On Sat, 17 Jan 1998 23:36:59 -0500 Trevor Boicey <tboicey@brit.ca>
writes:
> I'm not sure I would agree with this.
>
> Obviously, improvement to both systems is important. The best
>triple webers will not really pay off with a stock exhaust
>and stock cat.
>
> However, I can't see how the intake and exhaust could be
>so tied. They aren't part of the same system, like the cat
>and the muffler which can be matched for best performance. As
>well, they don't handle the same air flow anyways, since a lot
>more gas comes out of the exhaust than is drawn into
>the intake.
>
Honeymoon's over Trevor, I'll dis agree with you here
The exhaust and intake are so tied. Simply put, what goes in, must
come out.
If you increase the intake volume (increase volumetric effeciencey), and
nothing to the exhaust, the resulting intake charge will be contaminated
with burnt gases that cannot exit the chamber due to higher exhaust
pressures.
Result - little or no increase in performance, and possibly a decrease.
(Remember that exhaust back pressure increases with RPM, but in a
non-linear maner - ie, the slope of the graph curves upward.)
Now, haveing said that, a little disclaimer. On an MGB the exhaust is,
in stock form, superior to the intake in flow characteristics. So a
marginal improvement to the intake side will generally result in a
performance increase (assuming a well thought out and viable
improvement), even with no exhaust modification. But a point of dimishing
returns quickly sets in where continued intake improvements soon
overwhelm the stock system ability to cope.
At this point, an exhaust upgrage is in order.
When planning induction improvements, one is forced to consider the
effect of the intake changes on the exhaust flow, if the objective is to
maximize the result of the improvement.
Rick Morrison
72 MGBGT
74 Midget
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