Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 (Tek) 9/28/84 based on 9/17/84; site shark.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!vax135!cornell!uw-beaver!tektronix!orca!shark!davew From: davew@shark.UUCP (Dave Williams) Newsgroups: net.auto Subject: Re: superturbochargers Message-ID: <1335@shark.UUCP> Date: Mon, 15-Apr-85 12:46:27 EST Article-I.D.: shark.1335 Posted: Mon Apr 15 12:46:27 1985 Date-Received: Thu, 18-Apr-85 02:52:15 EST References: <541@hou2e.UUCP> Reply-To: davew@shark.UUCP (Dave Williams) Organization: Tektronix, Inc., Engineering Computing Systems Lines: 64 Summary: Turbochargers are a subset of superchargers, but in recent years it has generally thought of as a different class of unit. A supercharger is used to stuff air/fuel mixture into the cylinders at a positive pressure (above atmospheric pressure). A normally aspirated engine uses the vacuum of the receeding piston to draw in the mixture. Obviously stuffing for mixture into the cylinders will result in more HP. Turbochargers are two chambered devices that use the hot exhaust gases to spin a turbine blade at a very high velocity. A shaft connects this blade to another blade in the other chamber that stuffs the mixture into the cylinders. The turborcharger is an on demand device that only kicks in when the exhaust flow is sufficient for it to pump out a positive boost. Turbos have become an easy way of producing added horsepower in production type cars as they are small, easy to work on, relatively inexpensive and only put an additional load on the engine when called on. They cause some restriction in the exhaust system which causes elevated exhaust temperatures. Early turbochargers suffered from a hp lagging effect which meant that the boost generated by the unit started to come on at some point, usually as much as .5 sec after the throotle was opened. Improvements in rotor design have taken care of this problem. A supercharger is driven my some mechanical means from the engine crankshaft. The usual way is to use a geared timing belt with the supercharger (blower) sitting on top of the intake manifold. Other variations have the blower siiting in front of the engine with a duct running back to the manifold. There are several types of blowers: the centrifugal, as used on the old Mercedes and Auto Union Grand Prix cars of the 30's and the Novi Indy racer, this is a fan blowing into a plenum, they produce mucho high end hp but suffer at low rpm's; the roots type use two interlocking 3 bladed rotors to produce the boost, this is the type generally seen on drag racing engines as it produces substantial boost throughout the engines rpm range, most roots type blowers are variations on the GMC diesel engine design. There are several other types, such as axial flow, but these are variations of roots or centrifugal designs. It takes about 35-50 hp to drive a supercharger and the boost is always there, so engine wear is considerably faster. Today turbo's are used on F1 and Indy cars, because of their light weight and smallness. These are high reving engines and are kept in the power band by ample use of the gearbox. The drag cars still predominately use the roots type because of the good low end characteristics. Some experimentation with some newly designed centrifugal units has been done. There was some talk in this group several weeks ago about nitromethane and nitrous oxide. Nitromethane is not a form of TNT as someone stated, but is a cleaning solvent used in the drycleaning industry. It has less BTU's per pound than gasoline, but because it has an oxygen bearing radical more of it can be stuffed into a cylinder without "flooding" the engine. Nitrous oxide, sometimes called laughing gas, is an oxydizer. It is injected into the intake manifold under pressure and allows more fuel to be burned. So there. wit -- Dave Williams Tektronix, Inc. Engineering Computing Systems "6000" "The workstations that made Wilsonville famous."