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Old 05-23-2014, 04:39 AM   #1 (permalink)
Not entirely mpg's
 
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Hang on, this'll be a strange one...

Hi everyone, name's Brian. I've been lurking around forever taking inspiration for aerodynamic mods and am slowly working towards getting my Mazda3 Skyactiv to break 40mpg. Now before you give me the look (as the EPA rating is 39mpg already), please let me explain:





My car lives a dual life as a track/canyon rat and fuel-sipping daily driver, so to catch Evos and M3's (and once a GT-R too) I'm running on 285/30/18 Bridgestone RE-11's. It's not your usual patient and I'm aware that I've already done a number on the car's stock fuel economy.

That said, after the most recent round of aero mods (large front splitter + half-undertray, full rear diffuser) I noticed that the fuel economy has taken a substantial leap back towards stock EPA numbers, reading 37mpg on a long, flat, straight stretch of highway (off the onboard computer, which hasn't been more than +/-1mpg off the mark in the past). I've been given hope that completing the car's underfloor and cleaning up the hatch/D-pillar airflow should get me closer to the magic 40, so here I am! Just need to get a proper data logging setup to prep up a more scientific mpg test than "check after one week" in the coming year. Pleased to meet you all!

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Old 05-23-2014, 08:10 AM   #2 (permalink)
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That is a nice looking car. Good luck with the project. I Subscribed.

I live in Baltimore too. what track do you go to?
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Old 05-23-2014, 08:38 AM   #3 (permalink)
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Aero mods free up horsepower for acceleration. Fact. Just keep the weight gains under control.

It looks to me like the rounded rear edge of the D-pillar is probably inducing a fair amount of turbulence at flow separation, you could add some small Kammback extensions to those and clean that mess up a bit, maybe add an extension also to the roof edge for the same purpose. If you're competing on track days you'll want to dig into the rules to keep everything kosher with the Tech guys.

For track days I assume you're already pulling all the unnecessary weight out of the car? Passenger seat, rear seat, spare tire? The less mass you have to drag out of the turns, the better.
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Old 05-23-2014, 08:49 AM   #4 (permalink)
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Welcome...

Have you thought about a removable grill block ? On during the week, removed for track days. It's usually worth about 5% and should get you back to 40.



>
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Old 05-23-2014, 10:33 AM   #5 (permalink)
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Old 05-23-2014, 12:25 PM   #6 (permalink)
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Thanks for the welcome guys!

Quote:
Originally Posted by elhigh View Post
It looks to me like the rounded rear edge of the D-pillar is probably inducing a fair amount of turbulence at flow separation, you could add some small Kammback extensions to those and clean that mess up a bit, maybe add an extension also to the roof edge for the same purpose. If you're competing on track days you'll want to dig into the rules to keep everything kosher with the Tech guys.
For the most part I'd like to avoid large new pieces in the rear just from an aesthetic standpoint, so I was thinking a couple rear spoiler fill-in panels (don't know the technical term... think Mazda CX-5, under its hatch spoiler) and trying out VGs just aft of the rear quarter window.

Quote:
Originally Posted by elhigh View Post
For track days I assume you're already pulling all the unnecessary weight out of the car? Passenger seat, rear seat, spare tire? The less mass you have to drag out of the turns, the better.
I unfortunately have to leave most of it in, except spare tire. The Mazda3 rear suspension toes out as you lift it up, so when my normal alignment is 0.00toe all around, taking everything out for the track makes the rear end VERY sketchy under braking. I just kinda deal with it as tire wear and street mpg's are more important to me.

Quote:
Originally Posted by redneck View Post
Have you thought about a removable grill block ? On during the week, removed for track days. It's usually worth about 5% and should get you back to 40.
As soon as I figure out a clean way to do it. Thanks!
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Old 05-23-2014, 01:23 PM   #7 (permalink)
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If you haven't seen this thread, it may give you some ideas on how to do a clean grill block: http://ecomodder.com/forum/showthrea...aru-27277.html
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Old 05-23-2014, 01:23 PM   #8 (permalink)
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Vortex generators have been at the center of a vigorous do they/don't they debate on these pages, and not having any I can't comment one way or the other. To me it looks like there should be some definite improvement but the placement is what will most determine how much benefit you experience. That'll take some testing. If you can lay your hands on some VGs, stick 'em on with 3M Command strips for easy attachment/removal and do some A-B-A coastdown tests.
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Old 05-23-2014, 01:44 PM   #9 (permalink)
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I raced a 79 RX7 in scca show room stock. I raced on 14" rims w 50 series tires the. Ran 15" 70 on the street
You could really improve your mpg with a set of street tires at least 5% larger diameter than stock (at 40+ psi)
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ECO MODS PERFORMED:
First: ScangaugeII
http://ecomodder.com/forum/showthrea...eii-23306.html

Second: Grille Block
http://ecomodder.com/forum/showthrea...e-10912-2.html

Third: Full underbelly pan
http://ecomodder.com/forum/showthrea...q45-11402.html

Fourth: rear skirts and 30.4mpg on trip!
http://ecomodder.com/forum/showthrea...tml#post247938

Last edited by mcrews; 05-23-2014 at 01:50 PM..
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Old 05-23-2014, 04:28 PM   #10 (permalink)
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can u really fit 285 tires under that thing? thats impressive if you can.

separate track/ street tires would help alot. You don't need nearly as much traction on the street, even in the canyons. a 225/45R17 tire on lightweight wheels will reduce weight, rotarional inertia cross section area, and probably rolling resistance.

removable grill block is a good idea. Finishing the belly pan would help too. side skirts as well. Its too bad you don't want to do a kamm back. It would pay off. I think there are ways to make it look good. Vekke on his 2L lupo made a nice kammback, metal, painted.

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