How are they getting so much horsepower out of marine diesels? Repower thoughts?

[RickB]

I have been contemplating a repower for some time now from my 8v71 to a number of different possibilities. 6v92 looks promising, better mileage 75 more horsies, series 50 looks intriguing as well and it will probably fit without major structural changes to my 81 MCI 9. Any repower thoughts out there boys?

Also how in the world are they able to get 6-800 horsepower out of marine 8v92's? I imagine there reasons we can't retrofit them into buses. Issue #1 is probably cooling issues I would imagine. I'm sure there are anwers to the myriad of questions rolling around in my brain regarding what it would be like to crest a 1 mile 7% grade at a reasonable speed with somewhere near a 9-10 mpg average?

The tone of responses to questions has been harsh to say the least on the board lately so I am asking all responses to refrain from prideful "my way is the only way" type dialogue. Sometimes a few who visit this board sound like a bunch of mean gossiping old ladies. Remember we are all just trying to get through this life with as few bus issues as possible, that is the tie that binds us together and the combined knowledge of busses contained within this group outweighs the men who designed them.

I truly appreciate all the creative do-it-yourself spirit that resides on these pages... Rick Barron

[Lee Bradley]

Nothing on repowering.

Marine diesels have virtually unlimited cooling but also they are built to run at one rpm for top power and they never run downhill.

[kyle4501]

Marine applications have an almost infinite ability to cool the engine, hence higher HP ratings.

I've been told by some tractor pulling guys that they can get 1000 hp per hole, but the life of the engine is rated in seconds, not miles.  

I heard somewhere that an engine is good for only so much fuel, then it is rebuild time . . . It sort of makes sense - more fuel = more HP = more stress = more wear.


I'm gonna look into more gears so I can keep it in the right rpm range & enjoy the 10 mpg my 4501 gets with the greyhound spec 8V71. Sure, it will slow down going up long grades, but I'll make up for it when I can skip a fuel stop  

I'm also gonna look into a 'normalizing' turbo to minimize the effects of less air at high altitudes. (If the boost is low enough, I won't have to change anything internal in the engine.   )

But, I don't mind "leading the parade"  

[c-coop]

we use 8v92's 750hp 1 super large turbo. 145mm injectors and 2400rpm,s average life span 1000 hours between overhauls, not very practical in a boat much less a bus   Chris

[Busted Knuckle]

Cooling is the # 1 reason we can't have monster horsepower engines in our coaches! A boat has the whole lake, river, or ocean as it's radiator, so if you buld a trailer sized radiator you should be able to build a half monster engine. Of course if your pulling a trailer sized radiator, your gonna need a monster engine to pull the weight!  FWIW    BK 

[tekebird]

unless you need  a new engine no repower will benefit you enough to make it worth while MOney wise.

the 6v92 will hardly get any noticably better fuel mileage than the 71. your only talking 16ci smaller of an engine.
going to a 50 will likely require a major wiring job.

I for one don;t care for the 50 in a bus, it is a shaker, and is not much better on power than your original mill

Now if you need a new engine then you have a whole lot of options.

[NJT5047]

I agree with Tekebird....to a point.  While a 6V92TA may not improve your mileage, it would clearly make a good bit more HP, and accelerate much quicker, than your 8V71na. 
A 6V92TA would be an easy interchange too.  Far easier than an S50.
All of the bits required for a retrofit are already available in buses.  Find a good takeout and slide the cradle and powertrain in place.  Change the radiators to newer style and you're ready to ride.   
Unless you change  your drive axle ratio or transmission (or both), a four stroke won't significantly increase your fuel mileage.   An S50 is optimal at 1200 to 1400 RPM while our 2 strokes are optimal at 1600 to 1800 RPM. 
4 stroke conversions are both expensive and complicated.   But....if done well, they are desirable when coupled with a nice coach.  The later S50s don't chatter at idle like the early versions due to improved counterbalancers.  2 strokes are naturally smooth running. 
There are a few guys around that could write a book on MCI 4 stroke conversions (Jack Campbell, and Gary Nixon, Jim Shephard's Eagle/S60/Autoshift, and recent posts on an excellent Cummins ISM conversion whose name eludes me {Alzhiemers is hell!} to name a few..there are others that I cannot name, such as the Cat conversion featured in BCM??...).   
Don't buy an ex-transit 6V92TA powertrain unless you wish to change the injectors, turbo, and timing.  Transit 6V92TAs make about the same HP as your 8V71N.   Still, I suppose some NJT engines would be worth changing these items...the silvers and purples are everywhere and most that don't smoke and will hold decent oil pressure at operating temps are good engines.   They'll outlast most of us when used as an RV powerplant. That's another issue when trying to 'drive' out your investment.   Most converters do it because they can..not for fuel savings. 
6V92TAs are good for 330 to 350 HP.  And these engines can be easily cooled in an MC9...with good radiators. 
If your 8V71N is running good, I'm not sure that I'd dink with it right now.  Not until fuel prices settle down.   We could, in the near future, see conditions that make our coaches obsolete...more obsolete than they already are.
In the meantime...I'm going busnutting next week.  Got to burn some diesel fuel! 
Have you called your senators and congressmen today and demanded they throw open any lands that a state chooses for drilling?   Then do it now! 
Cheerio, JR