At 3:39 PM 3/22/95 -0500, Silikal@aol.com wrote:
>Scott "snausages ;-)" Fisher wrote:
>>Obviously, the shorter the length of the primaries, the lower in
>>the RPM band this negative pulse will be generated.
>
>Obviously?
>umm...I think its the other way 'round.
If you got to the last paragraph (pant pant pant... come up for air!),
I say the same thing -- that is, it's counterintuitive to the way I
have understood it to work. But if you talk to a tuner, they will
all tell you that a longer distance to the collector will help low-
end torque.
Now, it's possible that this is due to some other effect, like the
overall volume of the primary/secondary pair. I don't know
that, and I don't know where to look it up. Smith doesn't
talk about it; is it in Van Valkenburgh? I'll have to check the
library (not mine, unfortunately!) Maybe Vizard explains it,
though I'd expect to remember it if he does.
Or is this one of those old rules of thumb that has been superseded
by modern research, like air pressure in tires? The old rule of thumb
was to lower the pressure when you wanted to increase the slip
angles; turns out if you raise pressures, you increase slip angles but
you do it more slowly and more predictably.
As I said, cars are complex and not always intuitive. That's what
makes it such a kick when something actually *works*...
>Imagine a pipe organ.
Been there, done that. The problem is, it works backwards from
the way we would think it works -- like adding a bigger front
anti-roll bar to make the back end stick better. Cars are weird.
>I also remember reading somewhere that the scavenging does not
>work on 6-cylinder cars due to timing of cylinders.
I've only worked with 4s and 8s. With V8s you want a crossover
pipe at the back of the headers; it's weird, the gases don't really
cross over, the pipe acts as a kind of buffer to let excess pressure
shoot across the crossover and reduces restrictions in the direct
pathway.
I'm sure that you *can* generate a header for a six that produces
scavenging; it just may not be practical due to space or geometry
constraints. Like if you needed 27 feet of tubing...
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