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mr_choung
12-18-2005, 02:20 PM
just wondering what size is best to do my exhaust? i just ordered borla headers and talked to a buddy of mine to do the test pipe back welded with a muffler! some of my buddies tell me to go 2.5 straight out? i've also read that 2.5 is to big for n/a and go with 2.25? last ?, should i go catless or get a high flow? thanks for the info guys!:D

Wiscon_Mark
12-18-2005, 02:26 PM
2.25"
Hi-Flow Cat

mr_choung
12-21-2005, 10:20 AM
why 2.25? is that just right for n/a? can't i just use a cherry bomb for a high flow cat (resonator) thing?

belladonna
12-21-2005, 11:29 AM
you should look up what your inspection code says for exhaust as to whether or not your area requires a catalytic convertor...a cherry bomb is a silencer and does not act as a cat. basically, all they do is make the exhaust note sound aggressive

Plays_with_Toys
12-21-2005, 03:54 PM
2.25" lets it breath better for HP, but it still retains your torque. Going to 2.5" illiminates the torque and gains you very little extra HP. Cherry bomb is best as a resonator, which changes the tone of the exhaust. If you get emissions testing done, you need a cat. Period. If you don't, hack away, just make sure the exhaust is exiting out the back. At which point, enjoy your wonderful new exhaust smell, cuz catless smells nasty.

Also, no cat will reduce backpressure, which will reduce torque. Some say to stay with it, others like to chop 'em out.

Huffer
12-21-2005, 04:18 PM
Catless isn't nasty...as long as the car is running well it's fine.

I run catless on my Impreza wagon in NZ - no EPA-type regs. 2" pipe w/ resonator. EJ20 non turbo.

strat81
12-21-2005, 04:29 PM
backpressure is restriction... restriction is bad...

you want exhaust flow velocity, not backpressure in your exhaust system.

also, if your car is obdII (should be 96 or newer... at least it is for other makes of cars), you'll be throwing codes without a cat due to the second o2 sensor after the cat detecting that you don't have a cat. your best bet would be a high flow cat.

phi11
12-21-2005, 04:39 PM
what are you going to do with the old header? (hint hint)

gil_ong81
12-21-2005, 04:39 PM
i too agree with 2.25".

it comes down a compromise between backpressure, and how fasat the gases move. larger diameter = less retriction = less backpressure, but the exhaust gases move through the system slower.

Huffer
12-21-2005, 05:52 PM
backpressure is restriction... restriction is bad...

you want exhaust flow velocity, not backpressure in your exhaust system.


A lot of people confuse the two terms - and use them interchangeably. :evil:

Wiscon_Mark
12-21-2005, 09:09 PM
backpressure is restriction... restriction is bad...

you want exhaust flow velocity, not backpressure in your exhaust system.

also, if your car is obdII (should be 96 or newer... at least it is for other makes of cars)

95+ Legacy is OBDII

yes, backpressure is bad, its caused by the exhaust cooling and slowing down the flow of the exhaust gasses...as soon as they cool, they slow down. So the better metals you have (that don't absorb heat, but encourage it to move out the tip) the more efficient you will be. That's why rally cars have ceramic coated and heat wrapped exhaust systems.

BAC5.2
12-21-2005, 09:39 PM
FWIW My Legacy passed a sniffer without any cats. They didn't do a visual. That will usually fail you. Mostly they do a visual on OBD2 cars in Maryland.

Backpressure is bad. Period.

Larger exhausts don't ALWAYS slow exhaust gases down. There is a compromise. Too small an exhaust = too much restriction. Too large = poor flow. Just right is the balance between the two that will make the most power over the entire RPM range.

To understand everything about exhaust, you need to be a fluids engineer.

Sarra
12-22-2005, 12:49 AM
backpressure is restriction... restriction is bad...

you want exhaust flow velocity, not backpressure in your exhaust system.

also, if your car is obdII (should be 96 or newer... at least it is for other makes of cars)

95+ Legacy is OBDII

yes, backpressure is bad, its caused by the exhaust cooling and slowing down the flow of the exhaust gasses...as soon as they cool, they slow down. So the better metals you have (that don't absorb heat, but encourage it to move out the tip) the more efficient you will be. That's why rally cars have ceramic coated and heat wrapped exhaust systems.

My 1995 Wagon was ODBI. IIRC, ODBII was stated as a requirement in 1995, but most MY95 vehicles were built in 1994, so some of them were ODBI, and some were ODBII.

2.25" should be fine. If you have a CAI, lumpy headers, porting, and valvetrain upgrades, then 2.5" would be of more use.

BAC5.2
12-22-2005, 02:29 AM
All Legacy vehicles were OBD2 in 1995 I think. The Impreza was OBD2 in 96 and OBD1 in 95.

I had a 95 Sedan. It was OBD2. Look directly underneath the steering wheel. You'll see the diagnostic port. My 95 had a production date of 10/94 I believe.

Wiscon_Mark
12-22-2005, 09:06 AM
All Legacy vehicles were OBD2 in 1995 I think. The Impreza was OBD2 in 96 and OBD1 in 95.

I had a 95 Sedan. It was OBD2. Look directly underneath the steering wheel. You'll see the diagnostic port. My 95 had a production date of 10/94 I believe.

+1, all 95 Legacys were OBDII, all 96 Imprezas were OBDII

belladonna
12-22-2005, 12:31 PM
My 1995 Wagon was ODBI. IIRC, ODBII was stated as a requirement in 1995, but most MY95 vehicles were built in 1994, so some of them were ODBI, and some were ODBII.

2.25" should be fine. If you have a CAI, lumpy headers, porting, and valvetrain upgrades, then 2.5" would be of more use.

half model 95s would be OBDII, but 95s built in 94 could possibly be OBDI...1996+ model of anything is OBDII....

strat81
12-22-2005, 01:02 PM
i know by 96 ALL were obdII (cavaliers are the same way... some 95's were obdI, some were obdII depending on when they were built)

i'd suggest 2.25 on an engine of 2.2 litres or less... unless you have alot of work done or are boosted.

mr_choung
12-22-2005, 07:01 PM
that's good info guys!
i've got a 2.5 litre but i think imma go with the 2.25! i'm still debating on cat or no cat? is there any high flow cat made just for impreza/legacy's or universal's is fine? and what brand is best?

voorhees
12-22-2005, 07:38 PM
stromung for high flow

belladonna
12-22-2005, 07:41 PM
cats are pretty universal...you just need to decided how big...

there are only a few name that really come to mind if you're looking for something designed specifically for Subaru and that's Milltek, Random Technologies and Stromung...

Wiscon_Mark
12-22-2005, 11:37 PM
We bought our 95 in September of 94 (first outback to roll off the truck at that dealer, we bought it right away) and its def. OBDII...I've never heard of an OBDI 2nd gen Legacy

Sarra
12-23-2005, 04:36 AM
Weird... Maybe I thought it was ODBI because that car always had a sniffer used during emissions testing.