this is long... if you don't want to read it, don't ask for a cliff's notes version, because there is actual data that is important...



so following autospeed's lead... i ordered a dwyer magnehelic guage that reads up to 3" of water... (if you don't know what i'm talking about go google it)... this is more than adequate for aerodynamic testing, but not nearly enough to test intake systems...

i wanted to test the following:

could vents be placed in the hood to help cool the engine and make the rad more efficient?
could a hood scoop be mounted to draw air into an intake?
what does taking off the weather stripping in the rear of the engine bay do?
is the fog light area, where the turbo's draw their air from, a good place to do so?
would adding vents, or a diffuser, to the rear bumper help the aero?

Hood

if you look on the underside of the hood, there are three areas that aren't braced and are just the outer shell... these are the areas we tested since these would be the easiest to cut... i tested the middle section at the beginning of the area, the middle, and the rear... the side section i tested the same way...

we tested the underside at each of these locations, and the outside in order to see what the pressure differential was... here's what we found

Middle Front: +0.5" under; -0.7" outer
Middle Middle: +0.5" under; -0.5" outer
Middle Rear: +0.6" under; +0.5" outer

Side Front: +0.5" under; -1.5 outer
Side Middle: +0.6" under; -1.0 outer
Side Rear: +0.7" under; -0.6 outer

What it means: the areas which are the best to draw air out of the engine bay, to vent hot air and increase flow through the rad and maybe the fmic are found in the front 2/3's of each section...

simple louvers would work (tai did something right ) or a larger single vent...

in order to create a hood scoop that would actually do something, you'd either need to place it several inches off the hood to avoid the laminar flow, or in the middle close to the windshield...

mike's cowl hood works well because it draws in the positive pressure from the cowl area, and deposits it in the middle middle section where there is slightly less pressure... we've verified this using wool tufts

Rear Hood Weatherstrip Removal

moment of truth:

at the rear middle of the engine bay we saw a +0.6" of water, and in the cowl area under the hood we saw a +0.8" of water... therefore (no surprise to some):

opening up the weather stripping at the rear of the hood draws air into the engine bay at speed, and allows simple heat venting at rest...

this most likely helps to cool the rear of the engine bay where the turbo and manifold are... but, i'm unsure as to how this affects the radiator flow... i'm inclined to think that it cuts down on rad flow because of the slight bit of pressure increase in the engine bay...

Radiator/FMIC Flow

in front of the rad: +1.4"
directly behind rad: +0.7"
in front of the fmic: +1.6"
directly behind the lower rad: +0.6"

these measurements were done with all stock weather stripping intact...

we measured the pressure at the rear of the fmic by going behind the rad... reason being: the fmic sits so close to the rad, that there is very little venting that goes on between...

this was also tested using joe's/bell's stage 2 4.5" cored fmic... take that into account... also, this was done with a lower grille cutout which i'm sure increased the amount of pressure that is seen at the fmic... i'd be more than happy to test this assertion on a ptgt that still has it's lower grille intact...

i am also missing the middle portion of the chin spoiler that is on the ptgt air dam... this helps to create a low pressure area just behind it in an effort to draw more air out from behind the lower rad and front engine bay area... i'm fairlly sure that if i was to add one that was approx 1" tall, i would be able to see some additional flow through the fmic due to a lower pressure area behind the lower rad/front engine bay...

Air Intake

the fresh air that the stock ptgt airboxes draw from is the driver's side foglight... this has never made sense to me as i didn't really believe that it saw much airflow or pressure sunk so deep into the airdam... this is also the same area in which the "brake ducts" are...

the pressure on the front of the fog lights was measured at +1.8"... the highest pressure area we tested (it might be higher at the very front of the bumper but we didn't test there)... needless to say i was impressed...

this means that the brakes are actively cooled by the air flow (the wheel well area was measured at approx +0.3") and it's a very good place to draw air in from... the trick is how to do that without compromising the brake ducts, or removing the fog lights... (i have an idea but that's to come later)...

so if you don't have fog lights, it's a no brainer... find the largest diameter flexible tubing that you can find, and run it between the fog light opening, and attach that thing directly to your airbox, and profit! better throttle response and more efficient engine breathing...

Rear Bumper Area

this was by far the most surprising for me... i had expectations, and they were not met...

pressure at the rear of the bumper: +0.5
pressure at the front of the bumper: +0.5

i had expected a low pressure area to be found at the rear of the car created by the wake of the car, and a high pressure area to be found under the car at the front of the rear bumper created by a paracute effect... nope.

i had an idea before this testing that by cutting two openings in the sides of where the license plate is, i would be able to increase flow, and cut down on drag a bit... nope.

is a diffuser a bad idea then? not necessarily... a diffuser smooths the air flow, and works with an undertray and front splitter to better create a low pressure zone under the car and smoothly transition it to a higher pressure flow behind the car... this is still a good idea, but it needs to be done with a full undertray to reap the most benefits...

Conclusion

improvements can be made... but they need to be done intellegently to benefit the most...

so go and do likewise...