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Discussion Starter · #1 ·
Has anyone posted on removing the cats? I'm looking to gain some mpg. I commute 7 hours once a week between NV and Idaho. My county of registration does not require smog. Any help would be greatly appreciated including where to get parts like flanges, ect. Thank you.
 

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2007 2.5XT Limited 4EAT
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It's certainly possible, but not a great idea to do so without tuning. Running no cats on an untuned car will eventually lead to a lean condition. This will be due to the O2 sensors registering an excess of unburned fuel, thinking the car is running rich, the computer will begin pulling fuel. You will also likely be getting a steady stream of O2 related trouble codes as well.(Maybe not immediately but it will happen) Removing the cats may achieve your your intended goal temporarily, but will cause serious issues down the road if you run it long enough without the cats.

Again, removing the converters without tuning is a bad idea. You can probably save as much fuel by removing the back seat and packing light on your trips if that is a possibility. These vehicles are not known for their exceptional fuel economy.

If you are dead set on removing the cats, parts can be found in several places. You can find aftermarket up and downpipes that have no cats, this would be the most expensive path. You can cut out the cats and scab in some length of pipe to fit. You can find these bits at just about any auto parts store. This option will require welding or a bunch of slip fittings and clamps. Lastly, you could find a local exhaust shop to do the work. This would probably be your best bet.
 

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MY05 Forester 2.5 XT 5MT
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+1 on what Snow3D said.

If you remove Cats without mapping, you will run lean and you will start to cause major engine troubles in the way of valve and piston damage.

As you posted in the Non-Turbo section, I assume you have a Non Turbo? I'm not sure if the non turbo ECU can even be remapped like the turbo ECUs can....

Being a Non Turbo, it is going to be very loud and sound pretty horrific with the Equal Length Headers - Think Honda straight pipe on steroids

Honestly, if you want better mpg, pick up a Corolla or something and leave the Forester to being a Weekend car or something as that is probably the cheapest way to better mpg as developing a mapping solution for a non turbo (If one doesn't already exist) could thousands including the pipes.

Edit: Removing the cats wouldn't necessarily give you an increase in MPG - The mapping solution is more likely to give you the gains in mpg but the differences might be hard to realise in the real world
 

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Discussion Starter · #5 ·
Thanks for the input guys. What kind of tuning software is available for Subaru? The motor is 2001 2.5L SOHC. The car has 276,000 miles on it. The motor had the head gasket issue blowing the coolant into the reservoir. I had the motor rebuilt recently and it currently has 11,000 miles on it. I've read that putting a spacer between the O2 sensor would help it from running lean. Perhaps removing the rear cat would be a compromise?
 

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2007 Forester Sports XT 4EAT
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@BigNorm no tuning software for the 2001. In the USDM, the first programmable ECM was in the '04 XT.:wink:

Also...
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Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 
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MY05 Forester 2.5 XT 5MT
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The spacer wouldn't help with running lean when doing drastic things like removing cats - The spacer idea is generally more a band-aid solution to passing annual testing.

EcuTek allows customising of maps on Turbo Subarus - No idea on the Non Turbos.
AccessPort - Allows you to download generic maps from the company's database from memory - Again for turbo applications.

OpenSource might be a possible solution but you would need to learn it from scratch unless you can find someone who has mapped a 2.5 non turbo in the past to get an idea where to begin. To do it safely, you would want a wideband oxygen sensor to alert you of trouble

I'm not too knowledgable on Non Turbo tuning but I'm pretty sure the Non turbos require a bit of backpressure to remain happy from memory?

What kind of MPG are you getting at the moment?
From memory the 2.5 XT manual officially got 25mpg combined, where as the 2.0 N/A manual got 31mpg combined, so I would expect a 2.5 N/A manual to get around 27-28mpg combined Or 22.5-23.3mpg combined using those smaller US Gallons. Perhaps chop a couple mpg off if you're running an auto.

Thinking about it, if you just want more mpg and don't need the practicality of the Forester, you could consider:
Low Rolling Resistance Eco and lightweight Tyres - Poor offroad though and might give questionable cold weather and wet weather performance.
Cleaning the MAP sensor
Cleaning the Idle Control Valve near the throttle
Stripping and cleaning and greasing the brake calipers
Check the intake system for any signs of leaks
Check the exhaust for any signs of leaks - Perhaps remove and clean the upstream Oxygen sensor
Checking the fuel system is tip top condition with fuel system cleaner etc

Remove the backseat and rear compartment interior to save weight
Fit lightweight wheels
Remove the AC compressor or just run a belt bypassing it to lower drag on the engine.

If you want to get hardcore, remove the rear windows and fit a lightweight alternative like perspex perhaps? - Likewise for any sunroof you might have and obviously removing the window motors and using clips/mounts to keep the glass replacement in place. - No idea if this is even legal where you are though !
 

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Discussion Starter · #8 ·
Thanks for the help guys. I often travel through snow and weather. I understand a lighter car would help mpg. Thanks for the cleaning tips. I've got to say that my car is running the best it ever has. I've always been one who likes to improve on the original idea. Are there any piggyback systems for tuning?
 

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2007 Forester Sports XT 4EAT
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<snipped> Are there any piggyback systems for tuning?
Yes, we have one installed in my son's '03 X. They are expensive & don't do a whole lot, other than let you alter the ignition timing. :frown:

The one on our '03 X controls the ignition timing & the 5th fuel injector... throttle body fuel injector. The AVO turbo kit wasn't designed for fuel economy! :biggrin:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 
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Discussion Starter · #10 ·
Thanks Bobby? Could you tell me the name of the tuner? I'm thinking of checking out Dobek and seeing if they have anything that would work.

And fyi all I currently have is my phone with no access to a PC. My name is Norm, I'm big, and I hail from Minden, Nevada USA. I can give you some more details but I may have to read the rules again. Lol.
 

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2007 Forester Sports XT 4EAT
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Thanks Bobby? Could you tell me the name of the tuner? I'm thinking of checking out Dobek and seeing if they have anything that would work.
They're history, gone out of business! Not a whole lot of "piggyback" programmers out there... my guess, there's not a lot of interest in this type of tuning. :frown:

If you've looked thru our '03 X Member Journal, you can see where I had to learn how to do my own programing... actually great fun, as computer poop is my other passion! :biggrin:

And fyi all I currently have is my phone with no access to a PC. My name is Norm, I'm big, and I hail from Minden, Nevada USA. I can give you some more details but I may have to read the rules again. Lol.
Filling out your "Public Profile" is entirely voluntary, but it does provide information that member's may need to reply to your forum posts. :wink:

Bobby...

['07 FSXT MODding Journal] ['03 X MODding Journal]
 
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2006 Forester
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I honestly do not think you can do anything to that to get better mpg. They kind of do what they do. I agree it would most likely do more harm, but you could possibly try to get the rear cat out if there are two... But i suspect you could have a worse off engine if that back pressure gets too low.
 

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2005 Forester EJ251, 2011 Forester FB25
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Sending this from Oz. My 2004 2.5, auto, returns 31 mpg (US miles) or better on a trip. No point in removing the cat. The exhaust system is already quite large diameter for a small engine.
 

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2006 Forester 5-speed manual
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A couple of fundamentals...

MPG on a trip is not altered in any significant way by the weight carried. In city use it certainly matters, but crossing Utah and going into Idaho will not bring up much in the way of traffic lights and stop signs. The Virgin River Gorge will hold no dread, though that long drag through Provo and Salt Lake City might add something.

What counts in such use is wind resistance and rolling resistance. As has been mentioned, extra pressure in the tyres will help, if you have racks on the roof you can remove them. I'd think ensuring some underbody smoothness (taken care of originally by a plastic undertray behind the bumper) might be of some use.

Otherwise, it's down to your right foot and experience checking the consumption against the speed at which you travel. My '05 Forester recently returned 705kms for a tankful. That's dead full to dry, run out, roll to the side of the road. I often do a tankful to see how it's going and this is the best I've ever seen. I regularly get about 630kms, sometimes 660 or 670, which I reckon to be good, and then there are times when I have twisty mountain roads and/or I press the loud pedal harder and get the needle further up the scale and it drops to 580 or so.

That's right, I know what consumption I get from trip to trip. If I don't drain the tank totally I record the mileage on the trip meter and fill to totally full and note the litres and the decimal places on the bowser as well.

There's no point saying, "I get 500kms from a tankful." if you don't run it dry. Some folk do that, they see the gauge get down to the E mark and start looking to fill up. Or have the yellow light come on.

My yellow light lately has been coming on 140kms and more before it runs dry. On my other car it was 70kms. These things are only an indication of what's going on, they're not factual.

With regard to the weight, some will say, "...but it's more weight to pull up the hills!" Yes, it is. But it's more weight pushing the vehicle down the hills and more inertia to get it further up the next hill before heavier throttle application is required.

I once towed a box trailer from Sydney to Brisbane with a ton... a literal ton... of building materials on it. 405kms per tankful totally full to dead empty. The return trip saw the trailer empty, so we were a full ton down in weight and travelling at the same speeds. 410kms per tankful totally full to dead empty. And that was on the New England Highway, with many long climbs and descents.
 

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Your county may not require a catalytic converter for smog reduction on you car, but the federal government does. As previous posts have commented on - a bad idea.

Dan
 

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None of these ideas mention the payback period on these modifications... if you spend $100 on modifications, you likely won't make it back in fuel savings for a long while. I would do this math on these ideas before doing any of them.
 

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Just to underline what I said earlier about the irregularity of gauges and warning lights...

My fuel warning light came on at 506kms this past weekend, it ran out of fuel at 707.4kms. So just over 200kms with the fuel warning light on!

Mostly open-road running, probably not quite as good as the road from Nevada to Idaho (more ups and downs and curves, a few towns). Open road speed held mostly at around 105kmh.
 

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2001 Forester S, 4EAT
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Since your "commute" is primarily highway at high speeds. Gaining HP will not equate to an increase in MPG. HP gains only benefit your ability to accelerate quickly, but does nothing for your vehicles ability to maintain a fixed speed on the highway. If there was some way to increase torque, then yes you would potentially see some MPG gain as you would then be able to maintain a certain speed while reducing your engine RPM speed and therefore raising your MPG.

But making your engine breath better to gain HP will not accomplish what you want in fact, making the engine breath better has the potential of actually decreasing your torque which is the opposite of what you want to do.

Horsepower Formula:

(RPM * Torque) / 5252=HP

As you can see in order to increase HP you need to increase either RPM or Torque or both. Unless you are prepared to drop $$$ for a turbo kit, etc.....
 

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I read some data that says that inflating tyres over the recommended pressure does not significantly decrease rolling resistance. Under inflation, however significantly increases rolling resistance. My experience indicates the data to be correct.

GD
 

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Australia has had cats fitted since the 1980s. We just followed the US emission standards then and now generally follow the European standards. However, whilst 91 octane is the lowest fuel available (and the norm for most japanese cars) the Subarus are tuned for 95 and most, including me, use 98 as there is little difference in price. Even with 98 the engine can ping in some circumstances.
 
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