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Date:         Thu, 16 Sep 2004 09:15:35 -0400
Reply-To:     Dennis <guskersthecat@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis <guskersthecat@YAHOO.COM>
Subject:      Re: Exhaust Pipe Question

I would disagree. A properly designed exhaust has low or no backpressure. On the contrary, by taking advantage of resonant pressure waves, a vacuum is actually created at the exhaust valves. Essentially the pressure front from the closing of one valve travels down the header pipe around the collector and then back up the next primary tube .. and bounces off the next exhaust valve about to open. At that point you may actually have a vacuum at the valve resulting in increased scavenging, decreased pumping loss, and thus better efficiency.

I won't rehash the volumes of information out there on exhaust theory but tube diameter, primary tube length and collector location all require careful consideration to ensure both high gas velocity and the aforementioned resonant effect. It's important to note that this tuning is generally focussed to a particular engine's planned power curve.

Check out the dyno tests at www.techtonicstuning.com

A quick intro to the theory: http://www.powerflowsystems.com/review/12-00.shtml

A properly designed exhaust means better torque, hp, and mileage. A good example is my daily driver car. It started life as a 90hp 1.8L VW Scirroco that maxed at about 35mpg (imperial). It now has a tuned 2.0 litre that delivers 145 HP, yet still delivers 39mpg (imperial) at 60mph highway cruise. It's all about efficiency...and internal combustion engines (particularly older ones) have lots of room for improvement.

My site http://my.tbaytel.net/guskers has a section on exhaust with references to autospeed's muffler tests. It is possible to have a quiet exhaust with straight through mufflers if designed properly. The exhaust I designed has two straight through mufflers, one five inch OD, and one six inch OD. It is only slightly louder than stock...although the first design with a smaller OD 2nd muffler was obnoxiously loud.


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