Return-Path: Sender: (Marvin Kaye) To: lml Date: Sun, 06 Oct 2002 21:31:23 -0400 Message-ID: X-Original-Return-Path: Received: from pop3.olsusa.com ([209.26.218.2] verified) by logan.com (CommuniGate Pro SMTP 4.0b8) with ESMTP id 1798929 for lml@lancaironline.net; Sun, 06 Oct 2002 16:53:27 -0400 Received: from harrier.mail.pas.earthlink.net ([207.217.120.12]) by pop3.olsusa.com (Post.Office MTA v3.5.3 release 223 ID# 0-71866U8000L800S0V35) with ESMTP id com for ; Sun, 6 Oct 2002 16:44:42 -0400 Received: from sdn-ap-003watacop0398.dialsprint.net ([63.187.209.144] helo=f3g6s4) by harrier.mail.pas.earthlink.net with smtp (Exim 3.33 #1) id 17yIOz-0006SM-00 for lancair.list@olsusa.com; Sun, 06 Oct 2002 13:53:26 -0700 X-Original-Message-ID: <000001c26d7a$c63fc1a0$90d1bb3f@f3g6s4> Reply-To: "Dan Schaefer" From: "Dan Schaefer" X-Original-To: "Lancair list" Subject: cooling X-Original-Date: Sun, 6 Oct 2002 13:53:47 -0700 MIME-Version: 1.0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4133.2400 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4133.2400 Gary Casey Wrote: "And since higher temperatures reduce strength and creep qualities it can be expected that running at higher temps and pressures will reduce engine life." Well, this statement also deserves a "maybe yes and maybe no" as well. As regards to temperature, most engines, at least the big Continentals for sure, are designed to operate at an optimum (relatively high) cylinder temperature and as a result, are designed with cylinder choke (the upper part of the cylinders are tapered to a slightly smaller diameter than the lower). The idea is that the choked region of the cylinders expand due to temperature (measured indirectly as CHT) enough for the cylinder walls to be close to parallel once heated to operating temperatures, e.g., once the engine is making a lot of power. If you consider high temperatures a bad thing and run your CHT's too low, the cylinders do not expand properly, as designed, and in short order the choke is scrubbed out by the piston rings. Ring sealing at the most critical part of piston travel (at, or close to the top of travel, where the pressure is highest) suffers as heat transfer through the rings decreases and blow-by increases. Compression drops and your jugs need topping, as a minimum. Additionally, the high combustion pressures developed in a jug with good compression gets behind the compression ring(s), pressing it (them) outward against the cylindrer wall, and aids in providing a good ring to cylinder wall seal. Granted, excessive (over red-line) cylinder temps, and the extreme pressures resulting from such maladies as detonation certainly will drastically shorten engine life (sometimes to just minutes). But in a non-detonation environment, choked cylinders operated at temperatures that are too low will also severely shorten their service life. Dan Schaefer