In a message dated 3/13/01 7:58:04 PM Pacific Standard Time,
marcsayer@home.com writes:
> You just discovered that the firing order and manifold design can lead to a
> differential in mixtures between the outer two cylinders and the inner two
> cylinders. On various cars this effect can range from hardly noticeable to
> extreme enough to justify radical manifold redesigns. When thinking of
> firing
> order as it relates to mixture, it is best to look at the firing order
> differently than the way it is most often expressed. So as to start with
> cylinder #1, the order is normally expressed as 1342, but to see how the
> firing
> order affect mixture organize the order as it relates to the carbs, begin
> with
> cylinder 2 instead. Then the order is 2134. Now you can see that when
> cylinder
> #2 is on the intake cycle it is drawing through a manifold runner/carb that
> has
> been inactive for two intake cycles. This means the air/fuel mixture in the
> intake tract is barely moving and must be accelerated rapidly. This causes a
> lean out as the air reacts more quickly than the fuel, and therefore
> cylinder 2
> runs a bit lean. Then cylinder #1's intake cycle begins. But it is now
> drawing
> through a manifold/carb that was operational on the very last cycle and so
> the
> column of air/fuel in the tract is already moving. It suffers no lean out
> as the
> air/fuel mix was already moving and did not need to be accelerated, plus it
> gets
> some of the slow reacting fuel from cylinder 2's intake cycle, so it runs a
> bit
> richer yet. Same thing goes for the intake cycles for cylinders 3 and 4.
>
Marc...so then, which header tubes do you suggest putting probes for an EGT
gauge?
Craig Carter
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