Yeah, There is actually someone on another forum that has been running B100 on his H1 with no mods at all and had no problem.
The thing with biodiesel is that is eats away at rubber etc. So you can run it with no mods but slowly it will make your rubber items that come in contact with it fail for example lines, orings etc.
So yeah you can run B100 on a unmodded H1 just i wouldnt go directly to B100 id start on a lower percentage eg. B20 then slowly move up since it will clean out your fuel system and tank and will clog up your fuel filters so if you gradually goto B100 and keep extra fuel filters wont have a problem and it is the way that I will be going and just replace the rubber with viton as they fail so the cost will be spread out and will get the full life out of my current rubber items before replacing.

 

Running an H1 on B100 wouldnt be a bad idea. BTW does the B100 have to be homemade or can you buy it?

 

I have been running Biodiesel in my H1 for years, as little as 2% and as much as 100% at different times:

BIODIESEL in a Hummer H1

As far as other additives go (besides running biodiesel), I would recommend Stanadyne's "Performance" additive; it is recommended by AM General (Stanadyne makes the injection pump and much of the rest of the fuel delivery systems in the H1), and it is also good for lowering the gel point of the fuel for those of you in colder climates, in addition to improving cetane rating and overall lubricity.

 

The biodiesel stuff works better than regular diesel because my neighbor has a cummins turbodiesel and switched to biodiesel and got an additional 20hp and 30lb ft of torque