Another Newbie Exhaust Question!
12-02-2009 | 03:32 PM
#1
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From: Elk Grove
Car Info: 02 WRB WRX Sedan
Another Newbie Exhaust Question!
I'm trying to fully understand what I can do with my exhaust. I have a GReddy Evo2 catback (was on the car when I bought it), and I'm interested in buying an uppipe and downpipe to complete the system.
I was looking up diameter sizes on my catback when I stumbled upon a vender mentioning that it "tapered down from 3 inches to 2.5 inches to mate with the stock downpipe." But my understanding is that the catback excludes the midpipe, so isn't it really supposed to mate with the midpipe rather than the downpipe? Or am I missing something?
Knowing that I only have GReddy Evo2 catback and nothing else done to my exhaust, what are my options for downpipes?
And while we're still on the subject, I fully understand the reasoning for going catless, especially with the uppipe. But how bad is it to go catted for the downpipe? I guess I'm wondering in terms of overall practicality (i.e. Do people run into legal issues often when fully catless? Does a catted dp change the smoggability of the car?). I'm willing to take a slight hit in performance if it saves me more trouble elsewhere!
Any help is greatly appreciated!
I was looking up diameter sizes on my catback when I stumbled upon a vender mentioning that it "tapered down from 3 inches to 2.5 inches to mate with the stock downpipe." But my understanding is that the catback excludes the midpipe, so isn't it really supposed to mate with the midpipe rather than the downpipe? Or am I missing something?
Knowing that I only have GReddy Evo2 catback and nothing else done to my exhaust, what are my options for downpipes?
And while we're still on the subject, I fully understand the reasoning for going catless, especially with the uppipe. But how bad is it to go catted for the downpipe? I guess I'm wondering in terms of overall practicality (i.e. Do people run into legal issues often when fully catless? Does a catted dp change the smoggability of the car?). I'm willing to take a slight hit in performance if it saves me more trouble elsewhere!
Any help is greatly appreciated!
12-02-2009 | 08:06 PM
#2
"midpipe" is traditionally the pipe between the donut gasket and the axleback (muffler). This is part of a "catback" and usually contains a resonator.
A downpipe is often considered to be both the short down section plus the stock cat-pipe section. Some downpipes are this entire section and some are just the down section.
Most catbacks will be 2.5-2.75" in order to mate properly with the donut gasket. Downpipes can be straight through 3" (like Invidia) or taper to the donut gasket (like Cobb and TurboXS). To most easily mate with your catback, you probably want one that tapers.
As far as cats, the flow of quality high flow cats is very good now. These will cost somewhere on the order of <5 HP in a typical setup. They'll only cost very significant HP if you're building for extremely high HP like a drag car. Because there's a fairly large difference in emissions going from no-cat to 1 high flow cat, I like to run a cat. I saw LA in the 80s before strict emissions and I understand the need for cats, and am willing to pay a little extra just to be a little responsible.
As far as Smog in CA, you'll fail visual without 3 cats if they look. This means you won't pass with an aftermarket uppipe or downpipe if they look. There are reports of people who've been lucky enough that the smog guy didn't look or didn't look hard enough, or saw one cat and was happy, and they've said 1 high flow cat was enough for them to pass sniff.
As far as uppipe, it's not easy to see down there and you are probably much more likely to get away with illegal equipment there.
A downpipe is often considered to be both the short down section plus the stock cat-pipe section. Some downpipes are this entire section and some are just the down section.
Most catbacks will be 2.5-2.75" in order to mate properly with the donut gasket. Downpipes can be straight through 3" (like Invidia) or taper to the donut gasket (like Cobb and TurboXS). To most easily mate with your catback, you probably want one that tapers.
As far as cats, the flow of quality high flow cats is very good now. These will cost somewhere on the order of <5 HP in a typical setup. They'll only cost very significant HP if you're building for extremely high HP like a drag car. Because there's a fairly large difference in emissions going from no-cat to 1 high flow cat, I like to run a cat. I saw LA in the 80s before strict emissions and I understand the need for cats, and am willing to pay a little extra just to be a little responsible.
As far as Smog in CA, you'll fail visual without 3 cats if they look. This means you won't pass with an aftermarket uppipe or downpipe if they look. There are reports of people who've been lucky enough that the smog guy didn't look or didn't look hard enough, or saw one cat and was happy, and they've said 1 high flow cat was enough for them to pass sniff.
As far as uppipe, it's not easy to see down there and you are probably much more likely to get away with illegal equipment there.
12-02-2009 | 08:17 PM
#3
"midpipe" is traditionally the pipe between the donut gasket and the axleback (muffler). This is part of a "catback" and usually contains a resonator.
A downpipe is often considered to be both the short down section plus the stock cat-pipe section. Some downpipes are this entire section and some are just the down section.
Most catbacks will be 2.5-2.75" in order to mate properly with the donut gasket. Downpipes can be straight through 3" (like Invidia) or taper to the donut gasket (like Cobb and TurboXS). To most easily mate with your catback, you probably want one that tapers.
As far as cats, the flow of quality high flow cats is very good now. These will cost somewhere on the order of <5 HP in a typical setup. They'll only cost very significant HP if you're building for extremely high HP like a drag car. Because there's a fairly large difference in emissions going from no-cat to 1 high flow cat, I like to run a cat. I saw LA in the 80s before strict emissions and I understand the need for cats, and am willing to pay a little extra just to be a little responsible.
As far as Smog in CA, you'll fail visual without 3 cats if they look. This means you won't pass with an aftermarket uppipe or downpipe if they look. There are reports of people who've been lucky enough that the smog guy didn't look or didn't look hard enough, or saw one cat and was happy, and they've said 1 high flow cat was enough for them to pass sniff.
As far as uppipe, it's not easy to see down there and you are probably much more likely to get away with illegal equipment there.
A downpipe is often considered to be both the short down section plus the stock cat-pipe section. Some downpipes are this entire section and some are just the down section.
Most catbacks will be 2.5-2.75" in order to mate properly with the donut gasket. Downpipes can be straight through 3" (like Invidia) or taper to the donut gasket (like Cobb and TurboXS). To most easily mate with your catback, you probably want one that tapers.
As far as cats, the flow of quality high flow cats is very good now. These will cost somewhere on the order of <5 HP in a typical setup. They'll only cost very significant HP if you're building for extremely high HP like a drag car. Because there's a fairly large difference in emissions going from no-cat to 1 high flow cat, I like to run a cat. I saw LA in the 80s before strict emissions and I understand the need for cats, and am willing to pay a little extra just to be a little responsible.
As far as Smog in CA, you'll fail visual without 3 cats if they look. This means you won't pass with an aftermarket uppipe or downpipe if they look. There are reports of people who've been lucky enough that the smog guy didn't look or didn't look hard enough, or saw one cat and was happy, and they've said 1 high flow cat was enough for them to pass sniff.
As far as uppipe, it's not easy to see down there and you are probably much more likely to get away with illegal equipment there.
i passed with my APS FMIC K&n intake and my invidia up pipe (catless) with vf39 and sti pinks with my protune.. and passed no problem... but all other parts were stock for the most part
12-03-2009 | 10:14 PM
#4
If you get a full 3 inch downpipe, you could use an adapter like this so you can mate it to your Evo2 catback.
http://www.rallysportdirect.com/shop...er-p-3911.html
http://www.rallysportdirect.com/shop...er-p-3911.html
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