Late into the details of the thread.... but is your hood designed like that for aero reasons? Is that for air to escape? What's the rationale behind a cowl design like that compared to having an exit after a ducted radiator? (probably a function of the front end design, but I am guessing...)

 

Why don't we take a collection to have Patrick's car and team tour North America so we can see the car, talk to the builders, and see the car run on interesting tracks.

Then we can gather for a pint and make fun of Mark Webber and Riccardo just to get him going... (I like Webber and Riccardo, they are awesome drivers and awesome people. But if we can't have a good argument about F1 drivers over a pint after playing with cars all day, what the heck are we living for?)

 

its to smooth the exit flow out of the hood, also , a lip located in key places can create a low pressure zone to further increase the pressure differential between the nose and hood area. the more air that exits the hood, the greater the downforce and the more effective the rear wing becomes.

 

it still becomes anecdotal, if you cant prove it actualy did what you think it did. say it was a complete failure in doing what you wanted it to do. increase downforce of the wing. (which i dont believe it can do for many reasons). but the lap times improved. the extra drag it could have caused , increased downforce , possibly , rear end stability, and allowed for the better lap.. always a problem in this result, is knowing if it was the driver just having a better lap and nothign changed. staticstical significance is tough to prove. However, since it was effective, then you say it worked.... however, if the added downforce was due to only drag of the lip, better results would /could be had by just getting more wing angle and a larger gurney flap. (for an example)
to your first point, yes, the main thing that happens to a wing when it is lowered, is that the AoA can increase as you get into the air flow deflected from the body. Scotts wing is so high, it, might be out of the deflection air flow and AoA could equal angle of incidence. there is no way that the air off the flap/spoiler is going to speed up. air flow doesnt do that . in fact, the air flow would likely slow down vs the air flow of the wing low pressure side. remember, the top of the wing is hiiger pressure low flow.... the top of his rear spoiler is high pressure/ambiennt presssure and low flow. the bottome of the wing, that opposes his rear spoiler /flap, is low pressure , fast flow. the only analogy i can think of is think of a venturi with a plate on one side of the narroest point? would that flap, increase speed of the entire venturi or partially stalll it? ii think the later... and i think its a major flow disrupter, causing stagnant air flow and higher pressure.

im not making assumptions, im taking basic flow theory and applying it. maybe it a little assumptive, but looking at it, it doesnt seem like there would (a.) be any interaction between wing and flap, and (b.) that if there was, the flow would not be sped up, but slowed down by the flap, reducing the effectiveness of the wing. its why you wouldn't make a bi-plane with the wings set up close to each other and opposite configuraiton. (low pressure sides facing each other) the plane would not fly.. the forces would counter act each other.
same thing here you dont want to speed up the air on top of the air dam, as that low pressure zone would lift the back of the car, while the upper wing wants to press down on the wing and the car. its counter intuitive in some ways, and easy to see why his "builder" might think it works, but i suspect it doesnt.

again, if the net effects are positive, i think more wing angle might produce better results... you dont want a low pressure surface, on anythg that attaches to the body of the car, it will create a lifting force on the car.. THATS why the wing is up above the car and creates downforce. if the wing is too close to the car and the low pressure zone is shared with the body of the car , its no longer a lifting (or downforce)body, its just a spoiler and effects flow and drag.


This is true.. but then the smart designer will try and recreate the same force, but be able to do it by lowering the drag for further improvements.
same as what happens with the huge NASCAR flaps... they work, but a wing works better..

if you vent the air flow out the hood, you will realize MUCH more downforce and less drag as well. there is a big low pressure zone in the middle/front of the hood. you relieve that, also use it to create less air flow going under the car through any inlet.. that normally will create more lift under the car.
diverting air flow from going under the car , creates more down force and less lift, and makes the rear wing more effective.

 

purpose: the air hitting the sides is routed to the sides via the splitter and kept from going under the car.. the air going to the center is routed to the hood vents creating downforce by relieving the low pressure zone in the hood area and keeping less flow from goiing under the car.
the bow'ed up splitter allows for the center flow air to feed the venturi tunnels underneath.
see if you can get a picture of the front up close.. that would be interesting to see!

 

L88 style hood is for cowl induction. We reversed the intake from the stock configuration.

 

that pressure zone doesnt change for greater intake pressure with speed, but you should find a way to vent the hood about the front wheel area, to vent inlet air to the radiator from going under the car. two benefits... air doesnt go under car and air is vented over the car via the hood vent.... both downforce adders. you have a beautiful splitter and inlet to the radiators, it woudl be a shame not to take advantage of it.
I use both . cowl and nose air pressure for my intake. they both are very close to the same . (as measured with a sunx sensor in many positions, including in the air box)
its tough to cut holes in the hood, but you will get a lot of gains. just think , all that work the splitter is doing, is going to waste once the air leaves the radiator and goes under the car. basically , its neutralizing about half the splitter effectiveness.

 

Having read all the posts, you guys need a windtunnel. then you could actually see what's happening. All of you guy's are right in your own way. Just need to verify your conclusions.

 

Lol...i'm up for it!

Yes of course it's anecdotal as there isn't any data (except for improved laptimes) in this hypothetical. I'm all for data. Just posing a question about the bottom line being lap times.

If only it was that easy Ernie.

 

You shouldn't be apologizing, I appreciate your posting this. I take a great many comments *** grano salis. And as everyone here is an amateur racer, the lap time improvements (without data) could easily be placebo, in that a driver could have more confidence carrying speed he could have carried anyway, but previously lacked the confidence.

Of course, everyone would like CFD, wind tunnel, and real track data. But AFAIK, everyone here is just a club racer/time trialer. It, IMHO, goes against the notion of club racing to have to delve that far into things to get a good setup. Personally, I don't even like that aero is allowed int he class for which my cars are built. When I started down that path, I don't recall if they were, or they just weren't taken advantage of. Regardless, every other class that allows aero is a GT class, and obviously, none of the other SP classes allow for non-factory aero. But it would probably cost $10,000 to get an optimized setup (i.e. parts and all of the CFD and wind tunnel time to get there) for these cars, and more if one were to just pay a shop to do the work.

As for the absolute statements. This is an internet forum, a great many people regress to that state. I appreciate Mark's insight, but I know his personality, and I weigh what he says accordingly. He has a lot to offer, but his argumentative personality gets in the way of most people's objectivity in what he says. And he certainly isn't the only blunt and argumentative poster in this thread. I have withheld comment in some cases as I know where it will go.

On the wind tunnel testing, there is one about 3 hours from me, and another about 4 hours from me. I've found one I can rent for $500/hr with a 2 hour minimum. I've given it some thought. It may happen, but not until after I've been running with a bit more aero than I currently have.

 

$$ for windtunnel time which you can not see, or a set of tires which you hug and touch. Its hard to justify which you can not see. But Aero setup will not wear out once set.

 

I would hug the wind tunnel... Just saying!

Ernie, my Chump team agreed that we will do some wind tunnel testing and adjustments after we sort out the car/team for a few races. We still have many seconds per lap to find in driving skill, set-up, strategy, and adjusting the car to the rules. If the car survives relatively well, we will give you a shout in the fall and discuss with you some aero work and wind tunnel time. We may also have you rip out and update the roll cage in the winter. You and your guys build a cage for these cars better than anybody, so you have our business for that...

By the way, it's Geoff Davies's old PCA class 924S car we are running, so a pretty well sorted car to start!

-Patrick

 

Now that I clearly see the "non-factory origin modified Porsche motor", it makes sense to me... must be an amazing car to drive! Well done...

I like Kibort, you're a good guy... type a lot... sure... but a good guy at the end of the day.

 

sorry, my response to this was thinking you were talking about the hood vent in the middle of the hood, not the cowl at the base at the windshield. That is a high pressure zone used for intake. looks like at exhaust vent but its really for inlet to the engine intake. (counter intuitive). its a high pressure zone that is used to increase density of intake air and give more power.

 

I don't know what that "gurney" does on my car. My speculations are exactly that: speculations. The car has not been in the wind tunnel so there is no exact way to know. All I know is that my car builder tested it on several of the cars he built and found it to improve the handling of the car. Absent a wind tunnel, all you have is testing to tell you what makes a difference and what doesn't. The car has done a 1:39.4 at Sears Point. It weighs about 2375 with driver and has ~270 RWHp for an 8.8:1 weight to HP ratio. So it works well.

The '73 RS duck tail spoiler decreased lift AND reduced drag. The "gurney" on my car is not really that much different in concept. Maybe it works in the same way as the duck tail. So someone making definitive statements about what it does without wind tunnel data is just making stuff up.

The bottom line is that I trust my well respected car builder who has built some of the fastest 911-based GT cars on the west coast over someone with zero experience in building top 911-based GT cars on their resume.