JOHN! John John John,
Please note that I said the only significant change was the prop.
Many of the
other conversions from one engine model to another, require replacement of
major
components (cranks, cylinders, etc.). I can't comment on whether or not
the C-85
was ever supplied with a Marvel-Scheibler carb, but according to Lee at
Skyport
Services, it appears that it was. But, all else aside, to change from the
75 to the
85 requires at most the following: carb modified to 1 3/8 venturi and new
jet, new
carb and engine ID plates, new oil gauge and cap assembly, new prop, and
new oil
cooling baffles. That's it. I believe that even you must agree that if
you put the
correct prop for a 85 hp engine onto a 75 hp model with no further
modifications, it
"will not" pull as high an RPM as the 85 hp will pull, all else being
equal. BTW,
Lee at Skyport will send you all the info. Just ask him.Larry John Cooper wrote: > 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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