1990 Country Coach 8V92 Engine Swap to 60 Series

[zxzx9r]

What is the gear that I have in the 1990 prevost with 8v92 and 5 speen auto tran?

[rv_safetyman]

As Brian mentioned, you must be careful of the donor engine .  There are lots of Series 60s with 700K miles that have a bad rod or piston.  If you get an engine with lower miles, you may be getting into EGR and most folks stay away from them.

I am surprised that folks have not brought up the height issue.  They touched on the gearing issue (30% taller gears are strongly recommended.  However, the height may be the deal killer.  I suspect that the Prevost will have the same issue as Eagles and that is that you will probably have to raise the floor structure a few inches.  That is hugely labor intensive.

To avoid the height issue in MCI and Eagle buses, folks have gone with the Cummins ISM.  Smaller engine but pretty darn good power and torque.

Jim

[rv_safetyman]

Concerning your gearing, the best way to answer that is to have you tell us what your RPM is at a given speed.  If you run the typical bus tire (~490 rev per mile) and you turn the engine at 2100 rpm at ~ 72 mph, you have 3.73.  I am not sure what gears were available in a Prevost, but with typical bus tires and a 1:1 top gear (any non-World Allison), you would need about 2.73:1 rear end ratio to gear according to DDC recommendations.  Doubt that ratio is available.  Some folks have adapted truck rear ends to get that tall of gearing.

Jim

[zxzx9r]

Well from all the info so far I might be better off to keep the 8v92 and up grade it to a 8v92TA. What would be a good tranny and gearing to use? The HD4060 6Sp or B500 might be cool, im not sure what kind of gear I can get?

[RickB]

The TA satnds for turbocharged and aftercooled. You have a 8v92 TA. I wish I had one.

Rick

[luvrbus]

If that bus has the original engine it is a 8v92TA DDEC 11  450 or 475 hp. 
There was 2 rear gears ratios for 1990 model 3.73 an 3.36.The 3.36 being the most common     good luck  

[NJT 5573]

Think you have a TA engine. You likely have the toughest Electronic Allison available for your 92 without purchasing a World. The World will have an OD, how fast do you want to go?

If you are having pyrometer issues, they could be false because the DDEC will not let you hurt your engine and the ATEC will not let you hurt the transmission. Both will derate the power or shutdown if they senses any issues.

HP downloads are probably available for your computer from DD, but you should have 50,000 break in miles before you open it up very much.

You are driving a piece of heavy equiptment, it will never drive like a sports car. The running gear you have is pretty much top of the line and should give you excellent service. If you really need it to run, sneak it into Bakersfield and Don can make it do wheelies, if that's what you want. After that, bring it by here and I'll put a parachute on it for you!

[niles500]

Mine is a 94' Prevost H3 w/ silver 8v92ta DDEC II stamped 500 HP (supposedly dynoed @ 515) with 1650 ft.lbs. - I run with the S60's all day long - now mileage is another story - FWIW

[belfert]

Belfert, how much torque do want it is not that hard to get 1400 to 1550 lbs from a 8v92 the new DD13 isn't much better   

It is the original poster talking about more torque.  I already have a Series 60.

[wayne]

I've had 2 series 60 trucks, good engines, not my favorites. The 8v92 TA is just as good, definetly different, and not as efficient but some people just love that 2 cycle sound. If I could pick my engine it would be cummins. I've had 80k lb trucks approach 9mpg. I had cummins do the rods and mains in one of my N14 cummins @ 580k miles. Dealer said I threw my money out the window, parts looked new.

[Hard Headed Ken]

Take a look under a Prevost with a series 60 and compared the differences to a Prevost with an 8V92. You can not put a Series 60 and B500 in an older Prevost that has an 8V92. The length of the Series 60 and B500 is not the problem, it's the diameter of the B500. The 40 foot Prevosts with the B500 have a different tag axle. It loops over the top of the transmission instead of going under it. It's not just the tag axle that's different, so you just can't swap axles either, the newer axle mounts differently, the radius rods mounts are in different locations and the air bags mount in different locations. If you have a short wheelbase 45 foot pre-Series 60 (and I don't think there is such a thing) then you maybe able to install a series 60 and B500 in it's place. The only reasonable choice you have for a Series 60 swap in place of the 8V92 and 5 speed is a Series 60 DDEC IV and Eaton Ultrtashift (model rto16910b-dm3). Don't use an Autoshift, don't put a clutch pedal in your bus. The Ultrashift is a 10 speed with a 2 speed reverse with 10th being an over driven ratio. It will work fine with any ratio your automatic Prevost came with. 3.33 would be the theoretical ultimate putting the RPM at about 1400 at 70 MPH, 3.56 would be about 1500 at 70 and a 3.73 would be about 1600 at 70 MPH. The fuel efficiently peak is 1400 for the 12.7 Series 60.

The DDEC IV engine is the most desirable. Evidently most people don't know that several mechanical improvements were incorporated with the DDEC IV change. The most important being that oiling nozzles were added in the block, spraying under the pistons to provide more cooling, the rod and wrist pin were changed from the old 2 stroke design, the rod bolted to the wrist pin to the more convention style of the wrist pin going through the top of the rod and the piston design changed from cast iron to steel. A DDEC IV level ECM is necessary for the engine and transmission to communicate. The ECM backs off the throttle when the transmission shifts, you just hold the throttle on the floor and the computers take care of the rest. I bribed a truck salesman to take fa test ride in a trucked with one of Eaton Ultrashifts. Press the accelerator and it reacts exactly like an automatic, it shifts just like an experienced driver would shift a manual transmission. You can feel it shift, an example would be an automotive automatic with a firm shift kit. We were on the ramp to the freeway and already in 9th gear, it shifted to 10th just as we merged into traffic. I was concerned it that it would be shifting continually at highway speeds, it didn't. We to let it lug down to 55 MPH before it shifted down to 9th . It is much slower accelerating than a conventional automatic, so if you make extra money racing your bus, you won't like the Ultrashift. You have to hold the brake on a hill. One of it's competor's, the ZF Astroinc requires the bus to be equipped with ABS and it will apply the brake for you. Of course the older coaches don't have ABS so ZF is really not an option. I haven't done any research on the Meritor version. If you know someone at an Allison rebuilder you will find that the B500 is not nearly as reliable as the 740 or 755. It's not uncommon for the B500 to fail at 300,000 miles in a seated coach. I know they don't give much trouble in converted coaches, but even if it would fit in my bus the only thing I could afford would be a used B500 from a seated coach with who knows how many miles or how it was maintained. The going price for used B500s is around $7000. I know you can get it checked on a dyno but that only proves it's good that day at that time, it's better than no test all but not much.  Considering a B500 rebuild costs around $9000 dollars I just can't take the chance of installing a used B500. The used Ultrasifts are selling for $3000 to $5000. They came with a 750,000 mile warranty when they are new (that's pulling 80,000 pounds) and they cost about 10 grand new. Other advantages for the Ultrashift include increased fuel economy, lighter weight, no oil cooler needed, the shift style is programmable, it has a touch pad that looks very similar to an automatic, it can be shifted manually using the touch pad if you want to control which gear it's in and of course it will fit behind the Series 60 when installed in the older Prevosts. To me it just makes sense. It's not as smooth or does not accelerate as fast as an Allison. Do your own research and make up your own mind.



The distance from the rear of the frame to engine mounts is the same on the Series 60 and the 8V92, the difference is that the 8V92 mounts bolt to the transmission and the Series 60 mounts bolt to the bell housing. That's about 8" inches difference. The Eaton Ultrashift is about that much shorter than the Allison 755. You may not need to change the length of the drive shaft. The 8V92 radiator will be more than adequate, it and related components (fan, miter box) will have to moved inboard as close as possible to the muffler to allow room for the intercooler. I plan on using the original fan drive, air filter and muffler. I know you think that is going to be restrictive, the 12.7 has 40% more displacement, but 8V92 is a 2 stroke it uses a 100% more air than 4 stroke of the same size. Combine those facts with the fact that the Series 60 will operated at a much lower RPM than the 8V92 did. I will confirm my theory with a manometer. The series 60 is taller, if your bed is against the rear of the bus it's not a problem. The original inspection cover is larger enough but it  will have be modified into a box or small dog house style. If you have a cross bed then it would probably be best to raise the floor all the way across like the Series 60 coaches come from the factory. The Series 60 engine is mechanically louder. I may need to add additional sound deadening material to rear of the bus.

Ken    

[DaveG]

Nice input Ken. Thanks for the detail.

[luvrbus]

That is good input on the older Prevost but this I do know a 1994 year H model will accept the 60 series without  any fab work only the the cradle.
They came with both engines a 500hp DDEC 8v92 or a very weak 11.1 series 60 and both were offered with the b500 Allision.     good luck

[TomC]

As mentioned before-to get around the size difference between the Series 60 (mostly the height) and the 8V-92TA, just use a Cummins M11/ISM.  They can be built to 500hp and 1550lb/ft torque for RV use.  The one big disadvantage to using the Series 60, you'll be restricted to service at Freightliner, Western Star and Sterling dealers (Mercedes-Benz owned).  Even though other dealers still work on Detroits since at one time all manufacturers offered the Series 60 before Detroit was bought by Freightliner, they still have to buy the parts from a Detroit dealer, and most then add their profit margin making the parts more expensive.  Plus, since the other manufacturers are no longer offering the Detroit products, the many of the mechanics are not certified for Detroit products.
Compared to Cummins that is still an independent engine manufacturer and virtually all truck manufactuers offer Cummins as an option-so service and parts can be obtained from any truck dealer.
While the Series 60 is quite possibly one of the best engines ever made, the Cummins ISM for RV use is just plainly a good idea. Good Luck, TomC

[Ed Hackenbruch]

So how does the cummins compare in size and weight to an 8V71?