Return-Path: Sender: (Marvin Kaye) To: lml Date: Sat, 08 Feb 2003 20:42:55 -0500 Message-ID: X-Original-Return-Path: Received: from [64.8.50.181] (HELO mta3.adelphia.net) by logan.com (CommuniGate Pro SMTP 4.0.5) with ESMTP id 2012653 for lml@lancaironline.net; Sat, 08 Feb 2003 08:44:33 -0500 Received: from worldwinds ([207.175.254.66]) by mta3.adelphia.net (InterMail vM.5.01.05.25 201-253-122-126-125-20021216) with SMTP id <20030208134432.FZDS1334.mta3.adelphia.net@worldwinds> for ; Sat, 8 Feb 2003 08:44:32 -0500 From: "Gary Casey" X-Original-To: "lancair list" Subject: exhaust temperatures X-Original-Date: Sat, 8 Feb 2003 05:41:17 -0800 X-Original-Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2910.0) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Importance: Normal <> I'll take a guess. Without knowing the orientation of the probes I'll bet the flow patterns are different than before. Much of the heat transferred to the probe occurs during the "blow-down" period. This is just after the exhaust valve opens and takes maybe 20 degrees of crank rotation. At the beginning the pressure in the cylinder is probably 100 to 150 psi so the velocity is very high. This jet of exhaust will typically attach itself to one side of the exhaust pipe, concentrating the flow. If the probe is in the way it will pick up a lot of heat, otherwise not. I've seen installations where the probes were carefully placed an equal distance from the cylinder, but because of clearance reasons were placed at various angles around the pipes, creating a difference in the reading. If the header pipes are larger this concentration of flow will be more pronounced. Why would it burn more fuel? The scavenging effect of an exhaust system depends on the length of the pipe and many other factors, with smaller pipes producing a more pronounced "tuning" effect. The thing that matters is the pressure at the valve during the overlap period when both intake and exhaust valves are open. It's possible that the new system, because of a different tuning or just because the overall back pressure is less, produces a lower pressure at this time in the cycle. This pulls more exhaust out and hence more intake charge into the cylinder. If you're lucky little or none will short circuit and go out the exhaust. Therefore, higher volumetric efficiency, more intake air and fuel flow producing more power. Since some is certain to short circuit, you are probably getting something like half the benefit - for every 2% more fuel burned maybe 1% or so more power. Gary Casey ES, still in my garage