C90-12 power settings

[garyh]

Can one of you fellows tell me what the correct RPM settings would be for 55,65 and 75% power .
Is recommended cruise rpm 2350 ?
Thanks,
garyh

 

[gbflyer]

Not sure what the power settings are, but I do know that the one I used to own liked to to run around 2450. They are great little engines, like to be run hard.

gb

 

[Jim Mizer]

According to my 1949 Maintenance and Overhaul Manual, Fig. 38B Engine RPM vs. Fuel Flow this is what I come up with.

65% 2150 rpm 5.25 gph

75% 2250 rpm 5.75 gph

85 % 2350 rpm 6.25 gph

100 % 2475 rpm 7.5 gph

I hope this helps, I had to do alittle enterperlating so there could be some variation but this should get you very close. Jim

 

[Jim Mizer]

Sorry I forgot 55% 2020rpm 4.25 gpm Jim

 

[garyh]

I have a 1984 overhaul manual for c75/85/90/0200 and the c90 graph shows what jim said but the c75/85 graph below it on the same page shows 65%=2225 and 75%=2340 rpm which is about 90 rpm higher than the c90 chart so i'm wondering if the c90 chart is flawed because i can't see why they should be operated a different rpm setting since they're nearly the same fundemental engine. I normally run my c90 between 2300 and 2350 all the time.

 

[Longwinglover]

Different camshaft...

John Scott

 

[JimC]

And different displacement.
JimC

 

[garyh]

I talked to my AP/AI today and he told me to run the c90-12f at any rpm i wanted- 2300/2350/2400 for as long as i wanted because you can't hurt this engine by running it hard. He is also a well known engine overhauler in this area so good info to know.

 

[JimC]

Gary, if you are running it on a J3, check with your AP/IA again.
On a J3, 90's are limited by the Type Certificate A-691 to 80hp in level flight (2375 rpm).

The 85's are also limited by the Type Certificate to 80hp in level flight (2525 rpm)
JimC

 

[JimC]

Gary, if you are running it on a J3, check with your AP/IA again.
On a J3, 90's are limited by the Type Certificate A-691 to 80hp in level flight (2375 rpm).

The 85's are also limited by the Type Certificate to 80hp in level flight (2525 rpm)
JimC

 

[garyh]

Thanks jim for that info but it's on a pa18 so no problem.
garyh

 

[Backcast]

Gary,
I can attest that GB's old cub flies best at 2400-2450 with floats on as well. Strong motor those C90's, my second one and I've been really happy with both.

Can't wait to go fly some more myself!
Tedd