changing a naturally asparated 6V71 to a turbo.

[Craig R]

I want to increase the engine HP & torque of my MCI MC5c that has an OE 6V71N in the engine compartment.

I have a couple of 6V71T's on pallets I was going to use to put together a turbocharged re-power.

The mechanic wants to, instead, add a turbocharger to the OE engine after an in-frame rebuild.

I'm afraid that there are important internal differences between the 6V71T and the naturally aspirated 6V71 that will still be there after a rebuild of the 6V71N - even with lower compression pistons.

Would folks discourage the mechanic from following his plan?
What would folks want to make sure had been done in the rebuild if the naturally aspirated core was used?

I welcome any insight regarding this matter that anybody can offer. Please enlighten me so that I can enlighten him - or zip my lip and let him do his job.

[bevans6]

The most significant difference, other than the turbo, are the pistons.  So if you do an in-frame that implies new kits, so you get the correct pistons and done.  You might want to switch to a bypass blower, adds a little efficiency at speed, reduces the drag of the blower a little bit.  Obviously all new exhaust plumbing, you need to figure out where to put the turbo (won't fit on top unless to move something).  I put the turbo of my 8V-71T in an MC-5C off to the driver's side.

Now, it you had an aftercooled core engine, that might be interesting, because they do have some internal block differences to install the aftercooler, but you probably don't.  There might be a cam shaft difference between a pukka 6V-71T and the natural, but I haven't heard that - Clifford might know, or some of the other Detroit whisperers here...  

When I installed my engine it was a NATO "tank" engine, and needed significant work to remove all the tank stuff and add back all the MCI stuff, several hundred hours of work at the end of the day.  It was not an insignificant task to add all the accessory drives, reconfigure the whole front of the engine to add the correct thermostat housings, the front engine mount, etc.  Depending on the exact configuration of your donor engines, I would say that starting with an MCI configured engine, in-framing for new kits, changing somewhat simple stuff like blowers, and adding the exhaust plumbing might be the simpler way to go.

Here is a pic of my exhaust and intake plumbing, for giggles.  Adding a "before" pic because I'm not sure I ever posted the engine in the NATO config, set up for an M110 Self Propelled Howitzer.  Not an actual tank, but a big piece of mobile artillery...

Brian

[chessie4905]

For more of a reward, find a 6v-92ta. Yes, turboing the 6-v71 will give nice results, but limted for the money spent. You could start with a good running take out. Then you will get a significant improvement, especilly on the hills.

[lostagain]

I am with Chessie on the 6V92. Same size as the 71 so it will slide in fairly easily. That is what I have in my 5C, with 9G90 injectors and turbo to match (I don't remember the model right now). Goes down the road good: 350 hp, 1050 ft/lb torque. To me, it would not be worth the trouble to do a 6V71. A 92 can be done for the same amount of work and money, with much better results.

JC

[Oonrahnjay]

For more of a reward, find a 6v-92ta. ...

      Simple.  Do it once, do it right.   You may have to do some of the reconfiguring that Brian was talking about (to make the 6V-92 fit where the 6V-71 was), but the performance difference will be big.  You might even find somebody with a 6V-92 that will take one of your 6v-71Ts in part trade.

[luvrbus]

So are your 6v71 takeouts T's or TA's, transportation or industrial engines post us a model number.As Brian noted there is a lot of work changing one over,you probably have a 600 series Allison automatic since it 6v71 in a MCI 5 .
I have a young man in my shop right now that bought a industrial 8v71 engine somebody told him it was just a cake walk lol 3 weeks later he has it almost ready to install it in a MCI.The 6v71 T's are nice little engines but you start A timing and adding larger injectors to get a little over 300 hp from it they don't live a long productive life  IMO  

[TomC]

I turbo'd my 8V-71. My mechanic (Don Fairchild in Bakersfield), first pulled one of the pistons and found it was two piece with "tight" bus type rings-not the looser truck style. So we went ahead with the conversion. What was changed-mainly had an air to air intercooler made that is mounted in front of the radiator (luckily when AMGeneral went from 96" to 102" width, they slid the engine over making for an additional 6" available in front of the radiator). Changed the injectors from N65 to 7G75, installed big bypass blower valve, installed fuel modulator, went from 5 row straight fin to 6 row serpintine radiator and installed misters, went from 6" to 7" air cleaner, changed muffler to low flow turbo type, cut additional vent in intake stack, installed two vents in the rear engine door. Went from 300hp and 800lb/ft to 375hp and 1125lb/ft. Made a BIG difference in performance. That was 13 years ago.
The main reason I went through all this is, I didn't want a 6V-92TA because of the wet cylinder liners that can leak over time (ask Don Fairchild about his 8V-92), nor could I install any other engine.
As to you turboing the 6V-71, if you use lower compression turbo pistons, with 7G80 injectors you can get 300hp and 900lb/ft torque. If you just install a 6V-92TA, with 9G90 injectors, you can get 350hp and 1,000lb/ft torque. And with the 6V-92TA, you'll just have to modify the intake and exhaust, and increase cooling. Good Luck, TomC

[bevans6]

As you work through the cascade of advice, remember a couple of things.  MCI engines and the MC-5 install in particular, are unique.  The accessory drives, the power steering pump location, the angle of the air compressor, the four belt accessory pulley for the 50 DN alternator, the bell housing, the flywheel size, the front engine cover with the engine mount boss, the whole engine cradle system, are all unique to your engine type and the MC-5C.  If you convert a different 6V-71T to fit, you have to change all of those things over from the old engine, which you have to pull out of the bus first.  Been there, done that, when I installed my 8V-71T.  Clifford said it would be a lot of work, and it was.  Just installing the power steering pump drive took around 100 hours, because you need to strip the back of the engine down to the bare block.   That's why I was kind of suggesting the in-frame route if you want a 6V-71T - your engine already has all that stuff done.  300 hp with the 80 injectors is going to smoke - 75's are about as big as you will get in a 71 CI hole without smoke at full throttle.  I have N75's in my  8V-71T which I reckon is 350 hp (no intercooler - yet) and that is around 265 hp in a 6 hole engine, or about the same as the de-tuned 8V-71's sold for line bus service back in the day.

Getting a 6V-92TA gets you an easy 350 hp, same as I have, and performance in a 5C is great.  But getting a random truck engine puts you right back at the strip it down to the bare block front and rear, install all the MCI stuff - bell housing, front cover, water pump, all the accessory drives have to be right, air compressor has to be the 75 degree lay-down version.  But - getting an MCI 6V-92TA gets you 90% of the way there - all the MCI stuff in it's rightful place, but you will still have to change the engine cradle - the MC-5C version is different to the MC-9 which is where a MCI 6V-92TA will come from, so it needs to be changed.  The other thing that will cause you grief will be the transmission.  A MC-9 came with a HT-740, you probably have a MT-644, and the flex plates are different.  OTOH, you might be able to fit the HT-740 in, but you will need a custom driveshaft and the output flange of the transmission and the input flange of the drop box changed so you can get a driveshaft to fit.  Oddly, my MCI manual has a section for automatic transmission featuring the HT-740 and not the MT-644, so who knows what you might already have?  The stock cooling system in the MC-5C can handle, barely, the heat rejection of my 350 hp, but that is with manual transmission.  It probably won't handle a 6V-92TA (which adds aftercooler heat to the heat load) and the HT-740, which is cooled also by the engine cooling system in a normal MCI installation (uses a dual oil cooler to cool the engine oil, which is normal, plus the transmission fluid).

So you have much to think about.  225 hp now, 265 - 300 hp with a 6V71T, 300 - 350 hp with a 6V-92TA, transmissions, cooling, swapping crap over between engines.  If you think you'll be happy with some smoke and 300 hp, I'd personally in-frame what you have, try the N80 (or more modern sophisticated 80 injectors) with your turbo conversion.  It's probably on the order of one third the work of a 6V-92TA swap.  And way less cost, since you already have much of what your need.  You might get lucky and be able to swap the piston/liner kits from one of your donor engines into the MCI engine, for example.  You get a random used 6V-92TA you might need to rebuild it anyway.

Brian

Turboing will give you around a 15% to 20% increase in power/torque, it's not a magic wand.

[Craig R]

Luvrbus, the seller from whom I bought the pallet engines identified them as Serial number 6VA141484 & Serial number 6VA141486 (each is identified as Model number 7063-7600)

Thanks for all your observations, guys (and gals?).

Craig R.

[luvrbus]

Late models (90-91) constant hp, California industrial engines with CA cams probably from a pump or some type  farming equipment

[Craig R]

6V71T? 6V71TA? In-head after-cooler?

[luvrbus]

TA's have a after cooler under the blower,they are easy to spot look for a water connection pipe at the front of the engine going to the thermostat housing coming out of the block   

[Craig R]

I'm sorry to say that the engines - and the mechanic - are a hundred miles away.
I was hoping that the serial numbers would identify them.

[luvrbus]

They are not after cooled engines according to the serial numbers,but that could have changed over the past 25 years too. 

[RJ]

Craig -

I, too, have an MC-5C with the 6V71 mated to an Allison MT-644 that we call Aesop's Tortoise, based on the Fable.

I also have a 1980 MC-5C shell parts bus that has a 6V92N bolted to an HT-740.  Yes, it's a shell, no, it's not for sale.  The 92 is a "green" engine, thus really not suitable for turbocharging at rebuild time.  But it runs really strong, and is tuned to the same hp/torque as the 8V71 with the 4-spd, roughly 275 hp or so.

I would love to tweak my coach to the same set up as JC's, but current situation says "it ain't broke, so don't fix it!"

So the '80 sits at my friend's house, it's powertrain ready for backup duty should Tortoise's 71 go south.

This plan will probably outlive me!

FWIW & HTH. . .