Article on air pressure under hood

[SmellyCat]

AutoSpeed - Undertrays, Spoilers & Bonnet Vents, Part 1

[tony_2018]

There's another article in there about a tps mod for us lean burn honda guys. I wonder if anybody tried that yet?

[hat_man]

So....not knowing anything about aerodynamics at all....what does this all mean? Are the most of us with factory "venting" of the engine bay (up around the wipers) benefiting or being hurt with the factory set up? Would extra engine bay venting (vents facing towards the back) help or screw up the "flow" over the hood? Or would moving more air through the engine bay hurt by lowering the engine temps?

I have thought about adding some some extra venting to the hood of my Ranger, but I also have a 100% upper grille block and a 50% lower grille block and now I have no fan as the fan clutch locked up over the winter and I just removed it. No extra drag from the fan but also less airflow. As of yet I don't over heat but summer is coming.

Is it better to block or restrict all airflow from the frontal area and just let the engine be cooled with airflow from the underside? And if so, is the factory "venting" enough?

Apologies the OP. Not trying to thread jack. Just very interested. Thanks

[kach22i]

Originally Posted by SmellyCat

AutoSpeed - Undertrays, Spoilers & Bonnet Vents, Part 1

Lots of good articles on that website, example below.

Custom shaped clear canopies and windscreens
AutoSpeed - Custom Bubble Canopies

Originally Posted by hat_man

So....not knowing anything about aerodynamics at all....what does this all mean? Are the most of us with factory "venting" of the engine bay (up around the wipers) benefiting or being hurt with the factory set up? .............

Good questions, seems like it would be a case by case thing.

I figure it must be like a math equation, one side has got to equal the other side.

What goes in, must come out - one way or the other.

[2000mc]

Originally Posted by hat_man

Are the most of us with factory "venting" of the engine bay (up around the wipers) benefiting or being hurt with the factory set up?

i'm not familiar with any modern vehicles venting near the wipers, are you sure youre not looking at the air intake for the hvac?

[tony_2018]

the vent is for air for the air inside the car, thats not a vent.

[kach22i]

Good point, I missed his bad assumption there.

Even hood/cowl induction is an intake at that location (faces windshield), something about the pressure build-up at the base of the windshield.

[hat_man]

Told you all I didn't know anything. LMAO. So I guess that's an intake then. If that's the case then if you leave the grille open and the area in front of the windshield is an intake also, then all the air must leave the engine bay from the bottom?

In my un-aero mind then I still have a question. The article says that you need a pressure differential across the radiator to create flow to move air through the radiator. If the area in front of the windshield is an intake, as is the grille area with it's big gaping hole, then would there be more radiator cooling if you closed the area in front of the windshield? Just to use some arbitrary numbers if the grille area has +10 units of pressure and the area in front of the windshield has -3 units of pressure (because it's on the other side of the radiator), this makes 7 units of pressure across the radiator. If you close the area in front of the windshield (making 0 units of pressure) this would make 10 units of pressure across the radiator, right? This is assuming the "exit" air flow is out the bottom of the engine bay. All the other areas are intakes.

And secondly, if all this is true, if you put a belly pan under the engine bay and the grill and windshield area are intakes, where and how does all that air leave the engine bay?

I'm sure there is a logical answer, but I just can't wrap my head around the concept.

[NachtRitter]

From what I can tell on my car, the air entering at the base of the windshield doesn't ever enter the engine bay... it either enters through the cabin (if you have the vents open, fan on, and recirc off) or it doesn't enter at all (if you have vents closed, fan off, recirc on).

It would make sense to have the air going into the cabin separate from the air going through the engine compartment, since the smells from the engine compartment (not to mention the potentially dangerous exhaust) would not be pleasant in the cabin.

[aardvarcus]

Originally Posted by hat_man

Told you all I didn't know anything. LMAO. So I guess that's an intake then. If that's the case then if you leave the grille open and the area in front of the windshield is an intake also, then all the air must leave the engine bay from the bottom?

In my un-aero mind then I still have a question. The article says that you need a pressure differential across the radiator to create flow to move air through the radiator. If the area in front of the windshield is an intake, as is the grille area with it's big gaping hole, then would there be more radiator cooling if you closed the area in front of the windshield? Just to use some arbitrary numbers if the grille area has +10 units of pressure and the area in front of the windshield has -3 units of pressure (because it's on the other side of the radiator), this makes 7 units of pressure across the radiator. If you close the area in front of the windshield (making 0 units of pressure) this would make 10 units of pressure across the radiator, right? This is assuming the "exit" air flow is out the bottom of the engine bay. All the other areas are intakes.

And secondly, if all this is true, if you put a belly pan under the engine bay and the grill and windshield area are intakes, where and how does all that air leave the engine bay?

I'm sure there is a logical answer, but I just can't wrap my head around the concept.

Those with more experience feel free to contradict my comments, but one of the reasons I have heard for not dumping engine air on the windshield is that it is more likely to be dusty or dirty. My car has a rubber gasket to 100% close off this area when you shut the hood.

I don't know if there is a best way to exhaust the engine compartment air, but many have dumped it out around the front tires. (This area is hardest to pan since the tires move, plus the air there is already turbulent.) If there is a gap between your pan and body all the way back, some of the air could travel there.

As for your fan clutch being bad, my advice is to get an electric fan and a temperature switch and install it. On a hot day in stop and go traffic is kind of the worst case scenario, as you aren't going fast enough to get a lot of air through your radiator, so the fan would provide some cheap insurance that your temperatures don't get excessive.