Return-Path: Sender: (Marvin Kaye) To: lml Date: Thu, 10 Apr 2003 16:28:56 -0400 Message-ID: X-Original-Return-Path: Received: from fire.phys.cmu.edu ([128.2.26.233] verified) by logan.com (CommuniGate Pro SMTP 4.1b2) with ESMTP-TLS id 2113007 for lml@lancaironline.net; Thu, 10 Apr 2003 16:21:42 -0400 Received: from fire.phys.cmu.edu (localhost.localdomain [127.0.0.1]) by fire.phys.cmu.edu (8.12.5/8.12.5) with ESMTP id h3AKKnGD020888 for ; Thu, 10 Apr 2003 16:20:49 -0400 Received: from localhost (jbp@localhost) by fire.phys.cmu.edu (8.12.5/8.12.5/Submit) with ESMTP id h3AKKmiP020884 for ; Thu, 10 Apr 2003 16:20:49 -0400 X-Original-Date: Thu, 10 Apr 2003 16:20:48 -0400 (EDT) From: Jeffrey Peterson X-Original-To: lancair mail list Subject: Re: Tuned exhaust. In-Reply-To: X-Original-Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII LML, I checked the numbers for the tuned exhaust explanation I offered yesterday and found that I had it wrong. At 2600 rpm each exhaust valve opens every 46 ms. The wave speed in the hot exhaust gas is about 1400 ft/s, according to the CAFE report on tuned exhaust. So, the acoustic travel time from valve to tail pipe and back to valve is 7.7 ms (for a 65" pipe). That means the returning pulse due to the valve cracking open is sucking the exhaust gas out of the cylinder for the latter part of same opening of the exhaust valve. In my pervious post I said that the return pulse aided the NEXT exhaust stroke. That would require 32 foot long exhaust pipes! All this has me wondering if Chuck Brenner's system works by multiple reflection. His system has a reflection at the tail end, and one at the 3->1 junction. And pulses can bounce back and forth a few times... Or, perhaps it's ok for the return rarefaction pulse to arrive in the middle of the valve opening. still helps clear out the gas. hmmmm.... it would be nice to have a controlled test of chuck's exhaust. -Jeff Peterson ------ JBP wrote: > Tuned exhaust is a close to a free lunch as you are likely to come across. > > Simplifying a bit, it works like this: When the exhaust valve opens a > pulse of exhaust gas enters the exhaust pipe. It's a sound wave, a POP, > which travels down the pipe. When the pulse hits the tail end of the pipe > there is a reflection of the sound. As it turns out, the reflected POP is > inverted. That is, the reflected pulse is a POP of LOW pressure gas. > This pulse travels back up the pipe to the exhaust valve and gets there > (assuming a 65 inch pipe and 2600 rpm) while the valve is open for the > next exhaust stroke. The returning pulse actaully sucks the exhaust gas > out of the cylinder. > > good for maybe...10-20 HP. > > cold air induction is another cheap power booster...more oxygen > molecules in every gulp. > > another 10(?)... > > and all with no moving parts. > > cheers, > > Jeff Peterson > >