Thread: Snorkel Head - Ram vs Cyclone style

Originally Posted by POD

I have a cyclone head on my snorkel and I'm surprised by how little dust it accumulates; on a 16,000km trip that took in the GRR, Tanami (twice) and a good many other outback roads, the collector accumulated less than 1cm of dust in the bowl.
I used to operate tractors in harvesting conditions where you could not open your eyes for the dust- the pre-cleaners needed emptying every day. I'm not sure that they are necessary though in most 4wd applications- perhaps if you travel dusty roads in convoy. Have been tempted to try a ram head on mine for comparison. The noise from the precleaner is noticeable when the LHF window is down, don't know whether a ram would be quieter.

Certainly - if you travel in convoy then dust loads will be much higher. However are you sure the cyclone is correctly sized to the engine? I have seen a cyclone on an isuzu landie fill up with 1cm of dust over a weekend 4x4 trip (with convoy driving).

The ram head is quieter IME.

Originally Posted by TonyC

Granted, but cyclones apparently don't work well at high speed, so horses for courses I guess.

In theory the collection efficiency of a cyclone is proportional to particle inertia, so it increases with air flow rate into the engine, and should be largely unrelated to vehicle speed. However, at high vehicle speed, the really large particles will have sufficient inertia relative to the vehicle (and cyclone inlet) to continue straight (i.e. towards the vehicle), rather than be sucked into the cyclone. This may mean that people don't think cyclones are as efficient at high (vehicle) speed, but they may in fact not be sucking in as many large particles.

There is also the effect of particle bounce at high particle (inlet) velocities, which can make actual collection efficiencies decrease rather than increase. However this is a function of engine airflow, not speed. With a correctly sized cyclone, this should not occur at typical cruising rpms.

Here is a graph of the effect of particle bounce on efficiency:
http://www.ogj.com/etc/medialib/plat....600.350.1.gif


As an aside, a forward facing ram head will suck in all particles ahead of it (so more dust than a cyclone), whereas a rearward facing ram head will suck in fewer large particles than are in the air stream, however the same concentration of smaller particles, as they are able to bend with the streamlines and flow in the snorkel.

I also try and avoid driving in dust where possible - even if it means driving a km or two behind when in convoy. However on dirt roads with lots of oncoming traffic, it is inevitable that you will suck in lots of dust.