Cold manifold???

Elvin Frank · Apr 1, 2013

When I bought my Super M the other day the PO said that it had a "cold manifold" off of an LP tractor. It sweats and I noticed some icing on and around the carburator. I guess my question is do I need to put my other manifold on or does it matter. What is a "cold manifold" ? thanks in advance.

Janicholson · Apr 1, 2013

Propane evaporates in above zero weather and needs no Heat. Gasoline needs a bit more heat in moderate weather to 50 degrees or so especially when high humidity can make frost both on, and inside the carb and manifold. Keeping the air cool or cold, makes it more dense, and thus more of it. this makes more power (assuming good vaporization of the gasoline). Were it mine, I would put an exhaust "heat stove" on it for cold operation feeding warmed air into the air cleaner. Carbureted cars of the 70s and later had them on the exhaust manifold with a tube to the intake snorkel. Almost all piston and carb based airplanes have them to prevent carb icing. A stove pipe with standoffs around the muffler, with a flex pipe to the intake where the pre cleaner attaches, works well, and can be removed in the warmer drier weather.
That manifold will make a bit more power. Jim

Bob M · Apr 1, 2013

A gasoline manifold has a "hot spot" at the top of the carburetor leg. It is heated by hot exhaust gases in the exhaust manifold. Its purpose is to evaporate gasoline droplets leaving the carburetor before they enter the cylinders. This improves combustion under cool conditions. The downside is the heated gas/air mixture results in a slight loss of power (warmer fuel/air mixture = less power).

An LP manifold has no hot spot. It is not needed since the fuel is already a gas when it enters the carburetor.

Pullers like the cold manifolds since they'll give a gasoline engine a little more power. But a cold manifold on gasoline also gives poor running in cold weather/high humidity unless an auxiliary heater is provided (manifold stove, etc) to warm the inlet air ahead of the carburetor.

Cold manifold???

Elvin Frank

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Janicholson

Well-known Member

Bob M

Well-known Member

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