[ROVERNET - UK] Air filters and vacuum gauge
Fletcher
gofanu at usachoice.net
Mon Feb 12 18:04:56 GMT 2007
Steve,
The stock housing actually does a very good job of distributing air,
but it is an ugly bugger. The backplates for the stock unit are superb,
and a very important part of the airflow. Square edges at the carb
intake are bad, you need that big radius entry. Either fit stock filters
in the can, or K&N elements in the can if you actually do a lot of
miles. If it's looks you want, use the stock backplates and go find some
suitable elements, as big as will fit in the space available, either
paper or K&N, and make your own top plates to hold them on.
The area of the pleated paper or K&N filters is the area of the unfolded
pleated filtering media. The area of the things you have is that of the
holes in the chromey cover, minus any reduction caused by the similar
perforated inner retainer and the alignment between the two, so
Perforated things are not on, unless they are far bigger than anything
that will fit in the space available. The restriction caused by the
holes also vastly increases the velocity throuogh the already poorly
filtering foam elements, sucking anything but the largest of birds right
through.
Be advised that the stock cans typically cause an intentional
restriction at high speed, as a matter of reducing intake noise. Any
change in this needs to be offset by different carb needles, or the
mixture goes way lean at the top end, which is sure death for
performance and pistons. For instance, I long ago learned that XKE would
not pull the hat off your head on the top end if the filter housings
were not in place and properly sealed. This is true of all engines with
"airhorn" type filters, any changes require mixture recalibration and
increase intake noise. It is actually a violation of US Fed law to
change this nowadays, due to noise regs.
Taking vacuum signals off the vac advance port may or may not work, They
are frequently so located that the signal is not representative of true
manifold vacuum, but rather gives appropriate signals for the spark
control. This varies by specific design of the advance system, and
changes from year to year and carb to carb. I forgot about the check
valve, yes, you have to be on the manifold side of that.
FRM
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