Eric wrote:
>
> My big news was the difference that my 'sort of' coldbox made. Running
> Pipercross filters and 'stub' horns on the SUs has meant that they have
> been sucking in hot air from the engine bay. Without messing around
> with a 'cold box' over the SUs I just made a 3" hole in the radiator
> shroud and ran a 3" flexible tube from the grill to just in front of the
> filter. What a difference it made.
>
Pardon the garbled nature of that description - I really was just
rushing out the door at the time but felt I needed to tell my little
success story. I am sure many of you know what a "cold air box" is an
what it does? :-) but for the others basically I am now feeding lots of
cold, fresh air into the carbies instead of the hot stuff in the engine bay.
The PiperCross filter and short ram tubes were fitted in an effort to
get more air into the carbies as I felt the rather heavily ported head
through to the extractors had a bottleneck in the breathing department
with the 'standard' MG SU filters. I didn't really think far enough
ahead in that by solving that problem I would be introducing another and
ended up quite disappointed that I didn't get the power boost I was
after. In fact I really picked up the fact when taking off to work in
the morning my car seemed to have more "get up and go" than it did by
the time I was halfway to work - really!
But I will leave someone else to better describe the theory behind my
$20 modification that has brought me such joy and a noticable boost in
horsepower, noticeable on and off the racetrack. That is, a significant
boost over the reduction in horsepower that my shortsightedness had
caused. Obvious to many but completely missed by me at the time (making
me feel a little silly).
>From http://www.carreview.com/Learn%5Eintakescrx.aspx
Cold Air Induction
If you've taken chemistry classes, you've probably seen the ideal gas
equation, PV=nRT. This relationship between the pressure, temperature,
and volume of a gas indicates that if the gas is colder, it's denser,
and denser air will provide more oxygen, allowing your car to burn more
fuel and make more power. A common rule of thumb holds that decreasing
air intake temperature by 10 degrees F will increase horsepower and
torque by 1%. The converse is also true; a 10 degree rise in intake
temperature will cost you 1% of your horsepower. Some aftermarket
"short-ram" airboxes for newer imports draw in air from under the hood,
which might work decently with an engine that's been sitting overnight,
but once it warms up, the aftermarket "performance" airbox will decrease
power.
--
Eric
'68MGB MkII
Adelaide, South Australia
"Nothing overshadows truth so completely as authority"
ALBERTI
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