BC

To do base bleed on the 928 there would need to be a large cut out of the rear bumper, right? About the side of where the indent is for the rear plate?

slate blue

By BrendanC
Well the reason I posted the F1 pics was that I think the most logical place for outlet would be just above the number plate. So you would have a double deck diffuser look on the 928. I did measure the area, in terms of height it is O.K in comparison to the Ferrari 599 GTB but I think it may be a little small. That is where the sums come into play. However you might be able to add an extra outlet on one side for the exhaust. Using that to better cool the exhaust.

So apart from the downforce benefit, your CD factor if directly proportional to the Mitsubishi would drop by 0.03 i.e the S down to 0.35 but this would not include the advantage, albeit small of a flat floor, the big advantage with the flat floor is downforce. So what this achieves is that given there is a certain amount of air going over the body, by that I mean over the sides, underneath etc, every where over the body. The less that goes over the body in an uncontrolled way (not including the air re-routed from the bonnet ducts as these are slowing the air above the car) the less lift that is being produced.

Likewise by not having the engine bay vented to the underbody you are not slowing that air and as such you are keeping the local pressure low according to Benouli, creating downforce and you are filling the wake the body is making with the base bleed. It is a very efficient way to deal the issue of where to exhaust the air.

BC

So as I mentioned earlier in this or another thread is:

The 80/20 rule would get us 80% of the benefit from 20% of the work:

1) Front intake for underbody and engine
2) Flat underbody
3) Heat egress from top of hood and fenders to reduce pressure
4) Dual level diffuser at the rear

Where does the top level of the diffuser where the number plate is get its air flow from?

slate blue

Not going to argue against the 80/20 rule, only say that depending on what the goals are that may dictate exactly how far anybody takes a project.

I would say that the vents in the guards and hood are probably pretty easy in terms of time.

By BrendanC
As to where does the air come from to feed the top level of the diffuser/base bleed. It comes from the engine bay. The air is trapped between the car body and the flat under floor. It travels along there where the exhaust is and exits out just under the number plate and most likely around the exhaust outlet for cooling.

Here's another pic, this one shows the twin outlets for the base bleed.



and a close up, they are the long rectangularish shape.


Greg

slate blue

Mark K you said in one of your posts in this thread that a Nascar team bought a fan/blower, actually I don't know how many of those fans you sold them. I don't know what you call them. I saw a shot of the 599XX vacuum pumps/fans that they mount in the boot. They look like a centrifugal supercharger and are about the same size. So how much air do they move? Are they really noisy? Do anybody know how turbos are rated? In terms of airflow that is.



The underbody Fans of the 599XX and below the Nurburgring Lap of the 599XX

http://www.youtube.com/watch?v=FJj8atDGBzk

Greg

mark kibort

I dont understand. are the ferarri fans used for evacuating some under body air for downforce? the centrufugal blowers are pretty weak as far as air flow. great at pressure, bad at pressure. axial flow fans are just the opposite. (generally). we used 3 or 4 fans with the nascar trucks, for downforce. some other teams are using them for brake cooling.

slate blue

Yes Mark the Ferrari is using them to lower the air pressure under the car, it must be working to some extent, the air exits out where the tailights used to be. Did you see that lap?

So have you any figures regarding yours or others fans?

Greg

Dave928S

What a lap! .... soooo precise! Either the fans are working or that driver took some extra brave pills before that lap .... I've downloaded to watch again ... thanks for posting Greg.

ptuomov

You should run one or two rear-mounted turbos to generate the power and then use the compressor side(s) to move the air from under the car. Garrett's web site has the compressor and turbo specs.

I am not sure how this is going to help the downforce in any car that has ground clearance that makes it streetable.

slate blue

Tuomo I looked up Mark K's site and found a calculator that gives a cfm and cubic metre figure. Mark's E-Ram can pump around a 1/3 of a cubic metre so using two or three of them could get up to a cubic metre of air per second. Now if they are using these on the Nascar trucks they do not have flat bottoms to my knowledge so a flat bottom would be a big advantage in this regard.

I saw a study and 65 mm of ground clearance is a level that can still generate large amounts of downforce. Also the technics are getting better at sealing the floors. If you look at the photo below you can see how McLaren has changed the front wing and how it is trying to seal the second plane of the wing.



The semi circle at the edges of the wings creates powerful vortices to seal the wings. If you go back just a few years you will see they didn't have these additions to the end plates. McLaren even used these on its floor in the MP4-22, it doesn't appear to be on the 599XX? It may not need it at the height it runs.



So the floor can be sealed, question though is a what level, do you use a variable suspension setup like which is sold by KW or would a street legal 100 mm setup suffice? The downforce can all be quite easily measured with the Cosworth equipment.

How far off the ground is the 599XX?



The XX generates large amounts of downforce, many hundreds of kilos, for light car that would have a large effect. You only need to watch the video to see that, half a minute quicker than the Enzo around the Nurburgring.

Greg

mark kibort

There is just not enoughflow out of a turbo to help in downforce. probably less than 25% of that of an eRAM. we measured near 900 cfm out of the old eRAMs, and they are quite a bit more now. turbos are usualy only double the flow of the engine its designed for, and its a positive displacement device. Ducted fans are much more efficient in moving air and thats why the nascar truck team was using them. venting the under the center of the car air flow, to the rear truck bed, gave them the downforce in qualifying to shave off near a second a lap. (roundy round guys)

mk

mark kibort

Here is the vent in the rear of the new racer, as well as the front additional inlets to feed the hood vent and provide more cooling

mark kibort

I would like to know more about the ferarri set up. are those intakes to the engine that are being fed by the centrifugal blowers? (or tubos, is there a hot side not shown?). or are they electric? if not electric, they wouldnt work so well, as what happens when you need most of the downforce, (i.e. off throttle decel or around turns) out of turns, yes, it could work, but all other times, that would be a very poor source of air flow through a centrifugal blower, especially if it was a turbo for the engine intake for obvious reasons.

mark kibort

Looks like its electric! very strange that they used electrical centrifugal blowers. they could get a lot more effect with axial flow blowers in this case, no doubt. I think I need to call them!

From the article:
Except for the roof and windshield, not much of the 599XX is cannibalized from the all-aluminum 599GTB Fiorano. All four fenders, for instance, feature F1-like aero “fences,” vertical panels behind which air is scooped out from each wheel well. To relieve heat and pressure, the hood likewise features nearly as many holes as Augusta. The winglets on the C-pillars—resembling Alfred E. Neuman’s ears—funnel air inward, forcing it to slide down the Lexan backlight, then along the ducktail trunklid, and finally over the carbon-fiber blade spoiler. And then there’s the huge underbody fairing and rear diffuser, whose center section is air permeable. Two electric fans mounted inside the trunk suck air through that permeable panel and then vent it through the holes previously occupied by taillights. The air is discarded in individual huffs and puffs (like a subwoofer stomping out rap music), which, we are told, detaches the wake from the rear of the car. This is apparently a good thing, according to the F1 engineers who designed it—along with the winglets—during hundreds of trial-and-error hours in Ferrari’s own wind tunnel. The fans automatically quit sucking underbody air at 155 mph, a speed that suggests the car is traveling in a straight line and thus needs no extra downforce. Speaking of which, all of this aero chicanery creates 617 pounds of downforce at 124 mph and 1389 pounds at 186 mph. For what started as a street car, that’s a bunch.

BC

I can think of no better way to spend money than buying one of those and driving it around a race track.