1000 replies!

Remember man, its about the journey not the destination. This is supposed to be fun, right? How many time's in one's life does one get to a build a bad ass custom race car? Enjoy it. If you feel stressed and rushed and pressed, just take a break. It'll be waiting when you're ready.

Remember man, its about the journey not the destination. This is supposed to be fun, right? How many time's in one's life does one get to a build a bad ass custom race car? Enjoy it. If you feel stressed and rushed and pressed, just take a break. It'll be waiting when you're ready.

Very true, thanks for the inspirational pep talk, much appreciated.

I started getting back into the car, doing wiring, and getting some small details figured out. I might have even found a local turbo guru to give me a hand with some stuff :)

When the project is fun, i enjoy it and almost feel as if i don't want to finish....but other times, I just can't stand the frustration. Comes with the territory.

More wiring to do tonight..

We'll see. I am tempted to just grab a cammed S52...very tempted.

But I'll try the turbo thing first and see how it does. If its a total disaster, i'll get rid of it and drop something NA in.


You can buy my Stickley 3.2 S50 motor :) Just sitting at the shop looking for a buyer!!! This was Chuck's own motor before the S54 in his car now. It has been freshened. Drop that in and go play.

Vince

Lots of nice S50/S52's available...but I'm going to stick with the turbo for now. I want to atleast see how it does.

Very true, thanks for the inspirational pep talk, much appreciated.

I started getting back into the car, doing wiring, and getting some small details figured out. I might have even found a local turbo guru to give me a hand with some stuff :)

When the project is fun, i enjoy it and almost feel as if i don't want to finish....but other times, I just can't stand the frustration. Comes with the territory.

More wiring to do tonight...

Heh, I know exactly the same feeling. Been working on an efi conversion on an older mercedes. Now that the car runs, I'm actually really bored now and sad that the car runs pretty damn well. But the reason it took so long were because of stupid wiring problems. Who would have known Mercedes had 4 volt "ground" points...

Quick updates...just had so much going on, the car is getting put to the side unfortunately.

I'm pulling the motor to check everything, and then it'll go back in and i'll button it up.

About 3 hoses are left to have made, and misc sensor wiring is on its way as well.

I finally decided to bite the bullet, and I went with Motec M800. I came across a fantastic deal I could not pass up, and I think it'll be worth it. Using the Bosch igniters, it'll power the stock coils just fine, and should be a reliable and powerful ignition solution.

AIM MXL Pro05 arrived this week, its still in the box, but I'm hoping to start working on it this Sunday.

Quick updates...just had so much going on, the car is getting put to the side unfortunately.

I'm pulling the motor to check everything, and then it'll go back in and i'll button it up.

About 3 hoses are left to have made, and misc sensor wiring is on its way as well.

I finally decided to bite the bullet, and I went with Motec M800. I came across a fantastic deal I could not pass up, and I think it'll be worth it. Using the Bosch igniters, it'll power the stock coils just fine, and should be a reliable and powerful ignition solution.

AIM MXL Pro05 arrived this week, its still in the box, but I'm hoping to start working on it this Sunday.

Ex-Grand Am ECU?

Baller Status:buttrock

Quit bitching Steve :)

Come on what are we talking about here. Building a E46 racecar with custom turbo engine, seamwelded body, custom cage, Ohlins race shocks etc at the age of 25. Most guys at the age of 25 can barely get a E30 together.

I'm in the same boat, finishing up my E36 which took almost a year longer than I had planned for. But that's what you get when you pay attention to details and try to do everything the proper way. Proper way = fast. But it takes a long time especially if you have to do everything yourself.

Its all good guys, its coming together. Motec is not from grand am... Actually I don't think its even from a car.

Quit bitching Steve :)

Come on what are we talking about here. Building a E46 racecar with custom turbo engine, seamwelded body, custom cage, Ohlins race shocks etc at the age of 25. Most guys at the age of 25 can barely get a E30 together.

I'm in the same boat, finishing up my E36 which took almost a year longer than I had planned for. But that's what you get when you pay attention to details and try to do everything the proper way. Proper way = fast. But it takes a long time especially if you have to do everything yourself.

Yep, i'm extremely privileged to have the opportunity to build such a project...I just wish i was not broke now LOL

I just came in from the city, going to pass out. Should have some good updates for next weekend...please hold :stickoutt

Should have some good updates for next weekend...please hold :stickoutt

anxiously waiting:)

Sorry guys, got a lot going on. Car is physically not changing for a bit as I collect some more parts. Some other things are taking priority, and the car is unfortunately suffering.

Its all good guys, its coming together. Motec is not from grand am... Actually I don't think its even from a car.

Apparently a lot of powerboats run Motec.

I just came in from the city, going to pass out. Should have some good updates for next weekend...please hold :stickoutt

And that folks is why the car isn't done.............

Chris

And that folks is why the car isn't done.............

Chris

Not even close, but good try ;)

That night was my bro's bachelor party, so thats a valid excuse :evil2

I'm running low on E46 cash due to some recent investments I felt were better than the car, and are more important for my future.

I only have two things left to purchase and I'm about done with buying stuff until something breaks lol

Radiator/intercooler is about it. Motec and MXL Pro05 are done, and hopefully will start on the install this week.

Motec was from a two wheeled vehicle...

I also met a chick recently, so thats taking some (ok a lot) of my time as well. Car chick though, rally crosses and everything, good deal.

Thanks for the support everyone, sorry for taking so long, but its part of life, no way around the delays.

I should have just bought an exige cup car and called it a day (maybe for 2010...).

I also met a chick recently, so thats taking some (ok a lot) of my time as well. Car chick though, rally crosses and everything, good deal.

those chicks and kids will really take it out of ya.;)

those chicks and kids will really take it out of ya.;)

Ha, no kids yet... But that's another reason I chose to do the E46 now...I can :)

This is her rallycrossing...

http://photos-b.ak.fbcdn.net/photos-ak-sf2p/v362/249/31/8804361/n8804361_42587225_4528.jpg

Nice, subaru Chicks rock. I should know I married one.

Well you shouldn't spend so much time and effort on the chick now. Turns out they have this incredible memory for romantic and date type things and after you marry them they complain whole heartedly about how you do not do this and that for them like you did when you were dating. :D 13 years and counting and I still can't live up to my dating self. And yes it is a good idea to finish the car now as it is much easier to sell finished running cars as opposed to rolling projects.

Well you shouldn't spend so much time and effort on the chick now. Turns out they have this incredible memory for romantic and date type things and after you marry them they complain whole heartedly about how you do not do this and that for them like you did when you were dating. :D 13 years and counting and I still can't live up to my dating self. And yes it is a good idea to finish the car now as it is much easier to sell finished running cars as opposed to rolling projects.


:lol One of the most depressing things I've ever read.

:lol One of the most depressing things I've ever read.

+1 :stickoutt

:lol One of the most depressing things I've ever read.

+1 :stickoutt

+ another 1:(

This is why, while currently in dating mode, Im setting undeniably low standards so as to not run into any problems in the future ;):redspot

Subsequently I am limited to an E36 chassis though still

I probably won't have many updates for a week, but Motec is on its way, and I might start on AIM mounting this week. I have to finish pulling the motor, slap in a trans shield I forgot, and then double check everything is buttoned up properly.

Hopefully the Rad/IC will arrive shortly, a couple hoses and some tube routing...and I can wrpa up the engine wiring harness and get this thing to the dyno for some tuning.

Lots going on with the biz dev, so the car is slow, but its getting there.

I mostly the spent the last weeks free time getting www.ProItSeries.com live, and it was officially launched before the weekend to show off at the NESCCA Mini Con.

Well you shouldn't spend so much time and effort on the chick now. Turns out they have this incredible memory for romantic and date type things and after you marry them they complain whole heartedly about how you do not do this and that for them like you did when you were dating. :D 13 years and counting and I still can't live up to my dating self. And yes it is a good idea to finish the car now as it is much easier to sell finished running cars as opposed to rolling projects.

Not married yet, currently engaged. But I know for a fact that I won't be able to live up to my dating self. Haven't been able to make it to the track too much these past couple of years, but finally got the courage to finish the track car and got it out this past friday.

Steve - Good job finding a car savvy chick! All the more reason to finish the car sooner rather than later. Trust me, once things get more serious, it'll be hard to hide the fact that you're buying parts for the car rather than for her. Been there, and I'm sure everyone who is married will concur.

Steve - Good job finding a car savvy chick! All the more reason to finish the car sooner rather than later. Trust me, once things get more serious, it'll be hard to hide the fact that you're buying parts for the car rather than for her. Been there, and I'm sure everyone who is married will concur.

Thanks for the advice guys. I'm working on getting her on the roadcourse soon...she's been on autox/drag/rallyx, time for some real fun on the track :)

Anyways, stay in touch, I'll post some updates next week.

... it'll be hard to hide the fact that you're buying parts for the car rather than for her.....

Then the car becomes a 'family racecar', but...

redemption comes when the kids start popping out... so long as they come out saying something to the tune of 'Mommy, can we have a new rollcage please?"... no mommy can resist, truuuust me

Quick update, even though the aero is built, Robert is back from his F1 stint and finished up my aero analysis. Here is a sneak peek (don't mind the diffuser strakes, they are not in the final design):

http://jaffster.com/misc/Misc/jaffsterlift.jpg

Quick update, even though the aero is built, Robert is back from his F1 stint and finished up my aero analysis. Here is a sneak peek (don't mind the diffuser strakes, they are not in the final design):


HAha...your wing is on upside-down. :stickoutt
You need more @ angle on that thing, man!

HAha...your wing is on upside-down. :stickoutt
You need more @ angle on that thing, man!

Upside down? What do you mean?

Also, this is not the profile i ended up using, this was the test profile at lowest AOA. The actual wing is very aggressive. Notice how much it 'flares' up on the trailing egde.

http://jaffster.com/E46M3/8-5-08/main/p8040002.jpg

So, green is low pressure?

Got the front angle?

So, green is low pressure?

That first picture was Lift. Below is the drag (this was with a higher ride height). I did a fully "closed" car for these models to simplify things, obviously its far from reality, but there is a decent amount of useful information we have found out, specifically using the base model as a reference point to the "aero" model.

Of course I am not showing all the pictures/info...can't spill all the beans :stickoutt If anyone is interested in all the results, I'd be happy to sell them at a small cost to help offset the scan/modelling $.

http://jaffster.com/misc/Misc/jaffsterDRAGfront.jpg

Here's the only question I want answered...is the bottom of the rear windshield a high pressure or low pressure region? In other words, does it make sense to place vent holes at the bottom of the rear windshield?

Here's the only question I want answered...is the bottom of the rear windshield a high pressure or low pressure region? In other words, does it make sense to place vent holes at the bottom of the rear windshield?

This is where the model will change if I did an empty cavity inside.

Reality is air is coming in from multiple places, mostly the side windows. This changes the pressure inside and if you had 'vent holes' in the rear lexan, it would change it further.

From the buffeting I've had and seen in these cars, the vent holes do help get rid of some of the pressure buildup in that back seat area where the window comes down (reduce drag essentially).

The bigger things we are looking at are the splitter and rear wing placement and sizing. I will say PTG's last version of the ALMS splitter is something I want :)

With the splitter diffusers in front of the wheels, and the front wheel well extraction vents, the front end drag should be reduced a decent amount. Having a slanted radiator with vents out the hood would help a lot too, but with my intercooler...that's not happening.

Upside down? What do you mean?

Also, this is not the profile i ended up using, this was the test profile at lowest AOA. The actual wing is very aggressive. Notice how much it 'flares' up on the trailing egde.

Based on your first image, your rear wing is flying up (pretty strong) in that configuration. Obviously, it's going to start pushing down as you angle it, I was mainly joking about the result shown in that image.

Trailing edge flare is just one part of the equation, the incidence of your wing's chord is going to be much more critical.

Here's the only question I want answered...is the bottom of the rear windshield a high pressure or low pressure region? In other words, does it make sense to place vent holes at the bottom of the rear windshield?

Low pressure. That area will be low pressure on almost any vehicle. Vent holes make sense, as do vortex generators or trip strips along the top edge of the rear windshield. Aircraft have used active blowers along the trailing edge, feeding high pressure to that area.

It's an optical illusion of the model then, its definitely oriented properly, its just at a very low AOA.

My wing profile is a pretty high df wing, has lots of drag too b/c of the trailing edge, but its ok...i'll have a turbo to overcome much of the drag lol

You can clearly see where the VG's should go on the roof, and this is why I started using them on Watts car back in 2005...when they added the blurb into the rules :stickoutt

I still have to figure out my diffuser and splitter setup...i don't have anything made yet, and don't have enough cash for anything crazy. Plus...they'll prob get beatup, so a simple ABS setup might be the ticket to start.

Based on your first image, your rear wing is flying up (pretty strong) in that configuration. Obviously, it's going to start pushing down as you angle it, I was mainly joking about the result shown in that image.

Trailing edge flare is just one part of the equation, the incidence of your wing's chord is going to be much more critical.



Low pressure. That area will be low pressure on almost any vehicle. Vent holes make sense, as do vortex generators or trip strips along the top edge of the rear windshield. Aircraft have used active blowers along the trailing edge, feeding high pressure to that area.

It's an optical illusion of the model then, its definitely oriented properly, its just at a very low AOA.

Optical illusion how so? Green being low pressure, you have a nice even low pressure spread on top of the wing, indicating that it's lifting upward. Any wing will fly upward at a low enough AOA, it's just a matter of where that point is. As I said before, I'm sure that wing would push downward hard with a bit more angle.

Optical illusion how so? Green being low pressure, you have a nice even low pressure spread on top of the wing, indicating that it's lifting upward. Any wing will fly upward at a low enough AOA, it's just a matter of where that point is. As I said before, I'm sure that wing would push downward hard with a bit more angle.

Reds and yellows (positive CPY's) are lift; greens and blues (negative CPY's) are downforce. Same for drag. Positive = drag, negative = thrust.

Make sense to you now?

So you are generating downforce on the decklid which generally a low pressure area?:eyecrazy Your diffuser must be generating some crazy low pressure area under the car.

Flat bottom car...the rear diffuser in this model was actually hurting performance.

Remember, this was moreso a "theoretical" comparison model/test, as we used a base line model to mimic the oem car, and see what the aero changes did to it.

Its not realistic in that all the openings and pressure drops the car would see, even the flow from side exhaust and open windows...they are all not accounted for.

It was a fun test though, and there were several features of the model that proved to still show some very accurate results. Overall I'm happy with it, and confirmed a couple ideas I had planned, and also helped put together some new ideas..

Reds and yellows (positive CPY's) are lift; greens and blues (negative CPY's) are downforce. Same for drag. Positive = drag, negative = thrust.

Make sense to you now?

Not really.

As SSburns pointed out, the area at the bottom of the rear windshield and the areas behind the wheel should all be low pressure. And the front of the car should be high pressure. All are consistent with your pictures.

Additionally, the CFD legend almost always uses "hot" colors as high pressure and "cool" colors as low pressure.

It isn't unfeasible that your wing is developing upward lift at low AOA, many of them do.

I'm relaying what the aero told me...I'm a meche remember :) There is a reason he's doing the aero not me.

He explained via a couple emails whats going on, and it makes sense.

I've got to close up at work now, I'll post more info later.

all the aero stuff might be cool, i've gotta admit i'd like a cool diffuser and stuff,
but just how much difference is this going to REALLY make in your lap times compared to the basic aero of the average mod level club racer?

I mean, are we talking seconds difference or hundredths of a second difference?

all the aero stuff might be cool, i've gotta admit i'd like a cool diffuser and stuff,
but just how much difference is this going to REALLY make in your lap times compared to the basic aero of the average mod level club racer?

I mean, are we talking seconds difference or hundredths of a second difference?

If we're comparing your basic CM car with a MaShaw ltw adjustable wing, no additional aero, and a basic front splitter....there could easily be a couple seconds on high speed tracks. The difference in lateral grip could be a decent amount in high speed turns. A couple MPH here and there, it adds up.

In RACING, the better driver will still win, regardless :) Much better drivers out there than me, so its all up in the air.

Again...this is more of a fun project car, although it has been simplified drastically from my original plans, b/c i just want to get it out there and race it.

I don't want to build one, but I'd really like to get an E46 ITS car together so I can run the ProIT series. Maybe next year I'll pickup one from Autotechnic.

The confusion is in the lack of legends. These aren't contours of pressure - they're contours of downforce and drag. And the colorbars are just set to what we use here at work. They're pretty standard AFAIK.

Green is not low or high pressure, green is downforce or drag, depending on which image steve is posting. Downforce can come from high pressure on an upward facing surface of the car, or low pressure surface facing downward. What you are really seeing is components of pressure. So maybe the pressure is high but the orientation of the surface means its component in X/Y is low. Does that make more sense?

The reason both the wing and tray are green is because the upper side of the wing produces downforce through high pressure and the underside of the car through low pressure. I think I sent Steve contours of normal pressure if that's more intuitive he can post it. Most CFD software can only do pressure contours but the with good post processing stuff you can calculate whatever you want.

Contours of lift and drag are much more useful - after all, the goal is drag/downforce, not a specific pressure somewhere!

Steve, if you leave the CPX/CPY designation on the plot that should clear up go fast's concerns. Just leave out the legends if you want it all secret.

Guys, these are NOT contours of pressure - they're contours of downforce and drag. And the colorbars are just set to what we use here at work. They're pretty standard AFAIK.

Green is not low or high pressure, green is downforce or drag, depending on which image steve is posting. Downforce can come from high pressure on an upward facing surface of the car, or low pressure surface facing downward. What you are really seeing is COMPONENTS of pressure. So maybe the pressure is high but the orientation of the surface means its component in X/Y is low. Does that make more sense?

The reason both the wing and tray are green is because the upper side of the wing produces downforce through high pressure and the underside of the car through low pressure. I think I sent Steve contours of normal pressure if that's more intuitive he can post it. Most CFD software can only do pressure contours but the with good post processing stuff you can calculate whatever you want.

Contours of lift and drag are much more useful - after all, the goal is drag/downforce, not a specific pressure somewhere!

Steve, if you leave the CPX/CPY designation on the plot that should clear up go fast's concerns. Just leave out the legends if you want it all secret.

I think I understand, but it's still escaping me how there is significant downforce on the base of the backglass and decklid, unless our assumption of this being a low pressure area is incorrect and/or the pressure under that area of the car is just that much less than that on the decklid.

Steve are you going to sheet the interior or run windows? Probably the same gains but way cheaper.

I think I understand, but it's still escaping me how there is significant downforce on the base of the backglass and decklid, unless our assumption of this being a low pressure area is incorrect and/or the pressure under that area of the car is just that much less than that on the decklid.

Many fast sedan style drag cars extend long flat rear decks from the back of the car with little to no rake in them. Helps keep the car stable and the tires planted.

Steve are you going to sheet the interior or run windows? Probably the same gains but way cheaper.


Windows aren't CCA legal, and even partial windows or aero deflectors are in a grey area.

You can run them in GTS. :buttrock

The back of the car itself (trunk, rear windshield) doesnt develop any downforce, only drag. the rear windshield and deck lid are areas of high pressure because 1/4 to 1/2 of the way down the back windshild the air looses its laminar flow and becomes turbulent so the air there is moving slower than the air around it making that an area of high pressure. The rear wing need to be up high enough to get out of this area of turbulance and acts as a reverse airplane wing seperate from any forces (downforce, lift) generated by the car itself. The car itself can generate downforce if air flows faster (low pressure) underneath the car than air over the car(high pressure), this is done by having a flat underside. the rear diffuser slows air leaving the rear of the underbody minimizing the pressure difference of the fast air under the car to the surounding air which minimizes the turbulent wake behind the car and reduces drag. hope this clears up some confusing on some aero effects.

Just a practical approach. But if I wash my car and take it for a drive the waterdrops will be blown off by the wind, except for the rear window, where drops still remain from top to bottom. To me that's a sign that there is no more laminar flow across the whole rear window right?

The back of the car itself (trunk, rear windshield) doesnt develop any downforce, only drag. the rear windshield and deck lid are areas of high pressure because 1/4 to 1/2 of the way down the back windshild the air looses its laminar flow and becomes turbulent so the air there is moving slower than the air around it making that an area of high pressure. The rear wing need to be up high enough to get out of this area of turbulance and acts as a reverse airplane wing seperate from any forces (downforce, lift) generated by the car itself. The car itself can generate downforce if air flows faster (low pressure) underneath the car than air over the car(high pressure), this is done by having a flat underside. the rear diffuser slows air leaving the rear of the underbody minimizing the pressure difference of the fast air under the car to the surounding air which minimizes the turbulent wake behind the car and reduces drag. hope this clears up some confusing on some aero effects.

The area of the back windshield is high pressure, but creates drag :confused The corresponding area on the front windhsield, must be even higher pressure then.

If i remember my fluid dynamics classes accurately:
Turbulent air actually moves faster, but when laminar flow is lost, a boundary layer of relatively stagnant air is created with a relatively higher pressure. If your idea of turbulence creating higher pressure were completely accurate then the area directly behind the car should be generating thrust.

A flat floor (i.e. a straightline) doesn't cause the air to move faster underneath the car. It does however minimize turbulence and formation of a stagnant boundary layer.

Hopefully this clears things up guys. FYI, the color bars are set so that -0.001 is green and 0.001 is yellow. I.e., the colorbars are not linear so that I could separate out the Grey to be from -0.001 to 0.001 - completely neutral regions. So green does not mean "significant" df/drag. It actually means very little, lol. Obviously this depends on the darkness of the green but you get my idea . . . Blue is where the real DF is, and that's the suction side of the wing and the area above the front splitter.


The back of the car itself (trunk, rear windshield) doesnt develop any downforce, only drag. the rear windshield and deck lid are areas of high pressure because 1/4 to 1/2 of the way down the back

The trunk/windshield combo may cause lift/downforce and drag/thrust in different areas. In fact, on the image steve posted you can see there is a transition from one to the other - yellow to green. Consider pressures on parts of a surface, not just the net affect. A rear windscreen may produce lift, but that does not mean the *whole* windscreen produces lift - just that the parts that do outweigh those that don't. Hope that's not a convoluted explanation.

windshild the air looses its laminar flow and becomes turbulent so the air there is moving slower than the air around it making that an area of high pressure.

Flow over a racecar is most likely all turbulent from the front axle on back. I think you are confusing the BL (boundary layer) with flow separation outside the BL. http://en.wikipedia.org/wiki/Boundary_layer FYI, pressure is generally constant throughout a BL, and changing from laminar to turbulent produces almost no real change in pressure.

The rear wing need to be up high enough to get out of this area of turbulance

I think you mean the wing needs to be placed outside the wake.

the rear diffuser slows air leaving the rear of the underbody minimizing the pressure difference of the fast air under the car to the surounding air which minimizes the turbulent wake behind the car and reduces drag. hope this clears up some confusing on some aero effects.

The diffuser brings low pressure back to ambient pressure, ideally without loss in total pressure (inefficiency). It does not the wake behind the car. That wake is a result of the massive separation on the rear of the car. No diffuser can turn flow around a near 90 degree angle.

The area of the back windshield is high pressure, but creates drag :confused

It is both high and low pressure in different areas.

If i remember my fluid dynamics classes accurately:
Turbulent air actually moves faster, but when laminar flow is lost, a boundary layer of relatively stagnant air is created with a relatively higher pressure. If your idea of turbulence creating higher pressure were completely accurate then the area directly behind the car should be generating thrust.

Again, I think we're confusing flow separation with laminar/turbulent transition. Both produce almost no change in pressure . . .

A flat floor (i.e. a straightline) doesn't cause the air to move faster underneath the car. It does however minimize turbulence and formation of a stagnant boundary layer.

This isn't true, and I don't know what you mean by "stagnant boundary layer." A boundary layer is a layer in which flow goes from stagnant (at the wall) to freestream (away from the wall).

Again, I think we're confusing flow separation with laminar/turbulent transition. Both produce almost no change in pressure . . . ).

If I remeber correctly the stall angle of wing is defined by the AOA when the flow begins to seperate from the upper surface (in a lift configuration). If this the case and your statement above is correct, why do you lose lift when you get seperation? Isn't this also the premise of a gurney flap, to prevent seperation and increase lift/downforce?



This isn't true, and I don't know what you mean by "stagnant boundary layer." A boundary layer is a layer in which flow goes from stagnant (at the wall) to freestream (away from the wall).

OK maybe it is a matter of degrees. The more seperation you have the thicker the boundary layer so the greater amount of air moving at a velocity below that of the freestream.

I believe that my point is still valid that a flat floor by itself doesn't increase downforce by increasing the overall velocity of air flowing under the car. You'd need a convex shape to effectively increase the velocity. Otherwise airplane wings would be flat on top.:) It may however decrease turbulence and/or seperation.

Still seems strange that the base of the rear window is an area downforce when it is typicilly thought of as an area of low pressure, be we haven't yet confirmed this.

If this the case and your statement above is correct, why do you lose lift when you get seperation?

Once a flow separates, usually the pressure at the separation point is the pressure at all locations behind it. That's where the lift losses come from. That and the total pressure loss from the stall affects the back pressure behind the wing and changes the flow coming onto it. That can have a big different on pressure over the wing. But at the actual point where separation occurs, the pressure change is often zero or something very close. Same for BL transition. This is why I find contours of Cp less helpful.

I believe that my point is still valid that a flat floor by itself doesn't increase downforce by increasing the overall velocity of air flowing under the car. You'd need a convex shape to effectively increase the velocity. Otherwise airplane wings would be flat on top.:) It may however decrease turbulence and/or seperation.

A flat tray with a thickness (who builds infinitely thin ones, right? :stickoutt) will always produce downforce in ground effect. If you round the lower leading edge of that flat floor it will produce more, and if you round the flat floor itself properly it will produce a much more. If you hover a brick over the floor in the wind tunnel, the brick will make downforce.

Now if what you're really getting at is that the flat floor itself doesn't accelerate the flow, you're right. But then even with a curved floor the real driving forces are the suction at the rear of the car and high pressure at the front of it.

Still seems strange that the base of the rear window is an area downforce when it is typicilly thought of as an area of low pressure.

It can very often be an area of downforce. Granted whatever (very) small DF it generates is ultimately washed out by the suction at the roof/window intersection. But its local DF nonetheless. I've never considered it to always be a low pressure region. I have heard say that the entire rear window generates lift, and that is usually true. But I think most people's conception of a decklid always producing lift comes, IMO, more from popularity than results.

Once a flow separates, usually the pressure at the separation point is the pressure at all locations behind it. That's where the lift losses come from. That and the total pressure loss from the stall affects the back pressure behind the wing and changes the flow coming onto it. That can have a big different on pressure over the wing. But at the actual point where separation occurs, the pressure change is often zero or something very close. Same for BL transition. This is why I find contours of Cp less helpful.



A flat tray with a thickness (who builds infinitely thin ones, right? :stickoutt) will always produce downforce in ground effect. If you round the lower leading edge of that flat floor it will produce more, and if you round the flat floor itself properly it will produce a much more. If you hover a brick over the floor in the wind tunnel, the brick will make downforce.

Now if what you're really getting at is that the flat floor itself doesn't accelerate the flow, you're right. But then even with a curved floor the real driving forces are the suction at the rear of the car and high pressure at the front of it.



It can very often be an area of downforce. Granted whatever (very) small DF it generates is ultimately washed out by the suction at the roof/window intersection. But its local DF nonetheless. I've never considered it to always be a low pressure region. I have heard say that the entire rear window generates lift, and that is usually true. But I think most people's conception of a decklid always producing lift comes, IMO, more from popularity than results.

Great explaination!

In the case of the brick in the wind tunnel can you explain the " ground effect" that produces a lower pressure on the bottom side of the brick? I assume that the magnitude is highly dependant upon the ground clearance?

Rarcecar Engineering mag. http://www.racecar-engineering.com/search.html?q=aerodynamics

Lots of aero articles. May not apply, but good reading none the less.

Rarcecar Engineering mag. http://www.racecar-engineering.com/search.html?q=aerodynamics

Lots of aero articles. May not apply, but good reading none the less.

I know someone who contributes to that magazine, (1-2 articles per issue) good recommendation.

I've consulted with Mcbeath on several projects, nice guy, and has some good basic wind tunnell access and gets some good documentation. He does a lot of very basic testing that shows immediate "real life" results.

Great explaination!

I forgot that the brick needs a diffuser (as does any underbody), else you're wasting the pressure differential you have on separating the underbody flow.

In the case of the brick in the wind tunnel can you explain the " ground effect" that produces a lower pressure on the bottom side of the brick? I assume that the magnitude is highly dependant upon the ground clearance?

Think of the lower side as have greater compression because of the proximity of the ground. And yes, the closer it is the ground the stronger the effect, up to a point.

Think of the lower side as have greater compression because of the proximity of the ground. And yes, the closer it is the ground the stronger the effect, up to a point.

"Greater compression" as in raising the pressure, or more compression as in more air through a smaller cross-section increases velocity.

Until you go into braking and your front end hits the ground closing off all air flow and affecting suspension compression :)

This build is just plain sick. Great job

Danke.

Engine was pulled and put back in tonight for some finishing touches.

I'm going to be installing the M800, Aimsport MXL Pro05, and 5000 other misc crap to make the engine make some noise.

New business (and new girl...) are taking up my E46 time, but it's getting there...stock market isn't helping though.

Check out one of the things i've been busy with at work though, www.proitseries.com I should have built an E46 ITS car for this series (hint hint 2009)

Steve,

Just as I asked the guy from "TeamDI," or whatever they are, who announced this series, but failed to answer any questions about it, what makes ProIT any different than the existing IT classes that are run by SCCA on a regional level?

Steve,

Just as I asked the guy from "TeamDI," or whatever they are, who announced this series, but failed to answer any questions about it, what makes ProIT any different than the existing IT classes that are run by SCCA on a regional level?

Jon,

Unless I am mistaken, your question was answered = here:

http://forums.bimmerforums.com/forum/showpost.php?p=14650773&postcount=3

And here http://forums.bimmerforums.com/forum/showpost.php?p=14650778&postcount=4

Let me know if those answers were not enough information to satisfy your inquiry.

Update on the build: Engine is back in the car, I just need to bolt up the trans tunnel mount and hook everything back up and start buttoning it all back up again.

Jon,

Unless I am mistaken, your question was answered = here:

http://forums.bimmerforums.com/forum/showpost.php?p=14650773&postcount=3

And here http://forums.bimmerforums.com/forum/showpost.php?p=14650778&postcount=4

Let me know if those answers were not enough information to satisfy your inquiry.

Update on the build: Engine is back in the car, I just need to bolt up the trans tunnel mount and hook everything back up and start buttoning it all back up again.

Yeah, not really, hence my asking again.
But really not a big deal.

Danke.

Check out one of the things i've been busy with at work though, www.proitseries.com (http://www.proitseries.com) I should have built an E46 ITS car for this series (hint hint 2009)

If you decide to build one call me if you have any questions.

Rob

Auto Technic
860.350-8407

If you decide to build one call me if you have any questions.

Rob

Auto Technic
860.350-8407

If you have any E46's for sale, let me know :)

question for the aero experts......what's your opinion of the effect of a roof spoiler at the rear roofline? these seem to be popular with the show-n-shine crowd, but do they really make a difference from a performance standpoint?