X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 15 Nov 2010 07:34:00 -0500 Message-ID: X-Original-Return-Path: Received: from web57502.mail.re1.yahoo.com ([66.196.100.69] verified) by logan.com (CommuniGate Pro SMTP 5.3.10) with SMTP id 4577627 for lml@lancaironline.net; Sat, 13 Nov 2010 07:48:43 -0500 Received-SPF: none receiver=logan.com; client-ip=66.196.100.69; envelope-from=casey.gary@yahoo.com Received: (qmail 94369 invoked by uid 60001); 13 Nov 2010 12:48:07 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=uQoc7hXz9FC2DmKnkClPPFhQ2R5IjjHbJ5c+HtiXvv3AF0LefuGjtVf59SzYy4VSenMc4MHE+5FJAn2VB+ibswlmvY7BDBf4Lyb/sBGd8ax/d6v56RM1e5nq6VTpQtVysSOOfPRxhdocekqKOhJgMphfmz9U/v4TmPCOg2pt9Bk=; X-Original-Message-ID: <963415.93610.qm@web57502.mail.re1.yahoo.com> X-YMail-OSG: aoISYNwVM1kOdiqM2FyjlndTPU_s5mTlW14TyVcNz2nti1. LhobclxfB9h60A2ZKQW08gxd94c_pYC2a85NaBzrGs0GkKsJUAIPT6o82O1t 0U0FCNpKgp5v9AtNVn7yMRKN84j.aC.MKBBbgB4fo7cM8QWPG.QD5kAymI8U zCGWghusepLHvKNNtpOqBSC8.hWj.resPhWz.pPjK1UFH4LyTDgNqrggxyiV m4yI3SUzKYMt6LrqKzQ4cZIun58n3z1.vktvR_RBinTgKc4TsXatbG4Id1.w KOjvdRA0XjcJHLtPUJLYNfZgiRO19r7HbApcopshx1ZNX_sflVA-- Received: from [97.122.152.1] by web57502.mail.re1.yahoo.com via HTTP; Sat, 13 Nov 2010 04:48:06 PST X-Mailer: YahooMailRC/504.5 YahooMailWebService/0.8.107.285259 References: X-Original-Date: Sat, 13 Nov 2010 04:48:06 -0800 (PST) From: Gary Casey Subject: Re: NC2 Legacy Performance questions X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1921002393-1289652486=:93610" --0-1921002393-1289652486=:93610 Content-Type: text/plain; charset=us-ascii Craig, I have a 10:1 compression engine and I'm not 100% comfortable with the detonation margin. But there are different combustion chamber shapes in the various engine, so results will vary depending on the engine. The octane requirement goes up out of proportion to compression ratio, but the incremental benefit keeps getting smaller. I think if I were doing it again I would settle for 9.5 as being a reasonable compromise. I understand Lycoming builds helicopter engines at 9.5, but they run at higher rpm so are less susceptible. And a Lycoming rep told me that the crank and main bearings are not likely to last 2,000 hours at 10:1 (a statement from their legal department?). Some have said that in some engines the timing should be set at 25 degrees with 10:1, but I don't believe that. I had one that was set that way and I could hear an occasional audible knock. I now have the Lightspeed set at 22 (can't retard it any more than that) and the mag at 20 and so far, so good. Gary "Craig Jimenez" What's the group's general opinion about 10:1 compression? I like the idea (higher efficiency). I found that raising the compression on my old Grumman AA5 from 7.x to 8.5 vastly improved the climb and high altitude performance. I'd be interested in your practical experiences of going to 9 or 10:1. --0-1921002393-1289652486=:93610 Content-Type: text/html; charset=us-ascii
Craig,
I have a 10:1 compression engine and I'm not 100% comfortable with the detonation margin.  But there are different combustion chamber shapes in the various engine, so results will vary depending on the engine.  The octane requirement goes up out of proportion to compression ratio, but the incremental benefit keeps getting smaller.  I think if I were doing it again I would settle for 9.5 as being a reasonable compromise.  I understand Lycoming builds helicopter engines at 9.5, but they run at higher rpm so are less susceptible.  And a Lycoming rep told me that the crank and main bearings are not likely to last 2,000 hours at 10:1 (a statement from their legal department?).  Some have said that in some engines the timing should be set at 25 degrees with 10:1, but I don't believe that.  I had one that was set that way and I could hear an occasional audible knock.  I now have the Lightspeed set at 22 (can't retard it any more than that) and the mag at 20 and so far, so good.
Gary
 
"Craig Jimenez" <jimenez.craig@gmail.com>

What's the group's general opinion about 10:1 compression?   I like the idea (higher efficiency).  I found that raising the compression on my old Grumman AA5 from 7.x to 8.5 vastly improved the climb and high altitude performance.  I'd be interested in your practical experiences of going to 9 or 10:1.


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