according to my parts book, the plungers in the fuel pump for a 9u d6 are the same as a 7u d4 ?! seems kind of odd seeing as how the pump housing is a lot smaller on a 4 then a 6....?

Hi Team,
the D315(D4) is a 4 cylinder version of the D318(D6) so all basic parts are the same where applicable for the number of cylinders required.

Cheers,
Eddie B.

Is there an air intake upgrade / retro that uses a canister filter for these old 9u's ? or is there a cannister that anyone would suggest, i can build the piping to and from it

There was a Cat update of a dry air cleaner. Depending on how much you want it genuine Cat many air cleaners have been adapted.

that Leeds to the question--which type of filter is better--oil bath or element?

I always thought that dry type air cleaners let engines breath better than pulling oil up through the air cleaner housing on the oil bath type.

I was thinking that the oil substrate would tend to have more particles stick to it than a paper element--but it would have to be cleaned more often than the paper as the paper has folds and more surface area?

i like the look of the dry canister filter systems with the precleaner up top above the hood....and since there isnt a pony motor in this machine anymore i figured i could use that space to mount the canister......but i need to figure out what to use for a canister haha. as far as which is the better system, all the newer stuff uses the dry system doesnt it, i would guess it would maybe depend on the quality of the filter thats in there as to how much it collects....?

There have been a lot of studies and even more opinions as which is better, oil bath or dry. Most studies show very little difference in the percentage of dust particles removed by either the oil bath or the dry filters. A major advantage of the dry filter is that as it becomes plugged it affects engine performance without losing filtering ability whereas the oil bath filter may have dust/dirt saturation and even oil loss without affecting performance leading one to think everything is OK until it is too late. It really boils down to how much time one wants to spend making sure the engine is breathing clean air. There are several other factors that can be considered but the clean air seems to be the major one. (Dry filters can use sensors for condition, oil can get into turbo if used with oil bath etc, etc.)

Heres a poorly maintained D4 oil bath air cleaner tube.