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What size exhaust to use on EJ18 converted Legacy (originally EJ25)?


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14 replies to this topic

#1 grossgary

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Posted 16 December 2013 - 07:56 AM

What size is EJ18 exhaust?

 

My exhaust needs replaced from the headers back due to rust.

 

It's an EJ18 in a 96 Legacy which originally had an EJ25.  Other threads mention that the EJ25 exhaust is larger than the EJ18.

 

I may run straight pipe, no converter, no muffler.

 

What size exhaust should I run for basic gas mileage in a daily driver?  I'm thinking I should downsize from the larger EJ25 diameter?



#2 grossgary

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Posted 16 December 2013 - 08:14 AM

Searching multiple forums I'm seeing guesses of 1.75" and 1 7/8" exhaust diameter as stock for EJ18.

 

Anyone know?



#3 Rooster2

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Posted 16 December 2013 - 09:35 AM

I don't think that pipe size matters that much. Yea, 1.75 or 1 7/8 should work just fine. The size is not a critical factor. Don't recommend a straight pipe. It will sound great for the first five minutes of driving, but then the sound becomes dronning noise that will drive you and any passengers crazy. Also, you won't really be able to listen to your car radio/sound system. Cops can ticket you as well.



#4 grossgary

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Posted 16 December 2013 - 09:43 AM

copy, i'll get a muffler on it. don't really want it to be annoying, currently has y-pipe only so straight pipe would at least be a huge improvement from that, LOL.

 

i think the store i frequent only has one size under 2" anyway i'll probably just get that.

 

been wrecked 3 times, totaled at highway speeds twice and rebuilt both times. it's been beat. but engine, trans, and mechanicals have lots of years/miles left so it's worth keeping on the road as a beater or to let friends borrow.


Edited by grossgary, 16 December 2013 - 09:44 AM.


#5 Bushwick

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Posted 16 December 2013 - 11:12 AM

If you have the dough, splurge for 2" after the "Y". Should help it breath a bit better. I always run "turbo mufflers" from Summit. They are still baffled, but give an increase in flow as well as a slightly more aggressive sound w/o being obnoxious. Very inexpensive muffler too. Auto Zone has a clone of it (think it's Thrush's "turbo muffler") and if you can find Summit Racing's price for the same thing online, Auto Zone will price match. They don't last forever, but have a decent sound and MPG will bump up a point or 2.

 

Also, be aware running cat-less on some cars will cause CEL unless you stack the 2nd O2 with anti-foulers. Also, since it's a federal law to have a cat, some places will refuse to work on the car with the cat omitted, and by law they are required to replace with OEM (so in your case ej25) before doing anything else. Although the EPA doesn't aggressively go after people that are running cat-less, a sharp-nosed cop can and the fines are super expensive (like $10k IIRC with possible jail = felony). Also, if you ever sell the car w/o a cat, the buyer can come after you in court and seek judgement for the cost of an OEM replacement unit plus labor, which would be the entire "Y-pipe" section (same rules apply to dealerships). This post would sink you if the DA found it. Play it safe and stick a $90 universal cat on meant for, or rather safe to run on the car, or just leave the EJ25 exhaust in place if it bolts up the same. It won't hurt anything. 


Edited by Bushwick, 16 December 2013 - 11:20 AM.


#6 grossgary

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Posted 16 December 2013 - 12:32 PM

i'll look into those mufflers, sounds like a good fit.

 

it rusted off, there's nothing to leave in place.  CEL doesn't matter in WV or to me. 

resale!!!  castrated from EJ25 to EJ18 and 4WD to FWD, and:

 

been wrecked 3 times, totaled at highway speeds twice and rebuilt both times

 

it's not worth anything in terms of selling it.



#7 Fairtax4me

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Posted 16 December 2013 - 01:53 PM

Stock ej22 pipe is 1 7/8" O.D.
Had to weld a section onto the front of the resonator pipe on my 95 and it was a trick finding a pipe section small enough to jam into the resonator.
I wouldn't want anything larger than that for an 18.

#8 Fairtax4me

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Posted 16 December 2013 - 01:53 PM

Double post...

Edited by Fairtax4me, 16 December 2013 - 01:54 PM.


#9 grossgary

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Posted 16 December 2013 - 02:22 PM

copy - EJ25 is also 1.875 or 1 7/8". 

 

so all EJ18, EJ22, and EJ25's have the same exhaust diameter?



#10 Bushwick

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Posted 16 December 2013 - 03:41 PM

It might run too rich w/o a cat and w/o stacking the rear O2. You can buy 2 spark plug anti-foulers from Auto Zone for under $5. You need to drill out the center hole on one of them. Then thread one into the other, thread other end into pipe bung, then thread rear O2 into them. It pulls the probe out of direct exhaust stream, but it can still sample the air (or something) and it tricks the ECM into thinking the cat is there. I ran my Saab like this for a bit. The CEL never came on (Mustangs, Civics, etc. do the same thing) but the car did run rich. Though all the extra power from no back pressure after the turbo I didn't care ;)

 

Yeah, those turbo mufflers are nice. I ran a pair on my Lincoln Mark VIII over the years and loved them as it gave "better than stock" sound, but people 2 miles away couldn't hear me flogging it. Running a 3" in/out on the Saab and it has a good sound. Definitely louder with larger "outs" on the muffler, but it's more mellow w/o the rasp or crackle. If you run a 1 7/8" pipe, you can easily buy a 2" in/out muffler and weld that on. If you get an adapter, you can easily jump up to a 2 1/4" muffler which will be a tad louder. If you are handy with a mig and thin-walled steel, you can dremel the "outlet" off a smaller muffler and stick a 2 1/2" "out" on. That'll increase sound too w/o being overly ridiculous.

 

@fairtax  the difference between 1 7/8" and 2" is virtually nothing (in fact 1 7/8" can fit inside 2" and accept a weld) and is typically easier to source.



#11 Fairtax4me

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Posted 16 December 2013 - 06:11 PM

copy - EJ25 is also 1.875 or 1 7/8".

so all EJ18, EJ22, and EJ25's have the same exhaust diameter?

Possibly, although the 18 never came in a legacy here, so we would have to compare Impreza exhaust systems on 22 vs 18 equipped cars.


It might run too rich w/o a cat and w/o stacking the rear O2.

Cat and rear sensor have no effect on A/F ratio. Rear sensor is only a check sensor to see if the cat is functioning normally, it has no effect on fuel.

@fairtax the difference between 1 7/8" and 2" is virtually nothing (in fact 1 7/8" can fit inside 2" and accept a weld) and is typically easier to source.

Au contraire!
A 1 7/8" O.D. pipe has a 13% smaller internal area compared to a 2" O.D. pipe.

Edited by Fairtax4me, 16 December 2013 - 06:45 PM.


#12 grossgary

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Posted 16 December 2013 - 08:43 PM

I just measured 1996 EJ25 midpipe 1.88" and muffler pipe 1.89".  So 1 7/8" it is.  Surprised the exhaust pipes are all the same size.

 


A 1 7/8" O.D. pipe has a 13% smaller internal area compared to a 2" O.D. pipe.

copy, i'll look for 1 7/8" hopefully they have that. 

maybe i should try 1.5" pipe for the EJ18   LOL



#13 Fairtax4me

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Posted 16 December 2013 - 10:01 PM

Could go to Home depot and get 1" cast iron pipes and run them straight back from the heads! True duals!

Edited by Fairtax4me, 16 December 2013 - 10:03 PM.


#14 grossgary

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Posted 17 December 2013 - 08:10 AM

Could go to Home depot and get 1" cast iron pipes and run them straight back from the heads! True duals!

sounds about right. LOL



#15 Rooster2

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Posted 17 December 2013 - 08:57 AM

sounds about right. LOL

Won't ever have to be concerned about the pipes rusting out.






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