[s-cars] Exhaust dyno results...

[Djdawson2 at aol.com]

In a message dated 9/15/2004 12:59:19 AM Mountain Daylight Time, 
bbell at surview.com writes:

> 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.

I'll have to look at the curve again.  Unfortunately, I didn't print that one 
out.  If there's interest, I can overlay the graphs of various runs and make 
them available.

> 
> 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've been a believe in both of those theories... a now don't know what to 
think.

> 
> 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


That is bizarre.  But this design is impacting things upstream of the turbo.  
I think it does matter there.  To keep the pulses "hitting" the turbine at 
even intervals does seem like a good thought.

> 
> 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.

I think that must be the case.

 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.

Hmmm...

> 
> Is anyone ever going to test an aftermarket exhaust?
> 

I will, if someone provides one for the test.  I won't buy one to test, 
however.
Take care,
Dave