hacker-pschorr

Ferrari 575M GTC:

PorKen

What about spacing out the rear of the front fenders by 25mm or so? That would vent the engine around the hood, and make a vent along the back of the fender for oil/intercooler radiators or brake cooling in the rear of the fender.

mark kibort

typically, the rear vents are for getting air out of the wheel wells.

the whole idea is to take advantage of differential pressure. in the middle of the hood is lower pressure, under the car is higher pressure. the nose has the highest and the base of the windshield has next to the highest. it makes no sense to vent the engine at the back of the hood, as this is the highest pressure. air would actually enter from here and go down underneath, unless you sealed this area up and used it for intake engine pressure.

think of the air on the side of the car as near the same pressure as underneath the car. the vents on the ferarri tell the story. the hood vents in the middle vent the air captured by the pressurized nose and vent it to the top of the car. this reduces the lift that naturally occures do to the air on top having to travel a greater distance than the air underneath the car. (ambient pressure underneath, lower pressure on top, higher pressure at the nose and base of windshield)

venting the engine for cooling is probably less than secondary, but if you see cooler water temps, thats peculuar, as the t-stat should maintain engine temps. oil would be the only temp that could be effected, but i bet that would be slight difference. If you are overheating, and the vents fix that, then that could be an expected gain, probaby due to better flow through the radiator, and not the air moving over the engine or under hood temp reductions. (thats a guess, not backed up by facts, just theory)

MK

mark kibort

--------------------------------------------------------------------------------

just did a battery of tests on the hyway today. The test were using a sunx sensor and remote pressure tube to find pressure values of the 928 at 60mph and 100mph.

the tests were conducted by placing the very accurate Sunx (+/- 15psi) sensor pressure pick up at 8 locations and then driving at 60 and 100mph and making a note of the pressure.

as some of you may know, i did cut a hole in the hood to vent air entering the engine through the radiator to allow it to vent to the top of the car, rather than creating lift under the car. some interesting results there. (100mph / 60mph)
(all values are positive pressure, unless noted)
In the intake, 8" from the opening , but in the tube.
.10psi, /.06psi. WOT dropped the .10psi to .6psi .

in front of the radiator
.12psi/.07psi

rear of the raditor, agains the engine around harmonic balancer area.
.10psi/.05 psi

Nose of the car, just below the nose, but above the inlet vents
.21psi/ .15psi

Base of the windshield, just around the wiper shaft area.
.12psi/ .08psi

right behind special hood vent on top of the hood
.00/ .00psi
with hood vent sealed
-.04/-.01psi ( vacuum)
This was interesting showing that with the hood vent closed there is a vacuum area, in the exact area that is show on the wind tunnel test results. its relieved by venting air when the opening is not sealed, thus showing ambient pressure with no negative pressure generating on the hood at any speed, even 120mph

further shows that hood intake inlets are usless! they are at a lower pressure zone vs our stock intake area or base of windshield area. automatic 1-2% loss of hp by using a hood intake scoop!

Ill post some pics of the set up if anyone is intersted. (or if anyone wants to see my hood cut out section. actually, im happy how it turned out. I have a feeling it may be a racing must, unless you have a real top notch spliter already.


MK

here are some pics of where i got my hood cut out shape and location from

drnick

mark, show us your hood vent!

jon928se

Some idle thoughts on Xmas eve

Vent the hot air from the rad exactly where nick has done - level with the front of the front wheels as that is the most convenient low pressure zone.

Vent under body air via the cockpit using at least two 6" dia ducts to the roof roughly at the aft end of where the sun visors would be had they not been removed in a track car.

The inclusion of a splitter - why do they call them a splitter ? - is likely to increase positive pressures at the front of the car.

that's all folks

mark kibort

1. Thats exactly where my vent is located.

2. sure you could use these 6" ducts, but i woud be in the center of the car. the splitter and wing allow for balancing the downforce. net effect should be near the same if i was to guess

3.splitters are used to take the pressure build up of the nose, and route the release of this higher pressure air to lower pressure zones. It can go under the car or around the sides. by design, the "splitter" takes the nose air and routes it to the sides. the longer the splittler, the more is routed to the sides, and the more downforce upfront you have. Plus that air can be routed up via dive planes to eventually help the rear wing hit more air as well.

mk

mark kibort

what do you think? actually, there is no turning back now!

I know, I know, How could i do this to the Holbert machine! But, i kind of like it now and it works too!

MK

Bill Ball

That looks great, Mark. Looks like it belongs there. Now, in the interest of science, put a temp sensor on the underside of the screen and one inside behind it and see if the vent is warmer than the rear engine compartment. Did you put anything underneath it to divert airflow up through it?

mark kibort

No diverting devices to the screen, but the wool strings point up at a 30 degree angle at speeds up to 120mph kind of proves things are doing what we predicted them to do!! With the pressure (or vacuum ) changing to a measureable difference on top of the hood, with the screen, it surely is working and diverting some flow from going underneath the car.

that sunx sensor does have a cousin temp sensor, which is equally as acurate. But, i dont have one! http://pewa.panasonic.com/acsd/sunx/products/dp4.php
I think the pressure sensor is around $100. It has a range of +/- 14.7psi and runs on 12volts

Mk

SharkSkin

Like Bill says, it looks like it belongs there. Very nice, Mark! it will be interesting to see if that helps balance out the extra rear stick that you gained with the rear wing.

drnick

that does look good, nicely done! in fact if you ask me it looks reasonably subtle.

mark kibort

Its going to be nice to have a car that is actually tuneable. Bet'cha you didnt notice the splitter. it was basically pretty usless before, because the little lip was off a narrow, older cup car. all the air was splilling off the edge and still was able to go under the car. Now, the width is filled in and ive extended it. My Bmw racers say that when they just extend their splittler 1" with an extension adjustment piece, they can make their car loose or cure push. I figure ive done 3 major things to cure the push. rear wing, filled in the splitter, extended the splitter and vented the hood.
I hope it may even create a slightly loose car so i can start putting some more wing back in . If so, it will be faster!

should i paint the aluminum screen flat black or leave it el'natural?
Im using some of this screen material from a company in LA ($50 sheet of grill screen material) on the rear holes where the bumper'ettes used to be. (plus ive made those holes larger too.

Mk

atb

Mark,

Any math behind determining the size of the hood vent?
Any benefit in making the vent hole size adjustable?

Vlocity

Mark :

I am really interested in your front splitter, did you make that yourself? Would you be willing to share some of you pics and dimensions?

Thanks.

Ken