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Author Topic: looking for information on converting a 892 to cummins big cam in a 83 prevost  (Read 2993 times)
muldoonman
1991 Prevost 8V92TA
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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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Jon
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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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Jon

Current coach 2006 Prevost, Liberty conversion
Knoxville, TN
luvrbus
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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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John316
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MCI 1995 DL3, DD S60, Allison B500.




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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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MCI 1995 DL3. DD S60 with a Allison B500.
wg4t50
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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.
« Last Edit: November 16, 2013, 01:48:45 PM by wg4t50 » Logged

MCI7 20+ Yrs
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chessie4905
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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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MCI7 20+ Yrs
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Central Virginia
HB of CJ
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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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TomC
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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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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
jray
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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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Jim& sherry Pagnotta
 83 prevost 92/754
Priest river Idaho
wg4t50
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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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MCI7 20+ Yrs
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RJ
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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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RJ Long
PD4106-2784 No More
Fresno CA
TomC
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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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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
rusty
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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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luvrbus
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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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