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2004 Forester Manual
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95 Posts
Discussion Starter · #1 ·
I find a lot of literature about this on this site and elsewhere on the internet, but i would like to hear everyone's take in a certain perspective towards their Foresters.

So realistically, your car is tuned to run most efficiently and effectively with stock parts. Engineers spent hours developing the way the parts work using advanced testing equipment, so how effective can dumping money on air intakes, headers, throttle body spacers, lightweight pulleys, exhaust parts, and any other part from the ridiculous list of "horsepower increasing mods" be? Especially when the cars computer tells everything to do what they do a certain way.

There is an amazing video that Might Car Mods (love those guys) did where they put a car on the dyno and compared horsepower ratings before and after a cold air intake install. Showing that the car made no, maybe even less horsepower. Is it likely that this is the case with all "horsepower increasing mods"?

I see people even on this forum installing such parts, grounding kits, intakes, headers etc and actually say they notice a huge difference, who attributes this sort of thing as a placebo effect? and who swears that they have noticed improvements?

Also, if anyone has personal experience manipulating their electronics to accommodate such mods id love to hear about it.
 

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2014 forester cvt
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109 Posts
I have spent a small fortune over the years on mods and dyno tuning. And I have learned a few things. Lets take a cold air intake as an example. You might gain power with a cold air intake and you might not. Depends entirely on the vehicle and how efficient the stock setup is. I know a guy who cut out all of the fins in his air box in an attempt to increase the volume of air available. He lost 10 hp. Lesson here is that the stock air box is a lot more complex than people realize. It is a system. And some are better than others. Lets say you buy a cold air intake and gain 10 hp at 6000 rpm but lose 10 hp at 4000 rpm. Which would you rather have? I will take the system that makes the most midrange power as that is where you will use it. On a 4 cylinder car I doubt a good cold air intake will gain more than 5-7 hp at best. And that is not enough to feel. So when people say they put on a cold air intake and it made a night and day difference you have to shake your head. Really? They spent their money and dont want to admit it made little difference or they confuse more noise with more power. If you stay outside the engine with an intake, exhaust and tuning you can probably see about a 15 -20 hp gain on a typical 4 cyl. car. That you can feel. But again, where is the gain? If it is all in the top end that would not be for me. Best you can do is find someone else who had spent the time developing a combination of intake, exhaust and tuning and copy their formula. Even then dyno tuning your specific vehicle is key. Otherwise it gets really expensive and frustrating.
 

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2010 Forester Active 2.0X MT 2x5 - MT with Dual Range reduction
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1,235 Posts
At least during the time of the warranty I never would do any tuning.

For example by chip tuning you will lose instantly the 5 year or 160k kilometers warranty of Subaru Germany.

As far as I know that's the same in all European countries.

I also don't believe, that there's a difference in the USA.

And if I ever would plan to do any tuning, I only would do it with parts offered by Subaru itself.
 

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2014 2.0XT Touring CVT
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114 Posts
At least during the time of the warranty I never would do any tuning.

For example by chip tuning you will lose instantly the 5 year or 160k kilometers warranty of Subaru Germany.

As far as I know that's the same in all European countries.

I also don't believe, that there's a difference in the USA.

And if I ever would plan to do any tuning, I only would do it with parts offered by Subaru itself.

This.. I am not going to mess with my XT until the factory warranty is over.

-Peter
 

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2014 Forester XT 8 speed
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113 Posts
I'll bite..

OEM vehicles are tuned to what their engineer deems ideal conditions, with ideal fuel, and they also have to take into account manufacturer tolerances (ie, two identical engines built to identical specs may not have the same HP rating. Give or take 5hp).

OEM's have to tune a vehicle for +8000ft above sea level, along with sea level. They do NOT adjust maps because a car is being shipped to a higher elevation. Weather, -45C to +45C, same thing. Fuel, winter gas, vs reg. 87, and so on and so on. And I know you'll say "the computer adjusts", well, it does, but only within those perimeters set by OEM. Tuning a vehicle narrows down those parimeters to your specific driving requirements. Which is why you will see gains in performance with a tune. More so with turbo cars. Those tunes may come at the expense of longevity/performance/mpg (pick two).

Performance mods (H/E/I/etc), as mentioned, vary greatly depending on what the vehicle is and to what extent it is modified, and to what extent the mod has been engineered.

As an example, on a wrx, you see very little gain from adding just an intake. Yet, if you upgrade intake,turbo, headers, exhaust, you will see a very considerable gain from just the intake. And at that point, the car needs to be tuned, so even more gains.

My truck (as another example, stock 2003 GMC 1500HD w/6.0L), has a custom blackbear tune on it, that is it. And I saw an increase of 15% on my MPG, not to mention drivability has greatly improved as the shift points have been optimized. Now is that going to happen all the time, on every vehicle, not likely. The tuner has done a ton of research/development, and knows how to optimize the fuel maps. My truck is an example of where by changing the exhaust, I will lose power. Which is why mine is stock. Backpressure can be a good thing sometimes.

IMHO, mods can make a considerable difference, as long as they are researched and executed properly.

But you must determine what you are trying to accomplish with the mods.
 

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2007 Forester Sports XT 4EAT
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From what I've read & from my experience, there isn't much hidden power to be found in the NA... nonturbo engine. :frown:

I'm not saying you can't get more power, if you're willing to throw lots of money & time at the project. We did that on my son's '03 X & it was great fun, but in hindsight, I'd never do it again! :icon_eek:

I still want power, so you can see I've moved on to an '07 FSXT. :biggrin:

Bobby...
 

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2014 Forester XT 8 speed
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113 Posts
I think it depends..
We did some "performance" mods to our 98 2.5rs, and it made the car way more enjoyable to drive. But, we replaced failed oem parts with cheaper aftermarket ones.
Like flywheel/clutch, we replaced it with a 12# flywheel, and it made a HUGE difference in how the car drives, as in when you blip the throttle to rev match to shift gears the engine actually responds when requested. Not to mention it does accelerate faster due to less rotating mass on the engine.

Headers, we lost a bit of tq down low, but we gained hp in the 5-6000 rpm range. But we mostly did that mod for sound.. Wanted the UEL boxer rumble..

Would I spend money to just do mods on an older N/A car. Only if I needed to replace parts that failed.
 

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2017 VW Golf SportWagen 5MT
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People modify their cars because they can, agree with it or not. If you look up posts of people with aftermarket headers and exhaust on N/A cars, they will almost always state they are after sound, not power. You can shift peak power around RPM range, but you won't make more unless you change cams, it is well known and accepted.

Turbocharged cars are modified because it is fairly easy to double the stock power output.

Stan
 

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2019 Crosstrek 2018 Forester XT
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15,013 Posts
Here is the comprehensive list on what mods increase Power on the EJ NA Engine:

1.
2.
3.
4.
5.
6.


This completes the list.
 

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2017 VW Golf SportWagen 5MT
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I'm in the process of building a naturally-aspirated aircooled VW engine. I'm increasing displacement, bumping up compression, using a cam with more lift and duration, increasing valve size and head port volume and velocity. I'm aiming for almost doubling the stock output. There is no reason same would not work for a Subaru engine, but you'd have to build it accordingly, keeping balance between every part in mind.

Stan
 

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2012 XT Touring 4EAT
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3,751 Posts
Red spark plug wires (any brand) - good for +5 hp.

Replace the whole engine with a turbo engine. Or, simply buy an XT

I agree with 2.5x_sleeper - there's not a lot of easily accessible extra horsepower lurking in your n/a engine. If you could find a 'sports' or high(er) voltage coil pack and open the plug gap, that might help. You could add a lubricator which should give a slight compression boost.

---

Wait, I've got it. You need an electric supercharger. Here's a great video testing an electric supercharger and also suggesting a really nifty DIY alternative.
 

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2012 XT Touring 4EAT
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I'm in the process of building a naturally-aspirated aircooled VW engine. I'm increasing displacement, bumping up compression, using a cam with more lift and duration, increasing valve size and head port volume and velocity. I'm aiming for almost doubling the stock output. There is no reason same would not work for a Subaru engine, but you'd have to build it accordingly, keeping balance between every part in mind.
On a Subaru, you could change pistons to increase compression, or maybe mill the deck. Find a set of XT heads which should give you better breathing and possibly better cams. But you would have to do a serious custom tune to get all this to work together.

On your VW, I once saw an air cooled engine re-built with roller bearing mains and big ends - needle bearings just about everywhere else - awesome bit of machine work. It would spin about 12,000 rpm... but not permissible in FV or FVee.
 

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2002 ES300
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Switch to lightweight components. Lightweight crank pulley, lightweight wheels, and etc. not necessarily gaining horsepower, but freeing it up. This you can get up to speed more quickly rather then using it to lug dead weight around.
 

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2017 VW Golf SportWagen 5MT
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On your VW, I once saw an air cooled engine re-built with roller bearing mains and big ends - needle bearings just about everywhere else - awesome bit of machine work. It would spin about 12,000 rpm... but not permissible in FV or FVee.
Roller bearing cranks were popular 40 years ago but they have downsides like not being able to handle detonation. You won't see them used much nowadays, traditional type bearings are more common. Everything has it's downsides. But, to your point, increasing RPM limit is a great way to increase horsepower.

Stan
 

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2012 XT Touring 4EAT
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... So realistically, your car is tuned to run most efficiently and effectively with stock parts. Engineers spent hours developing the way the parts work using advanced testing equipment, so how effective can dumping money on air intakes, headers, throttle body spacers, lightweight pulleys, exhaust parts, and any other part from the ridiculous list of "horsepower increasing mods" be? Especially when the cars computer tells everything to do what they do a certain way.
Okay, if red spark plug wires and electric superchargers won't do it for you, then try this: Get the specs on a BRZ engine. It's N/A but puts out a lot of power. Basically, you could use the BRZ engine as a model and turn your engine into a 2.5 liter BRZ (the BRZ is 2.0 liter, as I recall). There are a lot of OEM Subaru and aftermarket parts available to help you on this journey.
 

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1998 Forester S 4EAT
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Nitrous.... as long as those welds on your intake will hold. lol
 
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