K&N filters

[Lawrence Leong <leongccl@domain.elided>]

Jim wrote:

>I was ready to order a drop in K&N filter for my GTV6, but began to
>wonder whether modifying/converting to a cone set up might be better.

My 33, with twin 36IDF carbs, came with K&N "filtercharger" cotton 
filters so perhaps I could chime in a bit here.  The PO had installed 
the oval filters direct ontop of the carbs.  This effectively reduced 
the induction length, and drew hot air from the surroundings.  

Nett effect, top end above 4000rpm was great, easy revving all the way
to readline.  Nice induction bark that could be heard from miles (the
"ticket me" roar).  However, anything lower than 2500 was really gutless.
Going up carpark slopes was terrible, worse still, every morning I
had to climb up a slope to get to the road.  Its a wonder my clutch 
lasted so long.  

Also, back spray from jets resulted in much petrol leaking and staining.
The cotton element also smelt strongly of petrol (on reflection not a 
good sign and a receipie for disaster).


Later, I replaced the curved air horns and fabricated a venturi fixture
to mount the K&Ns where the air box used to be.  The increase in 
induction length increased the lower end torque a bit, overall 
performance was just slightly reduced.  Ran it this way for about 18 
months.  

Eventually I switched back to the stock air box.  Why?  Every 6 months
I would clean the K&N, and with this setup, I noticed a heavy layer of
(large particulate) dust downstream of the filter.  This meant that 
the filtration effect was very poor.  Since the large particles had 
stuck on the cuved section, one wonders how much dust really went thru.

Yes, air flow was better than the stock filter, but I suspect filtration
efficacy was at best half (SWAG).  

With the K&Ns directly on top of the carbs, I couldn't see the deposited
dust, so ignorance was bliss.


I've not tried cone filters, but if anyone wants to buy my 33, they can
take over the K&Ns, and do a comparision with cone filters, K&N 
"filterchargers", K&N drop-in, and stock. :-)

>I put a drop in K&N in my 91 Spider and, although it's a superior
>filter, noticed little difference in performance -- maybe it breaths
>just a bit better -- I would expect that the intake design, not the
>filter, is the most limiting factor.

Yes, the intake system is more the limiting factor.  Once the stock
air box went in, carpark climbing and morning hill climbs were more
tolerable.  Car still revs freely, but beyond 5500rpm, not as quickly 
(seat of pants?) to redline of 6300.

Much quieter as well, and hardly any traces of deposited dust particles
on corners within the induction path.  A small trade off.

>Any experiences with the cone filters?  What seat of the pants
>performance differences are noticeable?  Is there a signigicant increase
>in induction noise?  Is there a way to make more "cool" air in addition
>to increasing volume?

Seat of the pants experience.  You gotta tie it in with a free flowing
exhaust (more air in, but it still has to go out, right?), freer 
revvving engine esp at top end, nicer sound, poorer performance at
low end.  Exhaust system may contribute to resonance at cruising speed,
if you are deaf like me, that may be tolerable :-)

Not sure about increasing more "cool" air.  Only way I know is to duct 
it in.  I guess that the other factor is the area of your filter.  A 
smaller area requires higher flow rate -- I think of it as volumetric flow 
(product of area and air velocity).  If this is idea is off, let me
know.....

Hope this helps.
Cheers
Lawrence

86 33 1.5 QV (for sale)
92 164 2.0 TS

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