Nemesis8

iTrader: (3)

... at high speeds offer more downforce on the car since the air entering the front bumper goes up and over the car's front windsheild rather than under the car?

Thoughts?

eviltwinkie

probably not...unless the vents are the size of the hood and protrude out alot. you already have fast moving air going over the car so the vents are not going to be contributing more than what's already there....

Nemesis8

iTrader: (3)

Yea, I thought so - just curious I guess.

eviltwinkie

Killed the cat you know...heh

rotarygod

Actually it should. Take a look at the caption under the 5th picture down. It says:

"At speed, air entering the nose stagnates under the hood, and lifts the nose. By letting this air exit, the pressure under the hood is lessened, and front end grip is increased. This arrangement also increases airflow through the radiator."

http://www.yawpower.com/sep2004.html

h-khunterkiller

i have one and it lift, like it want to come open. So is like riding with no hood or its weight

eviltwinkie

RG I would beg to differ...you would have to be at a pretty rediculous speed for the effect to actually work. In "real-world" situations I think it would be safe to say you would probably not see the effect. Maybe 160+ it would add 25lbs?

Nemesis8

iTrader: (3)

I did not think about helping the radiator flow, that is a good reason also.

eviltwinkie

Cooling is the ONLY reason I am looking to add vents to my hood or replace with the CF Vented hood. You asked about downforce...never said anything about cooling...

Astral

From the description pasted by RG, it seems that it doesn't offer more downforce, rather than reduce the lift that's currently there. In a way, it's more downforce that you used to have, but only because the lift is reduced.

eviltwinkie

Yea but again I doubt that you could feel the effect unless you were at a significant speed in the 8. The car is already pretty nice as is...venting the hood would provide more cooling mainly, but under 100mph I HIGHLY doubt you would get any tangible downforce from it.

rotarygod

The original question asked "at high speeds". Beg to differ all you want. The physics still apply at any speed. They just get eponentially higher as speed rises. It's just like ram air or even the boost curve of a stupid centrifugal supercharger. It does work...the faster you go. Your car has ZERO downforce and the faster it goes the more lift it has. It has lift as long as it's moving. You don't own an F1 car or a handful of the other cars out there that produce downforce. Reducing lift in any form is a good thing. If there is an added benefit of better cooling then even better. Under 100 mph you don't feel much of any change. Under a 20 hp gain, you don't really feel it either (regardless of what anyone claims) so why do it?

eviltwinkie

Cause its 20HP!!! Heh...

h-khunterkiller

if you only have 5 horses you will definitely fell 20 lol

Nemesis8

iTrader: (3)

True, I did ask "at high speeds", that was the trick part of the question. I think this mod is in my future, and the extra benefit of moving air better for the radiator is a plus.

h-khunterkiller

thats why i did

mysql101

damn, some rx8 owners got screwed.

Trekk

With the vents already in the engine bay under the hood, I dont think a vented hood would help much on a rx8 in that fashion.

I've also seen on other websites. (off road mainly). that the best thing to do if tape small strands of yarn all over your hood and then go for a drive to see what the air is doing.

The yarn near the windshield should blow towards the headlights, while the yarn near the headlights should blow towards the windshield. Then you can get an idea where you want your vents. To close to the windshield and you "could" be forcing air under the hood at speed.

rotorocks

This is interesting.
I am actually thinking of doing vents on my hood for cooling purposes. Having vents will keep the engine MUCH cooler, especially when at low speeds and in the traffic. To see the cooling effect for yourself, try this experiment:

After a good hard warm up drive in a 95-100F sunny day stop and let the car idle for a few minutes with the AC off, then check the the coolant temp reading. The temp will go into the range of 100C and the engine will begin running hot.
Now pop the hood open, and watch the temps as they quickly decrease to around 88-90C (As reported by Int-X coolant temp gauge). I bet at a speed that effect will not go unnoticed either.

By the way I stumbled across this tread while looking for the DIY on the OEM hood. (No luck so far) So I'll just go ahead and ask, has anyone done vents on their stock hood? Is there a DIY on that?

quick_dry

Here is a series on wool tufting if people are interested in seeing it applied to a few cars - no RX8, but there is an RX7 in the later articles:
http://autospeed.drive.com.au/cms/A_108656/article.html
http://autospeed.drive.com.au/cms/A_108674/article.html
http://autospeed.drive.com.au/cms/A_108675/article.html
http://autospeed.drive.com.au/cms/A_108676/article.html
http://autospeed.drive.com.au/cms/A_108677/article.html

Another experiment is putting oil drops along the leading edge of a surface you're interested in, then going for a fast drive, and you can see the tracks the oil takes.

A hood vented at the right places should help reduce underboonet pressure (aiding high speed cooling) and downforce. If you relied heavily on a front splitter then you would need to retune it as the front pressure zone would be altered.

Here are a couple of CFD pics of an Aston martin, obviously different for an RX8, but general trends are the same.
http://www.ensight.com/gallery/150.html
http://www.ensight.com/gallery/151.html
http://www.ensight.com/gallery/154.html

chickenwafer

iTrader: (9)

You will reduce on the air pushing up on the underside of the hood, like others have said, because the air has a quicker exit than before.

But it's mainly for the cooling benifit. That exiting air is going to take engine heat with it. And because you're moving more air, more air is passing through your heat exchangers up front, and thus improving cooling.

Silver_Surfer

Too bad our fender vents/grills are bogus

eviltwinkie

You can buy a new OEM hood pretty cheap now a days...a DIY kit to graft on a set of vents would be nice...

rotorocks

Definetly. if i get the right info, this is what I plan to do. Nothing is desited yet.

Red Devil

Would love to see pics and a diy of the final product if you do this...