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Author Topic: 6V-71 Max Governed RPM  (Read 1175 times)
Stormcloud
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« on: April 25, 2012, 07:06:28 PM »

Hi, all:

A friend ( who doesn't yet post on the boards) has an MCI-2 with a 6V-71, governed at 2150rpm.

Can he safely/ should he increase this?  With the present powertrain, he tops out at about 66mph, and would like juuuust a wee bit more. What should the max RPM be?

Also, he had some DD3 chambers installed to update the braking system. His old parking brake was a hand-operated lever. He is now looking for some rebuildable DD3 chambers to surrender to the shop as cores.
Anyone got some around they are willing to part with? Let me know $ and I will pass it along.

Thanks.

Mark
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Mark Morgan    near Brandon, Manitoba, Canada
1972 MCI-7     'PapaBus'  8v71N MT654 Automatic
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« Reply #1 on: April 25, 2012, 07:10:30 PM »

2300 rpm no load was a popular transit setting for 6V71.

happy coaching!
buswarrior
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luvrbus
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« Reply #2 on: April 25, 2012, 07:15:18 PM »

 Mark,he is good up to 2500 rpm for a safe range it won't hurt the engine I have saw the 6v71 set on 2800 rpm for pumps if a automatic he needs to check and be sure of the max rpms setting for the automatic 

good luck
« Last Edit: April 25, 2012, 07:18:25 PM by luvrbus » Logged

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Stormcloud
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« Reply #3 on: April 25, 2012, 07:35:03 PM »

Bus has a recently installed 4 speed standard, and John has 12R-22.5 tires.

Thanks for the info!

Still looking for some DD3 cores.

Mark
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Mark Morgan    near Brandon, Manitoba, Canada
1972 MCI-7     'PapaBus'  8v71N MT654 Automatic
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« Reply #4 on: April 25, 2012, 07:46:24 PM »

FWIW, years ago we had 671N and 8V71N Detroits in our old fire apparatus that had "A" timing, N90 injectors and a full-load governor setting of around 2550.  No load rpm was about 2750 rpm.  The "shops" told us to keep them under 2400 rpm for highway cruising or fire pump operation.  Since the 6V71 has a good crankshaft, perhaps it would be doable for your Bus Conversion to do the same?  HB of CJ (old coot) Smiley
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bevans6
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« Reply #5 on: April 26, 2012, 04:38:39 AM »

Is there a chart or formula to calculate the drop between no-load high idle and full load max governed rpm?  I've been using 150 rpm, since that was what the specs on my engine said.  2450 no-load vs 2300 max load governed.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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TomC
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« Reply #6 on: April 26, 2012, 08:33:52 AM »

The top speed of the V-71 engines is not an issue-there were plenty of truckers in the 70's running the 8V-71 up to 2,800rpm.  The issue is if you have a Delco DN50 gear driven alternator.  These are rated at 6,500rpm max continuous and 7,000rpm max.  That works out to be 2364rpm and 2545rpm (with 2.75 to one overdrive).  I would set the no load governed speed at 2,500rpm and be done.

On my bus I have 4.56 rears, .88 overdrive on the V730 and 476rpm tires.  I can get 76mph out of it by turning just over 2400rpm-which is nice in a pinch.  I usually run at either 58mph @ 1850 or 60mph @ 1900.  65mph is just under 2100 which is the highest I would run a 71 all day long.  Over 2100 starts to take a big hit on fuel mileage.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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