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The trans in mine is kinda odd it has a fuller rto 12513 13 speed it was factory that is what the build sheet shows . I haven't seen to many v8 with a fuller behind them I've always seen mack trans .

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On 10/19/2014 at 7:14 AM, Superdog said:

displacement was the same,it was how they were set up,the 865 was a Maxidyne engine,engineered to be used with a 5 or 6 speed,with an operating range of 1200 to 2400 rpm ,they had 2 versions I know of for sure,most common was the 325 hp one and there was a derated 285 hp one,also

The 866 was designed as a Thermodyne engine,for use with transmissions having 10 or more gears,mostly paired withe the TRDL1070 Mack 10 speed and the TRTXL1070 12 speed Mack.Operating range was 1500 to 2300 rpm as I recall . Also offered in at least 2 versions I can remember,a 350 hp and most common was the 375 hp one.

Which one was the problem child? Or was it all of them? :lol:

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None IF maintained correctly.They needed the heads re torqued every 100-150K of work and the valves adjusted.From what I've heard many people ignored the proper PM work and that led to issues...

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The 866 in my truck has made it 41 years of service . The guy I got it from said it was a good truck for many years . So they were not all junk

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there were some with Fullers too.There was a FS797 at South bend that had a 13 speed and also factory air ride. I think it was a '73 also

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I have a 1964 factory service manual for the 864, the cubic inch on that engine is 863.94 but they call it 864 and 255hp, torque is 639 at 1700 rpm. the 865, 866 is 866 CID. when did the twin turbo 864 come out.

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I am going to say the twin turbo 64 came out in 1966.The Tulsa dealer here sold one in that year and I was told it was the first one sold west of the Miss river.

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Just double checked myself, there were actually three "B" models that had four digit model numbers. Had nothing to do with what we were talking but I was surprised to see that there were any at all.

Ron

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