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Old 11-05-2009, 08:31 PM   #1 (permalink)
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Starting Infiniti Q45 underbelly shield...

I am starting to formulate ideas based on what others have done on the forum.
I have some questions.

1. found this article at AUTOSPEED.COM and it does a very good job of validating the advantage of a smooth surface.
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Toward the end of the article there is this photo of the underside of a Mercedes Mclaren.

It looks like the side skirts are lower than the underbelly shield to keep the air moving along the inside of the skirt.

I have similar skirts on the Q



should the underbelly shield stay at the green line OR drop all the way down to the lower edge of the skirt? scrapping COULD be a problem if I go alll the way down.

In the front there is a gap formed by the factory ABS panels and the IMPUL front lip. I am going to work from the lowest edge of the body kit in front.


Also, covering the wheels? I really like how the Cadillac Crossover that someone posted did those wheels with a clear shield in the wheel slots
THe Qs are pron to warpped rotors. I have been lucky and never had that problem. Will blocking off the slots in the wheel raise the temps on the inside????

Thanks in advance for any help.


Last edited by mcrews; 11-05-2009 at 08:37 PM..
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Old 11-06-2009, 09:43 AM   #2 (permalink)
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Rear diffusers

Not trying to hijack the thread but I have an off topic question burning here:

The rear diffusers on the picture from autospeed.com: Do they improve aerodynamics? How?

/hijack off
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Old 11-06-2009, 11:07 AM   #3 (permalink)
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Wheels
closing off the wheels will increase temps in the rotor area... how much? I don't know. Getting a better flow under the car could help bring that back, but once again I don't know.
Side Skirts
The side skirts your vehicle has are probably more for looks than anything, so if attaching to the bottom is easier, I would go that way. Actually, you might consider extending your side skirts as car as close to the ground as you can. That's the way they are on cars that have them work. I would not worry about dragging based on that two inches.
Rear Diffusers
These are there to help smooth any irregularities in the flow and direct them into the wake, thus preventing them from scattering. It does help aerodynamics, but I don't know how much we would realize the benefits on our road cars.
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Old 11-06-2009, 01:37 PM   #4 (permalink)
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I could have sworn I posted on this.. O_o

If the Qs tend to overheat the rotors, don't cover the wheels. Repair bills will outwiegh the costs of MPG gains there.

Also, the SLR McLaren has very large vents on the hood and quarter panels, so entirely blocking the engine compartment is a bad idea- it'll lead to overheating and shorter engine life. Make sure that whatever air comes in can easilly get out.

I'd set up the belly pan to be as flat as possible, covering the lowest point (probably the exhaust). Make sure you account for the heat of the catylitic converter, pipes, mufflers, etc and use the proper materials.


On diffusers- They provide a surface for attached airflow to curve upwards, and both produce downforce and reduce drag.
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Old 11-06-2009, 02:40 PM   #5 (permalink)
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I should go back and edit my previous post... but Hermie is right about the diffuser, I was talking about the vertical fins on the diffuser, not the actual upward sloping smooth surface. I guess everything I said would still be correct with the exception that you should see some sort of gains from a diffuser, not necessarily the fins.
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Old 11-06-2009, 03:07 PM   #6 (permalink)
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I believe the fins simply direct airflow, unless they're angled like vortex generators.
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Old 11-06-2009, 03:19 PM   #7 (permalink)
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That's the way I understand it, keep the flow from trying to escape out the sides of the car past the rear tires... kind of like the side skirts do between the front and back tires.
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Old 11-06-2009, 05:15 PM   #8 (permalink)
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Thanks for the advise!!
Wheels: As much as I liked the clear slot covers in the Caddie, your advise to error on the side of caution is sound. I am driving to Texas in Late Jan. I might 'test' sometype of temperay wheel cover along the way. It will be cool uotside and very little braking. (lots of coasting!!!) There are some MAJOR flat and straight sections of hwy. But for now, the wheels are major backburner item.

Underside:
Hermie, I completey understand your point on 'air in - air out' re: engine compartment. But as I move farther back, I was thinking of leaving the cats exposed. Building something that is 'flush' but open around the cats. maybe a 1/4 to 1/2 inch gap between the pan and the cat. I could also use a screen material over the cat? And then covering the two mid mufflers or again using a hole in the material and filling the hole with screen.
My though on the screening is that when I'm sitting in traffic, the heat would disapate "thru" the sreening.

Rear under belly: the area behind the axel is 5 ft wide and 39inches to the rear of the bumper lip. That's a lot of smooth space and I look at vector gen. or difusors.

Grille block: I plan on using a clear piece of lexan that has a custom , thin rubber edge trim that will flush mount over the existing grille and opening seams. THe lexan will be about 1/2 inch over the whole grille on sides and bottom. THe top egde would 'seal' with the hood.

I can't thank ECONMODDING enough for being here and for each of the members for their efforts and insight.

My Goal is to average 30mpg on the round trip from Sato to dallas and back.
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Old 11-06-2009, 05:27 PM   #9 (permalink)
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I'm shooting for 30mpg in my '91 Ford Tempo. I started in the low 20's, which didn't seem right to me.

Quote:
Building something that is 'flush' but open around the cats. maybe a 1/4 to 1/2 inch gap between the pan and the cat.
That sounds like a good idea. If you're going to use coroplast (material for plastic political campaign signs), you're most likely going to need some kind of metal as a heat shield around the cats with some kind of insulation between metal and plastic. With the right tools, it can be done. I'm working with bare minimum.. All my tools are back in California, and I'm up in Oregon for college, and I'm working on a shoestring budget.

I'm also considering using screen material, but it would have to be the aluminum type, not the black kind. Aluminum can withstand the heat of exhaust pipes. I'll probably roll some paint or some kind of filler on the screen to smooth it out, leaving around the pipes open for the heat.

Looks are just as important as results to me with this. If it looks like something that rolled out of a junkyard, I'm not going to do it.
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Old 12-05-2009, 07:32 PM   #10 (permalink)
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front under panel installed

Here is the before:




and here is my inspiration:
2011 Audi A8
I took the advise from above and decided not to go for 100% coverage (at first) I want to keep some of the air flow the way the factory designed it.




here is what I made: found dimpled plastic sheet!
had to make to halves and splice.





put 8 mounting bolts around the panel edge that match the pre-drilled holes on the lower edge of the IMPUL.







I also transfered the factory wheel deflectors:





here is the final product installed. I used all the factory mounting points. The factory pan extends smoothly after my front sheet. The oil change flap is still accessible.








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