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2007 Forester XT
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80 Posts
Discussion Starter #1 (Edited)
My forester just developed a misfire and according to Subiworks in Murrieta the compression and leakdown indicate a burnt intake valve.

It doesn't seem like anything else is wrong with the engine, but I'm going to have Subiworks rebuild it once our house sells and we land in another.

So my question is, what are some other things that are reliability upgrades to do while the engine is out? I have a limited budget(limited as far as engine rebuilds go) So I'm not power hunting, I want an engine that is fun and reliable.

Already planned is forged pistons and a complete engine and turbo tear down, inspection and reseal. I also plan to discuss this with them once I've got the car there and have paid them, I don't want to jaw their ears for an hour without paying them.

Is the IAG cylinder 4 cooling mod worth doing?
Battery cable upgrades?

Again, no power stuff other than basic bolts ons maybe, I'm more looking for reliability. I'll also be moving the car to southern AZ.

Thanks. .
 

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2004 Forester XT Auto
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148 Posts
If you aren't upping the power, why are you putting in forged pistons? They don't do anything for you at near stock power levels, and generally don't last as long as cast pistons in addition to all the other downsides. If you must buy aftermarket parts for a stock engine, get a KillerB oil pickup, pan and a nice TMIC. An equal-length header will give you some small gains, I've heard it can help with uneven cylinder temps, and doesn't nominally require a tune. An AOS is another item that can't really hurt.
 

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2007 Forester XT
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80 Posts
Discussion Starter #3
Forged pistons on the recommendation of subiworks to reduce the chance of ring land failure(as I understand it) now or in the future, I am not going for power right now, that doesn't mean I never will.
 

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99 Forester 4eat
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46 Posts
IAG AOS - decrease fuel contamination
STI TMIC - increase cooling to fuel/air mix
VF48 - why not if your stock turbo is questionable
Grimmspeed 3 port EBCS - Tuner can control your boost easily
That's all pretty low key, VF 48 is a stock STi turbo so it's not wild but fun.
 

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2004 Forester XT Auto
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148 Posts
Yep, that's a good place to start for sure. I would've mentioned those, but OP was adamant that they only wanted reliability upgrades, not power. And there are other AOS units, most of them are equally good and IAG wasn't the first by a long shot.
 

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2007 Forester XT
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80 Posts
Discussion Starter #6
As far as air oil separators, what’s good and what’s not?

the grimmspeed unit seems to be the cheapest and easiest to install, APPEARS to be the most professional looking.

I don’t know what I don’t know about them.

I’ll definitely swap at least the oil pickup to the killer B, does their pan hang lower than the stock?
 

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1999 Forester S
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426 Posts
Forget the AOS. If you're not going for power, there is zero reason to spend $200+ on one (and even then, they are a waste of money). Run a quality oil and filter, make sure your MAF signal hasn't drifted, replace your PCV valve and any other rubber hoses while the engine is out.
 

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2007 Forester XT
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80 Posts
Discussion Starter #8
Forget the AOS. If you're not going for power, there is zero reason to spend $200+ on one (and even then, they are a waste of money). Run a quality oil and filter, make sure your MAF signal hasn't drifted, replace your PCV valve and any other rubber hoses while the engine is out.
What do you know about AOS that everyone else doesn’t?
 

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1999 Forester S
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426 Posts
Nothing you can't research and learn yourself. What follows is just my $0.02 as a vehicle design engineer:

The whole reason people install an AOS is to keep blow-by oil out of their inlet system, claiming that the blow-by reduces your octane of the intake charge, and thus reduces power output, right?. Yes, the oil droplets in the blow-by gasses will displace some volume of fuel and air, but unless you have an open oil leak into your inlet system, the volume is so insignificant that you'd never be able to measure the decrease in octane rating. Are their OEM applications that use an AOS? Yes, of course, but these are generally found on large diesel engines with 40+ quart oil systems and OCIs in the tens of thousands of miles that run nearly constantly. A Forester doesn't need the oiling system that a 13-liter, 580 hp diesel engine needs.

Now, in a racecar that is at WOT for large amounts of time and where every single horsepower and every fraction of a second count, sure, there is a justification to remove this blow-by from the intake charge. But, on a daily driven street car with mild bolt-ns that maybe only sees WOT getting on the freeway and racing between stoplights, you will never need, nor notice, any change by installing an AOS.

Hell, even Prodrive didn't use an AOS on the factory Subaru rally cars, they simply routed a blow-by dump tube from the engine to under the car (until the WRC/EU began regulating these sorts of emissions). Rally cars also run catalytic converters, so people who go catless "because racecar" simply don't have a clue...

On top of that, Subaru basically built a mini-AOS into the back of the EJ engine block. That plate behind the flywheel/torque converter that people replace due to leaks? THAT, with it's little fins, essentially creates a turbulence that helps remove oil droplets from the blow-by gasses.

For the reasons above and others, money is better spent replacing your MAF sensor with a drifting output signal, the primary o2 sensor that has 100k+ miles on it, getting a pro-tune, or any number of other modifications or maintenance.

I'm not paying to modify anybody's car, so go ahead and do whatever you see fit. Just keep in mind that an AOS on a street car is like a gaudy gold chain on a fat, balding middle-aged man. It might look cool, and it shows people you have money to burn, but it's not going to make you faster, more handsome or smarter.
 

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2001 Forester
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882 Posts
Since I do not own an XT, I cannot vouch for how strong the turbo is. But I can vouch for @soobcrazy point about large diesels need AOS. I drive a ML 350 Bluetec diesel, granted it's not a 13litre engine. But if I do not maintain or keep my intake air filters replaced early enough, the turbo on the 3.0L V6 will suck oil from the sump through the PCV system. There have been reports of owners where their oil sump level drops, but there are no leaks anywhere on the engine, and then the owner opens up their airbox(just before the turbo), and see oil collecting there as well as their turbo blades. They go to clean up all this oil, replace their air filters and the problem goes away.
 

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2001 Forester
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882 Posts
@senorlechero , keep also in mind that Diesels unlike gasoline/petro vehicles do not have a butterfly in the throttle body choking down the volume and velocity of air entire the engine. Therefore the butterfly also potentially negates the need for AOS due to smaller volume and velocity. The GO pedal on a diesel only controls the volume of fuel being injected into the motor. So when the turbo on the diesel spools up, it literally sucks as much air in as it can get the more the merrier.
 
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