Has anybody done an 8V71 to 6v92 DDEC repower?

[RickB]

Hi All,
I found a city bus with a 6v92 silver that looks really clean that is about to be scrapped. The guy wants $750 for it.
I thought that the transverse mounted city buses spun the wrong way for my MCI 9 but a friend said they spin correctly. So, how much would I be biting off to do this in both money and time?
I just went through the cooling system on my bus and put the bigger radiators and smaller pulley in so cooling wouldn't be an issue. I was clear with the guy that I would want everything from the wiring harness to the aftercooler, air throttle etc.
I was really disappointed on our first trip out of the summer in the bus the last few days. The 8V71 at least one tuned and built to mine's spec's is such an underpowered motor for this heavy of a bus. Flat ground and no wind and I'm a happy guy but give me any headwind or a long slight hill and it just seems so gutless.

If I am gonna do this I wanna do it with my eyes open, meaning I want to research it heavily and know beforehand what to expect. The 6V92 is not my first choice but I have driven them in a 9 before and it had alot more power than mine. I would rather do an 8V92 but I never see them priced in my price range the better mpg is a plus as well.

I would certainly do a compression check and an oil analysis on this motor which runs and sounds great by the way.

I am not interested in a four stroke repower so that is not worth discussing. That is just too much work for this father of two to consider.
I am really interested in the nuts and bolts realities of how much work and how expensive this would be.

look forward to your input...

Rick

[Tim Strommen]

What Brand/Madel "city bus" is it?

From my experience, the "T-Drive" busses spin the normal way (the same way a semi's engine spins), but the "V-Drive" busses spin the other way.

If you've found a V-Drive bus, you probably won't want to touch that one for an MCI...

-T

[RickB]

I believe it's a gillig like yours with a 740 attached to it.

[belfert]

I would suggest a four stroke repower instead if you're going to take the time, but it sounds like money is an issue.

A DDEC engine for a city bus may have various changes to meet emissions standards.  It may not acclerate as well as a 6V92 from a coach bus.

[Tim Strommen]

If it's a DDEC era Gillig, then it's definitely a T-drive.

I have a 6V-92TA and a 740, all mechanical (the only thing electric is the speed and air shift selector).  From what I've heard here and on the other board, that an 8V-71 to 6V-92 swap is fairly straightforward (all assuming that it's MUI, not DDEC).  The 8V-71 is roughly the same length as the 6V-92 from what I remember.

-T

[JohnEd]

I don't think that the hp was significantly different between the two.  But you can get 250 hp 8v71s and also get 6v92's that anemic.  350 is the max "stock" hp for a 692 and the 8v71 goes to 330 with the advanced cam timing and bigger injectors.  all of my numbers are notverified but i think the gist is the same.  your rebuilt 871 is worth something....look into that.  all that trouble and will not consider a 4 cycle that everybody that has done one raves about?  semi's are for sale for very cheap with it ALL and they are running well and their condition can be painstakingly verified.  if you can't leave he fold of the 2 then go with the 8v92.  same money and twice the power.

mtc worth,

john

[TomC]

Personally-I would turbo and air to air intercool your 8V-71.  Mine running just 9G75 injectors boosted the horsepower to a real hill flatening 375hp and 1125lb/ft torque.  It really makes a difference in performance, and it is still a reliable mechanical engine.  I wouldn't go with an electronic engine unless absolutely necessary.  All the fuel savings and conveniences can go quickly away with one or two break downs because of electronic failure (and it does happen).
Course, if you can get a decent running 6V-92TA with the transmission and all wiring and controls for $750.00, that too is a hard deal to turn down.  The 6V-92 is shorter, by about 7 inches then the 8V-71-so more room in the engine compartment.  Good Luck, TomC

[Gary '79 5C]

I am with John & Tom here and need to ask what injectors you are currently running?
Also how long have you owned your coach, that is how long do you know your 8V71 history. You might up the injectors & run the rack to raise its performance. But if it is tired and near rebuilding it is there.
Another thing you will be going to inherit with the 6V92 is the wet cyl liners. Little less forgiving than the 8V71.

Good Luck, and if the 6V92 was running well with all harness etc., for $750, I think I would bring that lost dog home.

[RickB]

Gary,
I have owned my bus for two years and it was completely gone through about 25k miles ago by the original converter. Motor,tranny, brakes, AC compressor were all rebuilt and are in excellent condition. I had the rack run last summer and while they had it apart I forgot to have them check what injectors it had.
My guess is that since alot of the MCI9/8v71 combo's were tuned for life expectancy and not for performance we got the lowest HP combo. It is my understanding that although the truck version of the 8v71 was regularly tuned to "318" HP that alot of these buses were tuned around 250-275 and that, in my opinion is just not enough power to move this bus through even a modest headwind.
What I am really looking for is advice about what the actual swap if I do it would entail.

The list of things that a four stroke repower would entail is just too long for me. Fabricating from scratch motor mounts, turbo plumbing and motor height issues are major, major undertakings and I am not interested in pursuing them at all. But I arrived at that decision through specific advice as to time and money that would be spent doing it.
If I find that this conversion to a DDEC 6v92 would be that kind of a time consuming undertaking I will look into having my current motor retimed and new injectors for more power at that point.

Can anyone specifically explain to me how difficult this engine swap would be and where most of my time would be spent if I decided to do it? Things like air throttles and electronic motor to non electronic tranny issues, aiftercooler plumbing, etc..?? I would imagine the motor mounts and coolant lines would not have to be replumbed but that is a guess on my part.

That kind of info would be so helpful in making an informed decision as to whether or not I should really consider this.

Brian Diehl has helped me make the decision that a 4 stroke repower is not an option for me, he also has been helpful in pointing out some of the issues I would face in this repower as well.

The nuts and bolts issues of a repower, specifically a non-DDEC 8v71 to a 6v92 DDEC are going to be most helpful to me in making a good decision as to whether or not to pursue this.

Thanks for your time folks,

Rick

[TomC]

Rick- several things come to mind.  You'll still have to remake the transmission mounts since you'll want the 6V to be positioned like the 8V to line up with the radiator blower pulley.  The big thing is running a mechanical automatic from a electronic engine.  You'll be running a electronic gas pedal (wires only going to the engine) with no mechanical means to hook up the throttle modulator for the trnamission.  You could use your existing gas pedal linkage and have the electronic throttle control in the engine compartment with the mechanical linkage still going to the transmission throttle modulator-but I don't know how the electronic pedal control will react to the high heat of the engine compartment.  The best is to also have an electronic automatic.
Then you have to run all the electronic wiring. 
I still maintain my original opinion-juice up your 8V-71 engine with bigger injectors and possibly turbo it also.  Good Luck, TomC

[buswarrior]

A transit 6V92 is commonly set in the 275 HP area, same as what should be in your 8V71 in MC9 stock trim.

The 6V92 will have a little more torque than the 8V71, and that's it.

Since you had the rack run last year, is it safe to assume that you get full throttle?

I don't know your big vehicle experience, but there are folks who will think a 400 HP S60/B500 equipped coach is too slow...

You might be looking for something that you aren't going to be able to economically achieve.

happy coaching!
buswarrior