ok so i just got a new 05 impreza 2.5 rs and well its alot diff from my civic that i messed around with. so here it is i really need some help just finding the best stuff such as manufactures and such to maximize my hp and trq..i know the standard stuff like cold air intake and exhaust and headers((which brands are best, i always went with injen intake,and greddy exhaust and header))but with a suby its a diff. story i believe so please help if possible. but what else can i do besides a turbo kit to get the most hp and trq out of my car. and how much hp can i expect to gain from this car going naturally aspirated. i was looking into chiping it but its so hard to know the right ones to get. thanks for your help ahead of time.

 

Look into doing a WRX motor swap, it's fairly cheap compared to other motor swaps. By doing that you really open doors to a whole new world, plus it is not recommended to throw a turbo on a natrually aspirated EJ25.

 

I'd stay away from an intake untill youre really doing a lot to it

as for "chipping" a good EM to go with is Cobb's AccessPort since it is easy to grow with

 

The first thing you are going to run into is your going to want to upgrade more than just drive train. You will soon want to be able to turn, and brake more efficiently. So start thinking about that. Most of it will be to get rid of under steer
The N/A 2.5l is usually good for about 5psi of boost but if you want to keep it around any amount of time you want to go with a better engine management system.

Ok on to performance parts.

-Header; don’t bother going too expensive you wont see that much of a difference between an equal length over the cheaper borla variant.

-Exhaust; The 2.5l N/A responds very well to 2 1/4" dia any bigger than that and you will actually lose hp due to lack of back pressure. So find your self a cheap stock wrx exhaust, modify the input flange (needs to be rotated 30is degrees) and replace the silencer and other restrictive bits with straight pipe. The exhaust will cost you about $50 and a good shop will modify it for about $75

-midpipe;
I personally love the stromung cat less pipe that I have but if you go this rout you will need to weld in a glass pack muffler into your exhaust system to cure it of the horrible rasp!! I went with the 28" thrush glass pack and love the sound and noticed no restriction difference.

-Intake ;
You will see tones of people selling the short ram ones which relocates it above the abs unit in the engine compartment. This would work out fine if you make a box that blocks it off from the engine compartment and you open that hood vent above it. Spend the extra $20 on an intake that puts the filter between the outer and inner fender behind the bumper. I just picked a good one up off of ebay from directshoponline for $50. My only complaint was the tubing provided was a little small and a pain to stretch it over the fittings.

engine management;
you wont see much in the way of performance until you upgrade the engine management. Basically the subarus in an effort to prevent engine knock made there cars self learning. So when ever you bolt on a performance component you notice some improvement but the car re-tunes around it. Allot of people have good luck re-teaching the computer after each performance part. Basically disconnect the battery for over 30 seconds, reconnect it, and drive like a madman for the next week or so.
Your best bet to defeat the computer is to go with an aftermarket engine management system. You don’t have to go crazy and get a stand alone but a SAFC isn’t going to cut it. The computer quickly learns around many universal management systems. You need to go with one that is designed specifically for your car to defeat this.

Turbo kits;
As I stated before the 2.5N/A is only reliable for 5is psi. What people run into is either connecting rod failure. But even if you strengthen the valve train, and get forged rods and pistons you still have an open deck engine. For $1900 shipped you can get a brand new ej257 short block which is the 2.5L engine out of the usdm sti. It has a forged crank and a semi-closed deck which people reliably put big psi through.
By far it is much cheaper to do the WRX 2.0l swap. I know it sticks to go down in displacement but you make it up in reliable HP.

Now you may be thinking 'well if the wrx and the 2.5rs block is about the same externally why not just take the wrx turbo and slap it on the 2.5rs'
That is what I'm doing and here is what your getting into.
You need an aftermarket engine management system.
The heads on a 2.5rs are different, the biggest difference is the exhaust ports are located too far forward. This all leads to a bunch of stuff you need to do to make it work. This can be done and has been before with great success. Search around for info on RS-T which what turboing the stock 2.5N/A engine is commonly called.

Hope all this rambling has helped a bit.
Here are some good sites
http://www.subaruwrxparts.com/index.html
http://www.mrtrally.com.au/shop/
http://www.subarugenuineparts.com/
http://www.cobbtuning.com/main.html

 

WHY would he want to hack up his brand new car? By the time he finished with that swap he should've just purchased a WRX in the 1st place. It probably would've been cheaper too.

Anyway, to the guy that originally posted, the N/A 2.5s in the RS are not made for turbocharging. You'll run into nothing but problems.

What I recommend to 2.5 RS owners is to slap on a few bolt-ons like an exhaust, cold air intake, header, and an ECU dyno tune. I would spend a lot more time with the suspension and brakes, which will make the car tons more fun to drive. Power isn't the only aspect of having fun. You can achieve just as much of a rush by taking a spirited cruise through the twisties with a car with a good suspension and brakes.

And don't forget that when you purchase rims, make sure they are lighter than the stockers, and get some stickier tires than stock RE92s. Hell, just get lighter wheels and stickier tires and you'll notice a substantial difference in handling, braking, AND acceleration. Unsprung weight is the enemy. The less you have, the better.

 

lightweight pulley!

 

Do nothing. Spend a year learning how to drive it really, really well. It is not a Honda, it is a genuine driver's car. You can make it faster by improving your skill.