They had the turbo system on it already, and added that cowl induction after the fact. That is how they noticed lower EGT's from adding just that.
If you want to read about it, check out the 7.3 IDI section over at the Diesel Stop, look for Hypermax cowl induction, it's a page or so back from the current page. The aadmin doesn't particularly like links to their site, so I was trying to just provide what I could, but sometimes, it just isn't enough...

 

The base of the windshield is a high pressure area. This is a fact. This area has been used for years by high performance cars to get a good supply of cool air.

However, if you put one of those bug guards on the front of the hood you will move the high pressure area forward and this does become a vacumme area.

David

 

Where would one find proof of this fact on Ford pickups?
Just askin'

 

Turn the heater on without turning the fan on. You get airflow while driving. The faster you drive, the more air you get.

But at the same time, there are places to get higher air pressure on a moving vehicle like the radiator area.

I also semi agree with the statement about bug shields.
They turn the entire hood area into dead air space that does take a good bit of power to shove down the road. The air flow is moved upward and over the top of the cab. Without a bug shield part of the air striking the windshield goes down to the lower pressure area on top of the hood.

Tests done by the energy department back years ago showed a bug sheild on a conventional road tractor took 50 HP to shove down the road because of the dead air space it created.

 

Ummm, well just because it is a Ford truck does not change the known physical property of airflow. There is NOTHING on a stock Ford truck hood that would dramaticly change the airflow over any other hooded vehical.

As stated, the only thing that will move this high pressure area from the base of the windshield is one of those bug guards. It will move the low pressure area forward.

And as Dave S mentions, turn your heater on without the fan, without a bug guard you wil have airflow that increases with speed. (higher pressure with a increase in speed at the base of the windshield) install a bug guard and that airflow WILL drop, as much as to a zero point as there is no longer the high pressure area at the base of the windshield.

Dave S also brought up a very good point about the usage of those bug guards on large trucks. There is a reason why you do not see them any longer on the fleet vehicals (you still see them on a one by one basis on owner operator rigs as they don't understand the effect, or are not privy to the test results) is the fuel savings by removing them is greater than the potential windshield replacement.

Good one on this Dave S!

David

 

If there is such a dramatic difference in not having a bug guard...what about a grill guard? I have a round tube chrome setup that bolts to the bumper-frame. I put it on AFTER I did the "soup bowl" mod and I am still getting around 17mpg. The best I have seen for mileage is 19.9mpg....but that was traveling back roads at about 45-50mph in OD. I also have not noticed any difference in engine temp because of the grill guard. I will get some pics posted in the morning so you can see what I mean.

-Dave

 

Your grill guard is fine, it is not designed to send the air up and over the windshield. Good mileage you are getting!

David

 

Sounds like the bug guard is coming off my truck first thing!

Good to know that info about the cowl being a high pressure area, but I agree with Dave's statement that the grill area would pretty much have to be an even better source of high pressure for a functional ram-air.....

 

I'm pulling mine off today as well to see if it makes a difference. I put mine on because the lumber rack I installed (regular cab not extended cab) did not extend beyond the front of the windshield (long story as I did not believe the sales guy and was in rush so bought it anyway as he did not have the right one in stock). It made a terrible howl going 45mph that almost sounded like it was inside your head. The deflector helped a bunch. I recently had the front of the lumber rack extended beyond the cab so I can take it off now.

If anyone has any mileage comparisons that would be interesting to know.

 

OK, you guys all think you got me with that heater comment, but I'll come back with this.

Do you think that little wisp of air you get through the heater is doing your engine any good? Doing 60 down the freeway it's about the same as my fan on low.

All I've been saying is that's not the best place (or even a good place) to get "ram air". Only reason they did it was it was easy, and with the turbo, ram air was the last thing on there minds.

 

There are some design considerations to be thought of when using the cowl area (base of the windshield) for air intake and pressure generation.

First of all as stated, it is like having the fan on low. This is correct, but there is a reason for this. At the lower part of the cowl, on both sides of the truck are rather large drain holes, sealed up with a thin rubber flap. (you need to remove the front fenders to see these) As the rubber flap offers no resistance to air flow outward, it is therefore hard to build any pressure in the cowl plenum. Of course you can plug these, but then what are you going to do with the water and leaves that will collect?

I haven't seen these drains mentioned yet - and they are a important consideration if you genuinly want to build pressure of any meaningful amount in this area.

You also don't want to bleed off any air thru the HVAC system, so you will need to block that off if you want to build pressure. Ford's "off" position does not seal off the heating system. Of course another consideration if you live in the northern climates is heating and defrosting of the cab...

SO I agree 100% with Spectramac on this -- the cowl area is not the best place to get "ram" air

David

 

I never meant to get anyone with my comment about the heater, as I said there is positive pressure there, but there are much better places to get even higher pressure.

If I ever get time to work out the plumbing required I am seriously considering intake stacks like the old International trucks had. Position a pair of those in the air deflected over the top of the cab and I think the pressure would even be greater than what is in front of the radiator.

I have seen a couple of snorkels that have the intake opening located slightly above the windsheild in that deflected air stream, but they also use hard bends to route the air back down to the cowl area to go into the engine compartment along the slope of the windsheild. Referance the 160 degree bend restricion in the article about ram air Malcolm provided and then add another 120 degrees or so of bend under the hood.

The bug sheild facts were published in many trucker magazines back in the 70's and 80's every time we had a fuel shortage. Test results indicate that more horsepower is used by a tractor trailer rig dragging the dead air between the cab and trailer and the large hole in the air at the rear of the trailer than wind resistance from punching the front of the rig through the air.

One of the moving van companies put a boat tail faring on the rear of the trailer, side skirts on the side of the trailer and tractor, farings on the front of the trailer and rear of the cab and a ground effects type fairing under the front of the tractor. Mileage doubled, power increased considerably just adding a bit of aerodynamics to the rig. Look at most modern conventional tractors today, the company rigs are all more aerodynamic than they were in the 70's. Even the pickups we drive are way less aerodynamic than the new Strokers are.