Return-Path: Received: from [65.33.166.167] (account ) by logan.com (CommuniGate Pro WebUser 4.0b7) with HTTP id 1735191 for ; Tue, 17 Sep 2002 08:24:26 -0400 From: "Marvin Kaye" Subject: Re: [FlyRotary]Re: 20B turbo specs Compressor Maps To: flyrotary X-Mailer: CommuniGate Pro Web Mailer v.4.0b7 Date: Tue, 17 Sep 2002 08:24:26 -0400 Message-ID: In-Reply-To: <003c01c25e3f$3f1b4ea0$1702a8c0@WorkGroup> MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format="flowed" Content-Transfer-Encoding: 8bit Posted for "Ed Anderson" : > > I had Turbonetics(Dave Austin) size me a turbo. What do you guys think? > > recommended - TO4E 60 based on: > ...snip... > > based on 180hp(?) shows max 231hp w/out aftercooler, 256hp with > aftercooler. > > It seems to me that you are looking at 13b hp ratings. A NA 20b will do > 250 hp without a turbo. Hi Barny, Sizing a turbo is a combination of calculations to help you select the compressor needed from compressor maps and operating conditions/parameters based on experience. Selecting the A/R (Area/Radius) ratio for the turbin exhaust housing is more problematic (meaning you may need to experiment some in order to get the right A/R size). Mass flow (Lbs/Min) is generally one parameter used to size the compressor. Various "trims" are specialized for the fine tuning of the compressor wheel selection. Much of this can be gained from various Turbo books on the topic. There is one thing that needs additional consideration for turbo aircraft selection. That is "Compressor Surge". It turns out (particularly if your are using higher boost levels) that IF you maintain the same boost at altitude that you do at sea level, that the ratio between manifold pressure vs ambient pressure will increase. This can push the operating point of the compressor into the "Surge" zone. Compressor Surge is an unstable operating point that can destroy a turbo unit. Normally at the lower boost levels this is not a problem. But, one that should probably be looked into before committing to buy a turbo unit. That being said, its hard to beat copying someone who has sucessfully selected a turbo with the right parameters provided they are operating in the same engine regime that you will operate with. You probably do NOT want to select a turbo for a 20B based on one that has proven successful for a 13B as your engine will have basically 50% more Mass flow. This means using a compressor/turbin section selected for a 13B would result in less efficiency (more heated air) as well as likely overspeeding of the turbin due to the greatly increased mass flow through the turbin. You will also encounter more flow restriction that a properly sized turbo. The first parameter to consider in selecting your compressor is Mass Flow. Most compressor maps use Mass Flow as an entry parameter. You can calculate the mass flow of your engine by figuring the engine air flow (cubic Feet/ Min) at the rpm you intend to run the boost and using a 12:1 Air/Fuel ratio also figuring mass (weight is close enough) of the mass flow. Mass flow = CFM X (0.0756) + (CFMx(0.0756)/12 will get you in the ball park at sea level. The first factor is the mass of air (CFMx0.0756) flowing into your engine. The (CFMx(0.0756)/12 factor is the mass of the fuel (at a 12:1 A/F ratio). So together these two factors will give you a fair approximation of your mass flow (lbs/Min) which you can use to ball park your compressor selection. Hope this helps. Ed Anderson FWIW