mechanical to DDEC change?

bevans6 · December 21, 2009, 05:01:24 AM

In my research to decide what to do if I decide to re-power the MC-5C I've decided that I have no clue what would actually be required to change from a straight mechanical engine like I have now to an electronic DDEC controlled engine of some vintage. Add to that the possibility of changing to automatic transmission... What is required? the strongest possibility is to a 6V92 and 740 trans of some sort.

As a side issue, what bellhousing size do I have and what do I look for? I've thought it was SAE #1 but you know what they say about assuming things...

Thanks, Brian

robertglines1 · December 21, 2009, 05:22:32 AM

sounds like at least 20 grand..from what you said on previous post you were happy with the 8v71..if you want to go automatic...there are conversion kits advertised for 3500 to 4 grand. Being a car guy you can do a in frame or slide engine out take in your shop this winter and have at it..or just buy oil every 500 miles for awhile...these are probably the same thoughts you have....I don't think the performance of a run of the mill 6v92 will be much greater than what you have...the auto I like.

blue_goose · December 21, 2009, 05:37:29 AM

From what friends have told me there isn't enough room for the 740 transmission in the mc5. Othere that I know have used the next size smaller 640.
There are lots of city buses for sale that you can buy cheaper than just the engine. If you get a doner bus you will have everything you need to do the electronic change over. Check Public Service Auctions they have lots of buses with 6v92 and T drive.
Jack

TomC · December 21, 2009, 07:49:40 AM

Finding a 6V-92TA mechanically operated with a Allison HT740 also mechanically operated will be a reliable power plant. Normal 90 injectors will give you in the 350hp and 1100lb/ft torque range. It's relatively easy to line up the front of the 6V-92TA (which is facing backwards) in the same position as the 8V-71N so to have the engine align with the radiator cooling fan drive. You will have to enlarge the radiators, and overdrive the fan more, enlarge the air cleaner and the muffler, but then will have a real hot rod to drive. The difference in mileage between a mechanically operated 2 stroke engine and a DDEC engine can be as much as 1 mpg. Course, careful driving techniques can make that difference much smaller. Personally- we don't drive enough to take advantage of the DDEC savings vs the royal pain in the you know what to get it running properly. Besides-one electronic failure resulting in having to have the bus towed to a repair facility and the repair bill will negate all the savings you had with DDEC. I don't think DDEC is worth it. Good Luck, TomC

lostagain · December 21, 2009, 08:23:57 AM

IMHO, I would just overhaul what you have. I think a engine/trans. swap is too much trouble and money. Find a newer bus with the power plant you like. None of them are perfect, the grass is always greener on the other side of the fence.

JC

bevans6 · December 21, 2009, 08:40:02 AM

Appreciate all the advice. The googling I've done (which oddly sometimes finds relevant threads on this board easier than the board search function does!) tells me that I don't want to mess with a DDEC project. Plus I value the simplicity of the MUI engine. Sure it's do-able, but the bus is supposed to be a means to an end, not the other way round!

It's a 90% shot that I will just stay with what I have, I can buy a lot of oil for the cost of either a rebuild or a re-engine, but until you know what the choices and dependencies are, how can you make a choice? What really has me daydreaming is an 8V-71T out of a firetruck! And even I know that's probably a bad idea!

Brian

Van · December 21, 2009, 08:48:51 AM

I would shop for a build able 871, and do it up nice. Ask Don Fairchild about his Hot Rod 71,once built it can be swapped out at your convenience, I think would be the way to go. Van

NewbeeMC9 · December 21, 2009, 05:34:38 PM

Wasn't there a combo where you could do away with the drop box?

RJ · December 21, 2009, 09:34:05 PM

Quote from: blue_goose on December 21, 2009, 05:37:29 AM

From what friends have told me there isn't enough room for the 740 transmission in the mc5.

Jack -

The HT-740 will fit in a MC-5C, but only with the 6V92 engine.

The MT-6XX fits the 5A & 5B with the 8V71.

For Brian's application, the easiest would be to buy a running MC-9 or A series with a 6V92TA/HT740 powertrain and swap. Same powertrain from an Eagle, Prevost, Gillig Phantom Transit, etc. would also work, but slightly more involved.

FWIW & HTH. . .

TomC · December 21, 2009, 10:46:45 PM

The 8V-71 at 318hp and 860lb/ft torque is just about at the top of the horsepower range for the MT640. If you want more power, you can either turbo the 8V-71 with the manual transmission or go to the 6V-92TA and HT740 route. Good Luck, TomC

blue_goose · December 22, 2009, 04:57:05 AM

RJ you are correct on the 740 with a 6V92. I don't know anyone that has done that, but lots that have used the 8V71 with the 640.
There is a Bus on Public Service Auctions now that has a 6V92 with the 740. I haven't looked today but yesterday it was at $1000.00 with no bids. I think it ends today.
Jack

luvrbus · December 22, 2009, 05:15:24 AM

the factory installed automatic in a MCI 5 C was a 740 with a 6v71 fwiw

good luck

TomC · December 22, 2009, 07:27:42 AM

Since the factory installed the 6V-71 with HT740, then since the 6V-92TA is the exact size, can be installed also. Good Luck, TomC