Spent a bit of time this evening unfucking yet another "Racing Inspired Cosmetic Enhancement" that the previous owner did. This is the duct that is responsible for 100% of the airflow into the top-mounted intercooler on an SJ (2014-2018) Forester XT. The intercooler is responsible for cooling down the air charge generated by the turbocharger.
On the bottom is the modified part - he cut HUGE holes in it, cutting the amount of directed air by a third to a half, decreasing engine performance significantly and increasing the chance for knocking and pre-ignition. All just so they could mount bright yellow and blue Hella brand car horns in a higher, more visible position.
This is why people hate buying used performance Subarus. If you're going to do it, just go into it with eyes wide open if you see any signs of modifications and ESPECIALLY if you're not familiar with working on cars yourself. I had a WRX which is like 90% the same mechanically so I'm mostly aware of how everything fits together but this one slipped past me for the longest time because the WRX has a good scoop for the intercooler while the Forester doesn't.
This just in: the prime demographic for cheap economy cars with potent engines/tuning potential are often people who don't have the knowledge or money to modify them properly.
Water and nitrogen....maybe an all purpose fertilizer just before winter to restore micronutrients to the soil. Just remember, what's good for you grass is good for the weeds, stay on top of them early!
Yup. Apparently it was a combination of the Forester having a taller, flatter front with the hood higher up (flow of air around the car didn't favor a hood scoop as much as on the WRX/STI) and focus groups/surveys indicating that prospective buyers preferred not having a hood scoop?
Honestly I'm not sure either way, but swapping back to an intact duct had an instant impact on how the car felt. Luckily it's a relatively cheap part (<$30) and installation is just a few pop clips after you get the front grill off.
Yeah heaps of 4wds have got rid of bonnet scoops too, with proper ducting they still get entry of air over the cooler. Well as long as you're moving anyway, but that also applies to bonnet scoops so no change there.
1st gen Mazdaspeed 3 has no hood scoop on the TMIC. There's a shroud on the IC, and a big duct from the grill to it thats gasketed to the shroud. Works great.
Same with Outback XTs and Wilderness, I have a '24 OBW, TMIC with ducting to scoop cold air ahead of the radiator....a lot of heavy plumbing on the hood just to avoid tossing a WRX snout on the hood of a station wagon.
as far as i am aware basically all mass-produced turbo subarus have a top mount intercooler because it makes assembly much easier and isn’t a huge performance thanks to the large amount of space between the engine and firewall. and since the mid 2010s the only subaru with a hood scoop is the wrx.
that being said, the ascent absolutely rocks a hood scoop
This is why my wrx will forever remain mine. I am halfway done on one too many things, and if anyone got this car right now I’d be accused of vehicle abuse lol.
They had a universal mount, all I did was literally just use another mounting hole 3 inches lower. I didn't have to drill any holes or even use a nut - there was already a threaded hole right there. That's the crazy thing - they mounted it all the way up high and cut up the duct purely for aesthetic reasons. They just wanted the Hella horns to be vertically centered and visible in the upper grill...
Never thought of my 2017 Forester XT Touring as a "performance vehicle." More of a "damn I have a kid now and this is practical but I can still pretend" vehicle.
Why I love my bugeye. previous owner barley did anything to the car but fuck the quarter and fenders up which been fixed. Everything I've done is properly installed. I spent the extra time and money to make sure it didn't need to be redone.
So either the owner didn’t installed properly or whoever did a shitty job! I drive a 2011 wrx the only thing I did was changed the headlights and fog lights colors, dealership gave me a huge lecture on aftermarket fog lights
The replacement part costs less than $30 and takes like 5 minutes to swap out. Repositioning the Hellas took a few minutes and a new M6 flange bolt. Most of the time was actually spent on fiddling with the wiring to tuck it away better it and trying to find where I left my bag of zip ties.
You have to know what to look for before you can take a thorough look. I checked for everything that I was already familiar with after messing with a VA WRX for years, but the intercooler ducting is one of the things that is actually different.
OK, because I'm nice (but mostly because I like the sound of my own proverbial voice) I'll break it down for you:
Turbochargers do their job by compressing air. This allows more oxygen molecules to fit into the compression chambers of an engine than you would normally be able to.
Compression is an exothermic reaction. In other words, squeezing all those air particles into a smaller area creates heat.
This "air charge" from the turbo (the hot, compressed air) needs to be cooled down because lower temperatures have a direct impact on how much power is produced by an engine - especially in a direct-injected engine. Cooler temperatures = more air can be forced into a smaller area with more fuel so that the spark plug can ignite it at the proper time.
Most modern engines can control intake and exhaust valves in the engine bay to optimize for efficiency, horsepower, safety etc. depending on a bunch of different parameters being fed to the engine management system. Cooler temps = valve behavior can be adjusted to be more aggressive and for more power.
The intercooler is a critical part of how a turbocharged engine can make more power than a naturally aspirated engine in a safe manner by cooling down the air charge from the turbo.
Air-to-air intercoolers like the one used by the Forester XT and WRX depend on outside air flowing over a bunch of fins so that heat can be "pulled" (exchanged) from the compressed air from the turbo. The more air you have flowing over it, the more heat that can be pulled away from the air charge and the more power you're able to get with cooler air entering the combustion chambers.
The SJ Forester XT in particular uses an air duct to direct air from a higher pressure zone at the front of the car to top-mounted intercooler. When you cut nearly half of the duct apart, the amount of air you get to the intercooler is reduced significantly. This negatively impacts everything described above.
Even when the turbocharger is NOT building boost having cool air flow over the intercooler is still critical. Because the intercooler is on top of the engine it will always slowly be warmed up by radiant and convection heat from the engine.
Because the air is coming from the front of the car, the amount of air reaching the intercooler is also a function of road speed. Keeping the intercooler at lower temps while out of boost will also mean that the thermal mass of the IC will help to keep temperatures for the initial boost charge from the turbocharger lower as the car picks up additional speed. In the real world this means that you will feel more immediate power as you put your foot on the gas to build up more boost.
I drove the car immediately before and after the change - the difference is immediately noticeable every time I put my foot on the gas pedal. Maybe you find it hard to believe that a $20 piece of plastic can be so important, but if you understand how a turbocharged engine works it should be obvious to you why it is.
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u/ticktocktoe 1d ago
This just in: the prime demographic for cheap economy cars with potent engines/tuning potential are often people who don't have the knowledge or money to modify them properly.
Next up at 11: grass is green.