Just to throw in a few cents (sense) worth... I recall seeing somewhere that there was a min. length published for the Coupe and that if the prop were shorter it was not a climb/high alt. prop, but as the FAA would call it a "crime prop".
I hate to respond without complete information, but I am at the office and all the manuals are home. Ron N2273H ----- Original Message ----- From: John Cooper <[EMAIL PROTECTED]> To: <[email protected]> Sent: Wednesday, December 29, 1999 2:26 PM Subject: Re: [COUPERS] Take off / landing performance > > Larry- > > > > > God you know how I like to argue! > > Well, you've come to the right place! <BG> > > > According to Lee at Skyport, and their > > sample 337 > > OK, 337 so we're already talking about modifications, right? > > > form, 75 hp uses 7351 prop. 85 hp uses 7150 for standard-cruise, and 7148 > > for > > take-off, climb, and high altitude. No mention of 7146 prop. Max RPM for > > 75 hp is > > 2275, and 85 hp is 2575. Once again, according to Skyport, to change from > a > > I agree with the RPM's. You'll note that I said "Many C-85 installations", > not "All C-85 installations use yada yada yada" > > > C75 to > > a C85, requires a new engine baffle kit, and one of the following: if you > > have a > > Stromberg carb, it requires a 1 3/8" Venturi, and a p7881-45 Jet. If you > What I meant was that if you buy a C-75 from Continental, the only part > that's different from the C-85 is the carb. As you noted, the venturi is > smaller. > > > have a > > Marvel-Scheibler Carb, Model a10-4240, no changes in carb required. I > > assume the 1 > > 3/8 venturi is what you're referring to. What size in the C75, and why is > > no change > > required if you have a Marvel? > > TheC-75/85 were never certified with the Marvel carb, only the Stromberg. So > maybe that's why there's a 337 involved. Also, I only referred to converting > the engine. Once you've converted the engine, you need to use a prop > appropriate for your "new" engine. Baffling, like the prop, is not part of > the engine, thus is outside the scope of this discussion. > > > So, I think what you're saying is that in order to convert FROM a c-75 to a > C-85 you need to > 1) convert the engine > 2) get the right prop > 3) install the converted engine correctly in the airframe. > > BTW, if you put the c-75 carb on and put a prop on that lets it rev way > higher than it should, it still can't make more than 75 HP because the carb > is the limiting factor. In order to get the engine to rev above the rated > RPM you have to reduce the pitch on the prop, which results in lower manifold > pressure and the HP falls off even though the RPM is higher. Sort of like > downshifting. Once the engine exceeds the RPM for max HP, the HP falls off > regardless of the RPM. > > On the other hand, the C-90 is rated 90 HP with fixed pitch prop at 2475, or > 95 (5 minute limit) with a variable pitch prop at 2675. But it's got a > bigger carb and btw was certified with both Stromberg and Marvel carbs. > > So there. > > John > > (Wonder what's different about the baffling?) > (A C-75 with a carb that is ok for a C-85 WILL make more than 75 HP if you > can get the RPM up. So what you've got there is really a C-85 with an > extreme cruise prop. The prop rather than the carb is the limiting factor. > Hmm, I'd like to see the engineering data on that conversion...) > > > > > > > > John Cooper wrote: > > > > > In a message dated 99-12-29 10:18:32 EST, you write: > > > > > > > As you know, the only > > > > significance between the 75 and the 85 is the RPM. The prop is what > > gives > > > > you the > > > > extra revs. I would think that going down to a 46 would mean you > > really > > > > have to watch > > > The C-75 has a smaller carburator throat. That is the ONLY physical > > > difference and the 75 simply can't breath well enough to make 85 hp, no > > > matter how high you get it to rev. (finer pitch results in lower prop > > > loading so your higher revs are at reduced manifold pressure, hence lower > > > power.) Continental approved conversion to 85 HP: change carb. > > > > > > Many C-85 installations call for the 7148 as the standard prop. 46 is > > climb > > > and 50 is cruise. > > > > > > John > > > > > > > > __________________________________________________________________________ __ ____ > To unsubscribe from this list please send mail to [EMAIL PROTECTED] > > _____________________________________________________________ > Get your favorite topic delivered daily. > http://www.topica.com/t/11 __________________________________________________________________________ ______ To unsubscribe from this list please send mail to [EMAIL PROTECTED] _____________________________________________________________ Get your favorite topic delivered daily. http://www.topica.com/t/11
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