On a race car it is imperative to keep blowby fumes from building up in the
crank case. Race breathing systems tend to rely on large vents from the
crank case breathers and big filtered intakes in the rocker box. The
crankshaft wanging around hopefully shoves the bad fumes out of the vents
and sucks in clean air through the valve cover filters. Since the crank
case vents have to be routed to catch cans, rather than any kind of negative
pressure area I question the efficiency of the design.
Early street cars used "road draft" tubes to provide a source of negative
pressure. These hung below the engine and on the MGs the rocker cover inlet
was hooked to the air cleaner for a source of clean air. The suction
created by the road draft tube pulled clean air through the engine and out
the tube, where it could asphyxiate the bunnies looking on curiously from
the side of the road.
Later cars used a PCV (positive crankcase ventilation) system that had a
valve that would bleed crankcase fumes to the intake system under light
vacuum conditions. Later Bs' ran the vent hoses to special ports on the
carbs. With these two designs the clean intake air had to be restricted to
reduce mixture leaning. Hence the restrictor built into the oil filler cap
on earlier cars and in the rocker vent pipe on later cars. This system
allowed a more controlled "postive" ventilation of the crankcase, and
therefore was a "good thing". The bunnies liked it too.
Your B has these later carbs, which work really well for the street.
There is no need to worry about PCV valves failing. If you decide to remove
the charcoal can. Then the rocker cover vent would need to be hooked to
some form of filter. I have seen plastic gas filters used (not as cool, but
lots cheaper than K&N). There is absolutely nothing wrong with leaving the
charcoal can system intact as it does nothing to reduce power, and does lots
to keep noxious fumes out of the crank case and atmosphere.
In racing the crank wangs around so much, the oil slops all over and
the pistons tend to have big clearances and skinny rings. The stock vent
system will not be sufficient, hence the diry big filters and on my car 2"
crankcase vent tube. (I did not do it, the builder got the idea from a
Huffaker car).
But keep in mind, bunnies don't like race cars. Too noisy and the
tires are really wiiide.
Kelvin.
> -----Original Message-----
> From: Karl Shultz [mailto:karl.shultz@ibm.net]
> Sent: Saturday, June 12, 1999 10:14 AM
> To: MG List
> Subject: K+N Breather filters...what do they do?
>
>
> All,
>
> At a recent autocross, I looked under the hood of a very fast B.
> Instead of the breather hoses running to the charcoal canister, there
> was a little K and N filter attached. I've seen these things before.
>
> What do they do? I might like to try them on either car.
>
> --
> Karl Shultz
> 95 Integra GS-R, black, loud, low
> 73 MGB, orange, sputtering badly
>
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