Exhaust: Do we really need back pressure?

[haygood at myway.com (Brian Haygood)]

My understanding is that you don't specifically need backpressure, but you do need to make sure there is not negative pressure.  When the pulses travel down the pipes, you want them to pulsate between a little backpressure and no backpressure, ideally - not pulsating from positive pressure to negative pressure.  I've been talking to a land-speed-record holder guy on this and he keeps telling me he is going to get me lots of documentation, but he isn't coming through.



Keeping the gasses hot means that the gasses have a greater volume and so must have a greater velocity.  Again, the point is to keep the gasses flowing quickly so they suck more exhaust out of the cylinder as it opens.  Tuning the header so that the pulses happen at the right time to do so comes in here.  Do some searches and you will find a couple of methods for calculating header diameter to tune this - not that you asked about that. 



Wish I had the numbers from my guy to give a good story here, but he hasn't sent them yet.  



BH









 --- On Thu 02/15, Peter < peter@thescirocco.com > wrote:

From: Peter [mailto: peter@thescirocco.com]

To: scirocco-l@scirocco.org, Cory_Langford@bcit.ca

Date: Thu, 15 Feb 2007 17:03:51 -0500

Subject: Re: Exhaust: Do we really need back pressure?



I don't think you need any back-pressure...<br><br>All Techtonics stainless exhausts come with Borla mufflers and they're <br>straight thru.<br><br>Peter - 302.832.8989<br>http://thescirocco.com<br>----- Original Message ----- <br>From: "Cory Langford" <Cory_Langford@bcit.ca><br>To: "Scirocco list" <scirocco-l@scirocco.org><br>Sent: Thursday, February 15, 2007 3:45 PM<br>Subject: Exhaust: Do we really need back pressure?<br><br><br>><br>><br>> Just finalizing the exhaust set-up and I was wondering what the opinion <br>> was<br>> on running a completely free flow exhaust.<br>><br>> One of the tracks has a noise restriction, and one does not.  So I figured<br>> the simplest design was from the header to 2.5 inch pipe straight back (no<br>> cat, res. etc).  I figured I would have a removable muffler that can slide<br>> in when needed, and a straight pipe when not.<br>><br>> But I have seen some talk on the vw engines needing some back pressure to<br>> keep the exhaust gasses hot 
enough to travel quickly through to the end.<br>> So I was wondering if a simple straight pipe would have any down sides to<br>> it (beside noise)?<br>><br>> Cory<br>><br><br><br>--------------------------------------------------------------------------------<br><br><br>> _______________________________________________<br>> Scirocco-l mailing list<br>> Scirocco-l@scirocco.org<br>> http://neubayern.net/mailman/listinfo/scirocco-l<br>> <br><br><br><br>_______________________________________________<br>Scirocco-l mailing list<br>Scirocco-l@scirocco.org<br>http://neubayern.net/mailman/listinfo/scirocco-l<br>

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