LS1Z28-00

iTrader: (8)

yes at very high speeds ram air will actually produce some amount of boost. it is very low, which i guess is why he used kpa or w/e as a mesasurement. they say at 100+ mph you get 1 hp for every 100 hp your motor makes. so a 400 hp car will get approx 4 hp from ram air at over 100 mph. not really worth it if you ask me bc alot of times you wont be over 100 mph. but every bit helps i guess especially if you have a 4k hp dragster at 300MPH ??

Patrick G

iTrader: (14)

Yes Marcin. On the dyno, our vehicles would drop from 100KPa to 97KPa at high rpm at WOT. In a 1/4 mile race, we'd see our KPa drop down to 97 at WOT too. But over 150 mph in the standing mile, my WS6 was over 100KPa (a gain of 3 KPa) and my friend's Z28 was at 102 KPa at WOT (a gain of 5 KPa). The increase in pressure was a result of having the intake tract sealed to a good air inlet in a high pressure area. At 180mph, I'm sure it was worth a few free ponies.

wabmorgan

=



in more ways than one. It also weighs as much as 2 tons of bricks!!!!!

briannutter

I wouldn't be so worried about the bricklike appearance of the front. It will depend on how much of it is open to radiators more than anything. Most of aero-badness happens at the rear of the car. If they've got the angles of the rear fenders and trunk correct along with a sharp edge at the rear face, it will do better than appears. Also, they can put panels under the car to keep the air flowing smoothly underneath. We won't know CD just by looking at it and the final number may suprise us.

stevegrizzle

True, if the under car aero is at all better than the current fbody :puke: then it could definately make up some ground there.

wabmorgan

True... but it LOOKS like it has a LOT of OPEN space in that front end.

Off hand... it doesn't look like areo was a top priority in their design... looks like retro was.

briannutter

That's why I'll be buying one

wabmorgan

That's WHY I won't be buy one!!!! I HATE RETROS

briannutter

4g's are ok, but I had my '67 RS stolen out of the Wiseco parking lot back in 2001. Professional job. This is the Phoenix.

DrkPhynx

No..... This is the Phoenix ->

DrkPhynx

Actually.... the F-Body has always been pretty good. Especially the Pontiacs. (though the 4th Gen LS1 WS6s are a different matter)

During the 2nd Gen, the F-Body aerodynamics smoked the C3. I love how C3s look, but aerodynamically they are pretty foul. The Trans Am was not only clean, it was functional (surprisingly functional splitter and spoiler, plus little winglets to keep the flow out of the wheel wells, and the engine bay evacuators (to keep the pressure under the hood down), and in the case of the Formula, scoops front and center where they would do the most good.

That trend continued in the 3rd Gen. That's why Gale Banks used a GTA to set records at Bonneville with. All he did was add safety equipment, change the wheels, and replace the engine (and lower it a bit). But as he says it "everything that makes this car a Trans Am is still here". He went nearly 300mph with it.

The LT1 4th Gens were pretty good too. The LS1s seem a bit less-so, but the Cd is still something like .32, which is really good. Not as good as the '84 T/As .299 with factory aero wheels, but still pretty good.

DrkPhynx

For a catfish, the front breather conversion would be better, but on a Trans Am (or Firebird), the plate cover you mention is not that big. And it's also at the tip of a very rounded point-like surface. It won't really build up that much pressure (or as a result, scoop that much air).

Don't get me wrong, it would work, and work well, but... just get a WS6 hood and airbox (if you don't already have one), debaffle the hood, and cut openings so that the lower 2 holes can also be used, and seal it to flow right into the airbox.

To get down to the plate cover, you'd need too much crazy ducting and cutting, and the difference in size and location isn't really going to make much difference in terms of flow, and certainly isn't enough to justify the work.

Elcaballoloco

iTrader: (3)

Thanks for the info! Some good info there. Do you have test results to show that the front plate cover wouldn't be that great of a spot?

I was looking at the CFD images that were brought up earlier in this thread and haven't been able to find anything with our cars.


Ok, new question of 4th gen aerodynamics...were is the optimum place to let the exhaust out? I run my Hookers with bullets dumped right about even with the middle of each front seat.

Urban Legend

iTrader: (5)

Damn. So what do you think then of the Ford Lightnings?

DrkPhynx

Look at the location of the "4 holes" on a WS6 LS1, and compare that (and their overall size) to the front license plate cover. They are practically in the same spot, and practically the same size.

Add to that the fact that the nose is so sharp top to bottom, and so rounded on either side, you can see how air would rather go around than stagnate. (think of it like electricity almost, always looking for the path of least resistance)

The biggest issue though is that the stock airbox is inline with both the intake manifold, and the hood (and bumper) openings. That gives a straight shot, right into the intake, from the outside air.

Air does not like to turn corners. Corners in any sort of air piping, be it N/A intake, turbo intercooler, or exhaust, should be as gradual, and smooth as possible. Kinks/bends/corners will just cause turbulence and slow down flow.

That means that by trying to draw from the plate area you're adding bends (and tight ones), which diminishes any added effect the location might have, which would be negligible in the first place. Then factor in all the work it would take to make it happen, and you see how it's not worth it.

As for exhaust, if you have an undertray, then dumping straight to the tray, aimed rearward, would help to accelerate underbody airflow and if the rear diffuser was made correctly, could help reduce drag and increase downforce (really reducing lift, but n/m). However, without such a well designed undertray, the stock location is the best, as someone had mentioned earlier.

The flow behind the bumper is very turbulent, and lower pressure than what's above it. Pumping the exhaust out there helps. Not much, but then, it won'd REALLY make much difference no matter WHERE you put it. This is why race teams don't worry so much. They put it where it's most convenient for ducting, exhaust flow, and weight.

For that nth, nearly unmeasurable degree of benefit, from an aero perspective, the best place would be the underbody tray I mentioned, or stock, or.... in place of the reverse lights.

However, the "best" location is actually a factor of your applicaiton - how much ground clearance do you have, how much noise are you allowed to make, do rules specifiy any sort of exhaust parameters, etc. You're just fine where you are.

Darksolder

I found it funny when looking at my sis's car (Opel Calibra 2.0 8v) that it is pretty damn slick with the drag

From wiki too bad GM couldnt help the american side of their family out like that

DrkPhynx

Don't lament too much. The Insight was the Honda egg that was supposed to be, at once, super fuel efficient and futuristic looking. Aero dictated the design of that thing.

.34/.35 is actually pretty good. It's also better than the Countach - certainly in effective use of air, but IIRC, in Cd as well. (which goes to show you that looks are not a good indication of much)

Also, wings and spoilers create drag. So do wide tires. And intakes. Put on super skinny tires, and strip the wing/spoiler and intakes and you'll see that number go down.

Back in 1984, GM was rather proud of their .32 (and .299 with the right wheels), and for good reason. So don't feel bad about what you have now.

http://www.thirdgen.org/newdesign/br...4transamcd.jpg
^^ Magazine ad from back in the day, too large to post as anything other than a link.

briannutter

I think I agree with this, but it's a tricky area. Behind the reverse lights is a wake. Where there is turbulance, there is higher pressure *usually*. At the same time, being sucked into the wake of a semi truck says there IS a low pressure area there. You would help aerodynamics of the car by filling this void with exhaust volume *I think*. Here's a bit of contrary evidence though:

When we tested in the tunnel, we found the wake at the back of the car actually pumped UP the pressure underneath the car (creating lift) when it was equipped with a cowcatcher airdamn, blocked grill, and side dams. It actaully had LESS lift when we took the side dams off. I was completely baffled by this when I saw it, but it's fact for that particular car model due to the short deck and sedan top. The effect wouldn't be as pronounced on a fastback. but it does make you think twice about applying "common" sense. I found out that you really can't assume anything with aerodynamics...testing in the A2 windtunnel gave us results we never would have expected. In our case, the use of a Pro Stock drag style spoiler extension moved the wake backwards off the car..which kept the wake from pumping positive pressure underneath...which put the sidedams back to a positive use.

I need to build a manometer. Maybe I'll do a test with a megaphone style exhaust while I'm at it

Also, I wasn't going to mention my experiment, but since we're on the subject..... I removed the radiator from the front of my c4 so I could completely seal up the front end. I'm in the process of putting two small Griffens rads (w/ electric fans) and ducts exiting on either side of the rear licence plate. The easiest way to explain my car is: it's now a convertible with naca ducts on the trunk surface (for no drag) leading to down to the radiators front face. In theory, the ducts will force air into the wake behind the car. This should lower drag AND lift. I'll know when I put it in the tunnel to see how effective it is.

DrkPhynx

Any time you move air, you create drag. "NACA ducts" are not drag free for this very reason. You have induced drag, just like you get from wings. It may reduce parasitic drag, and could be seen as splitting hairs, but there is still drag, and it's proportionate to the amount of air being moved. (this is why heavier planes require more thrust to attain a given speed - Something most notable in the Bf-109, as newer engines, armor, and armament added weight, and didn't always increase parastitic drag, but top speeds never quite matched what the added power would suggest) - I'm not going to get into the nitty gritty of wing-loading and power loading here though, it's not germane.

Lift is created 3 ways.
- Newtonian : where the pressure of the air on the undersurface of something causes the object to move with the direction of the pressure. This is a minimal component of lift (on a wing at least)
- Bernoulli : where the speed of the flow over the top of a wing is faster than that of the flow underneath, this speed difference causes a pressure difference and forces the wing up. This too is minimal. Many people, even pilots, swear up and down that this is the source of lift, but this idea would make symmetrical wings (like on aerobatic planes) impossible, as well as inverted flight, and require monsterous impossible wing designs.
- Coanda Effect : Fluids will follow a surface. Take a round glass and just touch it to a small stream from the faucet, watch how the flow follows the curve of the glass. That's the Coanda Effect - on a wing, the boundry layer follows the top of the wing, this pulling of the air down and back, results in that air pulling air above it, down and back with it. This mass movement results in the wing pulling itself up into the air. (meaning lift comes from the top of the wing, not the bottom, but it's not Bernoulli governing it)

Why mention that? because that's more or less what you're trying to do with your NACA ducts and rear radiators. Depending on the speeds you travel and other devices such as spoilers, wings, etc, you may counter act this, but you'll have to do a lot of testing to ensure that you are.

However, you're right that you will help fill the lowe pressure zone behind the car.

Something else to consider about flow under a car (just because we're on the general topic) - if you look at most car's profiles, they look a lot like a wing from the windshield back. This results in lift. This is exacerbated by air getting underneath and getting trapped in the undercarriage, magnifying the lift via Newton. Essentially, that wing-like shape would be in "ground effect", which in aeronautical terms, is generally within the height of 1 wingspan of the ground, where the airflow is changed and drag is diminished and lift is enhanced. This is why you want to do 1 of 2 things on a car - either pull the air up at the back, making a more uniform tear-drop effect, eliminating lift, or, keep air out entirely to reduce pressure and not only eliminate Newtonian lift, but also cause air pressure to try to keep the car on the ground. (plus doing it with a splitter on the front creates front downforce)

Brain, I'd like to hear more about your windtunnel testing and experimetns and projects.

briannutter

Something else to consider about flow under a car (just because we're on the general topic) - if you look at most car's profiles, they look a lot like a wing from the windshield back. This results in lift. This is exacerbated by air getting underneath and getting trapped in the undercarriage, magnifying the lift via Newton. Essentially, that wing-like shape would be in "ground effect", which in aeronautical terms, is generally within the height of 1 wingspan of the ground, where the airflow is changed and drag is diminished and lift is enhanced. This is why you want to do 1 of 2 things on a car - either pull the air up at the back, making a more uniform tear-drop effect, eliminating lift, or, keep air out entirely to reduce pressure and not only eliminate Newtonian lift, but also cause air pressure to try to keep the car on the ground. (plus doing it with a splitter on the front creates front downforce)

Brain, I'd like to hear more about your windtunnel testing and experimetns and projects. [/QUOTE]

Ok, well you're exactly right about the top of the car. As I explained before is my car is "like" a convertible...that's not exactly the case. What I actually did was chop the top off my corvette. A pillar, b pillar, all glass. The resulting "hole" that's left over is being sheeted over by aluminum. think Lakester. The only thing sticking above door sill level is my rollcage and my head. I figured this was a quick way to get rid of 6 square feed of frontal area out of roughly 20. What I'm left with in terms of drag from the upper surface of the car is the wake behind my seat (and a little off the rollcage). To re-attach the air, I plan on using the rad fans to suck the air down in the area a couple feet behind my seat. pulling the core out of the wake so-to-speak. this should get air re-attached by the time it hits the rear deck of the car.

As for the front. I'm a bit undecided. I can go with a Nascar-esque nose (prior to the cot)...but I like the looks of my car to much. There are a couple aftermarket one-piece front ends that incorporate the airdam with a minimal grill opening. I *could* use this opening to build a venturi tunnel under the car, but I'm concerned with weight of the sheet and it will turn out like crap because I'm not building a car from scratch. For now, I expect to seal up the opening entirely (except for the naca ducts I've put where the headlights used to be that go to the brake ducts) and use a conventional splitter. The underside in the back is a bit easier to streamline and I'll be creating a "floor" and diffuser back there to keep airspeed up. My expectations are to get cd into the low 20's, reduce frontal area 20% and get the weight down to about 2700 lbs.