Subaru WRX Forum banner

1 - 12 of 12 Posts

·
Registered
Joined
·
67 Posts
Discussion Starter · #1 ·
Hello, all. I am looking at buying a 2017 and the salesguy showed me the engine room this morning. I really do not care much for the forward-facing scoop. I know from many years' racing sports cars that the scoop will be a magnet for dust, gravel and small rocks. After turning 90 degrees, they will probably not have enough energy to damage the intercooler but I would expect heat-insulating dust and dirt to build up on the fins and to find a few larger rocks rolling around on top.

So here's the question: Is there already some kind of filter inside that scoop duct or are there aftermarket sources for fitted filters? Obviously one could cut filter material to fit if necessary but a purpose-built filter with retaining hardware would be best.
 

·
Registered
Joined
·
367 Posts
Do not put anything in the scoop itself. Its meant for maximum airflow to your intercooler and putting things in the way is just limiting it. If you're worried about rocks and little things just take a pair of tweezers or pliers and move the flaps back into place. as far as dirt and things it doesn't get too dirty unless you're driving through huge mud puddles or a sand storm.
 

·
Premium Member
Joined
·
6,716 Posts
Dust and gravel is already going to make its way into the engine bay via the front of the car (radiator), as well as from underneath. In 15 years I have never had an issue with any significant amount of gravel making its way into the hood scoop. I've never had any dust build up on the intercooler either. It gets washed off when it rains, and it isn't covered in oil or grease (or at least it shouldn't be) for dirt to stick to.

There are a couple companies that make screens to keep out large rocks and such, but they need to have large holes as to not restrict air flow. It would be easy to make one yourself, but honestly it isn't needed. When you say "filter", I'm imagining something like a paper air filter, at which point you might as well ditch the intercooler altogether and detune the car to prevent knock in hot weather.
 

·
Registered
Joined
·
67 Posts
Discussion Starter · #5 ·
So maybe the experience is that stuff coming in the scoop is not an issue. If I get the car I'll just wait and see.

RE filter I am thinking of something like the oiled K&N foam. That offers almost no resistance to air flow.

Re maximum air flow, the amusing thing (to me) about that forward-facing scoop is that this kind of scoop is totally ineffective. The intuitively-obvious "ram air" concept does not happen. Instrumented cars in wind tunnels show a slight increase (IIRC 0.5" of water column) right at the base of the windshield. That is why you see professionally designed race cars like Corvettes with hoods having rear-facing air intakes that feed from this slightly higher pressure area.
 

·
For External Use Only
Joined
·
2,488 Posts
You see things on cars like corvettes because they're not forced induction with top mount intercooler setups.... the "ram air" concept does work very well for these applications.
 

·
Registered
Joined
·
367 Posts
Actually that's false. the scoop is not totally ineffective. The placement and design of said scoop is at a point on the hood that allows for maximum airflow and Raise to benefit the cold air for entering. It all depends on the design of the car in question. for the corvette yes the way the wind passes through the reverse scoop is more logical(and a raised front scoop would look weird) but for the Sti its better served being a front facing scoop by its body design.
 

·
Premium Member
Joined
·
6,716 Posts
RE filter I am thinking of something like the oiled K&N foam. That offers almost no resistance to air flow.

Re maximum air flow, the amusing thing (to me) about that forward-facing scoop is that this kind of scoop is totally ineffective. The intuitively-obvious "ram air" concept does not happen. Instrumented cars in wind tunnels show a slight increase (IIRC 0.5" of water column) right at the base of the windshield. That is why you see professionally designed race cars like Corvettes with hoods having rear-facing air intakes that feed from this slightly higher pressure area.


You would end up with a lot more dirt and grime build up on the intercooler and top of the engine with an oiled filter up there. Tiny oil particles would mist the intercooler fins, then any dust swirling through the engine bay would cling right to it. As it is, air entering the scoop is the cleanest source of air in the engine bay. After some spirited drives on gravel roads I would regularly find bits of gravel and mud up inside the engine bay (even on top of the engine itself), but nothing on top of the TMIC in the scoop. It all gets kicked up from underneath. A foam filter will certainly restrict air flow, as well as trap heat while sitting stopped. Heat that normally would freely escape through the scoop.


As far as flow goes, the WRX/STI (at least previous year models) has a big high pressure zone along the top of the hood. Enough air flows through the scoop and down the transmission tunnel that blocking the scoop off entirely results in a measurable increase in cooling from the nose of the car (ie. FMIC). Most professional Subaru race cars actually do run a reverse scoop, but with a v mount intercooler, and much closer to the front edge of the hood. Many of them re-purpose the factory hood scoop to pull clean air into the intake (or for an oil cooler). I haven't seen a single one that has a reversed OEM location scoop.




*A little wind tunnel food for thought..
stiwind.jpg
 

·
Water.....sometimes waves
Joined
·
1,611 Posts
No, No guys, I agree, subaru has been making these wrong for what? a couple decades now. It is time they change their flawed design. Indeed mine is much faster in reverse!

Sorry, couldn't help it. I hardly ever get anything in my scoop; not even leaves.
 

·
Registered
Joined
·
39 Posts
Just thought I'd share that the day before yesterday a sparrow flew in front of me and went straight into the scoop. I had to pull it out later. It didn't make it into the engine bay.
That being said, people worry way too much about little details like this. It's a sports car. It's made to be driven and driving is seldom a clean endeavor. Drive it like you stole it and if something happens, then fix it. No need to invent a new element of preventative maintenance.


Sent from my iPad using Tapatalk
 
1 - 12 of 12 Posts
Top