2013 Subaru Impreza WRX STI - Project Log

[UltArc]

Make sure you fish scale it, too. Looking good so far. If you were closer to Ohio, I'd offer you some coroplast lol.

[jedi_sol]

Originally Posted by UltArc

Make sure you fish scale it, too. Looking good so far. If you were closer to Ohio, I'd offer you some coroplast lol.

Lol, thanks for the offer

Bought some coroplast. Trimming it down. Wow, I get a lot done when I'm unemployed...

[jedi_sol]

Coroplast is trimmed and bolted down. Hopefully this is enough screws to hold down the coroplast so that it does not get ripped off.



I also used the left over coroplast to make a better looking side skirt.


Next up, attaching the under belly tray then road test.

[serialk11r]

Whoa, those skirts are low to the ground. Any scraping?

[jedi_sol]

No scraping so far. There is still about 4in of ground clearance . Since the skirts are made of coroplast, they should scrape down on their own to whatever level they need to be over time.

[wdb]

Just found this thread. Fellow STi owner here, mine's a 2005. I see you're getting 26.7 MPG average, congratulations! You have impressive (or should I say imprez-ive) willpower.

I managed 25-ish when I was driving mine on a long daily commute, but I drove myself nuts. It's an STi fer cryin' out loud! I didn't buy it for its fuel economy, I bought it because it goes like stink and never saw a corner it didn't want to pound into submission. I finally saved my sanity by paying the car off ASAP and buying a Honda Fit for the long commute. The Fit paid for itself in fuel cost savings alone, and the STi is much more enjoyable these days now that I'm not paying attention to the gas gauge.

Anyway, back to ecomodding. I see you're building an undertray. My model year actually has plastic ones under there from the factory (although it is in sore need of a diffuser). Have you looked into the possibility that factory bits might exist for your 2013 car? Even if you don't want to buy them, you might find mounting points for your homespun version.

[jedi_sol]

Yay, another sti owner!

My girlfriend won't let me buy go fast parts for this car, hence I'm pursuing my other modding hobby of Ecomodding. The secret to getting good mpg is pulse and glide, however you pulse in s# mode. This allows me to pulse for a very short time (let all 300 horses loose!) Then I can glide for a lot longer. So the car is still gets to flex it's muscles and I never get tired of sport s# mode.

Yes, the car handles like killer, hence I can take the "racing" line to conserve momentum by taking freeway changes at twice the speed as other cars, then blasting out the corner exit.

Unfortunately mine doesn't come with the middle tray . It only has the front engine tray and then a partial rear tray. Yeah I researched under trays for the car. 2008-10 sti (yeah I know they're essentially the same car as mine,)have an OEM middle under tray, but it's $75 a piece and I have to get them shipped from Japan. This tray I'm building costs me $60.

Yeah I found some good mounting points underneath the cr for the under tray. Next to the rear jack points there is a metal piece with holes that stick down. They don't appear to do anything special, I think they may be mounting points for the OEM under tray. Eventually when I'm done I'm going to build a front undertray and then a rear diffuser.

Sit rep: the screen window frames are too weak and the whole thing flexes under its own weight. They were rigid enough for my del sol undertray, but I guess the del sol was a way smaller car. I need to redo the whole thing in thicker aluminum bars.

Stay tuned!

[Xist]

Sit Rep?

I do not like cornering in Bacon. I thought that if it was bad, my dad's F-150 would scare me, so I did not want to drive it through canyons to or from my dad's house.

The big truck cornered much better.

Great progress! Good luck!

[serialk11r]

Originally Posted by jedi_sol

The secret to getting good mpg is pulse and glide, however you pulse in s# mode. This allows me to pulse for a very short time (let all 300 horses loose!) Then I can glide for a lot longer. So the car is still gets to flex it's muscles and I never get tired of sport s# mode.

Yes, the car handles like killer, hence I can take the "racing" line to conserve momentum by taking freeway changes at twice the speed as other cars, then blasting out the corner exit.

Hmmm since you're putting some serious work into your car I assume you have logged the car and aren't running so much boost that it goes rich, but I wonder if this is the best technique with a turbo engine. In some Eaton TVS promotional presentation there was a BSFC chart of a turbo 2.0L engine from one of the domestic manufacturers (I forgot which) and the engine did reach peak efficiency under boost, but then it went down considerably with increasing boost. Maybe if you limit the boost a bit you'd be able to pulse with a floored throttle and have an easier time getting the engine running efficiently.

Also taking exits at 2.5 times the posted speed is pretty fun

[jedi_sol]

Finished under tray, More Aero mods
Sorry for the lack of updates, been finishing up the undertray on my car and added a few more under-car aero mods.
I slightly tweaked the design of my middle under tray. Im going to wedge the outer edges into the OEM side skirt. I’ve also reinforced the Inner portion with aluminum C-channel bars. No more flexing! I also cut out a portion of the rear cross section so that the whole thing sits flush with the exhaust pipe.



Here is the middle tray attached to the car. The front cross bar is attached to underside of the OEM sideskirt with a bout 4” of double sided tape on each side. I made sure the CLEAN the underside of the sideskirt with rubbing alcohol to ensure a nice clean contact area. This makes the tape VERY STURDY. The rear cross bar is attached to the OEM jacking points.


Starting to build the rear undertray, which is tricky due to the dual exhausts. I started by used the aluminum window frame bars, attached to the rear crossbar of the middle tray, the other end of the window bars simply tuck into the rear bumper.


I used aluminum flashing to cover the exhaust pipes.



Now I need to fill the gap around the lower control arm. I simply used existing holes in the LCA and bolted on more coroplast.


Building the Rear Wheel Boat Tails (similar to Gen 2 Prius)
They are attached with aluminum L brackets that I double side taped to the underside of the bumper. Used leftover coroplast and black Plastidip.









I’ll eventually smooth them over and mold with the bumper with a thin layer of fiberglass

I also made an inner wheel skirt similar to Basjoos. Made with aluminum L brackets and double sided taped to the middle under tray


Covering the middle exhaust. I used aluminum flashing, double sided taped to the middle under tray (has not fallen off yet!), and fish scaled.


Covering the gap between the front OEM under tray and my middle under tray. I used existing holes in from the OEM under tray and bolted on coroplast



Im also making a more aerodynamic cover for my outside mirrors out of fiberglass



COAST DOWN TESTS – A B C
Take these results with a grain of salt because I did coast down tests throughout the week while finishing the under tray, I was too lazy to keep taking off and on the under tray. So this is more like an ABC coast down test. I tried to perform the tests when the outside temperature was the same around 55*F

Side mirror delete, upper grill block, lower grill block, middle under tray
37.6 sec average

**added rear under tray, rear wheel boat tails
37.57 sec average

**added middle exhaust cover, inner wheel skirts, front oem to middle tray cover
40.53 sec average!!
Also with these mods, I achieved the best commute home from work with 30.5mpg! The previous best was 28mpg.

Im taking my car into the dealership soon for service and will do another coast down test with all of the mods taken off to see if there is a difference.