John Veninger

Not going to work on my 650hp, large headers, race radiator from Ron Davis and a front low mounted oil cooler car.

Ben- Just what I was looking for. The question is placement. I have my hood raised in the rear to allow air to enter the intake filters at the base of the windshield.

DR- Correct, don't want any additional under air! Think my splitter along with the old style belly tray is really limiting the air entering the radiator from escaping

If that is correct, then that is where I would place the vents. Think Ben has them in the right spot, but I would move them closer to the edge since my airbox is large.

John Veninger

DR wrote:
Nice stuff and they make custom sizes!

TAREK

I'll have to dig up a pic. One of my widebodies (brought it once to Sebring when you were there) has 2 perfectly placed hood vents shaped like kidneys and the car always ran cool in hot florida. They're the perfect shape for a 928 and look part of the original design of the car

Fabio421

I have thought about adding air exits in the wheel wells. Here is one that sits just behind the radiator that a friend of mine made on his car. Its a turbo charged S-4 track/street car and he said it made a huge difference.

mark kibort

remember, on our cars, possibly not like the Aston Marton, the hoodvents need to be up front if you want air to exit the engine compartment. as you go backward, you get near a high pressure zone that will just force air into the engine bay and would possibly exit underneath the car.

the lowest pressure zone is about front of the wheel rim in location on the hood.

some good pics of what I did, plus the pressure profile of our cars:

https://rennlist.com/forums/928-foru...flow-help.html

JV, did you notice any difference in cooling with the new cut out in the nose? Not a bad idea if it works. you would think that more than enough air could be ramed in from the stock opening, but if more is better, i might do this mod too.

mk

hacker-pschorr

The "best" setup would be a vent right behind the radiator that runs all the way to the bottom of the car and seals off the radiator to the vent. Like the GT40, F50, most Can-Am cars etc...



It would be a damn tight fit, not sure I've ever see an front engine car with this type of setup. I wonder if you could pull this off by laying down the radiator at a 45 degree angle. Just thinking out loud....

DR

I wondered how long it would take for the fantastic GT40 setup to emerge. Not only a great cooling design, but positive aero results as a bonus. Can't remember if it was the first like that, but certainly the most famous.

jorj7

John,

I did it the simple way, just cut some slots in the hood.



Here are a few more links on this:

https://rennlist.com/forums/928-foru...net-vents.html

https://rennlist.com/forums/928-foru...r-of-hood.html

http://928.jorj7.com/wk-hood/

mark kibort

The net air flow of that design is not much different that it would be if the hole wasnt there. the air still passes through the radiator, but it exits under the car, which adds to the pressure under the car. ( Air moves via differential pressure, as the nose pressure, radiator pressure is still greater than the undercar pressure so the air just is forced below. )

The main reason for this design, and the reason i put the hood vent on my car, was to add some downforce. however, the cooling of the engine compartement is probably the added bonus.

mk

hacker-pschorr

Here is a GT40 style nose on a front engine car:

mark kibort

I think your vents are just where there is an equalibrium of pressure. so, I would imagine you would at least get some convection cooling. It all depends on how accurate the wind tunnel pressure values are. I did some tests and they are pretty close to accurate in position.

mk

DR

Mark,

Quick question, would the "raised louver" type vents like I posted earlier actually create a low pressure area behind each raised vent even in a high flow/pressure area and aid in scavaging the air out?.. or not?

mark kibort

Thats what Ive been told and have read. I think that little bump before the vent, if done properly, does just that. I think thats the main reason those GT40 type outlets usually have sometype of raised area before the vent exhaust area. the bump would accelerate the air speed, thus lowering its pressure. however, it wouldnt be much compared to the higher pressure , if you are talking about trying to convert a high pressure zone to a lower pressure zone for increasing air exit quantity.

mk

jorj7

That's why they are between points 8.5 and 9.5 on the pressure chart that
you posted above... To get into the low pressure area, but far enough back
to allow the air to flow over the engine and get some convection cooling.

DR

My bad, I was under the impression many were updated later on so the airflow thru the radiator did not exit under the car, but over the hood. Maybe I am thinking of much, much later....the closer I get to 50 the harder I find it to remember all this stuff.