The Cessna 120-140 Association Forum

I was curious about STC SE00979AT that allows using O-200 crank and pistons in a C-85, so I called Aircraft Specialties (the holder of the STC) to find out more. I was told that “officially” it was not for HP increase but rather for parts availability. One must use the carb and mags that are specified on the TCDS for the C-85, though there may be a change in mag timing. Has anyone done this modification and seen any measurable change in aircraft performance? A/C Specialties says it cost $5775.78 plus $1000 crank core charge.
Thanks!
Larry

I have done several of them. There is definitely an increase in lower end torque.

I beleive Randy is correct. I have one myself... Theres a lot of argument with the rpm limitation if it really increases HP, and I understand the arguments on both sides... No one ever argues torque factor and I think thats where the truth may lie. I'm handy but no mechanic and still a relative nube at owning a plane... But here is why I think Randy is right.

I was thinking of getting a climb prop, I have the 7148. Now even with the STC it still is a C-85 right? The climb prop is considered the 7146 typically on the c-85 in a 120/140. So I look up the Static limits of the c-85, and borrow my mechanics prop RMP reader, so its based on reality not a 73 year old automobile tach... Well glad I didn't order a new prop on a whim...

Static limit is 2300, my C-85 with 750 hours since the rebuild with that stc was turning that 7148 at 2280 static... So essentially I do have the climb prop if I want to stay in legal limits and that the 7146 would likely put me in the 2380 range. So yes on paper its still a c-85 but theres more oomph there.

Now mind you the gain is not earthshattering... It won't turn the 140 into a super-cub But no reason to not do it if you need an OH...