Engine for RV-10

[Fredrik]

Hi,

I'm trying to find out what's the difference between IO-540-C4B5 and -D4A5, the one Van's sells. According to specs the -C4B5 develops 250 hp at 2575 rpm (max) and the -D4A5 develops 260 hp at 2700 rpm. I read somewhere here that it has to do with the crank's dynamic counterweights are different but according to Lycomings parts catalog, those two engines have identical counterweights. Actually, those two engines seems almost identical, comparing parts.
Could it be that the rpm restriction is because of the engine/propeller/aircraft combo designation? I know that the -C4B5 is used on the Piper aztec.

Thanks for any enlightening input.

Fredrik

[Mike D]

I'm no engine expert, but I had the same question. I looked int it pretty well and the best I could come up with was that they are the same engine with different max RPM ratings so that the C4B5 produces a max of 250 hp. The purpose was to "de-rate" the HP for certain airframes. My understanding is this is a number thing only and the C4B5 is the same HP at the same RPM and fuel flow.

There are other threads on it here.

For what it t is worth, I bought the C4B5.

[Jesse]

That's exactly right. They derated the C4B5 for the Aztec to 250HP. They are identical in most aspects, and the C4B5 can be run at 2,700HP to make 260HP. Both are 8.5:1 compression and will make the same HP at the same MAP, RPM and GPH.

[Fredrik]

I was suspecting that. Thanks for the input.

[kiwipete]

I too brought an aztec engine. The things I needed to change were the engine mount ears from large to small hole and the studs on the prop gov. Pad needed to be longer.
If you look through the lycoming parts manual, the internals of the engine are identical. The oil dip stick is listed as different and some mag leads. But these will make absolutely no difference.

Good luck on finding a good engine. Just beware on the crankshaft AD.

Cheers

Peter

[Chip25]

So the only thing making it either turn 2575 or 2700 rpm is the governor? Is that the correct understanding?

[vic syracuse]

Originally Posted by Chip25

So the only thing making it either turn 2575 or 2700 rpm is the governor? Is that the correct understanding?

Yes, that is correct.
Vic