X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [69.171.52.140] (account marv@lancaironline.net) by logan.com (CommuniGate Pro WebUser 5.0.6) with HTTP id 918165 for lml@lancaironline.net; Sun, 08 Jan 2006 23:06:52 -0500 From: "Marvin Kaye" Subject: Re: [LML] Re: Shock heating and cooling. To: lml X-Mailer: CommuniGate Pro WebUser v5.0.6 Date: Sun, 08 Jan 2006 23:06:52 -0500 Message-ID: In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format="flowed" Content-Transfer-Encoding: 8bit Posted for "George Braly" : Mark, Nobody with knowledge on this subject is saying that shock cooling can not be created under extreme conditions. However, if one first deals with the issue of "how hot is 'HOT' " - - - and one appreciates that one cannot shock cool a cylinder that is not HOT to begin with, then one can begin to put some rationality into the evaluation of the subject. 15 years ago, there were a lot of people and engine shops that openly advocated routine operation of our engines with CHTs up around 420d F. Or 410 or 400. But nobody thought continuous operation at 420d F was a "bad thing". I think some serious re-evaluation of that notion has taken place. There is an ever growing overall view that something at or under the 380d F range for continuous operation is much more appropriate. Is that "HOT" in the context of engine operation ? Probably not. Is 420d F "hot" in this context, yes, it probably is. IF one has the CHTs under good control in cruise at 380d F or so, and one needs to come down hill - - then major changes in the throttle and RPM do not appear to be causing problems. My preference is to first roll the RPM back to 2200 or 2100 RPM to begin to slow down, and then, not much later, go ahead to reduce the MP substantially. At that point further reductions in RPM to the bottom of the green for RPM and MP are really not a big deal. I routinely make descents from 17,000 feet with the RPM at 1800 and the MP at 15 or 16" . I seldom touch the mixture control. Regards, George