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Author Topic: 8V71T ?  (Read 2497 times)
jmblake
Jason & Martha Blake
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« on: January 27, 2013, 05:18:37 PM »

A month or so ago I looked at  8V silver 92 and that deal didn't go through, so today we looked at a 8V71T that is in a firetruck. we heard it run and moved it around, it has jakes and the 740 goes with it, It started right up with very little smoke and sounded really good. It is a 1983 and has 32,000 mile and 5000 hours on it. it is putting oil out the drivers side drip tube at a pretty steady drip. So my question is if I can get this at a decent price and put new pistons, liners, bearing, and every thing else that comes with a rebuild will I have a good replacement  for the old non turbo 71, that I will be happy with the power,  it says on the tag its 370hp or I have been thinking of the series 50 as a switch also. The 71T would be much easier of a switch then the 50 series and is the price difference of changing over to the 50 be worth it for a few more mpg then the 71T. Iam a little confused on what to do so thanks in advane for any input. Jason
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bevans6
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« Reply #1 on: January 27, 2013, 05:59:44 PM »

mileage vs hours shows that it's idled a whole lot.  32,000 miles and 5,000 hours is what, 6.5 mph avg speed?  5000 hours is the equivalent of around 225,000 normal miles.  It may clear up the drip with an oil change and some highway miles.  A turbo should add a mpg or two compared to a natural 8V71.  It should cool better than an 8V92, but not nearly as well as a S50.  You would have to change the rear end gear for the S50 but the 8V71T would be happy with the gear you have.  S50 is electronic, you will need to do extensive rewiring, add an electronic throttle, etc, but probably not for the 8V71T (unless it's DDEC, obviously).  I costed putting a S50 in my bus at around $15K, I put an 8V71T in for around half that.  I was extremely happy with the power in mine, but I have a 5C.  The people I spoke to with S50's in their MC-9's loved them, but confirmed the cost to install.

Brian
« Last Edit: January 27, 2013, 06:04:45 PM by bevans6 » Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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jmblake
Jason & Martha Blake
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« Reply #2 on: January 27, 2013, 06:15:07 PM »

Thanks Brian
I followed your switch and Iam leaning real hard to do this. I would probably still rebuild it before I would install it, just to ease my mind of something happening far away from home. I have a retired DD mechanic that will rebuild it just for something to do. so all it would cost is parts. I already installed the big radiators so hopefully cooling isn't a issue. What kind of MPG are you getting? Thanks Jason
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chessie4905
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« Reply #3 on: January 27, 2013, 06:28:57 PM »

If that coach were mine, I'd keep looking for a good 8v92,  derated to 400 hp or less. Since you have a nice selection of rear end gears that the GMC's don't, you can gear it to cruise at a lower rpm and take advantage of the torque. The 350 to 400 hp versions can cruise at 14 to 1500, unlike the high hp ones and will last a long time with less heat build. At least then, you can always upgrade it later to 450 or so if you desire. That 8-71t is going to be at it's practical limit, right out the door. Plus you are going to rebuild it anyway. You can check with Leid Diesel in Newville,Pa., and see what they may have that will work for you.
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GMC h8h 649#028
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TomC
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« Reply #4 on: January 27, 2013, 09:47:29 PM »

Keep in mind that the 92 and 71 series has the same bearing size on the crankshaft. The smaller piston of the 71 series can stay cooler much easier then the 92 series. Also, 71 series with their dry liner put up with sitting for long periods of time compared to the 92 series with it's wet liners can leak coolant down into the crankcase-especially in cold weather. The 71 series will put up with higher continuous rpm-like 2200-2500. A 92 likes to run 1600-1800.

The last 8V-71TA that Detroit made had 80 injectors for 400hp and 1200lb/ft torque. That fire truck engine probably has the same 80 injectors, but no aftercooling-hence the lesser horsepower and probably about 1150 lb/ft torque. Granted the series 50 will give you 9-10 mpg compared to 6-8 mpg with the 8V-71T. But also figure out how many miles of driving it would take to make up the difference-in 100,000mi you'd save about $7,200 in fuel with the Series 50-but have one or two break downs because of the electronics with paying for a tow and all that money saved with fuel goes down the drain.  If it were me, I'd go with the Fire truck engine-they were built especially well and add an air to air intercooler to it. From my experience, you'll be very pleased with the outcome. Then you'll also still have the bitchen 2 stroke sound without the 4 cylinder vibration. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #5 on: January 28, 2013, 02:11:18 AM »

Tom, You read my mind exactly, adding the CAC (air to air cooling) is a b iggie too, besides I love the 8V-71.
Dave M
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bevans6
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« Reply #6 on: January 28, 2013, 03:02:46 AM »

I don't know what mileage I got, I've only driven it around 1,200 miles due to other factors.  It was 6.5 - 7 though.  I had to park it to wait for me to fix an injector leak that was putting fuel in the oil.  Got what I need to do that, so this spring I should be on the road again.  If the fire truck engine is a mechanical, that would be a huge plus for me.  I lost an alternator at the very beginning of a trip once,  All I did was not drive at night so I didn't have to run the headlights.  It was fine for the next 1,000 miles just getting charged at night in the camp grounds.  At the time I had to think on it a bit, but a mechanical Detroit uses or needs no electricity once it's running - none at all.  I find that fascinating.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
jmblake
Jason & Martha Blake
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« Reply #7 on: January 28, 2013, 04:24:20 AM »

Thanks for the inpt guys, My thoughts are along with Toms thinking. We are planning on keeping this bus  but until I retire in about 20 years when we can actually put some miles on, we are lucky to put 4000 mile a year, so thats alot of sitting time. By the time for retirement who knows where things will be, this I think will keep me happy with a little more power and not a lot of expence in the change over since I have a donner engine in the bus for parts. Thanks Jason
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chessie4905
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« Reply #8 on: January 28, 2013, 04:50:01 AM »

btw, how much does your coach weight?
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GMC h8h 649#028
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jmblake
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« Reply #9 on: January 28, 2013, 05:20:57 AM »

Around 36,000 then I pull a 2500 GMC Pickup.
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luvrbus
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« Reply #10 on: January 28, 2013, 06:34:55 AM »

A 400 hp detuned 8v92 is a lot better than a maxed out 8v71 IMO
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Life is short drink the good wine first
jmblake
Jason & Martha Blake
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« Reply #11 on: January 28, 2013, 07:13:03 AM »

The only problem with the 92 is if it doesn't come from a mci then I would have to search to try and find everything to make it fit including the cradle or I could modify my cradle. Jason
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Ralph7
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« Reply #12 on: January 28, 2013, 06:10:05 PM »

       My Fire Truck 8-71TA is rated at 375, take a good look at that 8-71T it is possibly a TA, Cliff may be able to tell you how to tell the difference....
       That Fire truck engine will sit right nice, 1 exchange the oil pump pick up and oil pan!  2; on the motor mounts at rear of the bus you need  R&R the truck end covers,water pump to install the bus inverted V mount. 3; Does the trans have a water cooler or an air (radiator with fan) to cool the trans. AIR is best, my opinion! 4; TRICK Huh?? will you keep the big alt.,,, IF so you need to spend the time to change the rear gear case from the bus engine to the truck engine.
       5; the exhust needs to be 5inch, my old MCI was ok  but I changed to a lower restricted muffler.  6; cut out the oil bath air filter and mounted the big paper filter on the right side so no 180degree air tubing.
       7 tweek the throtle linkage to the gov. no major job!
      8; Above all get those radiators throughly cleaned  inside and out, then seal them.
      9; My milage 5.5-6.5 , but my bus is loaded with spare parts, oil,  tools, tools, a good selection os 1/4-1/2 bolta nuts, etc. do not want to weigh this bus. Puls I tow a dodge 2500 4X4 with my RZR, truck gross about 7200
     Bottom line if you do the truck engine , pull your bus engine park it beside the truck engine and get a ton of gaskets .
      Can you get the engine an trans an air cleaner and if it has a air trans cooler get it.
      Better yet get the whole truck and take tons of parts.
     Timothy down at Newville will be a big help to your mechanic, they may know each other!
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Tom Y
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« Reply #13 on: January 28, 2013, 06:52:18 PM »

Jason, I saw the 8/71 for sale in an ad this weekend. The guy emailed his #, I was going to post it here till I saw yours. If you decide not to buy will you put the info here so it may help someone? Thanks Tom Y 
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Tom Yaegle
chessie4905
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« Reply #14 on: January 28, 2013, 07:06:36 PM »

from my understanding, most 8-71 parts will swap over to the 92 series, except maybe water pump and oil plumbing.Try Bernhard bus; maybe they would have a takeout.
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GMC h8h 649#028
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