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Old 06-09-2006, 01:22 AM   #2
Scooby Specialist
Member#: 62629
Join Date: May 2004
Chapter/Region: MAIC
Location: Richmond,VA
1996 OBS in Green
2.5 N/A w/ full exhaust



There are other “power” mods that are popular that if anything improve the feel of the car. The lightweight pulley is generally considered a useful mod. It reduces the drag of rotational weight on the crankshaft “releasing” about 3-5hp worth of energy to the wheels. The biggest benefit being better throttle response and faster revving.

COBB sells their Power Pulley for $135, Rallitek sells Perrins Lightened Pulley for $130. Unorthodox Racing carries two types, one lightened and one lightened and underdriven. The Underdriven pulley has a smaller diameter than the stock pulley so it has even lower parasitic drag on the crankshaft. The down side is that is doesn’t drive accessories on the car as well as stock so there may be some loss of electrical power. Most vendors price the UR pulley at $150. Mr Josh sells a pulley for about $75.

Lightweight Flywheels provide the same type of gain as the pulley. It is generally recommended that you don’t do both the flywheel and the pulley as it may cause the car to idle poorly. Some owner report no problems but the recommendation is from knowledgeable sources.

Grounding kits provide better electrical grounding to the cars sensors and electrical system. The theory being less electrical interference provides the car’s ECU with better data and the car runs better and stronger. Most users seem to notice smoother idle and excelleration. Some dynos are available that suggest a small 2 – 4 hp gain. These kits can be found on EBAY and most aftermarket suppliers. Paranoid Fabrications sells a nice kit onfor between $35 and $50 depending on the level of wire and fabrication desired. He can be found on . A DIY kit can be put together for about $10, instructions for this are all over the Web.

While not a new concept in N/A performance enhancement, suppliers for this part for the EJ25 seem to be just one. Area1320 sells a EJ25 TB spacer and has dynos on their site showing around 4hp gain. However most users have reported a significant gain in fuel mileage. Somewhere in the neighborhood of 4 mpg. At $150 this could pay for itself quickly. One caveat is that supplies seem to be pretty limited as the shop makes these on a part time basis. It is not their primary business.


In your searching (assuming you do any) you will find in every thread about N/A power at least one naysayer who calls you stupid for trying to make N/A power. Their solution is to always swap in a WRX motor or turbo your existing 2.5L motor. The argument being that it provides more power and is less expensive or a better value.

Here is my opinion on the issue. First lets address the cost issue. If you buy a USDM WRX motor you will generally spend $1500 -$3500 on the motor, this should include a wiring harness and ECU. This is money that is spent in one lump sum and is not always easy to do. These motors are almost always used so reliability is a concern. There are many threads of folks buying bad motors and having to chase down the seller to get their money back.

Additional associated with the swap include exhaust parts, uppipe, downpipe and turbo cross member. On top of that is the hours spent splicing the WRX wiring harness into your RS / L harness. For a first timer expect about 30 – 40 man hours. My time is worth about $40 an hour in my business that is an additional cost of $1200. So figure a full $4000 of real dollars as the swap cost. You may need driveline components as well.

With the swap you get a WRX engine that dynos at around 170whp. A stock EJ25 dynos at about 100whp. If you have an older Impreza your car is also lighter than current Impreza so power to weight becomes a factor as well. A 1996 – 2001 impreza only need about 150whp to equal the power to weight ratio of a bugeye WRX. I will illustrate.

A 1998 Impreza weighed about 2800 lbs ( the coupe and sedan less, the wagons more). Based on 100whp a GC style impreza has a p/w ratio of 28:1.

A 2002 WRX weighs about 3100lbs, with 170whp its p/w ratio is 18.24. To equal that p/w ratio the GC owner only needs 152hp at the wheels. This can be achieved with cams, intake, headerback and EM. New these parts would run about $2000. Do some smart shopping and your budget is closer to $1200. You also don’t have to spend the money all at once so you can use WAM (walking around money), those readers who are married know how important that can be. Keep in mind that these numbers assume the two vehicles are dyno on the SAME dyno under similar conditions. Dyno results varily widely from one dyno brand to another, one location to another and even the operator of the dyno can have and impact.

You also don’t have the down time of a swap. Parts can be bought and installed a little at a time, so the car is down for a weekend. Cams are the only parts that put you out for a week or so. The addition of heads can put the N/A owner close to WRX power levels. Coupled with the RS’s better gear ratios, a properly tuned RS can give even Stage 1 WRX’s a run for there money in most situations.

Auto-x favors the tuned N/A car. The WRX needs to spool out of every corner ( the ’06 model fixes this to some degree) unless left foot braking is well executed. The N/A motor sees good power from 2500 rpms to redline.

For the $4000 that a swap would cost a prudent N/A impreza owner should be able to reach the hi comp piston level of build, assuming the labor is DIY. This should give you at least 200hp at the wheels. Keep in mind that their only a handful of ppl attempting a build to this level and it can be time consuming. But a stock WRX needs a Stage 1 mod package to reach these levels, and at that the p/w ratio is still an issue.


N/A power is available for a reasonable cost, don’t let the boost fanboys tell you otherwise. But if you want 300hp in your current non-turbo impreza your money IS better spent on a swap. If you want WRX levels of power without dropping $3000-$5000 in one lump then consider the build instead.

P.S. for us 2.2L owners, add in an additional $500 to $1000 for a 2.5L motor to swap. Fortunately this is a plug and play procedure for the most part. So down time is at a minimum. Also you can do things like heads and cams before you drop the motor in saving you more time.

There is also the Frankenstein motor. This is a 2.5L block with 2.2L heads which bumps compression up to the 11.2:1 area. I haven’t seen any dynos but the math makes sense. A 2.5L block can be found for $250 - $500 and heads can come off your existing engine. You simply swap intake manifold and everything else over to the new longblock. I am considering doing the cams pre-install as I have a set of ’94 dual port heads (I can take advantage of the new EL header available) I picked up for $100 at my local u-pull-it junkyard. Power with Borla headers, intake is reported to be in the 150whp range. I’m interested to see what cams, EL headers and PPP6 do at the dyno and the strip. Hopefully I can have this done by the end of this year (’06)

For those interested their is good post here on 1/4 times.

To see what is possible with enuf resources check zzyxx out

Matt Monson's thread with dyno info
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Last edited by Rally_wgn; 06-23-2006 at 12:07 AM.
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