Getting fresh air in the engine compartment

I know there is a lot of talk about sealing up the engine compartment but what are you guys doing to get some fresh air in there? What if you cut away the fiberglass where the grill is? Does that cause problems? I know somebody cuts away a piece behind the back license plate, can this be done on a fiberfab body?

The airflow into the engine compartment is provided by the grille on top.

That opening is big enough for your carburetors to pull air through it AND for your engine's fan to do its job. The fiberglass under the grille should only be closed in at the top and bottom; the sides should be open to allow that air to get in.

The fiberglass also keeps rain off of your alternator or generator, whichever your car has.

The fresh air to the fan comes from that opening. The fan is the conduit for that air to cool the engine; the air goes through the fan hole, then is contained within the shroud on its way out the bottom of the engine compartment.

The engine itself doesn't actually live in the engine compartment. It lives right below it. That air, forced over the vanes on the cylinders by the fan, coming from the engine compartment, then comes out the bottom side as hot air.

Hot air wants to rise ... right back into the engine compartment. When people say they want to seal that compartment off, they want to minimize the air gaps the hot air from below can use to seep back into the "cool" side of the tins, thereby increasing the cooling efficiency of the fan. The hot air below usually wants to flow out the back of the car while its moving, but while idling it'll really warm things up if it has a way to come back topside.

Making that compartment watertight isn't really the goal, but making sure the flat tins at the bottom -- the pieces of metal which reach from the engine's fan shroud to the edges of the compartment -- don't have any big holes in them is kind of critical to the operation. It prevents the fan from recycling hot air.

Hope that helps.

Some people cut a hole in the firewall right in front of the fan. I did that and added a blower with 3" ducting.

You can also cut away under your grille to bring in more air. JPS sells a mesh kit that resembles a fencing mask. You use it to cover the opening. I was concerned about water getting in so I fabricated a louvered opening.

For those really hot days you can install a hood prop. The photos below should be self-explanatory.

As Terry stated - the FF/CMC build manual has you cut out a raised 1/2 moon section just above the transmission on the firewall which allow fresh unheated air to get sucked into the fan and the carbs. They also specify using rubber as a splash shield to either side of that opening. I've seen a similar round hole with hardware cloth (screen) covering it on VS Speedsters. The heat shield just above the exhaust and the one above it - keep engine from sucking in hot exhaust air (see build manual).

https://www.speedsterowners.com/library/FiberFabB/images/FiberFabB042.jpg

Cory--that was a great explanation of the "cool side and the hot side"
and why you want to keep the air on each side separated.

The phrase that the engine doesn't really live in the engine compartment was good too---that's why it's below the tins.

Well done. Thanks.

You can also add these additional cooling holes

I like the pic but does it make the car louder having the vents up top? Also I know nobody really drives these in the rain but is that an issue with cut outs in the lid? It would be nice to do the half moon up in the front firewall and maybe add a cutout behind the license plate for some cross ventilation. What do you guys think?

"I know nobody really drives these in the rain"...tell that to the brave souls that came and went to Carlisle this year. I'm sure they can all tell you a story or two about not driving them in the rain. I'm planning on tracking down my set of rain hats soon.

I drive my car year-round. Other than trying to keep rain off of the alternator, I don't think it matters what gets wet. As long as your connections are good and you take precautions against salt (probably not a huge problem in San Diego), you should be okay mechanically.
How YOU hold up in damp conditions will probably be the deciding factor.

look at a stock 356 lid, the holes are at the top of the grille they are in close proximity to the top of the fan shroud. when i cut mine in, and started the engine i put a piece of tissue on the grille, you can see it put it in. bill