[s-cars] Exhaust dyno results...

[Bruce Bell]

Dave,

Thank you so much for sharing your research with us. I also find your
exhaustive results fascinating. I looked again at your "killer dyno
results" chart and noted that other than some light "squiggles" in the
torque curve it was basically fairly smooth. Did you find a similar
curve with the open exhaust run? Or, were there distinct peaks in the
torque curve at somewhat regular intervals. I've found that with NA
motors, if the exhaust is too free flowing, that the torque curve often
takes on a multi modal look due to the harmonics. Perhaps with such a
short pipe this may not be the case.

Conjecture #1: Reducing backpressure allows quicker spool-up. 
Conjecture #2: Exhaust scavenging doesn't work in a turbo application
because 1) there is tremendous backpressure in the EM and 2) the turbo
disrupts the pulses so that there is no significant negative waveform.

I'm thinking your simple test dispelled both of these conjectures. The
first because at low boost there isn't enough backpressure to
significantly retard boost onset (in the urs), and the second.... well I
keep thinking back to this Lehman(sp?) manifold and wonder why so much
energy and time was spent on balancing the runners.  This is truly an
unorthodox design!
http://pictureposter.audiworld.com/77543/strange_em.jpg

I've been guilty of believing conjecture #2; but, the only way I can
visualize the loss of power (torque) with only the downpipe is the lack
of properly tuned waveforms post turbo. Without getting out my tape
measure and slide rule, I'm guessing you'd have to be on the high end of
7000 rpm's before the negative waveforms would manifest themselves in
the downpipe.

Is anyone ever going to test an aftermarket exhaust?

Bruce
Given up on water mike, I'm drinkin' the sacred cognac!