Jadz928

Ken,
First off, great work! Good looking and an effective mod.

It appears to me there is not much difference in pressure any where along the hood profile. There are no gross pressure drops.

Did you come across any physical limitations which pushed the vent further aft?

ptuomov

With the EUR doing it's thing, it's now $250 before shipping.

It's hard to judge the hood line curvature without actually measuring or test fitting the piece. Someone will have to try this.

Ducman82

i might have to do that. but right now im debating on carbon fiber with Naca vents and a vent... i have just never worked with CF before.

ptuomov

The vent opening has to be rear of the radiator fan shroud to do its job properly. This means that the 968 Turbo RS intercooler air exit vent would need to be placed significantly further back on a 928 from where it is on 928 Turbo RS.

Apart from the fact that they are simply different cars with different dimensions, it's also worth remembering that on a 968 Turbo RS the vent is the exit fromt he intercooler air channel which is sealed off from the air that goes into the air intake or the radiator.

ptuomov

Ducman82, my esthetic preference is to use body colored went in balck car and leave the carbon fiber visuals for later model year cars.

Ducman82

o, id paint it car color. let the hondas have exposed CF

Vlocity

Thanks !

The main consideration for me was moving the vent back as far as practical to give the air exiting the radiator a chance to "turn". I also believe that I picked up a major benefit from the leading edge lip of the vent, which will add to the pressure reduction on the opening side.

Ken

mark kibort

There probably is no "major" benefit to the lip. this is because , due to the shape of the 928 front area, that area for the hood vent, is a very low pressure area, in which case there is very little flow directly over the surface of the hood there. (separated flow). ducting it from radiator would help a bit, but I think just an opening will work fine. if anyone has a sunx sensor as I do, you can take some pressure measurements at speed and see what is going on, or video some tuft movement attached in that area.

Jadz928

Mark,
I wouldn't be too sure about that. There is plenty of flow but higher pressures.

I'd propose those measurements are at or near the surface.

If the vent "lip" disrupts laminar flow across the hood surface, it make create a pressure drop.

Plus the lip is raised off the surface which may allow the vent to utililize lower pressures, similar to how a "ram air" induction works.

How far off the hood surface is it, Ken?

mark kibort

everybody is doing it now!

some great shots from the crew at sears this last weekend in the PRC race.

https://rennlist.com/forums/racing-a...-6-2010-a.html

Jadz928

mostly 11's, no Fofo's

mark kibort

no, there is very low pressures in the area we are talking about. if you look at the stream test, the boundary layer is pretty substantial. (high off the hood) the stagnation points are high pressure. where we have the vent, there is still is separation based on tufts Ive run. however, you are right, at that point of the hood vent and the lower pressuer, there is substantial flow. a lip might help, but already there is a pressure differential. NACA ducts work to make something out of nothing, with no lips, but the shape.

the key thing here is to have the vent aft of the radiator, and before the middle of the front tire as a location. aft of that, you get into the higher pressure zone.

mark kibort

just to give you an idea, the headlight covers i have got sucked out at 100mph until i fixed my re-inforcement, attachement set up. (area 5-6 of the flow chart)
we put the vents in the location "8".

Vlocity

The lip is 1.38 inches high. I can't find one of the articles that I used as reference right now, but none of those discussions included just cutting a hole, as it wasn't considered an optimum idea. I think Louie discussed that in a previous thread.

Ken

mark kibort

sure, its all relative too, right. look at the flow patterns. will 1.5 " get you in the flow? maybe. if so, what does it do to drop the pressure over the hole. I can easily measure the change and do an experiment. i would say, the change will be very minimal. If you look at most all of the ALMS cars that have wind tunnel and experts helping with the design. near none of them have a lip prior to the opening. the gains in pressure drop, might be offset by increased drag which would be a product.

I already posted the vent vs the no vent pressure changes, and it was very subtle, but the tufts point up at a 45 degree angle , even at 120mph. closed, the tufts lay flat, like the pictures here. there is a lot of venting, and this all help with downforce. (and cooling when the car is sitting still . )