Air filters
Been researching air filter for some years on motor bikes,
rally cars and finally 4wds.
The poor old air filter is often blamed for all sorts of
performance problems. Sometimes it's justified. Speaking
specifically about the 80 Series, here's a review of my
observations.
1. Factory air filters flow well but do allow fine particles to
get through. For example run a clean rag inside the inlet tract
down stream of the air filter and it'll be dirty. A well
maintained foam filter won't let this happen. Obviously the
particle size it traps is smaller than that trapped by the factory
filter. (my experience here is limited to the Finer filter).
Also after blowing out the factory filter, pointing the air gun
back into the filter will result in a cloud of dust back through
the filter. This is scary stuff indeed and suggests that you do
need to wash the filter in water (as per the instructions) before
installing. That said, the dust particle size that does get
through is probably small enough to not cause accelerated engine
wear.
2. Regular maintenance of a foam filter is critical. By
regular, I mean daily in dusty conditions (you're following
someone down a dusty track) to say 3,000km max around town.
3. The light duty Finer filter flows better than the heavy duty
version but is prone to leaks around the base when dirty. The
heavy duty version incorporates steel plates top and bottom much
like the factory filter and the inner foam is bonded to the
plates. If you do run the light duty filter, a generous smear of
water proof grease along the top and bottom
surfaces is encouraged.
4. The factory filter is designed to flow well enough with the
standard inlet tract. If a Safari snorkel is fitted (which does
away with the cyclonic unit in the front guard) then the filter
becomes a source for restriction (however, Safari does recommend
using the factory filter).
5. The amount of oil in the Finer filter has a big impact on
the flow restriction but surprisingly little affect on its
filtering properties. People often over oil the filter which is a
mistake.
6. Almost all the horror stories about foam filters are due to
improper service. You really do have to be anal about cleaning
them often and taking extreme care when fitting.
7. You can use a second outer band over the filter for really
dusty conditions and remove it say half way through the day. (A
thin light duty outer element stretched over the heavy duty filter
is a good choice).
8. Foam filters are messy and a pain to service. Have a spare
in the cupboard.
9. Drying a washed factory filter is a pain. Have a clean spare
and stick the freshly washed one (wrapped in a clean lint free
cloth) in a cupboard to dry ready for the next service.
10. Spare foam outer elements can be stored easily in the car
ready to be replaced as needed on a long desert trip.
11. For performance, the best oil for a foam filter is 2 stroke
motorbike oil however it drains out of the filter too quickly.
Don't be tempted to use it.
12. Fresh foam filter oil is mandatory. The oil is thin to
allow even and thorough penetration. The thinning agents evaporate
leaving a sticky goo that does the work. If your oil is old and
thick, then you'll invariably have to over oil the filter to get
it right through the filter.
13. The cost savings of running a foam filter are marginal.
14. The correct solvent used for washing a foam filter is
critical in its performance. For example, washing in petrol will
clean it but will break down the foam cells, drastically reducing
the filter's effectiveness. It may also affect the bonding agents
used to keep the foam in place. Mineral turpentine is recommended.
15. After washing a couple of times in turps, you need to wash
it well in warm soapy water. This is what really gets it clean.
If you're still with me I'll share some interesting info with
you... With all the industry hype about foam filters (some good
and some bad) there's a lot of folk lore about the flow
performance. There is no doubt however about the foam filter's
ability to filter air. They do so very well indeed and filter
better than the factory air filter.
So, in an effort to achieve a definitive answer on performance,
I decided to measure the pressure drop across 3 different filters.
Hooked up a pressure gauge with the high pressure side plugged
into where the factory filter warning switch plugs into the air
filter housing. This measures the air pressure before the filter.
The low pressure side was plugged into where the factory filter
warning switch plugs into the inlet tract side of the air filter
top.
This effectively samples the pressure drop across the air
filter and things like snorkel etc have no influence on the
readings.
The filters tested were the heavy duty Finer filter (slightly
over oiled), the standard Finer filter (oiled just right) and a
5,000km old factory filter which was blown out and washed.
Test performed on a 1HD-FT turbo diesel with Safari intercooler
at 3,000rpm, full throttle in 3rd gear (up a bloody big hill).
| Standard Finer filter |
5 inches of water |
| Heavy duty Finer filter |
6 inches of water |
| Factory filter |
6 inches of water |
The standard Finer filter flows slightly better than the
factory and heavy duty Finer filters. It should be noted however
that this motor pumps a lot more air than the 1FZ-FE, 1HZ and
1HD-T, so the pressure difference is more pronounced than that one
would expect with the other motors.
Cheers
gc
'97 1HD-FT - Melbourne Oz. |
