what is number 4 diesel

[haganes]

Well also denser fuels have high energy density which means better fuel economy?? right??

with this i conclude, that IDI 650rpm lister will happily chug on no-4 diesel. Probably compression can be upped little bit to improve performance on thicker fuel and take advantage of extra energy in dense fuel.

if it really is #4, there is no astm spec to govern the cetane rating or sulfur content. 

further, if it is true that this came from marine use, my guess is that it is IFO-180 which is what the big ships burn.  it has a viscosity of 25 - but the big problem for you would be the extremely high sulfur content (5%) and ash may be as high as 0.15%.

so my point is you have no idea what the properties are of the fuel you are buying.  i do not recommend touching the compression.  buy a little and see how the lister dances.

regards,
captain steven