2.25" vs 3.0" exhaust
Guest
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1.8L?
So would a 2.25 work well on my little 1.8 as well? I've heard mixed opinions on 2.5 and 2.25 for 1.8s- some shops have tested 2.5s and say they show more gains AND no low end losses.Some others say a 2.5 will make me lose my bottom end torque which is the 1.8's meal ticket so I need to keep the low end. Also, it seems I need a total custom exhaust 'cause my flanges are different than any other model Impreza apparently (1993 L sedan)...anyone know some good affordable exhaust guys in the metro Denver area?? Thanks!
I would go w/ a 2" on your 1.8L. You might see a 1-2hp increase at the very top end of the rpm range but you'll have crappy throttle response due to a drop in low end torque.
Registered User
Joined: Nov 2002
Posts: 313
From: nasioc.com
Car Info: 2000 RS Coupe/1990 Mazda Protege, zoom zoom..
FWI, I have a 2.25 stromung midpipe with a scooby sport and borla headers.
great combo. butt dyno says its good as well.
on an RS you dont really want to go any larger than 2.25
When I bought my car it had a 3' diamter exhaust on it, and it had NOOOO low end power, even with the headers, when I switched to the above set up, I got all my power back
Jay
great combo. butt dyno says its good as well.
on an RS you dont really want to go any larger than 2.25
When I bought my car it had a 3' diamter exhaust on it, and it had NOOOO low end power, even with the headers, when I switched to the above set up, I got all my power back
Jay
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back preasure
well lets see here....you want to know about exaust ....
ok, the basic idea of an exaust system is to flow the exaust gasses away from the engine. due to laws and the fact that you dont want to go deaf there are many restrictions on your exaust system. lets say you have a ej25 (2.5 liter), the optimal cat back system is saposedly 2.25 in. why dont you want a 3 in exaust ?
well you want the max. possible exaust gass VELOCITY flowing completly through your exaust during the complete exaust cycle. Too keep the air flowing at the highest rate possible all the way through your exaust for each cylender that fires , requires a saposed equal length of travel for each exaust port. This starts at your headers and continues untill the collector,(the place at wich each pipe on the headers merge) this is where you loose most of your velocity. the idea behind this is that when one cylender fires off some exaust down the pipe, there is another cylender waiting to fire next....and you dont want the first one to slow it down. so therefore a perfect exaust system would extract all 4 cylenders exaust gass at exactly the right time to avoid any back preasure at all.....but nothing is perfect and your suby needs SOME backpreasure in order to not loose low end power because even @ full throttle, at only 3,000RPM there is just not enough exaust vellocity to require a 3 inch pipe. And it would slow the gasses down having to travel all the way through that huge 3 inch pipe.
hope that helped. =) if you want to stuff your brain....go to www.cobbtuning.com/tech/exhaustdesign/index.html
ok, the basic idea of an exaust system is to flow the exaust gasses away from the engine. due to laws and the fact that you dont want to go deaf there are many restrictions on your exaust system. lets say you have a ej25 (2.5 liter), the optimal cat back system is saposedly 2.25 in. why dont you want a 3 in exaust ?
well you want the max. possible exaust gass VELOCITY flowing completly through your exaust during the complete exaust cycle. Too keep the air flowing at the highest rate possible all the way through your exaust for each cylender that fires , requires a saposed equal length of travel for each exaust port. This starts at your headers and continues untill the collector,(the place at wich each pipe on the headers merge) this is where you loose most of your velocity. the idea behind this is that when one cylender fires off some exaust down the pipe, there is another cylender waiting to fire next....and you dont want the first one to slow it down. so therefore a perfect exaust system would extract all 4 cylenders exaust gass at exactly the right time to avoid any back preasure at all.....but nothing is perfect and your suby needs SOME backpreasure in order to not loose low end power because even @ full throttle, at only 3,000RPM there is just not enough exaust vellocity to require a 3 inch pipe. And it would slow the gasses down having to travel all the way through that huge 3 inch pipe.
hope that helped. =) if you want to stuff your brain....go to www.cobbtuning.com/tech/exhaustdesign/index.html
Last edited by IllNastyImpreza; Sep 16, 2003 at 06:26 PM.
Registered User
Joined: Feb 2003
Posts: 527
From: Glen Rock, PA
Car Info: 95 Impreza coup, green, 5speed 1.8l awd
as for the 2.25" on a 1.8 it makes a difference and i didnt notice much if any loss of low end torque and more on the top but then again I have a chip, flywheel and drop in K&N filter
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I'm not worried about losing throttle response or low end because of my pulley set and an actual intake (not CAI) but 3" alluminum pipe with a REAL K&N cone filter in the bay and that gave me a huge increase in torque and throttle response. The guy doing my exhaust is an expert with back pressures on small engines and has done quite a few Suby systems- he said a 2.25 would be ideal for what I have now- 2.25 is 2 steps up from the stock 1.75 pipe on my car. Also it's only $350 installed!
