Yet another area of my ignorance rears its ugly head.
Somebody on the britcars list (I think) mentioned having achieved
major performance improvement by installing a larger "secondary
pipe" on their car, which they indicated had a twincam of some
sort. I nuked the article and didn't think about it until just
now. Does anybody remember this? What kind of car was it? What
were the original and aftermarket sizes used? Why would this
help? Did he lose any low end responsiveness?
We're pretty dumb when it comes to exhaust (too)--we bought the
Lotus "Sprint" headers and slapped them on the car early in its
development cycle, with a 1-3/4" straight pipe going back to a
(glas-pack-type) 4A Supertrapp. This works well for times when
we have to run under a 90 dB noise limit; we just pull enough
plates to make it and live with the power loss. Then we stuff
them all back in for events where we don't care. We can't
really afford to spend hours on a dyno figuring out what the
best number of plates would be; we just vary between 10 and
20 (I think--I'd have to look to be sure) and go by feel.
I guess I have two more questions: 1) would using a larger pipe
just downstream from the Y where the header tubes come together
be a good thing? and 2) has anybody done a real thorough com-
parison of torque curves, etc. between a Flowmaster and a
(somewhat oversized) Supertrapp? The Wallaces just put on a
Flowmaster, and Bob says the car now runs so much leaner he
thinks he needs to re-jet. I hesitate to move in this direc-
tion, since freer flow (to me) means better top end but some
low-end degradation, and we've got more top than we can use
but never enough bottom. That's also why I haven't pushed
for larger pipe from the headers back. Am I all screwed up
or what?
Feel free to educate me, but be gentle. And remember, our
engine internals are stock Series 3 SE, and we can't change
that.
Donkey Moocho,
Karen
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