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Author Topic: 6v92 vs 8v71  (Read 9974 times)
TomC
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« Reply #15 on: August 06, 2008, 08:12:33 AM »

If I had the MC5, my hands down choice would be the 6V-92TA with automatic.  Recently, Detroit built up a DDEC 6V-92TA for Jay Leno's bus at 435hp and 1350lb/ft torque (course that will only last maybe 200,000 miles) with the World B500.  Now that would make a real hot rod out of a MC5-but of course they have a giant radiator on it also-maybe could fit the 8V-92TA radiators? Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Dallas
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« Reply #16 on: August 06, 2008, 08:30:30 AM »

Interesting that the overheat problems come up so often on the MCI *V92 upgrades.

Has anyone ever considered changing from the squirrel cage/side radiator configuration to the more modern single radiator across the back like the late 102C's and D's and E's use?

I've seen several of the D's and DL's with the high horse power 92's using the rear radiator configuration that seemed to work much better than those tiny side radiators.

I know someone here is going to bring the cost into this conversion, but it seems to me that you could make a couple of the side to rear conversions for what it would cost to do all the other bandaid fixes that are being done.

This was jut a thought from my befuddled mind.

Dallas
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luvrbus
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« Reply #17 on: August 06, 2008, 08:54:04 AM »

Dallas, that is interesting there was a MCI 9 at Southern Oregon Diesel that had 1  large radiator across the back with 2 fans driven by belts 1 from the engine and 2 across to the fans he told me it came from a school bus and he had a 475 hp 8v92 with no heating problems.And I also saw a 9 with a 4x4 radiator mounted on the right side he also had a 8v92 with no problems so he said
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blue_goose
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« Reply #18 on: August 06, 2008, 04:38:39 PM »

I don't think there is room enough in the MC5 to put a turbo with a 8v71.  You could put the turbo behind a 6v92 like the Eagle buses.  If you don't put too much power with a 6v92T you could still use the 640 allison trans.  Some of the prople that tried to change a 8v71n to a tubro had lots of problems. 
Jack
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TomC
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« Reply #19 on: August 06, 2008, 11:58:01 PM »

Well Blue Goose-I haven't had any problems with my 8V-71N converted to a turbo.  Just had to enlarge the radiator, muffler, air cleaner, etc.  It now runs very well with virtually no smoke coming out of the exhaust stack on a major hill pull.  I am quite pleased with it and firmly believe it is the best route to take if you want more power, and especially the advantages of turbocharging for altitude compensation.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #20 on: August 07, 2008, 02:34:06 PM »

Tom C
I didn't say there were problems, just questioned the room for the turbo.  There is just enough room for the allison 640 and 8v71.  Where did you put the turbo and the extra parts for the turbo?
Jack
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Don Fairchild
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« Reply #21 on: August 07, 2008, 03:03:58 PM »

If you don't have room for a front remote mount turbo like the Eagle you can always side mount it, and it will be closer to the charge air cooler The problem you will have is if the 8V71 is built right the 640 won't handle the HP and TQ A properly built 8V71 will run along side an 8V92 and run quieter smother and use just a little less fuel. You might be down 25-30 ft lbs tq from the 92 but you wont miss it.

Don
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Busted Knuckle
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« Reply #22 on: August 07, 2008, 03:06:45 PM »

Interesting that the overheat problems come up so often on the MCI *V92 upgrades.

Has anyone ever considered changing from the squirrel cage/side radiator configuration to the more modern single radiator across the back like the late 102C's and D's and E's use?

I've seen several of the D's and DL's with the high horse power 92's using the rear radiator configuration that seemed to work much better than those tiny side radiators.

I know someone here is going to bring the cost into this conversion, but it seems to me that you could make a couple of the side to rear conversions for what it would cost to do all the other bandaid fixes that are being done.

This was jut a thought from my befuddled mind.

Dallas

Dallas so funny you should mention that! I been think'n bout this swap lately myself! Hmmm could be something here! Now don't all you guys with deep pockets go buy'n up all the used D style radiators there are now!  Grin  BK  Grin

PS it would go right nicely withan upgrade to a "D" rear cap!
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Busted Knuckle aka Bryce Gaston
KY Lakeside Travel's Busted Knuckle Garage
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Grin Keep SMILING it makes people wonder what yer up to! Grin (at least thats what momma always told me! Grin)
Busted Knuckle
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« Reply #23 on: August 07, 2008, 03:08:27 PM »

If you don't have room for a front remote mount turbo like the Eagle you can always side mount it, and it will be closer to the charge air cooler The problem you will have is if the 8V71 is built right the 640 won't handle the HP and TQ A properly built 8V71 will run along side an 8V92 and run quieter smother and use just a little less fuel. You might be down 25-30 ft lbs tq from the 92 but you wont miss it.

Don

Quieter? what ya say? I can't hear ya over my big honk'n hot rod 8V92! LOL!  Grin  BK  Grin
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Busted Knuckle aka Bryce Gaston
KY Lakeside Travel's Busted Knuckle Garage
Huntingdon, TN 12 minutes N of I-40 @ exit 108
www.kylakesidetravel.net

Grin Keep SMILING it makes people wonder what yer up to! Grin (at least thats what momma always told me! Grin)
TomC
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« Reply #24 on: August 07, 2008, 04:01:03 PM »

On my 8V-71 with V drive the turbo is mounted above the right (upper) valve cover with a rather long pipe coming around the front of the engine for the left head exhaust pipe.  With the long run, it takes about a mile for the turbo to warm up, but once warm, it does a great job.  I used a early Series 60 turbo with waste gate to restrict the turbo pressure to about 15psi.
You can basically mount a turbo where ever it is convenient.  Course it is best to mount it as close to the exhaust manifold as possible.  There is nothing wrong with using two 4-71 turbos-one mounted on each exhaust manifold then T'eed together at the blower.  This is done on the hotter running engines.  For instance, some hot rodders with 12V-71's use two 8V-71 turbos to get big boost-course you also need big injectors-along with a big wallet for all that fuel burned.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
NJT5047
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« Reply #25 on: August 07, 2008, 07:08:07 PM »


I know someone here is going to bring the cost into this conversion, but it seems to me that you could make a couple of the side to rear conversions for what it would cost to do all the other bandaid fixes that are being done.

Dallas

Dallas, what about the cost?!!      Grin

Sorry, couldn't resist!  JR  Wink

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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

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mccarlk
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« Reply #26 on: August 07, 2008, 08:02:25 PM »

Don ,when you said a properly built 8/71 ,what do you mean, the 871 i have is rated for 318hp, a far cry from 475 out of a 892, what can i do to bump up the hp, also could i not run a truck style rad where the rear engine doors are with some heavy duty electric fans to help any heating problems?, thanks again guys for all the input
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treat every day like is your last, just make sure you dont spend all your money,in case its not!!!!!!!!!!!!!!
RJ
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« Reply #27 on: August 08, 2008, 04:31:37 PM »

McCarlk -

FYI, a little history:

MC-5 A & B models all came from the factory with 8V71s mated to Spicer 8844 four-speed manual gearboxes, no automatics were available.  (Yours has to be an after-market retrofit.)

MC-5C models were available with two different powertrains:  Either the 8V71 mated to the four-speed stick, or a 6V71 / HT-740 combination.  The 8V71/HT740 combination found in other MCI models is too long to fit in the 5s, hence the 6V71/HT740 option.

Now, the 6V92TA is, for all practical purposes, the same size as the 6V71, therefore:

The best "bang-for-the-buck" in your MC-5a would be a 6V92TA bolted to an HT-740 Allison.    Cool

Have the six tuned for 350 hp (usually just an injector change to 9G90s), and you'll have a very sweet little hot rod.  You will have to side-mount the turbo, however, as the blower compartment floor is too close to the top of the engine on a 5.

Make sure you install the larger radiator cores and squirrel cages from the MC-9s with 8V92s, and you should have plenty of cooling available.

Is it worth the cost?  Who knows, it's a toy and a hobby!   Cheesy

FWIW & HTH. . .

 Wink
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RJ Long
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lostagain
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« Reply #28 on: August 08, 2008, 04:52:24 PM »

We drove lots of MC5s in the '70s for Brewster's (Banff, AB). The As and Bs with the 8V71 and 4 speed manuals were great. Lots of power compared to the 7s with the same powertrains: better power to weight ratio. Then in 1978, I remember picking up brand new 5Cs in Winnipeg with the 6V71/auto trans combo: real dogs, no power, disapointing!

If I were you, I'd go for the 6V92 with a turbo and auto. There might be a way to mount the turbo on the side like I did on my 4-71, if you have the space there. You have to get creative with the intake and exhaust plumbing.

Those MC5s are the greatest bus.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
mccarlk
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« Reply #29 on: August 08, 2008, 05:53:50 PM »

hi rj, my bus was set up with a 871 and the 600 series auto, im just afraid to put the 871 back in because almost everybody on the board always has problems with the power on the 871, ifi was to build my engine with the turbo pistons could i run a turbo on it? i could remote mount a turbo?
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treat every day like is your last, just make sure you dont spend all your money,in case its not!!!!!!!!!!!!!!
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