I'm pretty sure this makes no sense.

The picture of the race car with the vents on top of the fender illustrates my point very well.

Before those vents were required the front end of these cars was lifting due to high pressure inside the wheel wells. The airflow over the top of the fender was faster than the airflow inside the fender. Slotting the top of the fender reduced this effect. Before the rules changed cars were getting airborne and nobody was quite sure why.

Open wheel racers are subject to even more tire drag caused mainly by the airflow over the tire. Interestingly, a rotating tire develops less drag than would a stationary tire which caused some wind tunnel testing difficulties until the rolling road test beds were used.

It is a pretty simple idea: pushing a vertical obstruction through the air creates high pressure in front and lower pressure behind the obstruction. Covering the obstruction with a fender doesn't change this basic fact.

The top surface of the rotating tire drives airflow forwards and downwards into the high pressure zone already created by the forward motion of the car and the barrier presented by the contact patch, increasing pressure in that zone and creating drag. The high pressure from this zone is usually exploited for brake cooling and for some road cars, for engine intake. It's a popular spot for oil coolers and twin intercoolers.

It is true that the CFD (that's computational fluid dynamics for the non engineers) of airflow around a moving wheel, whether fender enclosed or open, is incredibly complex and has not been correctly modelled or measured so far. However, I was trying to keep things simple.

In general, you will find a high pressure zone right in front of a moving tire, a corresponding negative pressure zone behind the tire and a flow separation point approximately at the top of the tire, it moves forward with speed of rotation. The fender vents are placed to cause maximum extraction of the high pressure zone. Just incidentally, this phenomenon is also exploited to cool the brakes, front and rear.

Whatever you do, do not modify your engine cover or air filter boxes in a manner intended to draw air from anywhere inside the engine compartment. Of the two optimal positions available Jaguar has chosen correctly. Removing the plastic engine cover will have no positive effect on your car. Knocking holes in the air filter boxes will not improve anything either.

 

Those vents allow high pressure developed in front of the tire to exit the fender. The flow separation point is otherwise approximately at the leading edge of the vents. If they tried to put the vents further forward they could not work. The air is technically blown out of those vents but you can think of it as being sucked out if you wish. The fact is that the airflow over those vents is higher pressure than atmospheric. Which should give you pause for some analytical thought ( flow from high pressure to high pressure, how does that work?).

In my earlier post I said the best place for engine air intake on a road car would be in front of the tire, for this reason. Those vents do not improve brake cooling, they interfere with brake cooling airflow.

The vents do not look cool, they are there to protect the drivers. If the aerodynamicists could figure out a way to eliminate those vents safely they would. They create drag and reduce downforce, except for reducing the lift created by the front of the rotating tires under those fenders. The one road car that fit these vents just because they looked cool (they don't btw) was a TVR and shortly after that car was released onto market the hood molds had to be modified to block the slots. Stones were being flung through them onto the windshield breaking it. So much for cool.

Those vents are not a great solution, they happen to be the only feasible solution to the problem of high air pressure in the wheel wells at 200 mph+.

 

Were you going to explain your interesting ideas about airflow around tires?

 

You're half right.

The upper surface of a car does act like a wing but with appropriate spoilers and splitters under the bumper the upper surface can be induced to create genuine downforce.
The pressure pattern over the front of the car is generally higher than atmospheric, especially at the radiator opening and the base of the windshield. It is the overall shape that on average creates lift, aside as I say from ground effects induced by chin spoilers and splitters.

Without knowing the pressure pattern for sure I'm still pretty sure the tops of the fenders were operating at net positive pressure relative to atmospheric before the slots. The problem was discovered on the Mulsanne straight at Le Mans by the likes of Allan McNish resulting in further research into the problem. The pressure building up inside the fenders was found to exceed the downforce created by the closed top fender. The result was spectacular but McNish later admitted he thought his flight was to be his last one.

 

Just an FYI that is not a race car it is probably the most bad *** street car to be made to date that will decimate damn near anything on the track. There are going to be some butt hurt P1, 918 and Ferrari the Ferrari owners if they ever share a track with that car.

 

I don't think so but it is a quintessentially American viewpoint.

 

Replace the wheels with som 20" golf ***** and it will be more to Jagulars taste..........

 

Oh and the vents do look cool..........

 

Don't laugh, dimpling has been tried in an effort to reduce aero drag. It sort of works but looks a bit odd plus dimpling, as for stitching on a baseball, has its main effect during spin.

 

But the broken windshield resulting from them does not. The vents on the Viper appear to be in the outboard facing surface of the fender possibly for this reason. Of course that won't help the poor fellow trying to catch the Viper who will be treated to the stone chips.

 

This thread should have been moderated like 3 pages ago. Why don't you guys give it a rest, I think the keyboard warrior pissing match has gone on long enough.

What is interesting to me though are the IAT reductions by removing the engine cover. Any more data on this? I have always removed the engine covers on most of my cars and for some reason I haven't on this one. If it is that dramatic of a difference I may go remove it this afternoon.

 

How dare you make an attempt to bring this thread back on topic? What the H were you thinking?

I will be surprised if it is proven that there is a significant difference. As seen with experiments on inlet ducting insulation, the volume of air and the velocity it's flowing at means that no real difference.

 

Yeah I am not as concerned about volume of air as I am about the intake air (IAT) and underhood temperatures. Especially in this part of the US where we see extended periods of 90-100 degree temps, it makes a huge difference on performance. When it finally starts to cool down here in the late fall / early winter my car absolutely LOVES the cool air, from the seat of the pants it feels like you pick up an instant 20-30hp

 

You misread my post.

 

I tried to do more on Wednesday but torque wasn't playing nice. Another test I would like to try is sticking a thermocouple on top of the intercooler and see if the temp changes with the cover on and off.

Honestly with a supercharged engine the only way to really lower the IAT is a water/meth setup or beef up the intercooler. I have also thought about insulating the coolant lines that run to the intercooler not sure how much of a difference that would make.

I was the one who insulated the entire intake from air box to TB and I did not see a change in IAT mainly because the IAT sensor is AFTER the supercharger and there is hardly any heat soak on the intake when driving.

I would like to see someone rework the intake pipes that bend over the radiator, angles like that are never good for air flow but I am not sure if there is a better way to get air into the intake with the limited room we have.

 

It will be interesting to see how well they hold up, when Audi started doing them some 10 years ago they were breaking an hour or so into a race. Now the ACO lets them have huge holes in the fenders.

 

Why? The OPs question was answered in the first few posts and as long as the discussion is civil where's the harm?
You always have the option of reporting a post where you think there's a problem with this button

Or you could just ignore it.

I'm not sure that an IAT discussion is exactly on topic either.

 

Those huge holes are the safety mandated holes, reducing lift from the fenderwells. According to the internet pages I looked at the main concern was any deft angle seemed to immediately raise the air oressure inside the wheelwells causing the front of the car to lift. As soon as the front spoiler/splitter breaks with the airflow the entire front of the car becomes a giant wing and upside down pitching is the result.

The venting was apparently insufficient at the speeds these guys do hence the new mandated holes. Begs the question of what constitutes an open wheel race car these days.

Also in the articles was mention of "accidental" breakage of the vents by the tire guys during pit stops before the holes were mandated....

 

Air to water intercoolers tend to run at higher temps than air to air and the old trick of water spray onto the intercoolers doesn't work so well although it might be effective if the intercoolers use a front mounted radiator to cool the actual intercoolers.

Air to air intercoolers use only the one heat changer, air to water should use two for best cooling. I can't see how removing a little plastic cover can have any useful effect or surely Jaguar wouldn't bother to fit one.

 

IATs, underhood temps and heat soak are not a related conversation to the engine cover removal? Look at the first few posts of this thread.

The mostly jagular-driven banter has been ongoing in several different threads and he has had this addressed in the past. People keep responding to his obvious trolling, so like I said this and the other threads should have been cleaned up a while ago.

Thanks boiler for the constructive notes. Kyanite has been debating a water/meth install in the near future so if he goes through with it maybe he can do some IAT testing for us. Heat soak is definitely a performance killer off idle so yeah I would be curious to see some empirical tests on that.