larry.g.unger@lmco.com wrote:
>>>Let me put this another way ... if a set of K&N filters
>>>do not increase volumetric efficiency, then why is it
>>>that when you fit a set it is recommeded that you fit
>>>a set of richer needles?
... and barneymg@juno.com replied:
>
>>Could be that the richer needles are the source of the
>>power gain, justifying K&N's claim to increased power
>>with their setup.
Well ... uh ... no ... thats not how a set of SUs fuction.
Fitting a set of richer needles without increasing the
volumetric efficiency of the engine would not result in a
power gain ... just an overly rich mixture
Peter Burgess does a better job than I could of explaining
this:
"Fitting the high flow filters means the engine does not
have to pull so hard against a restriction. That restiction
originally caused slightly more fuel to be pulled from the
jet and, as standard, the mixtures were correct for the
engine's operating range. Without the restriction to pull
against, the mixtures will become slightly weak when the
high fow filters are fitted. To supply the correct amount of
fuel to go with the improved airflow, across all engine
speeds, the standard 1.5 inc SUs will need a change of
needles. The HS4 SU carburettors fitted to the chrome
bumber Bs - with the 'fixed' needles and hexagonal nut
mixture adjustment - will need the standard FX needles
changed to No. 6 needles." ...[snip] ... "The change of
needles does not mean that fuel consumption will increase;
the engine's improved breathing actually means that power
is produce with less throttle opening necessary than was
previously used, so consumption can actually improve.
That is as long as you don't enjoy driving the car harder
just to hear the gorgeous intake growl from the carbs to
often!"
IMHO, fitting a set of K&N filters, a set of richer needles,
and a 'cold air duct' to a 'B' would provide a significant
improvement in performance ... but I have been known to
wrong. ;^)
>Safety Fast! ... larry.g.unger@lmco.com
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