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IO540 C4B5 RPM Limit

B

bob888

Well Known Member
I have a C4B5 engine, originally from a Navajo as far as I can tell. Lycoming rated this at 250 HP and 2575 RPM. Is there any reason not to run it at 2700 rpm, same as the D4A5? I think the crank, counterweights, etc are the same. Anyone doing it?
 
I believe a lot of people are doing it. Do a quick search, as it's been discussed here before. I've still not found a great all-in-one resource for versions and differences in the various 540 engines out there. It'd be helpful for those looking to repurpose a used engine!
 
bob888 said:
I have a C4B5 engine, originally from a Navajo as far as I can tell. Lycoming rated this at 250 HP and 2575 RPM. Is there any reason not to run it at 2700 rpm, same as the D4A5? I think the crank, counterweights, etc are the same. Anyone doing it?
Click to expand...

Nope -- it will run at 2700 just fine. There are a number of us with C4B5's.
 
A few years ago when Bart was still at Aerosport, he told me that at least some of the engines with a derated HP output (by using a lower RPM limit) did have some lighter weight components.
Connecting rods were one part that comes to mind, that he mentioned "could" be a factor in running them at higher RPMs.
 
Prop Hub limitation?

As I recall a certain series of Comanche prop hubs were rated at 2575 rpms so thus the lower rpm's and lower horse power.

Steve
 
C4b5 to d4a5

I've just been through this with my engine. If you look through the lycoming parts manual

http://www.mstewart.net/Downloads/PC-615 IO & AEIO-540 series Parts Catalog circa 1992.pdf

You will find that the internal parts are exactly the same. A few accessory parts are different. The mounting ears from large to small, the studs for the governor and remove the hydraulic pump mount if one was fitted. The oil filler and dip- stick are listed as different but the c4b5 one should still fit happily under the Rv-10 cowl.
So there should be no reason not to safely run it at 2700 rpm and 260hp.

Cheers

Peter
 
So it looks like all of the injected versions should internally be the same...
Bart was likely taking about differences with the 235 HP carb'ed versions.
 
Even the 235 IO versions. A friend down here has just converted his lovely C182 with the 260HP STC, which is the RV10 engine and different mounts. The IO540 removed has lighter pistons and rods.

Have to wonder why it was that way in the first place. :confused:
 
Yes, the C4B5 and the D4A5 are the same inside. You can run it at 2700rpm no problem. I have run hundreds of hours on a C4B5. Of course, once you set 25 squared for climb you're the same no matter what your redline is. We left our prop governor set at 2575.
 
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