OT - Heat riser question, but model A

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Model T Ford Forum: Forum 2014: OT - Heat riser question, but model A
Top of pagePrevious messageNext messageBottom of page Link to this message  By Tyrone Thomas - Topeka KS on Wednesday, January 15, 2014 - 08:58 am:

T's use what I call the heat riser to funnel heated air to the carb. Any reason why the model A not use it. Good idea to make one or not? And remember cars in the 70's used a riser tube into the air cleaner.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Mahaffey on Wednesday, January 15, 2014 - 09:31 am:

Tyrone,

Feeding hot air into the carburetor was not an optimum way to manage carburetion, and by 1927 when the Model A was devised the vaporization of gasoline was much better understood.

Some warmed intake air is OK under some circumstances, but it is always better to heat the air/fuel vapor after mixing, to break up droplets into smaller droplets with greater a surface-area-to-valume ratio, and then after-mix it with cold air. Ford experimented with vaporizer carburetors, including the Kingston B-1. (The B-1 patent drawing has it configured to fit on a Model A engine.)

The final Model A carburetor/intake manifold used the simplest possible vaporizer scheme, in which the intake manifold was bolted to a hot-plate on the exhaust manifold, with two, down-turned intake pipes. The earliest manifestation uses a double/coaxial Venturi in the Zenith carburetor, but that was soon dropped as an unnecessary complication.

Using the after-heater vaporization scheme, there was nothing significant to gain by pre-heating the intake air.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tyrone Thomas - Topeka KS on Wednesday, January 15, 2014 - 10:51 am:

I could never figure this out because in drag racing as well as other types i'm sure, they can get their best times during cool weather. Plus cold air is heavier.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange on Wednesday, January 15, 2014 - 11:13 am:

The reason that more modern cars (late 60's, early 70's went to heated inlet air (usually with a thermostatically controlled flapper door) was for emissions. The engineers tuned the carbs for a certain air inlet temperature (say 120 degrees F) and the thermostatic system was supposed to hold the inlet air to that temperature (once the engine was warmed up, of course). Just another step in the march to leaner, more tightly controlled fuel/air ratios.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Eagle Ida Fls on Wednesday, January 15, 2014 - 11:55 am:

The building up of frost on a T occurs at the elbow on the intake manifold. The model A has a shorter distance and is bolted to the exhaust manifold where it gets heat much closer to the carburetor than a T.


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