ClubWRX Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
I have a 2009 WRX. I was talking to my buddy who knows a lot about cars but not so much about Subaru. I asked him if getting a short ram intake was good because I've been told in multiple places that CAIs are not very effective on the WRX. He told me that getting just a normal K&N cone air filter instead of a SRI would be cheaper and less restrictive than the normal intake and the intercooler would cool the incoming air anyway (duh), eliminating the need for CAIs and SRIs. My question is: Is he right? Would the SRI or the K&N be a better option on the stock engine? What do you guys have?
 

·
Registered
Joined
·
6,751 Posts
No he's absolutely incorrect.

First off, his answer makes no sense because how are you going to put a cone filter on the car when the airbox is designed for a flat panel filter? Secondly, the intercooler is there because the turbo raises the intake temps. The intercooler can only cool the intake charge temps a certain amount, so the higher the air temps that go into it, the higher the air temps that come out. So you absolutely need to run a CAI and not a SRI if you want to actually get a performance gain. Running a SRI means your air temps are going to be higher than running the stock airbox, which means you're going to actually lose power.

Intakes in general on older WRX didn't do much if anything, but on late model cars they seem to make a small difference. If you want to run an intake, you need to run a CAI. The AEM is the best one out there for several reasons: It's a true CAI that sits in the fender well, it has a dry filter instead of oiled so it doesn't cause MAF issues, and it's made by the company Subaru contracted to make SPT products so they have an excellent, proven knowledge of the platform.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #3
Hmmm well when I asked in another thread if a CAI was worthwhile they said no because it was more restrictive than the stock airbox I dd specify there that I had a 2009 so I'm kind of at a loss now. Is the install of the CAI you mentioned difficult? Is the SRI with a good airbox/heat shield better than the stock? I understand that it may not be quite as good (performance wise) as the CAI but I'm now confused somewhat on the information. I'll go to that original post and quote what was said about the CAI...
 

·
Registered
Joined
·
4,319 Posts
Maybe you misunderstood your friend and he actually said get a K&N drop in replacement filter...which makes more sense. I think AEM also makes dry flow replacement filters for the stock air box as well. Check with Kronosperformance.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #5
No he was definitely sayin a K&N cone filter. So what's batter (after weighing the pros and cons of each) a CAI or a SRI?
 

·
Registered
Joined
·
4,002 Posts
No he was definitely sayin a K&N cone filter. So what's batter (after weighing the pros and cons of each) a CAI or a SRI?
In my opinion, its all preference. Some will argue that a CAI is better and vice versa. I personally think that if you need an intake, short ram is just fine. If you need one, let me know or check out our site www.kronosperformance.com
 

·
Premium Member
Joined
·
10,943 Posts
When the car is stopped a CAI will have the advantage of pulling cooler air from the fender well. If the car is moving the under-hood temps quickly drop to ambient, so the advantage of a CAI no longer exists. If you need every last ounce of power while the car is not moving, then definitely get a CAI (or stick with the stock airbox). If you only need the extra power when you are driving, then a CAI and SRI should be virtually the same.

Although there is more to it than just IAT. Particularly for people who are drag racing. When IATs rise the ECU will pull timing to prevent detonation, so when you're staging the ECU is compensating for the high IATs. Then when you make your pass you're basically running on a crippled map because the ECU doesn't have time to add that timing back in. Of course you can get around this issue with some creative tuning.
 

·
Registered
Joined
·
6,751 Posts
I don't agree that when you're moving the advantages of a CAI disappear. There's not enough airflow to lower the temps since there's the big plastic plate on the bottom of the engine bay so fresh air can't get in there, so you only have the small area of the grill up front to introduce fresh air. I could be convinced otherwise with a detailed log of under hood temps at a stop and while traveling at different speeds, but I'm not right now.

With a CAI there's no question and no argument to worry about. You know you're always getting cold air from the fender well.

OP, your friend definitely makes no sense then. WRT the stock airbox flowing more air than either a CAI or SRI, that's absolutely not true. Both of those will flow more air. However, the stock airbox really provides enough air for any setup short of stage 3. You could get a very small boost in power with an aftermarket intake, but they're really more for sound than performance. I wouldn't have bought mine if I didn't get it so cheap ($150). I like the sound of it and I know I'm not losing any power with it for sure and maybe gaining a few ponies.
 

·
Premium Member
Joined
·
10,943 Posts
Well I don't have the under-tray.. although what I've read is that it actually increases air flow by creating a low pressure zone at the back of the engine, therefore sucking more air through the front.. for whatever it's worth.

I did data log IATs about five years ago and at 45mph and above the reading from my sensor in the MAF on my Perrin SRI was identical to the ambient reading from the GM sensor I put in the fender well. 35-45mph there was less than one degree difference. Stopped for just 20 seconds the MAF reading would shoot up nearly 40 degrees..
 

·
Premium Member
Joined
·
10,943 Posts
Of course not everyone will have the same results. But a 45mph wind is a lot of fresh air, and I'm guessing the placement of the holes in the fender directly next to my air filter had it blowing in directly across the filter faster than the engine can ingest air.

My new setup is going to be more finicky dealing with IAT differences because of speed density, so I'm going to take more measures to isolate the filter from the under hood temps.
 

·
Registered
Joined
·
1,393 Posts
Get the CAI, when moving, and everything is cooled down to as cold as it will get it makes no difference IAT wise... BUT when moving slow or stopped heat-soak starts to happen and it can take 15 to 20 blocks of driving to get the IAT back down again... for those 15 to 20 blocks if you step on it, the ECU could be pulling timing so you are running with less HP. As for the argument that the IC will cool down the air charge IAT well, most TMICs are only about 60% efficient so that would leave 4*F hotter IAT going into engine for every 10*F hotter air that the short ram is sucking in... It can EASYLY get 40 to 80*F hotter IAT at the MAF sensor so that would mean 16 to 32*F hotter IAT into throttle... I think most people would rather lower the intake temps into throttle than raise it... JMO

Edit; Oh, and that also goes to those thinking it doesn't matter that hotter air is entering because the turbo will heat it up anyways... Yea it will, but every degree hotter air entering the turbo makes it that much hotter coming out of the turbo which again people think the IC will deal with it but it's not 100% efficient so...
 
1 - 11 of 11 Posts
Top