After a number of years w/o it, I put the heat riser back on the exhaust manifold since I still had the riser on a shelf and I'm trying to keep a somewhat factory look even though I really don't need it much in Phoenix and now have an electric choke. With summer upon me I'm wondering if this is just introducing more hot air than I need. I'm really not sure how the actuator on the flap in the snorkel works or if it works. I don't see it moving at operating temp. Can someone school me on this? I feel the whole snorkel is a bit restrictive but I'm not wanting to ditch the factory air cleaner. What is everyone else doing?

 

I thought there was a vacuum line connected on top of the snorkel, that vacuum line connects to a vacuum switch that screws into a coolant port. When engine is cold, no vacuum signal to air cleaner assembly, which keeps flap closed. When engine coolant warms up, the vacuum switch opens passing vac signal to air cleaner assembly which then opens flap.

The spring holding the flap should be light enough that if you give it some throttle the air being sucked by the engine is enough to override sprin tension, opening flap regardless of whether there's vacuum signal to it.

All that said, given where you live, I would not run a heat riser, especially with a Carter/Edelbrock style carb. Those are already prone to heat soak and vapor lock due to their design and passing exhaust heated air into to them will make the problem worse is my thinking.

To keep the factory look you could shove some aluminum foil (probably not even needed) in the heat riser itself to block air flow and either find a way to secure the flap in open position or remove it completely.

That snorkel will flow plenty of air for any stock engine. If you had bigger cam and were exceeding 4500 RPM on a consistent basis then I might worry. If you're still concerned about airflow you could always flip the lid over to give yourself a small gap for more airflow or if you're really trying to maintain stock look but need more airflow, drill some 1 inch holes on the underside of the assembly between outer wall and the element itself.

In your case I'd try and find the original tubing that connects the snorkel to the radiator support so you're drawing air from outside the engine bay to try and keep the air charge temps down as much as possible.

 

Thanks for the ideas. Vacuum modules and snorkel ducting started in the 80's. None of that on the bumpsides. I suspect the flap is run by some kind of bimetallic material like the old choke tube system. I don't see any replaceable item on the parts diagram.

As it is, I'm not running hot and will just watch it as things heat up this summer.

 

Should note there is a exhaust heat riser and a air filter inlet air heat riser, you are talking the later.
Most of the time that valve moves with vacuum. Manifold vacuum goes to a temp valve in the top or side of the filter housing and then out to the valve.
That temp valve is to maintain an even temp going into the carb.

Now if there is no vacuum motor for the valve then there has to be some way the valve moves based on temperature pulled from the manifold.

Now the exhaust manifold heat riser valve forces hot gases up to the intake manifold to heat the floor to keep the air / fuel mix mixed when it is cold out.
If the intake is too cold the fuel drops out of the air and just dribbles into the motor and runs like crap.
This valve can work the same as the air filter valve, either vacuum or temperature of the exhaust manifold.
Vacuum would be from the manifold to a temperature switch to the valve on the manifold.

BTW for more power you want to keep the air coming into the carb a cool as you can. So if it can pull cool air from in front of the grille that would be good but even from under hood is better than hot air from the exhaust manifold.
As for the heating of the intake manifold you also want to try and keep that cool too. In the summer when out and heating the intake the fuel in the carb can boil.
This really shows up if the motor is hot and you shut it off to run into a store. When you come out and you now have a "hot start" problem because the fuel in the carb boiled and the fumes made it into the motor and flooded it. Next time go WOT when starting and see what happens.

Leson is now over
Dave ----

 

The flapper works just like a engine thermostat it also has a wax pellet in it and over rides the spring pressure by hot air from the exhaust manifold and expansion of the wax pellet just like the wax pellet in a engine coolant thermostat over comes the spring pressure in it. At some point Ford switched to vacuum.

 

Thanks! Learned something new. Can't say I've even thought about how a thermostat operates, just making sure it does. Similarly I'll be looking in the snorkel after driving to be sure my 'wax is working'.