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Author Topic: 8V71NA versus 6V92TA  (Read 4661 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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« 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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« 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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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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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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« 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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« Reply #15 on: February 14, 2011, 01:58:27 PM »

To know whether or not you can turbo a 8V-71NA, you need to pull at least one of the pistons to see if it is a two piece piston and what rings you have.  I lucked out in that although my pistons are the high compression 18.7 to one pistons, they are two piece and have the tighter transit type piston rings that will seal turbocharging boost.  I only went from N65's to 9G75's-and with a Series 60 12.7 liter waste gated turbocharger to keep the turbo boost down to only 15psi.  Then too-I installed an air to air intercooler in front of the radiator and bypass blower valve.  You can just keep the same injectors and install what is called a smoke turbo-which will keep your sea level performance the same at altitude.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #16 on: February 14, 2011, 02:19:28 PM »

Or you can get it over to luvrbus and for a sum larger than the national dept we will pull the engine and built you a hot rod 8V71TA @ 425HP. That will get you up the hill and if you keep your foot out of it on the flats will get decent miliage.

Don
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RoyJ
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« Reply #17 on: February 14, 2011, 05:55:40 PM »

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??

Paul, I know you didn't agree with me the last time, but I will stand firm and say you must take transmission losses into account when calculating torque.

%torque loss = %hp loss, for any geartrain, or else the math simply won't work. We'll assume 12% loss.

Since the bus is rolling, you also need to add rolling resistence. For a typical tire which we can assume .02 coefficient, giving 540 lbs of resistence.

Your net trust now becomes: 8240*.88=7251 lbs, and your total resistence becomes: 6160 + 540 = 6700 lbs

So regardless, you'll make it, but it may be closer than you origionally thought.
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buswarrior
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« Reply #18 on: February 14, 2011, 06:46:03 PM »

Yup, one day when I got the ca$h,

I'm going to get Don to build me a motor.

A fine, fine, motor.

Until then, don't worry, be...

happy coaching!
buswarrior

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Barn Owl
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« Reply #19 on: February 14, 2011, 07:07:51 PM »

How about this:

An automatic transmission has the benifit of torque multiplying:

"The torque converter portion has the ability to multiply torque from the engine. The impeller (sometimes called the pump) has specially curved vanes and is driven by the engine's crankshaft. The turbine also has specially curved vanes and is connected to the input shaft of the transmission. Adding a third element, the stator (also called the reactor), gives the assembly the capability it's named for. The stator has vanes and is mounted on a one-way clutch, to allow it to freewheel in only one direction. The stator assembly is located between the impeller and turbine and redirects oil that bounces back off the turbine. The force of the redirected oil assists in rotating the turbine, resulting in torque multiplication. When the impeller's speed is high and turbine's speed is low, torque can be multiplied by as much as 2:1. When the impeller's speed and the turbine's speed are about the same, torque can be transferred at almost 1:1."

http://www.carcare.org/Auto_Transmission/torque_converter.shtml

HTH
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L. Christley - W3EYE Amateur Extra
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« Reply #20 on: February 14, 2011, 07:17:46 PM »

V730 with 8V-71 has a 2.53 ratio torque converter.  So with the 1.77 to one first x 2.53 torque converter, you have a 4.478 first, then like my bus with the 4.56 rear end ratio-has 20.42 to one overall starting gear.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #21 on: February 14, 2011, 07:49:51 PM »

  Its been my understanding a V730 wouldnt fit an MC5 with an 8V71?Huh

  Nobody said but I dont think a 7 speed will either. Anyhoo, I'll just pretend its the lil engine that could and pray.....if I can find a Bus, that is
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Barn Owl
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« Reply #22 on: February 14, 2011, 08:08:52 PM »

Quote
Its been my understanding a V730 wouldnt fit an MC5 with an 8V71?Huh

Yes, you are correct, it is for left hand transverse mounted setups. I think a 4106 with a v730 would make it up your driveway easier than a MC5. Gut feeling biased opinion only, no proof. One day I will remember to check the grade on my road. It is very steep and long (7/10ths of a mile, various grades).
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L. Christley - W3EYE Amateur Extra
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« Reply #23 on: February 14, 2011, 09:49:05 PM »

Oh silly me, V is for "V"drive, duh. 
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RJ
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« Reply #24 on: February 15, 2011, 12:00:08 AM »

Paul -

On the MC-5A and B, you get your choice of:

8V71 + 4-spd #8844 Spicer

8V71 + MT644/645 Allison (very rare OEM)


MCI made some changes to the rear of the chassis on the 5Cs, so your options are a little different:

6V71 + HT740 Allison

8V71 + #8844 Spicer 4-spd manual

8V71 + MC644/645 Allison (very rare OEM)

or the hot rod

6V92TA + HT740 (not OEM, Tim "The Tool Man" Allen upgrade)

This last combo can also be installed in the A & B.

FWIW & HTH. . .

 Wink
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« Reply #25 on: February 15, 2011, 05:15:42 AM »

If you are calculating driveline efficiency, you can use a number like 12% loss and be pretty close.  I use 8% to 10% for the loss in the differential hypoid gear, which is a sliding tooth gear design, and 1% to 2% for each helical gear pair in the train.  In first gear, an MC5 with a Spicer has two helical gear pairs in the transmission, and two in the drop box, so the loss will be between 4% and 8% plus 8% to 10% for the diff, so a total of between 12% and 18%. 

I don't know anything about driveline efficiency in an automatic transmission in first gear, though.

Brian
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« Reply #26 on: February 15, 2011, 10:43:52 AM »


Paul, I know you didn't agree with me the last time, but I will stand firm and say you must take transmission losses into account when calculating torque.

Your net trust now becomes: 8240*.88=7251 lbs, and your total resistence becomes: 6160 + 540 = 6700 lbs

So regardless, you'll make it, but it may be closer than you origionally thought.

  While I may not completely agree with you, I do hold out the possibility im wrong. I figure im near the ragged edge, you just wanna shove me closer to the edge and make me more cautious. Certainly no harm in that and I appreciate the help. 

  The snows about gone, the melt water is about ran off, time to start grading my runaway truck ramp.
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« Reply #27 on: February 15, 2011, 02:36:42 PM »

I don't know anything about driveline efficiency in an automatic transmission in first gear, though.

Brian

Brian, I would think that in 1st gear, converter unlocked, the overall efficiency would be super low, as a lot of power is wasted as heat in the turbines. But efficiency won't matter, because torque multiplication is more important in this case. I read modern ZF autos have an "in gear" efficiency of 97%. This is just the planetary gears though, not including converter and hydraulic pump.
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« Reply #28 on: February 15, 2011, 02:42:18 PM »

While I may not completely agree with you, I do hold out the possibility im wrong. I figure im near the ragged edge, you just wanna shove me closer to the edge and make me more cautious. Certainly no harm in that and I appreciate the help. 

  The snows about gone, the melt water is about ran off, time to start grading my runaway truck ramp.

You know Paul, as a worst case scenario solution, you can deflate your rear tires, effectively cutting the rolling radius to 13 inches or so, and go up with ease.

Not a recommended daily procedure though Grin
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« Reply #29 on: February 15, 2011, 11:17:37 PM »

To know whether or not you can turbo a 8V-71NA, you need to pull at least one of the pistons to see if it is a two piece piston and what rings you have. 

  Cant they be inspected through the side access covers?

 
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