Intake through Sump

[boom3]

Dumb question.

Why does the intake go through the sump?
Is it for room?
Is it to preheat the cold air a little?

[WenEng]

Conventional wisdom is that heated intake air in a carbureted engine atomizes better prior to entering the cylinders. On a fuel injected engine, cooler air with a cold air induction system (intakes outside the sump rather than running through it) provide more oxygen thus more power. The ECI website states that for every 10 degree cooler the intake air is, there is a 1% increase in power. Somewhere within all that, there is more than likely the truth that carbs make better use of heated air to atomize fuel, and injected engines get more power with the cooler air.

[L.Adamson]

The carburetor bolted directly to the heated sump is suppose to give it an advantage in regards to carb icing. That's why you'll see Lycoming manuals and Piper POH's calling for carb heat only when required, instead of the older Cessna POH's that call for carb heat on every landing. Many Cessna's used Continentals in which the carb/air isn't slightly pre-heated. This would technically give the Continental a slight edge in horsepower per cubic inch.

I'm a Piper descendant. My RV doesn't get carb heat on every landing.

L.Adamson --- RV6A

[aerhed]

This was originally called "Lycoming Hot Spot Induction" or something like that. It's purpose was better atomization despite loss from higher temp air.

[pierre smith]

...but some folks opt for the cold air induction system.

Best,

[David-aviator]

If you ever had a C150 quit on a 90F day due to carb ice, you'd know the answer to the question. The darn thing just conked out one day at 9500' but on the glide down it started running again at 5000'. The next airplane had the 0235L2C. It never had a carb ice problem.

But all that being said, there are plenty of old Continental's still being used on Cub's and other very light airplanes and they do get the job done, one way or another. But that particular 150 was so quirky, some days carb heat had to be used on take off. That particular airplane, 6930G, was still flying the last time I checked. I sold it in favor of building the LEZ.

Fuel does seem to atomize better an warm air than cold with these small recips. There is a lengthy discussion elsewhere on this forum on that subject. More O2 molecules does not always mean more power. Temperature is a factor and Lycoming figured that out a long time ago when they decided to go with the intake through the sump.

(But that is not true with a turbine engine. For sure they like cold air, the colder the better. That's one reason a jet is so much more efficient at high altitudes, it's mighty cold up there every day.)

[boom3]

Interesting, thanks for the replies!

The atomization thing definately makes sense on the carbed engines.

I guess the carb being bolted to the sump would make the carb just plain warmer as a whole. Ice can still form due to the venturi in the carb but the temperature spread is higher.