Make a fastback style engine lid? (Part 2) - MR2 Owners Club Message Board
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post #1 of 36 (permalink) Old March 2nd, 2010, 18:32 Thread Starter
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Make a fastback style engine lid? (Part 2)

CONTINUED from here: https://www.mr2oc.com/showthread.php?t=378507

Just because I really liked this thread and wanted to answer this question:

Quote:
Originally Posted by nyprime
I know everyone brings up the point of how these are going against the natural flow of air, but if that's the case then why are there so many other mid engine cars that do have fastback style backs? NSX for example, wouldn't they all be going against the normal flow of air? I'm sure there's better reasoning than that.
Quote:
Originally Posted by Levi
I don't think anyone has said that
I said that it goes against the MR2's natural flow of air.

This example of from Dan:



Taking a look at the NSX, I believe this cars vents the engine through the side vents and out the rear of the car. In the above picture that would be the area above the diffuser and below the license plate/bumper. So in this case, a scoop doesn't hurt anything because it's not going against the natural flow of air for the car. The air is already being directed out the rear, the fastback scoop is just adding more of it.

However on an MR2 the air naturally vents out the engine lid (the reason for the slots). When we close that and add a scope to it, we now have two forces of air (one from the bottom, and one from the top colliding in the middle).

Air above the car going through the scoop.
|
|
V
Engine bay.
^
|
|
Air coming from below the car.

- Nick

Last edited by NooKa; March 2nd, 2010 at 18:59.
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post #2 of 36 (permalink) Old March 2nd, 2010, 18:39
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So if we just make a vented cover without a scoop, there shouldn't be a problem with cooling right?
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post #3 of 36 (permalink) Old March 2nd, 2010, 18:49 Thread Starter
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Quote:
Originally Posted by Mr. Anderson
So if we just make a vented cover without a scoop, there shouldn't be a problem with cooling right?
Nope, maybe even improve it a little bit. (I'm 99.9% sure it would improve cooling, but since I can't wind test it, I'll say "maybe").

Even if you had a scoop on a fastback engine lid, I doubt there would be a problem with cooling. It just wouldn't help it at all, and aerodynamics would suffer. After all, people run the Toms Scoops with no overheating issues.

- Nick

Last edited by NooKa; March 2nd, 2010 at 18:57.
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post #4 of 36 (permalink) Old March 2nd, 2010, 19:04
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the fastback enigne lid has been proven to do very very very little, look and the noble write up, they did wind tunnel testing.


But it does looks bad ass! and i like it.

here the answers u all are looking for.
http://www.nobleforums.com/showthread.php?t=3722


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post #5 of 36 (permalink) Old March 2nd, 2010, 19:05
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post #6 of 36 (permalink) Old March 2nd, 2010, 21:37
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The article blames the negligible change in drag on the rear wing and said that it is probable that the fastback may have fulfilled its intended purpose. As a post in that other thread suggests, removing the rear wing could possibly increase the effects of the fastback design, granted you'll lose a significant amount of downforce. Since the effects of the MK1 stock wing is negligible... it might be somewhat beneficial to install a fastback infill panel for high speed driving.
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post #7 of 36 (permalink) Old March 2nd, 2010, 23:30
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but as the article states either way u, use it, with wing or not its not a great increase either way.


so i can help, like canards can help, but minimally, and it is definitely in most causes just an aesthetic appeal.
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post #8 of 36 (permalink) Old March 3rd, 2010, 00:01
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To me, the article sounds pretty inconclusive. Lot of probables and unanswered questions.

Nevertheless, I do agree: I don't see a liftback working well for a MK1, neither aesthetically, mechanically, nor aerodynamically (based on the CFD and my amateurish understanding of cars). Now that I think about it, it seems like we'd just run into similar issues as Noble albeit on a much smaller scale. Might be better off to remove the largely ineffective spoiler to reduce weight rather than add weight with a fastback infill panel.
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post #9 of 36 (permalink) Old March 3rd, 2010, 03:58
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pros: descrease drag, helps bring smoother air to a rear wing (especially a functional one), likely keep the engine bay cooler, likely helps prevent lift in the back, looks good. All in all i think its there to add stability to the back end.

Cons: it isnt the end all of all problems, and in turn creates a few more (pushing the front up)

I think this is a mod that is in line with looking at the big picture, aero isnt about one thing thats fixes everything. Its going to be alot of little stuff all over the place that creates a balance.

I dont know if any of you have hit a sweeper at 115 mph, but in a mkII the back end feels sketchy. Im farely certain that this mod will help keep the back end more stable during high speed cornering or in the straight, so long as other aero is taken into account.

Added bonus is the extra room you will have by not having the standard engine cover. With a V6 in my 2 I cant fit a strut brace in the back, engine sits too high. With the slant back I could fix that problem, gives me those extra few inches i need. And every inch counts. Not aero related but its two dead pigeons with the same stone.
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post #10 of 36 (permalink) Old March 3rd, 2010, 14:51
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Why was it locked?
Anyways. Like kiroshino said the noble shows there is almost no effect on drag coefficient because the fastback make the spoiler more efficient in terms of downforce, but as we don't lack of downforce in the back comapred to the front, we can run wingless and then get more improvment in drag coefficient no? Probably it's almost nothing but still. And the fastback should be lighter or same, compared to the oem engine lid.

Last edited by broody; March 3rd, 2010 at 14:55.
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post #11 of 36 (permalink) Old March 3rd, 2010, 19:10
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Quote:
Originally Posted by broody
Why was it locked?
Anyways. Like kiroshino said the noble shows there is almost no effect on drag coefficient because the fastback make the spoiler more efficient in terms of downforce, but as we don't lack of downforce in the back comapred to the front, we can run wingless and then get more improvment in drag coefficient no? Probably it's almost nothing but still. And the fastback should be lighter or same, compared to the oem engine lid.
If you've ever taken a high speed sweeper in an MKII then you'd know that we need downforce all around, the rear gets squirrely.
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post #12 of 36 (permalink) Old March 3rd, 2010, 21:09
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FWIT, we're doing the very same on our MKIII GT racecar. In our case, it is a complete redesign of the rear end, taking the Spyder hard top design to a fastback with much lower trailing edge. While we have no way of comparing the before and after in a wind tunnel but it is expected that w/o rear wing, it should reduce drag marginally and w/ rear wing, it will massively increase the efficiency of the wing.

Pictures of the plug process thus far: MR-S.R Fastback Plug

We can produce virtually any body pieces for any car desired... A simple fastback fill-in panel for a MK2 should be a very easy part to develop.

Tim
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post #13 of 36 (permalink) Old March 3rd, 2010, 23:53 Thread Starter
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Quote:
Originally Posted by TimStephens
Pictures of the plug process thus far: MR-S.R Fastback Plug
Looks good!

How do you access the engine bay though

- Nick
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post #14 of 36 (permalink) Old March 4th, 2010, 07:03
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Quote:
Originally Posted by NooKa
Looks good!

How do you access the engine bay though

- Nick
Nick,

Good question, still have to figure out the exact details of where the body panel breaks will be. The entire rear section is a removable part to access the whole rear of the car, but for quick engine access (check oil, etc.) the top of the fastback will have a separate removable panel.

Thanks

Tim
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post #15 of 36 (permalink) Old March 4th, 2010, 13:20
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Quote:
Originally Posted by broody
Why was it locked?
Anyways. Like kiroshino said the noble shows there is almost no effect on drag coefficient because the fastback make the spoiler more efficient in terms of downforce, but as we don't lack of downforce in the back comapred to the front, we can run wingless and then get more improvment in drag coefficient no? Probably it's almost nothing but still. And the fastback should be lighter or same, compared to the oem engine lid.

The back end of our mkII's doesnt produce ANY downforce, the tiny wings we have are useless, its all gravity holding the back end down, as the average mkII is going to be along the lines of 70% rear weight ratio, mine is anyways.

The fast back wont have any big effects until you are going, and going fast. At low speed maintaining even traction would be easier achieved by having a better weight distribution. Our cars will push if you turn tight enough, where a FR car like a viper or corvette is more likely to be chasing the back end around. At high speed our un even weight distribution is why we need so much more downforce up front to artificially balance the car out to match the superior traction of the rear. I'm guessing its the same problem with the noble.
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post #16 of 36 (permalink) Old March 4th, 2010, 13:32
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Well let's say we have a fastback hood with that scoop on top. With those, wouldn't water be an issue? Like if we're driving in the rain and it literally becomes a high speed funnel for water and dirt?

Then also regarding downforce across the entire car, what if we did this. Had a vented frunk with the whole radiator relocation or whatever so it actually serves purpose. Have that air when it goes up and travels over the roof, what if we guide it by creating little bumps on the hood to push it straight toward the fastback style hood and across the spoiler.

I can't think of any cars off of the top of my head that have it like that, but I know for roof bump deals that have that indentation that you have on the hood of other cars for "aerodynamics." In this case, it could actually server purpose for creating additional downforce. None of this is really supported by any evidence since we don't have a wind tunnel, but *shrugs* purpose aside, it could have aesthetic benefits as well.

Though doing that would mean that we just redesigned a good deal of the car.

From what I was reading, things to really help with our car is the little plastic air dams I think they call it that go in front of the wheels. Then having obviously a solid undertray from front to rear. After when the price goes up, the vented hood. Then the rear diffuser. Following that is everything that we've been talking about.

The last point I wanted to throw out there was that with the myriad of body kits available for our car, none of them created a fastback style hood.
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post #17 of 36 (permalink) Old March 4th, 2010, 14:22
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And probably none of those body kits were ever wind tunnel tested.

And as for speed bumps are you talking about the mini delta wings across the rear end of the roof on an evo? Those are vortex generators, they decrease drag and would further increase the effectiveness of a wing on the back of our cars. There are several aero threads on here that talk about them.

Speed flaps are what goes in front of the wheel wells, most new cars have them, and later mkII's in japan. They help beat the high pressure zones in the wheel wells, venting the wells via the fenders also helps alot (notice how many new cars have vented wells, they are functional).

As for the hood scoop down the fast back, unless thats venting directly onto your intercooler its kind of pointless. That nsx has it for that purpose. Same idea as the scoop on the hood of and sti too, just for the intercooler.
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post #18 of 36 (permalink) Old March 4th, 2010, 14:59
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Quote:
Originally Posted by Eversor
The back end of our mkII's doesnt produce ANY downforce, the tiny wings we have are useless, its all gravity holding the back end down, as the average mkII is going to be along the lines of 70% rear weight ratio, mine is anyways.

The fast back wont have any big effects until you are going, and going fast. At low speed maintaining even traction would be easier achieved by having a better weight distribution. Our cars will push if you turn tight enough, where a FR car like a viper or corvette is more likely to be chasing the back end around. At high speed our un even weight distribution is why we need so much more downforce up front to artificially balance the car out to match the superior traction of the rear. I'm guessing its the same problem with the noble.
I don't think there is any downforce the, but the rear is heavy, the light front is the one that need more downforce no?
And for the heavy rear at low speed, I think a proper trail braking technique should make the car turn fine.
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post #19 of 36 (permalink) Old March 4th, 2010, 18:57 Thread Starter
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For those interested in, "Speed Flaps" and venting the inner fender up front, here's a great thread talking about it:
https://www.mr2oc.com/showthread.php?t=234204

The wing in the back of the MKII does create some downforce. It was learned after the MKI that with the MR2's design, the wing needed to be placed further back to have any effect.
Which is why the MKI owners do the Plummey mod (moving the wing further back).

And in regards to the MKII not having any rear downforce, I have to believe it does with the air traveling up threw engine bay and out the top.

Jeff Fazio's old car Hyde, from http://www.jekylhyderacing.com had great aerodynamics IMO.
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post #20 of 36 (permalink) Old March 5th, 2010, 19:26
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Quote:
Originally Posted by NooKa
Jeff Fazio's old car Hyde, from http://www.jekylhyderacing.com had great aerodynamics IMO.
Great and simple.
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