The 90 MPH is when the "lift" resulting from the shape of the Crossfire begins to effect rear wheel adhesion. The wing spoils the lift and places a downforce on the rear of the car. This in turn is a parasitic drag.

A breakaway front air dam? I have had several of them break away. Including the whole front end of Crumpy's minivan. Does not make for a good day.

I also had a front extended air dam on my 75 Olds Starfire for a while. Looked like a cow catcher but created a wedge shape with downforce and supposedly lowered my CoD factor. But only a little as the car had a reported .33 CoD from the factory.

It ended up on the parking lot just about everytime I drove it so I took it off.

A front air dam wedging from the center at an angle back to just in front of the rear wheels is very effective.What you are trying to create is a mass of air, behind the air dam, that is actually moving in a general way with the car.

This is for onehundredeighty. When we tested air pressure on the Crossie for the infamous "ram Air" experiment, one of the highest pressure points was right in front of the front tires as the air passes under the front air dam of the car. That high pressure point is where my CAI inlet is placed.

I push close to 200 HP at the wheels, so I'm satisfied with the data we got on that trip.

 

For those that have removed the plastic pan under the engine, IMHO you have increased the wind resistance by increasing the turbulence in the engine bay.

 

Agreed totally.

I've said this for years. It's the very reason I leave mine in place. Steve (32Krazy) agrees, as he's tested it both ways, and one way is MUCH more turbulent.

 

And it would decrease your MPG on the highway due to the turbulence drag.

 

G-Ghost, If you pull the fuse on your spoiler motor, a red light flashes on the spoiler button as soon as you pass the speed where it normally goes up. That's to let you know the spoiler isn't working.
But when you get to a speed where most people feel that it's really necessary, (about 95 mph on my car) that's when an audible alarm sounds off to make sure that you know you're well on your way to the "Danger Zone".
My spoiler doesn't go up on its own until I reach about 65 mph. But since I usually cruise with the local traffic, and seldom ever drive over 75 mph, I choose to keep it down. Keeping the spoiler down when I'm on dry pavement at these speeds has never been an issue in the past.
But if I get caught in high winds and or rain, I always raise my spoiler at highway speeds.

 

Thanks for the info but can you tell me how you managed to reprogram the spoilers set deployment speed? never heard of it being done

 

is our .37 Cd with the spoiler up or down?

 

Pretty sure he ran a separate circuit tied to internal toggle switch... Not so much a reprogram.

 

Good Question Tech.

G-Ghost, John is correct. I just installed an on/off switch by tapping into the spoiler motor's fuse (#20 I think). That way I can keep the wing down until I choose when to put it up.
But it still only goes down at speeds around 35 mph....then I simply flip the switch off.
Forum member "AZSUN" installed a foot pedal switch that does the same job. (I was planning on using an old style dimmer switch myself).
But I like the way AZSUN's looks, so when I get tired of my current set up, that's probably the way I'll go.

Legal Disclaimer...perform at your own risk.

 

I don't do a lot of high speed runs, therefore the pans are off the car for good. The roadster has seen 160 with and without the pan...absolutely no difference in handling. I like the quartermile stuff...but, ask yourself this, unless you live in Kansas, Nebraska or Utah...just how long are you going to run 160 plus...I like the engine bay to rid itself of heat, and the pans stay off...with that said, it is very important to sustain high speeds, to control the air flow under the car. Anything hanging down will cause turbulance. The lower the better. The flow under the car is faster, and creates downforce. Take a piece of paper, fold each end by a third making 3 sides. Sit it on end as to make a tunnel. Have a little bit of air blowing down on the top, not enough to collapse it, but just enough to hold it down. Then with your mouth, blow into the tunnel and see what happens.

 

Sounds like something you would say to a Senator in a bathroom in Minnesota

 

LOL!
But you need to be at the airport, otherwise they get offended.

 

A car at speed is an airfoil, the pressure on top of the car is less and the air under it is greater. This lifts the car, you analogy is upside down. So maybe in Australia your principle works.

The air under the car is faster than the air over it. (sorry ... that's not correct)
Race car designers have worked on the under sides of the cars to get a lower pressure under the car than on top, but normally it is the reverse. The Mercedes car ad in a tunnel, if true, would rely on these forces.

 

Dave, you are an aeronautics engineer so I must respect your wisdom here . However, two questions arise.

If lift is created on the top of the rear deck how is the pressure less on the underside? Secondly, we all have seen how a wing creates lift. Does not a car's shape do the same?

Therefore the pressure under the car ought to , by logic, be greater than that going over the car. Hence the need to find aerodynamic ways to create downforce,; ie Wings and spoilers.

Finally, airpressure will almost always be greater under the average shaped car (which the Crossie most certainly is). Therefore will not the pressure wave create a positive air pressure bubble under the Chassis? Unless of course it is diverted to the outside of the wheels and chasis footprint.

 

Franc you flatter me, I could not have spelled aeronautics engineer if you hadn't shown me.
The pressure under the car is greater than the air over the car but it is the same as the ambient air pressure. It's the difference in pressure that gives lift.
I do not understand your first question..... less pressure on the underside?
We get all that dirt on the rear bumper because the air coming from under the car carries the spray from the road and this air rushes up to balance out the lower air pressure coming over the car. Nature abhors an imbalance of pressure.
Deploying the spoiler on the na I think would tend to keep the dirt off the bumper. I'll have to try that experiment.
Oops, I forgot this.
Sorry the air over the car is faster than the air under it, my mistake. Faster equals less pressure. I should proof read my posts better.
I wondered at first why you had high lighted that statement, a senior moment I'm afraid.

 

Your not an Aeronaughty engineer? I guess I'm remembering a booze amplified conversation we had at the Dragon.

Hmmmmmm.

OK so my question was valid in relation to your misspeak.
I feel better now.

I still believe you know more about air flow than most. Including me.

Now,, our feeble experiment with ram air gave me some clues and one of them was the high pressure area just forward of the wheels. The area behind the front air dam is lower pressure creating a downforce relative to ambient air in that area.

Therefore it is logical to assume that extention of a front air dam past the front wheels will cause the following;
A reduction in turbulence under the chassis
A reduction in air pressure under the chassis
A resulting increase in adhesion to the road and at the very least, better fuel economy.

As to Tech9's request, I believe it will also improve his co-efficient of drag ratio.

Lowering the chassis will only improve the beneficial forces.

Separately, I agree about the personality of the air flow at the back of the vehicle. I actually suggested putting a diverting baffle at the diffusers under the car's rear bumper. This would aim the air from under the car (a high pressure bubble) into the low pressure bubble just aft of the Crossie's big butt.

It would also, however, keep the bumper covered in slop from the road.

Sorry Dave for putting such a strain on an old Canadian's brain. Just getting even. No I can't remember for what. But, I'm sure there is a smart quip back there somewhere in our history for which I owe you a quick barb.

I'm just not quick.

roadster with a stick

 

At one point I told you that I had worked for McDonnell Douglas Canada and I had been to St Louis to the plant there in 1969, I also worked for DeHavilland Aircraft in Canada. I never claim to be what I am not though, I find my advantage comes from playing dumb, I'm very good at that. If there was a degree to be had in dumbness I think I would have a PhD.
There was an F1 car that had a fan underneath that evacuated the air, when the engine was revved the car noticeably lowered due to the lower pressure under the car. They said it was to cool the engine and got away with it for a while. The trouble was if it rose of the ground too much at high speed it lost the down force and became dangerous.
You can always rely on gravity though, bit by bit it pulls us all into the grave.

 

Admittedly you never told me what your skills were. Only that you didn't know the dimensions of the front gate in time to be useful. The rest I assumed. My bad.

OK ole man. You are waxing philisophical now.
Isn't it gettin' past your bedtime?

 

I don't recall a F1car with that, but I do remember the '70 Chaparral 8J race car.

 

straight from the book my friend...explain the theory then....do the test, and explain...air passes under car faster than above it...creating a pulling down affect...I was talking air movement, but you are the engineer....and I know the guys here in INDY must not know what they are doing...when I am down at the shop, I will give them that information.... You are talking downforce, and I was talking air movement....the chassis engineers here are finding better ways to increase the speed of the air traveling below the car...and yes, you still have to have the downforce, which you were referring to. But, they feel by increasing the passing of the air under the car, keeping enough downforce to hold it stable, will increase speeds. So, they are looking for better ways to move the air...by streamlining the underneath, and you still need the wings for downforce. So, the experiment, is moving the air under the car faster, will actually pull the car down...as shown by the paper demonstration they showed me... as for pressures, yes, more on top, less on bottom...but their theory seems to be working, and you see an totally different body look with the new racecars...most normal highway cars creat lift, and without spoilers, wings, would have no downforce at high speeds...the topic here was to lower wind restistance...spoilers creat resistance...but moving air more efficiently means less resistance to the point where you were still stable and controllable. There are so many factors when talking cars...are you going straight all the time, or are you racing thru corners too...all would have factors you have to consider when talking downforce and pressure...but, I think these guys here in INDY are on to something...