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Author Topic: 8V71NA versus 6V92TA  (Read 4320 times)
Ed Brenner
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« on: February 11, 2011, 04:34:28 PM »

Okay my Eagle has a 8V71NA 272Hp N60's Torque  ? (Tell Me)  MT654 Trans

Thinking of maybe putting in a 6V92 Ta / 740 trans from an eagle. What is the HP/torque of this engine if it is the stock configuration.

Need more butt but ain't going to extremes to accomplish it.

Thanks ED
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Ed Brenner
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« Reply #1 on: February 11, 2011, 10:15:44 PM »

The 8V-71NA with N60 injectors will have 280hp with 740lb/ft torque.  Take that to brown tag N65's and you'll have 304hp and 800lb/ft torque.  Advance the timing and use N70 injectors and you'll be at the infamous 318hp with 865lb/ft torque.  I believe 930lb/ft torque is the highest that the MT654 trans will take.
With the 6V-92TA, the stock injectors in the bus were 9A80's that gave you 295hp with 830lb/ft torque.  Take that up to 9A90 injectors and you'll be at 335hp with 933lb/ft torque.  Add the bypass valve to the blower and you'll be at 350hp and 1,000lb/ft torque-which is easily absorbed by the HT740.
You could turbocharge and air to air intercool your 8V-71 like I did.  On the dyno, with 9G75 injectors, mine is putting out 375hp and 1125lb/ft torque.  You could keep the same N60 injectors and run a turbocharger and get 300hp and 900lb/ft torque-still staying within the torque rating of the MT654-but getting all the good advantages of turbocharging-like no more smoke at high altitude, no power derate at high altitude, better fuel mileage, etc.  If I were you, I'd just turbocharge your 8V-71 with the N60 injectors (maybe also install air to air intercooling).  Mainly since I like the dry cylinder liners of the 71 series as compared to the wet cylinder liners of the 92 series that can and do leak. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #2 on: February 11, 2011, 11:03:57 PM »

Or you could just enjoy the ride........
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« Reply #3 on: February 11, 2011, 11:40:18 PM »

You could keep the same N60 injectors and run a turbocharger and get 300hp and 900lb/ft torque-still staying within the torque rating of the MT654-but getting all the good advantages of turbocharging-like no more smoke at high altitude, no power derate at high altitude, better fuel mileage, etc.  If I were you, I'd just turbocharge your 8V-71 with the N60 injectors (maybe also install air to air intercooling).  Mainly since I like the dry cylinder liners of the 71 series as compared to the wet cylinder liners of the 92 series that can and do leak. Good Luck, TomC

  Can someone check my math one last time? A Spicer manual trans in an MCI-5, 1st gear ratio is 4.25:1, rear axle ratio is 3.7:1? Standard tires approx 495 revs per mile, gives a tire radius of 1.7 feet?  900 ft lb's tq from turboed 871 with n60s X 4.25 X 3.70 = 14,152 ft lbs tq at rear axle? /1.7 foot tire radius delivers 8240 pounds of tractive force to the rear wheels?? A 22% grade requires 22% of the vehicles weight in traction? At 27000 pounds (high estimate MCI-5) this Bus would require 6160 pounds of traction at the rear wheels??? Am I correct to assume then, that on paper this Bus could climb a 22% grade in first with over a ton of tractive force in reserve power??

  So if my math is correct, it looks like I could go up to nearly 30K pounds with stock power (740 tq) and still climb it??
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Nellie Wilson
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« Reply #4 on: February 12, 2011, 12:30:29 AM »

Whooee! It may pencil out (the math is way over my head) but that's a lot of grade. My old gal can (gracefully) handle about half of that. FWIW.

Nellie
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Barn Owl
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« Reply #5 on: February 12, 2011, 06:06:19 AM »

Only having experience with the 4106 take it for what it's worth. There is no comparison between 8v71na vs. 6v92ta. LH 6v92ta from transits are plentiful and inexpensive for GM bus conversions, not sure about the RH engine that you would need. Having driven both, I couldn't imagine sinking money into anything but something with a turbo.
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« Reply #6 on: February 12, 2011, 06:27:52 AM »

With any large vehicle, we're not really concerned with the climbing ability of the vehicle in first gear once it is rolling.  The important part is the startability when sitting on a grade.  To figure that out you need to know what your engine produces at 800rpm for clutch engagement-which on a 8V-71NA is around 500lb/ft torque.  Then to figure startability, you take what your heaviest weight on the bus will be and multiply it by 10.7 and put that into memory on your calculator.  Then you take your starting torque-500 x first gear- 4.25 x rear end ratio- 3.7 x tire revs per mile- 495 and divide that by the figure in memory.  In this case I come up with your 27,000lb bus a startability of 13.47%.  Of which doesn't surprise me since most buses were designed to run on the highway.
Take those figures to the full 900ft/lbs with the clutch engaged and you're looking at a 24.25% grade climbing capability.  But-once again startability is the important part.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #7 on: February 12, 2011, 06:47:57 AM »

  I dont need to start from dead stop, were talking pure climbability, wound up against the governor in first, or at least at peak torque rpm in first.

  Appologies for going off topic.
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luvrbus
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« Reply #8 on: February 12, 2011, 07:21:05 AM »

Ed, got the serial number on the bus most Eagles model 10's were 277 hp with the 6v92 you set the 6v92 on 330 hp it will serve you well and get decent fuel mileage but don't go above 330 hp.
Sell the 600 series to the MCI 5 people lol that is a pretty easy swap on a Eagle from a 8v71 to 6v92 if the 6v92 has a front mounted turbo if not call me we can fix you up lol

good luck
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« Reply #9 on: February 12, 2011, 08:04:11 AM »

Here are some useful graphs.  My bus had a 8V71N with N65's and advanced timing (verified 20 minutes ago when I finally took the bell housing off and I am here to testify that the bell housing on an 8V71 is very heavy indeed...) and it had a hard timing starting on a 10% grade, lot of balance power and clutch to get going.  But give it 30 feet to reach the governor in first and it was going to go up some hills...  Estimated steepest grade I went up in first is around 20%, so I think you may be OK.  Depends on how steep it is where you have to start your run.

Brian

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« Reply #10 on: February 12, 2011, 01:02:10 PM »

Art - you never know when your going to have to start from a dead stop - If your climbing a grade you should be able to start on it - FWIW
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« Reply #11 on: February 12, 2011, 01:10:41 PM »

Art - you never know when your going to have to start from a dead stop - If your climbing a grade you should be able to start on it - FWIW

   No, its a driveway. I'll never have to start from a dead stop on it, and I doubt there is a bus anywhere that could start on a 22% grade. Im just trying to make sure I can climb it with the motor wound up using known figures. 
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« Reply #12 on: February 12, 2011, 01:12:37 PM »



ED  go ahead and get a hot 6v92 and turbo so you can help me kill all the mosquitos at Palmetto Cove for Kyle.


ned
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« Reply #13 on: February 13, 2011, 09:04:10 PM »

So can I just add the turbo and proper injectors to an 8V71NA and get away with it, or do I need to do a whole lot more?
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Dr. Steve, San Juan del Río, Querétaro, Mexico, North America, Planet Earth, Milky Way.
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« Reply #14 on: February 13, 2011, 09:57:19 PM »

Without some other serious upgrades, the 8v71 is not a good candidate for a full turbo.  There have been people that have done a limited boost turbo, commonly called a smoke turbo, that safely gives them some extra pep and more consistent performance at higher altitudes.
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