On Sun, 18 Jan 1998 17:37:40 EST gofastmg@juno.com (Rick Morrison)
writes:
>
>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
>
Guess we learned at the same school Rick- and in my experience the
theory is borne out - Skips original point was that the carbs are
basically too small but having tried all sorts of combinations its still
a question of balance (obligatory Moody Blues ref)
mike robson
69 roadster (stock filters and exhaust, had stock filters performance
exhaust)
70 BGT (K+N filters Monza exhaust)
72 roadster (pancake filters and a bloody great stainless steel pipe with
no box!)
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