Lycoming engine pump for HO360-B1B

QUESTION: I purchased a Lycoming HO360-BIB to use in an experimental aircraft. I have to convert from a rear pressure carb to a downdraft carb. I purchased a sump (part #71871) for this conversion. This is the part number from an early Lycoming parts catalog for most 180 hp 360s.

This sump has tubes that taper where they enter the sump. A newer parts catalog calls for a #78915 for the same engines. I have been told that any sump that has tapered tubes is for a 320 — not 360s. Did they use both 71871 and 78915 sumps on 180 hp 360s?

Cameron Smith
via email

ANSWER: Cameron, I’m certain there are others out there who have encountered the same situation, so maybe I can help. I do have some good news for you. The sump you purchased, p/n 71871, is OK to use for the conversion you intend to make.

If we were dealing with a certified application, then it would be an entirely different story. However, for an experimental application, you’re OK. The sump you have does incorporate the tapered induction tubes and was used on many of the early versions of the O-360 series Lycoming engines. The p/n 78915 that you mentioned was used on later models and utilized the straight induction tubes.

I suspect the straight induction tubes offered a slight increase in horsepower, but this shouldn’t keep you from using the sump you purchased. I hope this relieves any stress you may have been suffering from thinking you bought the incorrect sump!

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:

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