Landrover series oil bath air cleaner modification

Having tweaked the transfer box from 1.148:1 to 1:1, I now need just a wee bit more power in fourth gear as it’s a little gutless on hills. Thinking about this while driving up the B713 recently I decided to disconnect the oil bath air cleaner and see what happened. As soon as I pulled away without the air cleaner I could feel the increased gutlessness due to the increased airflow making the mixture very weak. Luckly I run on LPG so it’s just a matter of turning the flow adjuster a bit to richen up the mixture over the whole rev range. Much easier than pratting about with carbs and jets… :o) Anyway, I tweaked the flow adjuster and tried again, a fair bit of extra power was evident, which just goes to show how restrictive the oil bath cleaner is.

Most normal folk would just have tossed the oil bath and have fitted a K&N filter, but I kind of like the standard cleaner and I’ve never been 100% convinced that K&N type filters will really catch all the fine dust and they certainly aren’t going to stop the thing gulping a lungfull of water unless I make it a box of some kind. I have a Mitsubishi L200 pickup and have a stock of filters for it, quick check and the L200 air cleaner looks like it will fit in a gutted oil bath case.

I decided to do a little hillbilly flow testing to see how the air cleaners perform. If I decrease the restriction at the air cleaner, I’ll have to increase the fuel flow to compensate and I can measure the decrease in restriction by counting the turns (half turns for ease of counting) of the fuel flow adjuster. I set the idle to 2600rpm and adjusted the fuel flow for max RPM for each test without altering the carb idle screw from it’s 2600rpm setting. Here’s the results,

	Flow adj. turns out
No filter, just hose from carb	15
Standard oil bath	6
Oil bath without lid	8
Gutted filter case	9
Gutted case without lid	13
Gutted with paper element no lid	12
Gutted with paper element and lid	7

My gutted case and paper filter clearly flows much better than the standard oil bath, but the lid has now become the flow limiting factor. I wondered whether the restriction in the lid was the closeness to the intake in the main filter case or the louvered holes round the edge, so I inverted the lid to see what happened. Much the same result, so it’s the closeness to the intake that’s the problem. I extended the stud the lid mounts on so I could adjust the lid height with a nut.

	Flow adj. turns out
Gutted with paper element and lid	7
Lid raised 20mm	10
Lid raised 30mm	12

30mm gets the flow back to where it was without a lid so the plan is to add an extention to the existing lid. The problem with this is that the whole filter assembly is now going to be too tall to fit it’s mounting bracket.

I added the 30mm extention to the lid, cut the oil cup where it changes diameter, "telescoped" it together and gas welded the join to get the filter down to standard height. The oil cup is very thin and there's just no way it would have mig welded. Blasted and primed ready for a coat of gloss black and fitting in the morning :o)

Fitted the filter and tweaked the flow adjuster to see how it was performing. Not well was the answer, took the lid off and the flow improved a couple of turns. Decided to try adding a second louvered section instead of the blank sheet metal raiser.

The weather has changed from yesterdays very cold and frosty to mild and damp, so last nights settings are meaningless today. New table with a "no lid" setting as a bench mark,

All with paper element	Flow adj. turns out
No lid	10
Lid with 30mm sheet raiser	8
Standard lid with 30mm gap	10
Lid with two louvered sections	9

I'd have liked to have seen the double louvered lid with the same flow as no lid, but I can live with 9 and I've wasted enough time on what was supposed to be an hours simple bodgery.... :o)