i think soem of you guys are getting too hocked up on cd! its not the only thing to think about when thinking about this!

i know its not critical on a raod car down downforce will make a much quicker car around a ciurcit than mearly reducing Cd!

Chris.

 

Think about this a little.

The idea behind announcing your vehicle's Cd is to market it. To impress the layman with how good your design is. Clearly they will do whatever they can to maximize that number.

Yes, they did that in '84. And your point is........? You see, they did that in 2002, and with the C6 and, with every vehicle they test.

This means (as previously stated), an essentially level playing field. It's not the actual numbers that matter so much as the relationships *between* them. And the bottom line is that the '84 Trans Am, and the C6 are more or less equivalent in terms of Cd, while the LS1 era Trans Am is slightly worse.

This is in *spite* of the severe rake of the windshield on the 4th Gen, and the more vertical windshields on the '84 and C6.

You continue to claim that the LS1 era F-Bodies are the best thing ever because of their windshield, when the simple fact of the matter is, that is absolutely not true. There are so many more important areas, including the nose of the vehicle, and especially the tail. Both of which are far better on the '84.

This shows that the windshield angle has *relatively* little effect overall. Just like I said before.

 

As for windsheld rake... it is a very important factor to Cd.

As one other poster points out, there have been several models of these cars and the only way to really gauge the effecct of windsheild rake would to be keep everything else the same. Model for model. The only way to do that would be in a design lab. That way you are comparing apples to apples.(Of slightly flatter apples in this casee.)

Bty, the .338 number being quoted is actually for the Camaro. The Firebird/ Trans Am had slightly better numbers due to the pop up headlight. Hence, the model to model differances and how the front air dam, rear spolier and even wheels and tires effect Cd numbers.

Actully the C6 may be a good example. The C6 is sort of a reskin of the C5. The over-all body profile is the same including the windshield rake. Yet the C6 has better Cd. Even things as simple as elimating the door handles count. But again if they were to have added more windsheild rake it would have helped Cd numbers.

If you really want to the best areo shape thus far.... belive it or not.... go back to the Ford(cough) Probe V proto-type at .13 Cd.

 

What's you're background wabmorgan? It seems as though you have no actual knowledge of anything to do with aerodynamics and you're just mixing haphazard guesses with incorrectly applied pseudosciences to come to some conclusion.

 

The Ford Probe you reference had a big advantage in rear end shape over the Corvette. (or F-bodies)

If you noticed, I've been referring almost exclusively to the Trans Am in the F-Body realm.

The 4th Gen is basically a reskinned 3rd Gen, with much stronger internals. Dimensionally, they are roughly the same.

And yet, in spite of that, the 4th Gen is worse. And in spite of the increased rake on the front glass, the roof is still higher on the 4th Gen. (And that point is key)

This is the issue - *all else being equal*, increasing the rake might help, but ONLY if the top of roof can get lower. If it remains the same height, or get's raised, any benefit you might have seen is instantly tossed out.

But the thing is, you've been fixating on both Cd and on the windshield. Your claim is that the 4th Gen is better than anyone else claims, and it's specifically because of that one aspect. And.....that is incorrect. There's no other way to put it.

Beyond that, you also seem to be confusing Coefficient of Drag with actual Drag. This is also incorrect. They have a relationship, but one is not equal to the other, and it's quite possible to decrease one while increasing the other, or vice versa.

Drag is Cd * flatplate area * .5r(V2) [where r is air density and V is velocity]

Which has more drag, a brick or a 747? The 747 has a lower Cd, but it's moving much more air out of the way. So Cd is really an irrelevant measurement - other than in marketing where it can convince people who don't know that much about these things.

The more you angle the windshield, the larger it has to be. And therefore, the greater the flatplate area, which can actually *add* drag.

The problem is, it's not intuitive. I know where you are coming from, it *seems* to just make sense that angling it further back is better, but seriously, and truthfully, the angle of the windshield is NOT all that important to the overall aerodynamic cleanliness of the car.

Remember that the "teardrop" shape is the most aerodynamic. It's got a fairly bulbous front end without very much rake.

 

The windshield on the 4th gen is not taller... it is simply pulled foward from the bottom to the frount. They are the same height. As you stat the 4th is a re-skin of the third.

The whole idea is in getting the air over the car. The smoother the transistion from low frount end to the rear the better c/d is.

As for you comparison for a brink vs a 747 is a good one but the airplane is much larger than the brick so the compairision is unfair. Now compare the airplane to a building of equal size and of couse the air plane would win on the Cd.

That same brick you referanced would also beat your car in Cd factor due to the size differance.

The .338 Cd for the Camaro is nearly the same as the .34 Cd for the non-Aero 84 T/A. Yet the 4th gen car has wider tires and wheels.

 

He's not insulting, he's just asking a question. And a fair one to ask, all things considered.

 

Where did you get .338 from? I've never seen anything lower than .34 for 4th Gen, and it's not clear even then which one it's referring to.

You've stated that the 4th Trans Am is better than the camaro. Again, you're apparently basing this on intuition. The wing on the Trans Am is much more effective, and that means more drag. The headlight covers are also poorly fitted and allow a lot of air to go underneath. And with the WS6 hood, it's even worse still. The base model camaro/Z28 is about the cleanest of the LS1 4th Gens.

You also state .34 for the '84. Again, this is not true. The tested results are .32. And the only difference between the .32 and .299 are the wheels.

Someone else here has pointed out that the roof height of the 4th Gens is higher than that of the 3rd. I never measured my stock '84 or '88 GTA, and sadly don't have them anymore.

The 4th Gens (Pontiacs) have an awesome hourglass figure that looks mean as hell and allows for wider rims. However, this is bad for drag. (the camaros otherwise boring nature plays into an advantage here, as it's decidedly more flat sided) The 3rd Gens however are much more cyndrilical in shape. In '84 there was also a much less effective (though still functional) wing, and a more smoothly shaped and tapered rear end.

If you angle a windshield back more and don't lower the height of the roof, all you are doing is adding flatplate area and increasing drag. I think this is the stumbling point for you. Angle is not a means of measuring efficiency, and this stuff is not always intuitive.

I could point out other examples where flat fronted objects are actually cleaner than pointed objects of roughly the same size, but I really get the feeling you will never let this one go and I won't be able to convince you. All I can recommend is that you start taking the time to actually study this stuff. You'll find things aren't quite what you think.

 

Moving the base forward has always been the big problem with the 'vette. To put it up where it really belongs (like the Corvette Indy) would leave no room for the engine. The 'vette, like many sports cars, is more slippery backwards.

Fortunately, on the C6, GM realized that downforce is just as important as low drag. The C5 at 198mph is far more unstable than a new Z06.

 

backwards... I could see this being true for some cars... espically like maybe an old 70ish Bonneville where the rear window lays fairly flat and the frount end of the car is like a brick anyway. But who cares... the car weighed two tons anyway!!!!!!!!!!!!

But not the current Vette nor F-body.

The Corrvette Indy is a good example though.

 

Well since we're on the topic of aerodynamics, here's a question for you guys.

I'm thinking of opening up the whole front of the nose (behind a billet grill) so air will have a direct shot at the radiator and I can dump the pesky air damn under the car. Here's the deal, will the engine bay "pressurize" and slow the car down any by doing this? I've heard that it can but would it really affect a car that's only trapping 145mph?

 

It's just amazing. I love when people who don't understand something at all proceed to tell me things like that. Especially when I've tried time and again to politely explain it to them.

 

You're talking about a Front Breather conversion. The camaro guys at frrax.com are into that.

Whether you take it from the front, or from the underside, it's still going through the radiator and into the engine compartment. A centrally mounted opening with a wicker bill, something like the Evo hood (but not as far forward as that) would be about ideal - from a practical standpoint.

To go all out you could try something like the C5-R setup or those triple ugly racing camaros people have posted here. Same idea just done slightly differently.

An advantage of the front breather is that you can get down real low and seal up the underside of the car.

But when you say "trapping", you're into drag racing and that's not my thing at all. As long as you aren't in the air and that point, I'd think it would be ok. The lift you'd have shouldn't be so significant to affect the amount of control you need on a strip. Open Road Racing would be a different story though.

 

Guys I think one of the things here that has been lightly brushed on but not fully discussed is how the rear of the car or object affects air flow. As previously stated, the shape with the lowest cd. is a teardrop. The biggest reason for this is how this shape affects the air flow . Or to put it better, doesn't affect it. One fact that everyone here knows is that drafting in Nascar can actually push the front car faster. Did the car in the front lose frontal area? No. Did it suddenly have more rake in the windshield? No. The reason it gains speed is that the turbulence at the rear of the car is reduced. Look any object designed for truly high speeds, airplanes, bonnevile flat racers, etc. They all have one thing in common; a TAPERED rear. It has some effect at almost any speed, look at the shape of a bicycle racers helmet. It comes to a taper in the back also. by looking at it like this I could believe that the F-body and the Corvette COULD be more aerodynamic going backwards. The point was brought up about how much turbulence is .produced at the base of a windshield. think about how much is at the rear of a car. just my .02

 

See? lol

You do have an opinion, yes. But I'm telling you known, established fact. But you can't wrap your head around it and have the gall to tell me I don't know what I'm talking about.

 

Get ready for it. Hope your wall is soft and padded. lol

You'll now here about how it's impossible for any car to ever be cleaner backwards. In fact, I'm waiting to hear about how a teardrop is only clean when going point first.

 

No, I can see where that is true for some cars. Like car with a flatish rear window and a frount end with the profile of a brick.

As for the tear drop... what you didn't already know that... boy no wonder you are confused

On a more serious note, a tear drop may be the best shape, but that would be hard to engineer a car around.... unless you put the engine in the rear like the Buick Wild Cat or Indy Corvette. If you want to maintain that tear drop shape, you would have to have a windshield that was like 1/4 of a bubble and ran down to meet the nose in the middle. Point is, to keep that tear drop, the windshield could never rise about the apex of the curve of the tear drop.

 

Yes... As a car rushes through the air it creates an air pressure bubble in front and a vacuum behind it. When the second car drafts the first part of that vacuum is filled by the second car. The car in front then loses some of the rear drag. The second car still has a vacuum at its rear, but now has less air resistance in front. The two cars together can actually go faster than one by itself.

So... I guess one solution would be to have someone draft you all the time.

Maybe Not.

But maybe a rear end addtion could be fashioned to make the rear more areodynamic.... but do you want the rear of you car to come to a conical shaped spite point?????

 

You guys are touching on a lot of good points--even when you don't agree. But I'll fill in some of the gaps in the discussion to this point:

1. The hourglass of the Firebird does have more drag than the simple camaro shape, but only a little more. It is offset some by the more rounded nose, but not 100% due to some quirks in airflow around the lights--as was sorta mentioned. Still, it's not bad.

2. The biggest drag difference between f-bodies is caused by the mirrors. If you take the mirrors off the Firebird, it's nearly the same Cd as the Camaro. (From an aero standpoint--the Firebird mirrors are horrible!)

3. The primary advantages of a front breather is that it lets you smooth out airflow under the car. That's very critical at 170mph+, which many of the guys at FFRAX see sometimes. If done right, it can also reduce front end lift. If done wrong, it can massively build pressure under the hood and actually make things worse.

4. As for cars being more slippery backwards, that's a deep discussion and the references to teardrops are good. The Corvette is WAY better backwards. The Firebird would be except for the wing and the hourglass shape. The Camaro is about the same both ways. (The reason F-bodies are worse, in general, than the 'vette backwards, is that their back end sits so much higher in the wind tunnel and the under body is more exposed.)

5. Air exiting the car is critical. That's why all the high speed guys have diffusers on the rear. But like the conversion to a front-breather, it can be disastrous if done poorly. (Think drag chute, lol.)

6. Lowering has a big impact on Cd also, as does tire size. The aero numbers for all GM cars are based on the smallest factory tires. But hey, who wants those skinny little things?

7. One big advantage the Firebird has over the other cars mentioned is in downforce. While nearly meaningless at the strip, it's one of things that makes the 'bird a favorite of IROC and ORR. That big rounded hood and wing actually do work--but only significantly over 150mph. The Camaro wing is worthless.

I think you guys are figuring out the difficulties of making an appealing and functional car that is slippery. It's all about compromise.

 

[/QUOTE]But maybe a rear end addtion could be fashioned to make the rear more areodynamic.... but do you want the rear of you car to come to a conical shaped spite point?????[/QUOTE]
It depends on what I wanted to use the car for. If I was trying to break some sort of speed record, you bet your *** I would I would want the rear to come to a point.Think about it, the percentage of 6-cyl cars sold bears this fact out. Besides looks what are the reasons these cars went out the door? You could get a a whole lot more car for a whole lot less money. Cd is a great selling point to some, about 20 %. The rest of the public could care less. The cd. could be 45.7 and most of the public could care less as long as it looks good.