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Lycoming IO540 C4B5

B

bob888

Well Known Member
This engine was originally rated for 2575 RPM and not 2700 RPM as the newer ones are. Is there some inherent reason why it can't be run at 2700?
 
The C4B5 is rated lower (2575 RPM / 250 HP) due to the airframe/engine/propeller combo (e.g. Aztec) that it is intended and certified for. Specifically, I believe it was a propeller limitation if I remember correctly. If you look through a parts catalog, you'll find that the crank, cam, rods, and all other moving parts are the exact same part numbers as the D4A5. So, in the experimental world you should have no trouble running a C4B5 up to 2700 RPM and 260 HP on the RV-10, using the appropriate propeller, governor etc.

At least that's my understanding and plan to do the same thing! :)
 
I have a C4B5 in the -10 with a Hartzell 2 blade blended airfoil prop.

Been running it for over 900 hrs now with the governor set to around 2800 but I normally have it set for around 2650 to 2700 for take-off.
 
No problem running at 2700

mikeyj350 said:
The C4B5 is rated lower (2575 RPM / 250 HP) due to the airframe/engine/propeller combo (e.g. Aztec) that it is intended and certified for. Specifically, I believe it was a propeller limitation if I remember correctly. If you look through a parts catalog, you'll find that the crank, cam, rods, and all other moving parts are the exact same part numbers as the D4A5. So, in the experimental world you should have no trouble running a C4B5 up to 2700 RPM and 260 HP on the RV-10, using the appropriate propeller, governor etc.

At least that's my understanding and plan to do the same thing! :)
Click to expand...

Absolutely correct.. I too have a C4B5 and run it at 2700 with no issues. It dyno'd out at 260HP @ 2700 on the test stand.
 
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