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Tractor Talk Discussion Forum

Fuel consumption of 4-71 or 6-71 GMC

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CenTexFarmall

02-04-2008 20:59:25




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Does anyone have data on fuel consumption for the old GMC two cycle diesels? We have on old A.C. Dozer in the family with a 4-71. Seems to run for quite a while on not too much fuel. I'm wondering how that or say a 6-71 compares with a 4 cycle on fuel consumption as H.P./Hrs per gallon.




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JoeBob/IN

02-05-2008 18:28:01




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 Re: Fuel consumption of 4-71 or 6-71 GMC in reply to CenTexFarmall, 02-04-2008 20:59:25  
Have a 6-71 turbo in an '83 GMC tandem grain truck and like said before they don't like to be lugged. Best way to drive one is slam your hand in the door so you are good and mad then beat the living heck outta her. Seriously! They love to be beat on! Ours doesn't leak hardly at all yet. It really is a good engine and the sound is like nothing else. Weighing in at 58k she will consistantly pull 6 mpg.

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Janicholson

02-05-2008 06:19:26




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 Re: Fuel consumption of 4-71 or 6-71 GMC in reply to CenTexFarmall, 02-04-2008 20:59:25  
There are millions of 2stroke Detroits, but though innovative when first put in production, they have proven to be troublesome in two ways (or more)
They are not clean engines. Often from leakage and spitting fuel and lube. They are also not very environmentally friendly. They do not meet the specifications for clean operation needed today.
They are also not as thermally efficient as the 4stroke engines. GMC now produces 4stroke diesels for that reason.
They have good hp to weight ratio. They can make plenty of power if kept in the upper rpm band, not too much of a lugging engine.
I think the symetry of the components, and the flexibility of the rotation, drive end choices,and other features is unique and valuable. JimN

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CenTexFarmall

02-05-2008 10:32:13




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 Re: Fuel consumption of 4-71 or 6-71 GMC in reply to Janicholson, 02-05-2008 06:19:26  
Granted everything you said above. It's just interesting to me how long they've stayed around and the innovation at the time they were new. I've heard them referred to as "Leaktroits".

Didn't really get a good feel for the lugging ability, good or bad, as the clutch is weak in this one and will slip before the engine pulls down very much. Aggravating the problem is that the machine is saddled with way too much blade! It has a 10 foot blade that was on there when they bought it. It would be easier to use and easier on the machine with a smaller blade.

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dieselpaul

02-04-2008 22:12:05




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 Re: Fuel consumption of 4-71 or 6-71 GMC in reply to CenTexFarmall, 02-04-2008 20:59:25  

depends on load--not sure if you are comparing both engines to same dozer?



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CenTexFarmall

02-05-2008 10:20:17




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 Re: Fuel consumption of 4-71 or 6-71 GMC in reply to dieselpaul, 02-04-2008 22:12:05  
Well, let's say a steady load at 75% throttle.

I wasn't really thinking of a straight comparison, just looking for some numbers; any 6-71: Dozer, Bus, Road tractor- anything, just curious.

I don't have it on my place right now to run look at, but I'm pretty sure this model of Dozer with the 4-71 is an HD-55. My uncle (who is in charge of the estate) thinks it has 140 horsepower. Vintage data I found that came from AC put it at something around 60 to 65 horsepower, which seems about right. Apparently AC did make a later model with a 6-71, but I don't recall what the numeration of it.

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buickanddeere

02-05-2008 10:32:43




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 Re: Fuel consumption of 4-71 or 6-71 GMC in reply to CenTexFarmall, 02-05-2008 10:20:17  
A 4-71 running at 75% load will burn about 2/3 the fuel a 6-71 running at 75% load. The last of the Two Stroke Detroits were very clean compared to the well worn engines we mostly see & think of from 1940,50,60,70's. The Silver Series with turbos, bypass blowers and California injectors had respectable fuel efficiency and stack emissions.



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dieselpaul

02-04-2008 21:37:17




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 Re: Fuel consumption of 4-71 or 6-71 GMC in reply to CenTexFarmall, 02-04-2008 20:59:25  

the 6-71 also runs quite a while, but it will use more fuel.



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