The notion is that it may. It happened to also be the set-up on the Devek White car, in its day, the the higher pressure at the base of the windshield and cooler air will make a somewhat measurable contribution to perfomance. Note: Louis tests revealed that during forward motion with the stock set up the measurment of temperature was ambient at the inlet to the airbox, anyway, so the best you can possibly acheive or hope for is a minor ram air effect at the base of the windshield with a modified airbox drawing air from there.

Somewhere in my archives/library of 928 information I have air tunnel results of the pressure reading along various points of the car. I will try to locate it and let you now what the pressure reading is. It is the most significant spike in high pressure readings anywhere on the car.

 

Pat,

This what you were looking for?

 

Interesting chart. Notice that the highest pressure is right where the the air intake for the radiator is. It would have been interesting to see what the pressure reading was at the top of the radiator, where the stock engine air intakes are located.

If I remember right, I think Devek once posted that they measured about .3psi at the base of the windshield at 150+mph.

 

Note that point 3 (front grille) has a pressure 2-3 times as great as the pressure at points 11-12 (in front of the cowl).

Kind of looks like a heartbeat, doesn't it?

 

Z-

That might amount to a full pound of boost at the intakes, then...

Anyone have the graphic for the S4?

 

Yep that is it George. Thanks...I seem to have forgotten your 928 library is far mor extensive than mine!

Note along the car the highest pressure is right at the windshield (with the exception right at the very front of the car just in front of where the intake tubes would ordinarily be located.

 

Yep and there lies a small vacuum that almost forces the air into the intake tubes and the radiator. Like I said Porsche a very good job at designing the 928 already. Why screw around with genius design?

 

Its nice curves also create the lowest pressure along the area above the sunroof.

 

I have a simular set up and have been racing with it for several years. Ive sealed the inlets to the air box, so that the positive pressuer is available to the intake only. Ive since modified it further with an additional inlet to the air box and sealed the hole in the firewall.
check out www.928trackcars.com/kibort and look at the air box mod.

after we saw the dyno runs with the cover off, and the 5-7hp gains, we knew what we had to do.

we still have the tubes connected to the on-top of radiator inlets. the air box is now subject to the greatest flow and pressure whether it comes from the front or base of windshield, we are getting the gains with little restriction.

Mk

PS, you guys have to be kidding about the ac ducted to the intake system, right??????????????? I hope so.

 

HAHAHAHA, No chit Mark! We were really thinking about getting some fresh cold air into the box. The idea lasted all of about 30 seconds though.

 

All that I can say,
my sHARk RUNS in cool air!!
Big differance below 70.

 

I agree.

A 10-20 degree drop in temperature, and I notice a seat-of-the-pants boost in power.

So if the normal air intake charge is increased a few degrees by running over the engine,
I see no reason why getting colder intake air wouldn't give you a minor boost in power.

Insulated intake tubes at the very least, would help.

 

DoubleNutz - I'll admit that my prototyping is "1st grade" (grade A?), but I recommend reviewing your Sesame Street tapes, because it is becoming apparent to me that you are not reading what I so diligently (and so nicely formatted) am trying try to convey.

This post was about replacing the air box cover with, uh, air.

I did some preliminary searching on this board (and elsewhere) to see if anyone had posted anything similar to what I had done. I could find none so I posted my meager offering, which had a pronounced effect, on my car, even at 90 degree temps, and a tremendous effect at cold temps (goodspeed928, bcdavis).

Dan Perez, Z - I appreciate your need to have positive measurements. If I am reading it right (please correct me if not), Mark K., has had measurable results with his race prepped S4: "we saw the dyno runs with the cover off, and the 5-7hp gains".

DoubleNutz - I mentioned in passing that I had thought of a subtle (low visual impact) ducting idea, but noted that it would probably not give additional benefits over the open airbox and no upper fan shroud. However, given the interest of some, I expanded on my idea and presented same. If you have had experimented with an identical strategy, please do the readers and myself a favor and post your pictures, and results, with engine tuning details, so that I or others don't have to reinvent the wheel.

Additionally - please note, cuz you keep getting it wrong: my 24" duct idea gets it's air from in from of the radiator, not the cowl*, where, as you have so eloquently contradicted yourself, there is pressurized air forced in the grill (points 2 and 3 on the above chart). The very same location that the 3" factory tubes take in air, but hopefully with greatly increased volume/converts to pressure.

*because I don't want to do any cutting, IE non-reversible/replaceable changes to the car

 

What about Jacquemond snorkel hood vents, almost like ram air over the box?