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View Poll Results: What is the issue?
Crummy octane/gas, you moron! 0 0%
ECU is adjusting to clean filter/other ECU issue 0 0%
Short ram intakes sap power in high-end 0 0%
That's just how a 04 WRX accelerates 0 0%
Voters: 0. You may not vote on this poll

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Old 12-21-2014, 11:55 AM   #1
Scooby Newbie
Member#: 173499
Join Date: Mar 2008
Question Power Curve/Acceleration in Stock WRX Question

Hi Guys,

Here is my car's basic specs:
-Year: 2004
-Model: WRX
-Mileage: 78,000
-Transmission: Manual

-Axle-back exhaust
-K&N Short Ram intake

My question is regarding power delivery. Lately I have been experimenting with a mix of different fuels/octanes to try and save money. I know you all are going to say "there's your problem stop buying ****ty gasoline" but please read on as this may not be the "only" issue.

I had been noticing choppy/uneven power delivery under heavy acceleration in 1st and 2nd gear (half-to-full gas) regardless of octane. I use the car daily for commuting, so I don't drive it that hard, so usually I haven't noticed this for a while and I have no idea how long it's been going on. Also, I have always assumed that it's just slack/jitter in the drive train causing feedback patterns (at least in 1st gear).

Yesterday I took out the cone air filter on the short-ram intake (which was DEFINITELY in need of cleaning), and cleaned it thoroughly using the K&N Recharger kit. After it was fully dry and properly oiled, I re-installed it in the car, and went for a test drive with 88-89 octane gas.

I know using low octane screws up your compression and ECU, but I was too curious to see if the filter cleaning made any difference, so I let the engine warm up, tooling around town for a while, and it seemed that the low-end throttle response and torque had improved greatly. Then I decided to jump on the freeway and open it up.

As I accelerated through the top of 2nd gear, something very alarming happened - at 3.5-4.5 RPM the boost came on, and the car accelerated rapidly as expected - then when it came to 5-5.5k, the engine seemed to lose power, so rapidly that for a moment it seemed that the fuel cut out, or the valves rose or something as if reaching redline without a rev-limiter. It basically felt like I hit a "bump" and the car even slowed for a split-second. Stupidly, I kept my foot to the floor, and the car continued to climb to 6.5k RPM before I shifted.

I continued cruising, and then performed the same test once more. Through 2nd gear the power delivery seemed smoother the 2nd time, there was no jerking or power "dip", but the engine acceleration seems to be rather "mundane" past 5K RPM - almost as if the car isn't really accelerating anymore, just kind of climbing in RPM.

I looked at the Horsepower/Torque charts for the stock 04 WRX, and the power delivery "feels" to me congruous with the graph - that is I can feel the boost building and therefore torque building from 3K-4K RPM and the car is definitely accelerating it's quickest here - also the fact that torque drops off after this point while HP continues to steadily trickle upward seems to agree with what I witnessed.

I cannot remember exactly how fast the car was when I first bought it, but as it was treated rather roughly in it's early years, and I am just now beginning to really "take care" of it, I wanted to get some opinions on how the WRX's engine really should be responding, and if there is anything that sounds wrong with my car. The WRX if I remember was kind of slow at higher RPM's anyways if I remember correctly, but I like I said I haven't driven it hard for a while so I'm not sure if mine is behaving correctly. The power seems/feels great when accelerating through 3.5-4.5K RPM, but then it just seems to "flatline" after that.

Am I just not shifting soon enough? Have I ruined my ECU by using crappy gas and a short ram intake? Did I spray too much oil on my filter and have it suck into the engine? Do I need new spark plugs?

P.S. Another thought is that when I cleaned the air filter element, I did not remove the Mass Airflow Sensor and clean that as well - is this something I should do?

Any thoughts would be appreciated. Thanks! =]
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Last edited by WRC9000; 12-21-2014 at 12:01 PM. Reason: typos
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Old 12-21-2014, 12:53 PM   #2
Scooby Newbie
Member#: 399191
Join Date: Aug 2014
2002 WRX


Wrong octane fuel leads to pre-ignition...your right use the right kind of fuel. It's an 11-12 gallon tank your saving what 4-5 bucks a fill up?

I personally would not use any oiled media filters. No matter how dry you think it is, it will still coat the inside of the intake/MAF with residue in time.

You should clean your MAF with MAF cleaner...it's around 6-8 bucks for a can at your local auto parts store. Be sure to not just clean the IAT(little amber sensor) but down inside it also.

You can check your spark plugs for wear...they should be gaped .028-.030
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Old 12-21-2014, 01:03 PM   #3
Scooby Specialist
Member#: 383633
Join Date: Mar 2014
Chapter/Region: RMIC
Location: Yampa, CO
2002 Impreza WRX


This comes down to a few different things:

Someone was not following manufactures instructions on very important things like octane. This is your safety factor of the fuel to put it simply. The higher the number, the better the safety. So yes using lower octane is bad, stop it you moron.

The other is the MAF needs to be cleaned with the proper product for that purpose. Any contamination can foul the reading or overheat and ruin the sensor.

I also suspect you have old brittle leaking lines all over resulting in leaks. This will also cause serious problems. Have it boost leak tested.

Since your just starting you have a lot to learn. If you are truly interested in learning and possibly saving your car then go download a factory service manual for your car and read it before you begin work. Research on the internet.

Turbo cars are very complex balanced systems of match components.

You can do serious damage without knowledge.....
Shiftace420 is offline   Reply With Quote
Old 12-21-2014, 01:25 PM   #4
Scooby Newbie
Member#: 173499
Join Date: Mar 2008

Thanks for the replies, everyone. I'll try to stop using lower octanes... but sometimes the price is so low by comparison it's really tempting. And every time I told my Dad to put premium in it he would scoff at me - I guess he doesn't know anything about turbos.

I'll also look for that MAF cleaner, too.

Anyways the car gains a lot of miles fast (I average over 420 a week), so I think I am going to ask the service technicians to address a lot of issues at the milestone 90,000mi scheduled maintenance. They are supposed to do a pretty thorough maintenence around then, and I think there may be some belts or pumps in need of replacement as well... and I'll see if I can get them to look at the turbo too.

I've noticed a sort of "whining" or not-quite-squealing noise when cold-starting the car. Sometimes it goes away after warming up but it seems to persist more often now (started about a week ago). Anybody know what this could be? When I opened the hood it sounded like the belts, but I'm not sure, might probably be a component attached to them.
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Old 12-21-2014, 01:38 PM   #5
Scooby Specialist
Member#: 383633
Join Date: Mar 2014
Chapter/Region: RMIC
Location: Yampa, CO
2002 Impreza WRX


Yea the octane rating is very important on high performance engines. You will destroy your engine if your not up to spec. Dad is going to ruin your engine if he puts the cheap stuff in. Its rough when it happens, about 5k in most areas for new engine. If these cars were low compression N/A engines your dad would be right to scoff but these cars Need it.

Get it fixed, drive easy to reputable subaru shop(research). Cross your finger the damage is not already done.

Last edited by Shiftace420; 12-21-2014 at 01:44 PM.
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Old 12-21-2014, 02:08 PM   #6
Scooby Newbie
Member#: 318368
Join Date: Apr 2012
Location: Snohomish Washington
2007 WRX sedan


As others of said $4-5 more on gas is much better than Risking detonation with bad fuels. Also, someone can correct me if I'm wrong, that intake should require a tune. I know 02-03 models could run in intake without a tune but I "think" 04 and up should have a tune with an intake. If so that might help solve your fuel cut.
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Old 12-21-2014, 02:09 PM   #7
Scooby Newbie
Member#: 260812
Join Date: Oct 2010
Chapter/Region: SCIC
Location: Costa Mesa
2004 Wagon


The squealing sound could be a lot of things. Could be an accessory belt or a bad bearing in any of the 3 components driven by the two belts.

Open your hood and listen to where the sound is coming from. Remove the two accessory drive belts and start the engine to see if the sound is coming from a timing component. The timing belt idler bearings seem to go out early sometimes.

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Old 12-22-2014, 06:37 AM   #8
Scooby Newbie
Member#: 268632
Join Date: Dec 2010
Chapter/Region: South East
2004 WRX wagon
Suby Blue


A/C idler will make a whine, too.
pebelz is offline   Reply With Quote
Old 12-22-2014, 08:07 AM   #9
Scooby Guru
Member#: 32792
Join Date: Feb 2003
Chapter/Region: NESIC
Location: lincoln, ri
2003 GGA MBP
12.9 / 105+


omg this thread.
ride5000 is offline   Reply With Quote
Old 12-22-2014, 04:21 PM   #10
Scooby Newbie
Member#: 378119
Join Date: Jan 2014
Chapter/Region: E. Canada
Location: Ottawa
2004 Impreza WRX
World Rally Blue


I remember the stock powerband.

-nothing-nothing-3.5k*bit of power*4.5k-nothing-nothing

Do you still have the stock intake somewhere?
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