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Air filtration K&N Air cleaner
test. |
19 September
2001 |
In the past few years (well, must be nearly 6 years by
now!) since I got involved with writing for the specialist Mini Magazines I have
been continually fighting with the problem of limited space. This has limited
what I have been able to cover, both in subjects and in details. Up until
recently (say the past year or so) I have been covering fairly broad topics in
a fairly broad terms and detail. Basically trying to cover perhaps the most
popular areas dabbled in by the Mini owning masses. Having covered pretty-much
all that I think can be covered in this fashion, I decided time had come for a
more detailed look at specific items, supported and underlined by the frequent
number of questions concerning certain popular subjects on the message board
and in the 'Knowledge' section of Mini
magazine. Hence the articles on tuning specific engines in specific ways, what
the deal is when fitting 13-in wheels, etc. Air filters being one of those
popular and specific subjects.
In the forefront of Mini tuning, improving the
over-all breathing capability of the very asthmatic A-series the air filter
set-up is one that sees priority attention. All the widely available (and
widely varying) stage one tuning kits include at the very least a replacement -
and hopefully - high-flow air filter
element to fit into the standard plastic case, others going for the complete
replacement cone/pancake type. The oft-asked question associated with this is
'which is best - element in standard case or cone/pancake type?' To satisfy
some folk's desire, herewith is a test I did on a small-bore unit.
Contestants
Despite a fair increase in the number of after-market
air filter manufacturers over recent years, one still holds sway in the Mini
market.
All manner of materials have been tried and tested to
establish suitability for air cleaner duties - namely to filter as much
engine-damaging crud out of the air as possible whilst not restricting airflow
at all if it can be helped. Even when seriously clogged up. Two materials seem
to have been settled on, and are widely used by a number of manufacturers. Two
camps basically exist - the 'cotton gauze' mob and the 'foam' mob. Comparisons
have been made, extensive tests carried out, verbal and literary battles
fought, and many a personal experience thrown in in
an attempt to establish one or the other as being 'the champion'. The 'cotton
gauze' mob usually carry the day, and the one that was mentioned above as
holding sway in the Mini market despite all-comer's attempts to oust it is the
original (and many acclaim the best) cotton gauze filter manufactured by the
long established company K&N. The range they produce is massive, quality
outstanding - mirrored in what is available from them for the Mini/SU market.
Testing the whole range for the Mini/SU would have
been brilliant - but time and finances are short - and we really wanted to look
at specific applications. Considering I'd just covered tuning the small-bore
engine types, and this perhaps being the most prolific
engine size at the moment to which these stage one kits are fitted, it was
obvious where the starting point should be. Added to this the filters tested
should be those that are the popular, true direct fit in/bolt on replacements
with no other jiggery-pokery needed when fitting,
this shortened the candidates to two. The replacement element
that fits inside the standard plastic case in place of the standard paper element
and the cone type that replaces the standard filter casing as a whole.
Now, K&N generally reckon that fitting said cone
type filter would find another 6-7bhp on the A-series engine over the standard
set-up. There's no meaningful figure given for the element, but 'a marked
improvement' should be seen. So what did I see…
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And the first contender is…as this is a straight fight
between the K&N replacement element and the cone type I didn't bother with
trying the standard paper element. It's known to be seriously restrictive as
far as maximum power is concerned, and gets horribly inefficient when dirty. So
we have the standard plastic element with the hot air intake removed, leaving
an open nozzle. This ensures the coolest intake temperature from the standard
set-up. It's also the set-up I've been recommending over the cone type for
years, if for no other reason than it's a great deal quieter. I have also had
my reservations over the years as to the 6-7bhp claims from K&N - all my
testing hadn't shown this. My original tests conducted some fourteen years ago
went AWOL along with all my other stuff in my pilot's case alleviated from my
car by some low-life years ago, so I didn't have hard proof. This test was
going to hopefully set that right… |
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To add a little flavour to this 'shoot-out' I decided
to throw something else into the fight - a variation on the standard casing.
Giving credence to the rumours that the standard filter case is restrictive as
far as breathing potential goes - moons ago I carefully calculated the cross
sectional area of the 'nozzle' versus that of the opening that sits up against
the elbow on the back of the carb (bottom of picture); the nozzle proving
slightly smaller. The filter case itself is more than big enough, and the
filter surface area is unquestionably big enough when you consider the cone
type filter has sufficient filter area to cope with 110bhp! So to eradicate the
nozzle area as a possible restriction I have bored holes in the plastic casing
in the past, with seemingly good results. So I decided to try it here. I had
tried holes in both the position you see here and also around the front
vertical 'wall' on the casing. The ones shown here seemed to give the same
results as those in the front 'wall' of the case but without the fierce
increase in induction roar that accompanied the others. The six
three-quarter-inch diameter holes very nearly the same cross sectional area as
the oval elbow hole - so the original nozzle is a bonus. Those paying attention in the first picture will have noticed the black duct tape around the edge of the casing. To save time at the rolling road, I pre-drilled these holes then simply covered them over - thus shortening the test time. Note that the holes are drilled around the front edge of the filter so they are between the filter and the outside world. Pointless drilling where the air won't be filtered!
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Beautifully made and aesthetically pleasing - the cone
type K&N. Stainless steel backing plates, perfectly formed cotton gauze
filter with moulded sealing edges, and very simple fitment. The promise of
an extra six horses for such a simple swap that looks this good proves
beyond temptation for thousands of folk. But then all that glitters ain't necessarily gold. Long term the investment for any K&N
filter is worth it, as you'll never need to replace it ever again. A
million-mile warranty will see to that providing you wash it and re-oil it
carefully - following the manufacturer's instructions to the letter of
course. Main draw back with this type of total replacement filter is the
row. The induction roar when putting the engine under load (accelerating and
when cruising at speed) is ear-bleed inducing. But then again -
there's
those that love it. |
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Bonus of using the replacement element is it keeps it
looking very standard under the bonnet. Can be very useful in certain
instances, a-hem… It's a neat and tidy fit too - more than can be said
for the state of the under-bonnet/engine area of my poor old nail. 120,000mile
and still just hanging in there! The mechanicals are all OK, but the bodywork -
yoy! Andrew at GRV finds it highly amusing. He's
concerned that if I get it to go any faster, the front
is just going to disappear in a cloud of rust particles! As you can see, the
holes drilled through underneath are invisible with the bonnet up. |
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Bonus of
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Oh the shame - that beautifully crafted shiny new
filter being forced to dwell in that messy, dirty engine bay! It's a really easy fit job though, and why it was
chosen for this test. Fitted in minutes by even the most
unaccomplished DIY-er. The only draw back is
tuning it. This style of filter creates such a massive increase in fresh
airflow available to the carb; it will cause fuelling calibration problems.
There's absolutely no way the standard needle will be anything like adequate.
And this is a continual bone of contention for me. I'd love a pound for every
time I've been asked what needle would be needed for such-and-such an engine
with one of these filters on it, or even why a person's engine isn't running
very well since they installed one. Every shop that sells these should alert
the purchaser to the problem and be able to supply a needle that may not be
spot on for their engine - but at least have a fighting chance of getting the
fuelling somewhere near so the car can be driven to a rolling road for proper
attention. That's an extra expense vendors often neglect to
mention too - a rolling road session is absolutely vital to get the best out of
either of these filter conversions. Not only is the fuelling affected - but
ignition timing too. |
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Fine gentleman that Andrew at GRV (unfortunately now
not currently working there since they have moved to a newer,
smaller premises with no room for the rollers! EEK!).
Doesn't mind mucking in to help things go smoothly/quickly.
Once we'd done the two test on the standard filter
case, he was in there like a shot to whisk the old filter case assembly and
elbow off the back of the carb and stick the shiny new cone on. Mere minutes
later we were ready for test three. Before it was done though - I asked Andrew what he
thought the result would be. He said 'seen plenty of K&N equipped cars on
'ere of all sorts. 1300 Minis seem to benefit from them most, but I reckon the cone'll win by a couple of extra horses'. Now that's what I
had generally heard and had been advising for some years - as in 'it's not
worth going to the pancake/cone filter unless you want to be deafened, there's
only a couple of extra brake at the top end and fuelling is a pain to sort'.
Sound familiar to you? Turning the tables, Andrew asked me for my forecast on
the fight. Having driven the car with the standard case, then with holes in it,
I was sure there wasn't going to be anything in it. Andrew just smiled. Another thraping on the
rolling road for this super-sonic 1100 engine. I have to tell
you I am enjoying driving this engine around immensely. It is so tractable,
pulls so strongly, and is such fun, I'm starting to look for reasons to 'pop
down the road' in it. I always come back with a silly grin on me mush! Anyway,
back to the plot. Or plots in this case. |
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Graph A.
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Graph A shows the results of the standard case with
element (KCFILT1 trace), and the standard case with the holes un-taped
(KCFILT2). A quick buzz up on the standard case to get a base line (KCFILT1) -
and it gave the same figures as when I had it tuned up last month except we
picked up an extra 2 lb ft of torque (now 61 as opposed to 59 last time). Possibly because the engine now had 1500 miles on it instead of
300. Consistent that. Even that bloomin'
vertical 'hiccup' is still there! The second run was preceded by a quick run up to check
the fuelling wasn't going badly wrong. Last time on the rollers, the mixture
was slightly rich, but was left alone as finding a needle to provided spot-on
fuelling wasn't likely and 'tweaking' (filing) was out of the question as it
would be impossible to reproduce it accurately, and definitely not available
from any shop. I wanted to be able to use the results as recommendations for
future inquiries. It proved to be spot-on with extra air supplied by the
drilled holes everywhere except at maximum load/peak power where it had leaned
out slightly. To rectify this, we changed the needle from the 'AAA' to an
'AAM'. The result is trace KCFILT2.
A further 2bhp was gained, and another 3lb ft of torque. Serious
stuff for such a mildly modified small-bore engine. These peak figures don't
tell the whole story though - the graph clearly shows the gains were wide
spread. |
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Graph B.
Now the 'big one'. Graph 'B' shows
trace KCFILT2 with KCFILT3 overlaid - the result of fitting the cone type
filter. From the K&N 'blurb' and the prospect of an extra few horses - we
were expecting a leaning out of the mixture everywhere - but particularly at
the top-end. Boy were we surprised! The CO leaped from
3.8% with the standard case with holes to 5.5% with the cone!! Wild. And as the trace for KCFILT3 shows - a drop off in
power and torque - a max power of 54bhp and 63lb ft. The CO wasn't out of the
ballpark, and certainly not enough to cause the power loss. And again, the
graphs show these differences weren't restricted to peak power.
Summary
Andrew was more surprised than I was. My prediction
seemed proven, but better than I expected. Andrew was amazed the cone filter
actually made less power. But why?
Experience and a great deal of testing over the years
suggest the answer is in the way the standard filter case is designed. The
A-series engine with its Siamese 5-port design causes some very powerful
shockwaves within the induction system. I believe the elbow on the back of the
carb and the volume of the filter case dissipates these very effectively. The
cone/pancake type filters reflect these shockwaves back into the induction
system, causing induction pulse problems.
The unexpected increase in CO reading at peak power
would also suggest that the cone filter is causing a constriction at the carb
mouth, reducing airflow. A reduction in airflow will cause power loss through
depleted volumetric efficiency.
Conclusion
That famous phrase 'all that glitters
isn't gold' is perfectly illustrated here. Something that looks and
sounds like it should produce optimum results doesn't.
Without a doubt, the optimum set-up on a small-bore engine is the standard
plastic filter case with half-a-dozen three-quarter-inch holes drilled in it
and using a K&N element.
A bit of good news for those 'noise' junkies - those extra
holes give the induction sound of a Weber side-draught when under load, but are
as quiet as a mouse when on part throttle. The noise IS addictive though!
I would also state here that this is not necessarily
the case with the large bore engine units. I have had reports of gains of up to
6bhp when using a pancake (not cone) type K&N over the standard filter case
set-up from a reliable source. Unfortunately I do not know if that is the
standard filter case with standard filter, or with K&N element and other
suitable mods. That'll be another test then…