000lbs and averaged 8 mpg. I had a customer get 8.5 to Fresno and back with a LTL load. Never have we seen trucks getting in the 8's. There are some over 9 on the flat. Good Luck, TomC
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« Reply #24 on: November 16, 2013, 05:10:17 PM »

Hi tom.                                                                                 
 thanks for all your help. I appreciate your imput on the smaller block
 as you can tell by my posts. I am only versed in big blocks. 60 years
 otr trucker. this conversion has been a true labor of love. the 982 has only 30k on out of frame. just found antifreeze in the weep tube 
 tank. about 1/2 cup in 3000k mi. none I can tell in the oil also no white smoke.  my thoughts now if I have to pull the motor I think I will replace it with what I am most familiar with cummins or cat. hope
 to get some help finding the problem and cost to repair this coming week. when I put it in I never thought I would have it apart in my lifetime. I have consistently got 7to800k mi.from my other motors. Thanks    Jim.
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« Reply #25 on: November 16, 2013, 05:14:30 PM »

Looking back, Instead of making the 12V a turbo for two weeks, then switching back to NA, I should have changed the RT910 into the RTO910, but did not make the change until I put the wild 8V-92 in the MC7.

The light weight was why the RT910 did not have an issue, it would just spin the wheels  Grin  I was very surprised at the off idle torque the 12V had, no turbo, it had it all off idle, why they broke drive lines back in the day, surely you seasoned drivers have seen a truck sitting in the middle of an intersection with the driveshaft on the ground using the 12V, I sure have, did not understand why until my toy 12V, then perfectly clear.

The reason for not going with the RTOO11513 or 12513 waw the extra overdrive box on the rear end of the main box. Length was the issue, with the shorter RT910 still had to use a very special short driveshaft.

I guess the reason I was so interested in this change to the 12V was due to a guy pulling by me on I-80 in Pa, west bound on a long pull, when he slowly crept past me, on his hood was "Pair of 238's",  how you know the rest of the story as I had the 1693TA @ 425, I did not think it very funny.
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« Reply #26 on: November 16, 2013, 06:18:33 PM »

Just found antifreeze in the weep tube tank. About 1/2 cup in 3000k mi. none I can tell in the oil also no white smoke. 

Jim -

Before you spend any big money, you need to pull an oil sample and have it analyzed.  That will tell you if you have a problem or if it's just a hiccup.

Also, if you'll take a couple minutes and edit your forum profile to add a signature line, similar to mine below, it will help us better guide you to parts and service sources, plus you might find another busnut nearby!  Simply click on Profile in the menu bar above, click on Forum Profile Info in the LH menu and follow the prompts.  Thanks!

FWIW & HTH. . .

 Wink
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« Reply #27 on: November 16, 2013, 08:51:10 PM »

With any of the naturally aspirated 2 stroke engines, when you let out the clutch they almost immediately had close to full torque. As compared to the new engines. For instance-even though the DD16 can put out 600hp @2050lb/ft torque, it still only has about 1,000lb/ft torque at 800rpm clutch engagement. And then the power turns on relatively slowly. So with the stronger transmissions (1650lb/ft is pretty much the standard of the industry now), and the engines taking their time responding, you rarely see blown transmissions or rear ends anymore.
But-there is nothing, I mean nothing that sounds like a twin turbo 12V-71 with straight stacks! I wish I was rich enough-I'd put that into my truck! Good Luck, TomC
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« Reply #28 on: November 18, 2013, 06:04:41 AM »

I have an 855 in my Eagle. 740 trans, 3.38 rear end low pro tires. I would like to have a taller tire but will have to wear these out first. I drive at 65 and tow a Jeep at all times. I do not check every tank because I have a tank for my heat and geny that I pump most of it to my main tank on the way home. The tanks that I check (3 or 4 a trip) I get around 6 MPG. When I pull the trailer that goes down about 1 to 1 1/2 MPG. I have 117000 miles on the bus with no problems with the motor. ( knock on wood ) That motor will smoke on cool mornings. I have mine hooked to the heater so it always start warm  no smoke. It does put out a small amount of black smoke when going down the road. The 15 I am building has a 60 s. in it. The newer 4 strokes with electronic control are a  better motor.

Wayne
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« Reply #29 on: November 18, 2013, 07:46:04 AM »

Your antifreeze problem is probably the liner O-rings why people use some type soap to install those is beyond me when they do that it does cause a problem later on with the 92 series

 Every 92 series I tear down with that problem is from not using the right antifreeze,wrong o-rings or some one has used hand cleaner or soap on the o-rings they just turn to mush 

good luck
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« Reply #30 on: November 18, 2013, 09:08:05 AM »

With my AMGeneral transit, it isn't very aerodynamic since I still have the above windshield hump where the sign used to be. I drive at 60mph which is 1900rpm. I get 6 without gen running; 5.2 during summer with A/C and genset running; 4.8 pulling car with A/C and genset running. I weigh 31,000lbs and 34,750lbs with the car.

I'm hoping with the truck to get 7-8. Good Luck, TomC
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« Reply #31 on: November 26, 2013, 10:31:24 PM »

 Thanks  R J.                 
 for your comeback. and advice I pulled the inspection plates on the side of the block to see if I could find the source of the antifreeze one cyl. has a crack in the head. a year ago I had a stud break leaving 2 valves closed  creating heat in that cyl. drilled the broken stud and replaced it'it worked fine untill now.it shows up as cracked. the rest of the cyl.look perfect no carbon the injector patterns are perfect .found a good used head having it magnifluxed and reconditioned. I have been a cat and cummins fan for years the reason for the conversion inquiry. the silver 92 has low milage and at 475 hp. does a good job. thanks for the advice the hiccup was much cheaper fix.    Jim.                                             
 
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« Reply #32 on: November 27, 2013, 02:06:19 AM »

If the head doesn't work out for you I have 5 used and 1 new head for the 92 series also I know of a shop in Phoenix that does WW Williams machine work he will rebuild the head to the original DD specs for 450 each fwiw
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« Reply #33 on: November 28, 2013, 05:08:40 PM »

Been rereading some of the posts, and laughed when I came across the one from TomC regarding the sound of the 12V turbo. On mt first test up the mountain, had been following a new Kenworth with the new Cat 460E and a new Ravens aluminum flat bed (Empty, big arch no sides, just a bare unit).  we got into a little tussel, I went by him about 10 mph faster than he, when he asked what in hell I was running in the old bus, I told him it was wore out 318, I am certain he bent up the steering wheel as he was clearly unhappy with his new Cat 460E.  Great joy on my end, and as we all know a good running 12V can be impressive.  Guess I should have fessed up, but let him stew !
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