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This message was automatically forwarded on behalf of Bill Bayne. Please address any responses to the mail list or directly to Bill at: [EMAIL PROTECTED] -----Original Message----- From: William R. Bayne [mailto:[EMAIL PROTECTED] Sent: Wednesday, February 22, 2006 4:52 PM To: Ed Burkhead Subject: Re: [COUPERS-TECH] C-85 STC, Performance, Props-Correction/Addition rlytech On Feb 22, 2006, at 11:10, WRB wrote: > > -----Original Message----- > From: William R. Bayne [mailto:[EMAIL PROTECTED] > Sent: Wednesday, February 22, 2006 11:08 AM > Via: Ed Burkhead > Subject: Re: [COUPERS-TECH] C-85 STC, Performance, Props > > Hi All, > > With this STC, the C-85 prop is retained. "...increased > displacement and increased compression" equal increased "oomph". The > proportion that translates (respectively) to horsepower and/or torque > is, in part, determined by cam design and, in part by the rpm allowed > by a given prop. > > ...The Continental C-90 power curve directly translates all additional > rpm into additional horsepower. I would have been perhaps more clear had I said: The new crank and rods (increased displacement and compression ratio) mean the STC engine now produces power with rpm consistent with the Model C-90 Sea Level Performance Curve, except that retaining the C-85 carburetor penalizes it maybe 10-15%. The existing prop should allow the engine to reach 2475 rpm (tweaking pitch at maximum diameter), at which engine speed horsepower produced increases from approximately 85 hp (per Model C75 & C85 SLPC) to approximately 93 hp (per Model C90 SLPC)! So you DON'T "...get the same power..." even though "...your rpm limit doesn't change." The C-75 and C-86 prop loads shown by Continental are clearly not representative the standard wood Sensenich Erco put on the Ercoupe, which would wind up in cruise to 2450-2475 rpm. Projecting Continental curves to this rpm yields only nonsense. Metal props, while heavier, are sufficiently more efficient to offer an additional 1-2 mph over a similar wooden prop, all other things remaining more or less equal. This, at least in part, would reduce the penalty of having a carb jetted to deliver fuel for 85 HP. (Remember that the Stromberg jetted to produce 75 HP still supplied sufficient fuel for the C-75 Continental in the Ercoupe to reach C-85 rpms with the standard Sensenich prop) So none of the Continental prop load curves (or fuel consumption curves) remotely correspond to a prop optimally matched to the capabilities of the STC engine. > Accordingly, IMHO, the "bang for the buck" for an Ercoupe in good > condition is probably greater from this STC than any other single > option at overhaul time. > > Regards, > > William R. Bayne > <____|-(o)-|____> > (Copyright 2004) > > -- > > On Feb 22, 2006, at 08:59, John Cooper wrote: > >> At 02:39 AM 2/22/2006, Anne and John wrote: >>> So, how much extra horsepower can really be expected from this STC, >>> or how much bang for the buck ??? >> >> Technically, none. Given the physics of fixed pitch props and the >> fact that your RPM limit doesn't change, you get the same power. >> What changes is how much of that power is available at less than full >> power conditions. This is due to the increased torque capacity from >> the increased displacement and compression ratio. Read: improved >> climb performance. >> >> John Cooper, A&P >> Skyport Services ============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm
