C90 on a J3c-65

Yep, my bad, 2475.

MTV

Why are they comparing torque curves of C90 vs O200 @2750 rpms....C90 is limited to 2625 for 5 mins giving 95 hp and 2475 continuous for 90 hp. Is it not a benefit of the C90 that It makes it.s hp at lower RPM and allows the used of a nice long flat prop for takeoff/climb performance? Either way....a J3 is awesome with either an 85 or 90....or O200. I happen to fly my J3 with the 65.... Maybe someday I'll upgrade, but I have a C90 TCraft....and a C85-8 TCraft and those are nice airplanes....C90 one stays on Baumann 1500 floats.

On the J3, the C90 is not allowed the extra 5 minute power - it is limited to 90 max both during takeoff and during cruise (note that the J3 is also airframe limited to 80 hp continuous). However, they took the power and torque curves for all the engines up to 3100 rpm.

Look on the 7142 vs 7440 thread for sea level power curve plots for the C85, C90, O-200 & 9.5:1 O-200.
Or easier, here they are. C90 is plotted in blue, O-200 in red. Note that Continental had a bad C90 data point at 2350 rpm -- it was 1 hp low. The 90 and O-200 power curves really start diverging above 2600 rpm. The 90 doesn't outperform the O-200 till the manifold pressure falls below 21 inches. At sea level, it will also outperform the O-200 when the rpm is below 1700 (I've never seen that as much of a benefit....)

With the 9.5 O-200, I've turned a Mac 7535 to 2850 rpm during a 55 mph climbout and over 3100 in level flight. Stock O-200 will take it to about 2750 in climb and over 3000 in level flight. How long and flat does the prop need to be ?

I'm a T-craft fan, but a J3 fanatic......

I have to ask. Is there really much difference between the three engines if they were on a dyno. The crankcases are basically the same on the 85(200 crank),90 and 200 other than through bolts to allow higher RPM's. the 85 with a 90 or 200 crank makes all three have the same stroke, the bore was already the same and that only leaves the cams. One designed for use with a muffler and the C90 (preferred cam by many) for open pipes. By my thinking , the horsepower output should be almost identical in the lower RPM ranges.
Generally, as you rev the engine higher, you get more horsepower and so with each crankcase improvement allowing more horsepower because the engineers say it is ok to rev it more. The only other factor is the "empty weight of each engine" which seems mainly controlled by the items attached to it. Remove the starter, generator and vacuum pump from an O200, and it gets lighter. close enough to a dash 8 for me.
My thinking is, if you don't rev up the o200, you have a C90. Rev it less and you have a C85 with the 200 crank kit. Am I really off base here???

On the Tcds the c90 is still rev limited to 85 hp - so legal installations there really isn't much difference between those 2 - prop combos are better on the c85 from everything in researched which gives you better climb perf