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Discussion Starter #1
Updated 5-21-09
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I don't want to sound like a complete know-it-all...but this is what i've learned by having two NA imprezas in the GC8 body style...one was mostly stock...one upgraded out the butt....

I'm not a subaru mechanic or a "Professional tuner"...but this is the knowledge that I've gained through real-world experimentation through daily driving and autocross.

This thread is going to be a way of relaying info to the potential modder...not a "how-to thread" or a "Don't do this to your car thread"

I'll try to stick to well know facts...and not un-proven conjecture, although I might throw a little bit of theory in there...

Most of these facts/observations have been derived from working on the 99-01 RS...although most of this info can be applied to an 08 NA impreza.

Modding your engine or drivetrain should be done at your own risk, by the way, I assume no responsibility for mods you do...

Oh, and if I come across new info...I will update this post :)

(If this thread goes over well, i'm going to do a suspension version as well) :)

INTAKES

Ok, this is the first thing many people do with a new NA car that they want to add power to...

all you need is simple hand tools and you don't need to get under the car or own a jack/jackstands.

There are a couple types, stock, short ram, CAI, replacement hi-flow filter, and snorkel (oh yes, I've always wanted one of these)

Stock--best compromise for engine safety, power, and longevity (oh yeah, and it won't possibly void engine warranty)...the 08 actually has a type of Cold air intake (CAI) as it pulls air from the front of the hood...although it has several bends and obstructions.

Short Ram-- I haven't really researched these all that much...honestly, why would you want to pull hot-air from the engine bay? The filter is right next to your engine. You'll get alot less horsepower just by virtue of less cold air. The only possible benefit is less chance of water ingestion compared to a cold air intake...but these don't perform as well as the stock intake for low end power.

Cold air intake-- (CAI) these are usually viewed by the impreza community as the best option for more power, you just having to watch out while driving through deep puddles...the cobb CAI pulls from the fender well...the same place the stock intake does....i wouldn't recommend a CAI that pulls air from the bottom of the bumper (i've seen VWs with this setup)....it turns into a giant water straw for your engine :)

Snorkel Intake--Ok, so i've never seen a commercially available one...I've seen them used by Ralliart and STi for african rallies where they need to cross rivers during the course of a rally stage. I've heard snorkels give a type of ram-air effect into the engines at higher speeds and they don't have a problem with water ingestion....and how cool would it be to drive your car in 3 feet of standing water and not stall it (granted, some other engine mods and waterproofing would be required)

High Flow Stock Filters--STI offers one for some models, Perrin does, Avo, and of course K&N...they DO make some extra power, but not that much extra power. However, they can be a good compromise between a stock intake and a CAI. Modders just need to be careful when oiling their filter...oil it the correct amount...over oiling can lead to excess oil clogging MAF or MAP sensors (sensor type depends on model year) in the intake...underoiling will cause the filter not to function well...read the directions! :)

(I'm using the CAI as a testbed for the pros and cons)

(PROS)

-You generally get more throttle response to the mid to high RPM ranges.
-The engine itself sounds louder and more aggressive (some people like this :) )
-Looks cooler in the engine bay...could free up some space for a supercharger :)

(CONS)
-Because you are not using the snorkus found in the stock intake, you have a much greater chance for water ingestion into the engine...which could really suck...literally.
-You will lose some low end throttle response (ie, not as much power off-the-line)...the stock airbox tends to build up pressure inside of it and help your low-end-power.
-Can void your engine warranty
-An intake can tend to Lean-out your air-fuel ratio for your engine (even if you reset your ECU). It is unclear whether this lean-out is dangerous enough to damage your engine over time...some have claimed it does...some have run a CAI/aftermarket intake for years and over 100k miles no problems...I imagine if you use a well-tested intake from a known company (Cobb, injen for example) you be fine...but you probably will put a little extra wear on your engine.


All this being said...an intake is an effective way to gain power in the mid to top end, you just have to be more careful about where you drive (ie, deep standing water)...and be aware that you are most likely slightly decreasing the longevity of your engine (although this could mean the engine blows at 225k miles instead of 280k miles) ;)

Also, because newer imprezas have a different throttle body and variable valve timing (AVLS, unlike the 99-01)...some of the potential problems of intakes, such as leaning out or loss of low-end power, are less evident although still present.

SCCA Autocross Info (for those in the US)

So, putting an Intake on your car will bump you to ST class (formerly STS) from your stock category. Personally, I loved being in ST because the competion seems to be more fun than stock classes (and you are limited to street tires in ST). Now the one downside of putting on an intake for autocross is that you tend to need alot of low to mid-range power while take low-speed hairpins and the like...the intake can actually slow you down more for this since you lose your low-end... I feel faster at lower RPMs in autox with a stock intake...but your mileage may vary.

The general consensus is that the stock subaru intakes are pretty darn good as intakes go. It's an easy mod, but it might not be as necessary as you think.
 

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Discussion Starter #2
Re: Rallyshark's Guide to NA...lots of info...

HEADERS and EXHAUST SYSTEM

--Generic Exhaust Info--

An impreza NA exhaust has 4 parts in this order from the engine back to the tailpipe (This is the way the NA impreza has been for forever):

1) Header (or exhaust manifold)
2) Cat section (or track-pipe, 'decatted')
3) Mid-Pipe
4) Muffler Section
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There are two types of headers for the Impreza. Equal length and Unequal length.

Their names are pretty self-explanatory.

Equal length--The header pipes coming out of the exhaust ports on the engine are approximately the same length to the point where they connect to the Catalytic Converter or Track pipe.

Unequal lenth--The pipes are different lengths...

UNEQUAL
Borla (and the many knockoffs of Borla) produces Unequal length headers.
-They sound REALLY great, but they make a limited amount of power...and by great sound, I mean like a WRX.
(To oversimplify things, the pulsing sound of the WRX exhaust is caused by the turbo. The unequal length of the headers emulates this pulsing sound.)
-Unequal length headers can be "modded" to work without triggering a check engine light. (I'll cover this under the CEL section, but simply, but wrapping them with fiberglass exhaust wrap or getting them ceramic coated...and using a drilled-out spark plug defouler as a spacer on the second o2 sensor).
-Tend to be less expensive than Equal length.

EQUAL
COBB, TWE, Brullen, and OBX (I can only find OBX for sale currently) make equal length headers...
-They do make good power, close to 20whp (which is good for an NA vehicle). They can tend to sound raspy or "ricy" (as some people term it).
-You can prevent CEL lights by "modding" like the above type....however, they usually have more trouble with a random CEL here and there.
-Twice or three times as expensive as unequal length headers.

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I personally used Borla Headers on both of my older NA cars...they sounded great, and I was happy with the 13 or so less horses I was not getting by using the unequal length.
A note on the Borlas....

-Earlier generation borlas cracked for some reason...but they fixed this in later generations
-Newer NA imprezas (06 to 08) have a different type of oil pan and header layout which makes the borlas exit on the opposite side as stock, however, they still fit, you'll just need to mod your stock cat to bolt to the headers for the 08.



CATALYTIC CONVERTERS

It is illegal to run without a Catalytic converter in all 50 US states per federal law (and in most countries)...even if your state doesn't have emission inspection, like mine....

However, many people do...so I'll cover it.

You get a more free flowing exhaust without a cat than with, however, you pollute more.
The exhaust on your impreza will also start to sound more like a honda civic if you run without a cat.

You can buy a hi-flow cat, which will not pollute, and still give you a slightly muffled, but free flowing de-catted sound.

I have always run with a cat, mostly because I won't ever have to worry about passing emissions testing with one, the impreza has a really nice sound with the stock cat, and it's one less thing you have to buy for your exhaust :)

The amount of power you get while running without a cat is somewhat small.
De-cat at your own discretion, it will make you slightly faster if done right.

If you throw a CEL and your car starts adjusting the Air-Fuel Ratio, then it could negate the gains of a decatted exhaust though....CEL fixes are a must when decatting.

CATBACK (MIDPIPE + MUFFLER SECTION)

There are many brands and types to choose from...choose whichever one you like the sound of most.

Through the testing of many impreza owners and people with much more time than I, the optimum pipe diameter for your NA exhaust is 2.25"....most non-turbo exhausts offered for the impreza are at this size anyway.

Some may ask..."why not just have a really wide exhaust pipe 3" to 3.5"?" The answer: lack of Backpressure

Whereas too much backpressure hurts performace because the exhaust is constricted on its exit out of the exhaust system, too little backpressure can cause the exhaust to flow badly as well.

I'm not a flow engineer or anything, but I know this is the case, so I just accept it. Turbo models may experience a 2.5 to 3" or 3.25" exhaust to be good (depending on other mods).

EDIT:

Borlas ARE in improvement over stock headers on the 99-01...5 hp maybe....i would estimate less power gains for the 08 because it looks as though the 08 headers are more efficiently set up and have better flow. Borlas on the 08 will probably only yield a different sound, probably the same power, maybe even a slight loss.

SCCA Autocross Info:

You can use any exhaust system and it will bump you to ST (however, if you remove your cat it will bump you into a higher class.) Considering you will gain limited power from removing your cat, and be bumped to a class with cars that can be heavily modded...i would suggest you retain your stock cat, but upgrade everything else. Also, if using an aftermarket exhaust in ST, make sure your cat is in approximately the same place as stock under the car (another rule).
 

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Discussion Starter #3
Re: Rallyshark's Guide to NA...lots of info...

ENGINE INTERNALS (Cams, heads, pistons)

So most people who are serious about going NA are going to mess with internals. In the case of the 99-01 2.5L SOHC engine, this isn't too much of a problem. There are lots of companies that offer some options, TWE, COBB, and some others I'm sure.

Unfortunately for the 08, there appear to be no plans for anything on the internal end from what I can tell. But who knows, if the demand grows, then parts will be made.

For the Subaru NA engine of the past. You can pretty much do almost anything to it...they have recently officially stopped offering internals from COBB, except cams...but the cams will get you almost 20 awhp. Not too shabby. You can buy higher compression pistons, exotic metal valves, springs, and retainers, cams, all that jazz...

I'm sure a company like Cobb or Rallitek WOULD make you a custom NA engine, you'd just have to pay for it...luckily though, you would get a nop notch NA engine. Probably making WRX power levels (maximum of about probably 250 bhp reliably)

The big reason why these things aren't offered for the new engine is that the new engine has AVLS (active valve lift system) which throws a monkey wrench into just swapping an old performance camshaft in there.


Delta has released cams for the NA 08-09. They are being sold by Rallitek. Rallitek is also selling heavy duty valve springs and retainers which would be a prudent investment.

Older subaru NA valve sets and piston sets for the 2.5NA engine should also be able to be used with the EJ253 (08/09 2.5i engine)

If you start putting internals into an engine, you're going to need engine management and a tune, plain and simple. You can get away with ported heads and a camshaft on the stock ECU, but that is about it. (See tuning below). Also, depending on your internals, an upgraded fuel pump and injectors may also be required. Upgraded head gaskets and cylinder sleeves may also be a good idea depending on the extremeness of your build.

Unlike intakes and exhausts, putting internals in your engine and upping compression WILL DECREASE THE LONGEVITY OF YOUR ENGINE. Headgaskets and things will have less life, eventually oil leaks will develop that won't develop on a stock engine. Not saying you will blow your engine in 50k miles...but if you wanna play with your engine on the inside, have a thick wallet.

SCCA Autocross Info:

Any internal engine mods will bump you to SM (street modified) in this class you will be competing against Mitsu Evos, WRX STIs, and other scary vehicles that are modded to high horsepower levels and have really upgraded suspensions. If you are concerned about autocross classing and do not have a rediculously good suspension setup, I would recommend staying in ST to remain more competitive. You can basically upgrade your suspension to anything you want (with some exceptions) and all bolt-on engine mods (with the exception of a turbo or supercharger) and remain in ST. Also in ST, you can't use R-comps, so you don't have to worry about people using them against you ;)
 

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Discussion Starter #4
Re: Rallyshark's Guide to NA...lots of info...

Lightened Engine Parts (Flywheels and Crank Pullies, Other Pullies)

Adding lightened accessories and flywheels and such has a different effect on your engine than adding an intake or exhaust. Let me explain.

The 2008 Impreza floats around 170 crank horsepower (also called BHP, brake horsepower). This means horsepower measured from the crankshaft.

As many of you know, there is also wheel horsepower (whp, in a subaru many say "all wheel horsepower", awhp). This means horsepower measured from the wheels of the vehicle.

WHP/WTQ factors in drivetrain losses and other power/torque losses in the system as it goes from your crankshaft on the engine to the ground.

The stock 2008/09 Impreza is somewhere around 130ish awhp/awtq. (Approximate numbers given by 3G Member "deltableh" from a dyno run).

So you ask..."Why do I lose potentially 40 horsepower just going to the wheels?!" and "How do I get it back?!?

Any drivetrain system has losses, AWD systems tend to lose more than FWD or RWD setups.

The answer/solution:

Lightening parts downstream of the crankshaft or things that run off of the crankshaft usually help.

-Lightened crank pullies are nice, Perrin makes one that I've personally used with success. Also made by Kartboy and various other companies.

-Lightened or Underdriven Accessory Pullies which run via belts off of the crankshaft (the crank pulley has 3 belts coming off of it...the power steering pulley, alternator, and the AC pulley)

-Lightened Flywheels (attached to the backside of the crankshaft) Fidanza makes a good one.

-Lightened Driveshafts (never used one, although I'm sure they help)

-Lighter Wheels

So basically with intakes, exhausts, engine internals, tuning, etc. you can add to your BHP and AWHP numbers...
...but lightened parts downstream of the engine will only add to your AWHP numbers.
(In other words, intakes, exhausts, etc add to the power of the engine, lightened parts only help eliminate the inherent loss of the drivetrain.)...but are good though.

Important Info about each of the above mods...

Lightened crank pullies are sometimes frowned upon because many have said that the stock crank pulley has a harmonic balancer in it and without this balancer the engine is going to fly apart. Info direct from subaru has stated that the crank pulley does NOT have a harmonic balancer in it....However, nobody has done extensive testing on the effects of a lightened (non-stock) crank pulley on a subaru engine (to my knowledge).

Underdriven Pullies (both crank and accessories) use pulleys that are less than the stock diameter AND stock weight. This helps the engine rev faster (less rotating mass on the engine)....the downside of these is that stereos systems that are upgraded tend to bog down because of their extra load and less alternator power...AC compressors also get less power and it makes the AC in the car less cold (ie, it sucks ;) ).

Lightened flywheels help you rev the engine faster, makes the car accelerate slightly better. Lightened flywheels have been known to explode under extreme loads....this is very rare though. (Most exploding flywheels are a result of people machining down a stock flywheel to a level with which there is not enough metal to keep it structurally sound). Saw some pictures of a skyline with a stock (machined down) flywheel that exploded, not pretty.

Some companies have successfully machined down stock flywheels with no problems, but they do not remove alot of metal either. Many claim that a lightened flywheel makes the car less "streetable," however, I had a 9lbs fidanza on my car for a long time with no trouble driving it in stop and go traffic, just need to get used to it (it IS rough at first though, hehe).

The next problem is one that I've personally experienced. When I had a lightened Perrin crank pully and a Fidanza flywheel, I kept getting misfire check engine lights (CELs). Many gurus have decided that these are "ghost" cels and triggered by oversensitive sensors in the crankshaft area (crank position sensor I believe). These ghost CELS, whether they are real or not, CAN cause you to fail your emission test in your US state depending on your state's procedures. So you may want to avoid this combo...some have even experienced a misfire CEL with only one of these mods, not both, but they are less common.

Never used a lightened drive shaft, don't know if they are good or if there are any drawbacks....

Lightened parts can help you gain back a good amount of horsepower, 10-15 best case scenario (which is alot in an NA car). You just need to decide if it is worth the time and the effort with the possible drawbacks.

SCCA Autocross Info

Lightened Crank will bump you to ST as well as any underdriven pulley setups. Lightened Driveshafts and Flywheels will probably again bump you to Street Modified (SM).
 

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Discussion Starter #5
Re: Rallyshark's Guide to NA...lots of info...

CHECK ENGINE LIGHTS (CELS) AND ENGINE MANAGEMENT/TUNING

Check engine lights should be rare for your car unless you totally mod the crap out of it. In which case, you could get ghost CELs that are not fixable (lightened crank and flywheel combo).

Below are some common tips to help avoid check engine lights.

When adding aftermarket headers or eliminating a cat, you can prevent a check engine light by putting a spark plug defouler (with the end drilled out) on the end of your bank2 o2 sensor. The defouler should then screw into the second opening of your catalytic converter or track pipe. This specific CEL is caused by the exhaust gas being much hotter than what the o2 sensor was designed for and causing it to fail/read faulty. The defouler acts as a spacer and removes the sensor from direct contact with the exhaust stream, cooling it down and causing it to function correctly again.

Also, when installing aftermarket headers you should probably do either of the following:

Wrap your header section:

DEI sells a good kit that I used....you coat your headers, wrap your headers and then coat the header wrap again. This will cause your headers to be touchable while hot, help keep underhood temps cooler, and wrapping them can sometimes eliminate the need (when using borlas and a stock cat) to use the defouler mod above. If you wrap your headers, make sure the wrap is COMPLETELY dry and tight before you mount it on your car and use it...any trapped water will cause the header to crack). and YES, the headers WILL smoke when you start the car up, don't freak out, hehe :) The smoke and bad smell will go away after a few days.

(NOTE: I had borla headers wrapped in the above fashion, (and the defouler mod) while using the stock subaru cat and never had a CEL from my exhaust...also had a stromung catback for reference...awesome sound by the way :) ).

Ceramic Coat your headers:

On a more expensive route, you can also get your headers ceramic coated...which is more expensive and can possibly work better, but it is not a DIY mod. Swaintech did a great job for 3G Member "battlesnake99".

TUNING

There are many aftermarket tuning solutions out there...Perfectpower6...apexi safc...expensive ones like hydra. (COBB NA Accessport coming soon as well!)

All have their advantages and disadvantages...i would recommend tuning using a professional (with references from other people) using one of the above systems...or another proven system.

There are open-source tuners that work just fine, however, if you don't know what you are doing you can blow your engine up in about 10 minutes :p

I've used perfectpower6 and it worked pretty well, I got rediculous gas mileage (400+ miles on a tank of gas...so probably 35+ mpg, extra power, probably around 10-15 horses)...However the tuning unit died on me.

I was just driving normally in 5th gear at 50 mph and the thing just stopped delivering spark to the coilpack...and the car died...in a rain storm...the unit was installed by someone whom I didn't have the greatest confidence in (previous owner of the car)...it probably would have worked better with a pro installation from an expert (but I bought the car with the tuner already on it, I didn't have a choice). SO...i removed the tuning unit and the car reverted to the stock ECU and everything was grand...but I missed the extra power and gas mileage.

I honestly think the pp6 failing was a result of the crappy install of the guy that did it...i have not found another case of one failing.

The 2002 and up imprezas actually have an easy to use passthrough harness for the PP6, (not one that you had to manually wire up with crazy looking diagram like it was on the 99-01). Rallitek offers the pp6 and it *should* work with the 08. Ask them to do a custom map for you as well.

I can't stress enough that you should get someone who knows what they are doing to tune your car, a bad tune can either instantly kill your car or kill it slowly over time. Had a friend with a "tuned" mustang...the tune was too much for the engine
and it just started falling apart...granted it was a ford engine...but still :)

Another note on tuning:

Getting your car tuned on a dyno is great as a baseline, but the only way to get a really great tune is have it road tuned (tweaking "dyno-tuned" numbers with a real life drive).
Road tuning can be dangerous as you have to do a third gear pull (usually on public roads)...be cautious, your tuner will probably have a good spot to do it if they offer road tuning.

SCCA Autocross Info and Conclusions:

Engine Tuning will bump you to ST...I think that is all. So basically, anything except eliminating a cat, bolting on a turbo/SC, or engine internals and you will keep yourself in STS (Street Touring) (at least from an engine mod perspective).
 

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Discussion Starter #6
Re: Rallyshark's Guide to NA...lots of info...

CONCLUSIONS & MORE INFO

Again, I'm not a certified mechanic, nor a subaru tech, nor a "tuner" that does this for a living. I'm an average guy that does alot of this stuff himself, has researched alot, and has pretty much been around the block with an NA subaru. (Don't ask me about a WRX unless it is a suspension or a basic working knowledge) :)

So, I know this is not the most thorough thread regarding upgrading an NA vehicle, it is just a starting point. Any subaru owner could spend years just researching one aspect of their car. I just provided you with an unbiased look at your options.

For those that are wondering, my second 2000 GC8 impreza had about $15k in mods on it....running the stock ECU, it probably had near 200 bhp. For the engine it had: Cobb street performer cams, stage 1 cobb heads, perrin lightened crank, fidanza lightened flywheel, cobb intake, exedy stage 1 clutch, borla headers, stock cat, and stromung catback....for the suspension it had KYB AGX struts, jdm v6 tarmac springs, upgraded endlinks and swaybars and strut braces all around, racecomp engineering camber plates, rear camber bolts...and lots of other random things that made it nice :) I shall miss her, she was a fast car that handled like a champ...but I sold it to afford my 2008...which was done to have a non-race car to haul my new baby girl around in...whom is due any day now :) EDIT: (She's 17 months old now :) )

For those of you that are WRX owners, thirst for extremely complete info, or just like to learn everything you can about cars...I'm now giving you the link to the Unibomber's Manifesto on Nasioc.com...he mostly focuses on turbo models, but TONS of good info in there, more so than I would post on this forum....his info on the NA vehicle (especially the 2008) is very limited and that's why i'm covering the basics here :)

Link-------------> http://forums.nasioc.com/forums/showthread.php?t=533787

As far as NA engine mods...talk to rallitek, they seem to be focusing on the NA more than any other company.
 

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Re: Rallyshark's Guide to NA...lots of info...

so will the borlas actually pick up some power over the stock header? iv heard the newer equal length design is actually a pretty good factory set up. i was considering doing an exhaust but didnt want it to sound like a honda, which is why i was looking into the borlas. definately not going to put them on if it decreases power though. one suggestions, i think at the end of each of your sections we sould try to compile a list of available aftermarket parts for the 08 pertaining to each section. as of now, i cant find anything power wise
 

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Discussion Starter #9
Re: Rallyshark's Guide to NA...lots of info...

Good idea Lurker about available parts listing.

The borlas ARE an improvement over stock on the 99-01...I would estimate around 5 horses and a definite sound quality increase. Not alot, but borlas are 300 dollars...half the price of the Equal lengths at least...and you can still use your stock cat..if you buy an equal length you ALSO need to buy a high flow cat, or test-pipe section.

On the 08...you are right, there are limited power mods available...if any. I'm sure they'll come out in the near future though.

I will be getting under my 08 in the next few days to scope things out as far as the sway bar situation and the exhaust setup...hehe. I'll update this forum on what I find.
 

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Re: Rallyshark's Guide to NA...lots of info...

Good idea Lurker about available parts listing.

The borlas ARE an improvement over stock on the 99-01...I would estimate around 5 horses and a definite sound quality increase. Not alot, but borlas are 300 dollars...half the price of the Equal lengths at least...and you can still use your stock cat..if you buy an equal length you ALSO need to buy a high flow cat, or test-pipe section.

On the 08...you are right, there are limited power mods available...if any. I'm sure they'll come out in the near future though.

I will be getting under my 08 in the next few days to scope things out as far as the sway bar situation and the exhaust setup...hehe. I'll update this forum on what I find.
well as im sure you know, the sway bar situation is that there is none. its really a shame. they have the holes to mount one up on the rear subframe, they must have just forgot to put it on all the n/a cars :'( the muffler, wholy crap is that thing huge. it looks like its for a full size diesel pick up!! anyways, i did put a set of wrx springs on my obs. huge improvement over the raised obs suspension, minimal cost, retains factory look/ride, but is a lot more firm and handles 10x better. lowered the car 3/4"-1" after the springs settled in. ill be getting a set of rallitek f/r sways soon.
 

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Re: Rallyshark's Guide to NA...lots of info...

ive got a nice list of compiled mods for a 2.5i 4dr automatic, ill put it up when i can.

as for me i know my first mods are gonna be swaybar/endlinks kit, lightweight pulley, and at least an axle-back in not a cat-back.

after that, i would save up and do an intake and a PP6 in one run with a professional tuner.

and thats all i can really foresee in the cars future, except maybe sport springs.
 

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Re: Rallyshark's Guide to NA...lots of info...

Hello everybody
I'm from the philippines.
Any suggestion on putting a supercharger bolt on, on my 2.0 RS Impreza. Ours here are 2.0 for the NA Impreza and 2.5 for the WRX
 

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Discussion Starter #16
Re: Rallyshark's Guide to NA...lots of info...

Technically a bolt on supercharger ceases to be NA...in which case, you're in the wrong forum...

However...

NA mods can support a belt-driven supercharger because you don't need the uppipes and downpipes stuff like that for SC setup and in most cases you can keep your NA engine mods (unless you need lower compression pistons).

From what I've found, all supercharger applications for the NA impreza are custom and there is not a huge market for them. There are several companies that offer turbo options though. Forced air tech is one of them...avo probably has a bolt on turbo application as well.

If you are very interested in a supercharging option for your NA impreza, you could contact COBB tuning and ask them about a custom supercharging rig for your 2.0 impreza, however, they are in the united states and could probably not get an equivalent JDM engine like you have (we have the 2.5 NA here).

You are probably going to pay alot for cobb to do this for you though, they did a custom SC setup for the B9 Tribeca and it works great....i don't know if money is an issue though...although it would work well and I'd be jealous ;)
 

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Re: Rallyshark's Guide to NA...lots of info...

has anyone used the lachute exhaust?

also is the tip from rallitech only for looks? or dose it at least help sound.

really interested in ording from lachute, but i want to hear from people who have delt with them before.
 

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Re: Rallyshark's Guide to NA...lots of info...

Technically a bolt on supercharger ceases to be NA...in which case, you're in the wrong forum...

However...

NA mods can support a belt-driven supercharger because you don't need the uppipes and downpipes stuff like that for SC setup and in most cases you can keep your NA engine mods (unless you need lower compression pistons).

From what I've found, all supercharger applications for the NA impreza are custom and there is not a huge market for them. There are several companies that offer turbo options though. Forced air tech is one of them...avo probably has a bolt on turbo application as well.

If you are very interested in a supercharging option for your NA impreza, you could contact COBB tuning and ask them about a custom supercharging rig for your 2.0 impreza, however, they are in the united states and could probably not get an equivalent JDM engine like you have (we have the 2.5 NA here).

You are probably going to pay alot for cobb to do this for you though, they did a custom SC setup for the B9 Tribeca and it works great....i don't know if money is an issue though...although it would work well and I'd be jealous ;)
thank you very much then.
However, if I do abolt on supercharger or turbo with my vehicle, does it entail me to change cams, pistons and etc.
 

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Discussion Starter #20
Re: Rallyshark's Guide to NA...lots of info...

If you do a bolt-on turbocharger/supercharger you won't need to change pistons and cams and engine internals necessarily...

You will need to upgrade your fuel pump, get engine management, all the necessary piping, maybe larger injectors...see the below link

http://www.forcedairtech.com/turbokits_gc8_stage1.html

The above link outlines basically what you'd need.

However...the stock EJ25 (SOHC) is an open deck engine which doesn't allow for much boost, maybe around 5 psi (and it decreases engine longevity...aka stuff will break)
-If you upgrade internals it will last longer and you can run more boost though. (I'm not sure how the internals of the EJ20 NA like you have there are).

Unless the NA subaru engines have changed drastically, you are better off upgrading to a turbo-type engine if you want to mess with a turbo b/c the NA engines just aren't strong enough for it.
-In other words, you'll usually spend more money trying to make an NA engine strong enough to handle more boost and give it longevity than you would spend just buying a WRX engine.

Food for thought though...an NA engine with high compression and low boost has alot of torque and no turbo lag b/c it still has the 10:1 pistons in there from the stock NA engine. They can be really fast!
 
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