[s-cars] Exhaust dyno results...

[Djdawson2 at aol.com]

In a message dated 9/14/2004 10:29:24 PM Mountain Daylight Time, 
calvinlc at earthlink.net writes:

> Dave,
> 
> I will have to respectfully disagree that a dual 2" exhaust is capable of
> supporting 680 HP.  I guess myabe I shouldn't say it that way...the dual 2"
> is not ideal for 680 HP.


You may be right... but you're not disagreeing with me, you're disagreeing 
with published data.  I'm just regurgitating what I've read.  Corky's book has a 
graph that clearly shows the dual 2" as sufficient for 680hp.  If you believe 
information from him, or not, is up to you.

> 
> I have long been a critic of exhaust systems and the sales pitch the
> manufacturers do.  I think that they are mostly a lot of hype.  However,
> there are many sound principles and tried and true methodologies.  Having
> built many many large displacement hi-po engines there is not a doubt in my
> mind that 2" duals will limit a 600+ HP engine.  I can give you empirical
> evidence from timeslips showing a 0.3 to 0.5 second drop in ETs at the
> dragstrip for going from 2.25" exhuast to 3" headpipes/2.5" tailpipe duals
> and keeping the same mufflers and headers on a 450ish HP machine.


I'm willing to bet money you're referring to naturally aspirated engines... 
which are completely different animals.

> 
> You can force 100 gpm of water flow through a soda straw but it takes a lot
> more effort than pushing it through a 1.5" PVC pipe....so I am sure that
> dual 2" will "support 680HP" but it certainly is not optimal.


Again, maybe you're right... I'm just relying on data from sources far more 
knowledgeable than I am.

> 
> Your test simply proves what has been known in the drag-racing community for
> a long time, it is possible to put too open of an exhaust on any engine
> combination.  Not only does this have to do with the pulsing action as
> somebody had mentioned before, but in the extreme it can make your
> combustion temperature drop too much.
> 
> 

Take it for what it's worth... maybe nothing.  I just wanted some answers to 
questions I had, and was willing to share the results.
Take care,
Dave