looking at a D6B serial number 44A5565 transmission group 8M4948..  can anyone describe the transmission group? speeds in what gears?  the tractor is an SA tractor with an engine upgrade to a 3306 i think or maybe a 333C?  the only number i can make out on the engine is 8S2354 on the exhaust manifold.  the engine is turbo and the install looks clean with live hydraulics tank mounted in front of the firewall and i think the hydraulic pump driven off of the bell housing.   would the D6B hold up to the extra horsepower etc?

8M4948 is a optional gear set for the D6B. It is a sliding gear transmission but I don't believe they were designated as a Special Application tractor.
If the exhaust manifold # is a 9S2354 it's a 3306.
What are you trying to achieve? It's still a single reduction gear final like the 9U. If your want to up the power you might consider going to the D6C with its compound reduction gear final and later 10Kxxxx s/n units will have the 3306.

Correction: The 9S2354 manifold is used on both the D333C and 3306
If there is a large cover plate on the front of the water pump it's a 3306. If it's an all cast housing it's a D333C

thank you Magnet. i am looking at special application or tractors used for farming. this is just a tractor i found as configured and am looking for as much information as i can get both from the books and from those who used them in farming. yes i was concerned with the single reduction final drives ability to withstand the modifications. it appears to have been common practice to increase HP on all of the D6 series tractors. I wonder how well the tractors held up under the stresses over time?

You will have to rely on others for the farm experience and I know there are plenty of single reduction modified tractors out there.
Seems to me the best option would be the D6C -17Rxxxx SA tractor if you can find one. Or the later D6D SA units.

Thank You Magnet,your information and opinions are spot on always and i appreciate your input. a D6D or D6C would be probably a little more tractor than is called for in my application. probably a D5 or something very similar would pretty much fit size wize. unless i am wrong there isn't a whole lot of difference in the D6B and the D5 basically. i know the D5 has many improvements though.,

 

is this a 3306

  The D6b is a good tractor. Mine was non turbo. It didn’t have the optional transmission group but we did have Holt Bros. Move third gear up to the 4th and put a lower gear in 3rd. It pulled a 14ft. Offset disc & ring roller also a 10x60 landplane. Farmed with the D6b for 10 plus years trouble free. We would put the blade on twice a year to pack silage too. Skinner

The D5 and D5B are still basically a 9U tractor, the major changes are in the engine.
The D333C is an improvement over the D333A, The 3306 the best of the bunch. Still hard to beat the old D318.
The engine in the picture is a D333C.
The old "Halton Tractor" tubo kit for the D318's increased the horsepower by about 20% over stock when using the late cam ground pistons and latest rods.

any idea what the hp might be for an engine D333C turbo like the one in the photo above?  does anyone know what the spec is on the 8M4948 transmission group? speeds in what gears?