Anybody have or know where I might find a diagram of the air pressure surrounding the chassis of the XJ at a given speed? Most specifically, of the hood of the XJ at speeds between 45 and 75 MPH. Example:

 

Almost guarantee no

 

All red

 

A xj is a brick on wheels it won't look anything close to that.But i gotta ask why?

 

Okay, extra-strength post ahead.

I wanted to install hood spacers to cool my engine, but then I learned about the high-pressure region between the rear of the hood and the windshield caused by the changing direction of the air. I figure if that happens on most cars, then the air pressure increase on the XJ is relatively large. So at speed, hood spacers would most likely serve to only suck air into the engine compartment, which would in turn affect the amount and direction of air flowing in through the radiator, and negatively effect engine cooling.

So, I decided that the best alternative would be to install hood vents at the point where the pressure is lowest, because the then higher pressure air of the engine compartment would be "sucked" (but really, blow itself) out, cooling the engine more quickly. Now, physics would tell me that this low-pressure area exists at the most curvaceous (for lack of a better term, hah) part of the hood. Pressure diagrams of other vehicles seem to correlate that.

Like you said, the XJ is not shaped like most vehicles, and I was hoping for a pressure diagram to find the most effective hood vent position. If I had to guess, it would be in the center, somewhere above cylinder 4 or 5, and most likely two of them to account for the styling of the OEM hood, wider across than they are long, and with their vents facing rearward to reduce rain and insects getting into the engine compartment.

I also imagine that they would keep the windshield spectacularly dry at highway speeds in the heavy rain.

Your thoughts, everyone?

 

Somewhere on the internet exist a page that some dude taped yarn all over his hood to test for low pressure areas, but I can't find it. The guy on this thread seems fairly confident on low pressure areas being at the front for high speeds and back at low speeds.

http://www.naxja.org/forum/showthread.php?t=1082881

You could always tape yarn on your hood and decide for yourself?