Tuning, Performance and Handling
Performance Filter Cool Air Ducting
Ever noticed a reduction in power from the engine when the weather is hot? On
cars with performance filters such as K&N or Piper Cross the filter is
mounted directly above the carb... and right inside the engine bay! This means
that the air flowing to the filter has to come over the engine and through the
radiator. So the air entering the carb is already baking hot. Although not a
problem in the winter when the air is very cold outside anyway, this can cause
a reduction in power in the summer, or in hot weather.
Technical reason: When the air is hotter the particles are expanded slightly
and so less oxygen enters the carb. As oxygen is the main component required
to make the fuel burn economically, this make the mixture richer. Which puts
the tuning of the engine out slightly and causes the reduction in power!
Understand!?
The solution is to add a cool air duct, this is a very simple job to do and
requires only a section of ducting and some cable ties. Ducting is available
from most car accessory shops for about £4 for a 1 metre piece, or try DIY
shops where it is probably cheaper and you might be able to get more than 1
metre. Decide where you want to route the duct before you buy it, or you'll
end up with 2 bits taped together like mine!
Basically all you need to do is run the duct from the air filter round to a point
where it can get air from outside, it needs to be pointing forwards so the air
will be forced in and up to the filter. The easiest place to put the duct is
down the drivers side of the engine and out next to the radiator, this will
only require a 1 metre length of duct. However, I had mine here and it started
to rub a hole in my bonnet sound deadening so I've moved it to the passenger
side, where is runs down to the top of the gearbox and then down under the car
and is cable tied onto the tie bar mount. Either method works, and on OHV
engines it should be even easier to fit as there is more space. Don't make it
too permanent though as you may need to take it out in the winter to avoid
carburettor icing!
