I ordered my new silver 5-speed WRX with the sunroof two weeks ago. Since then I noticed a post about a new factory cat-back pipe. Can someone tell me:
1) what is the cat-back pipe? 2) what are the benefits? better economy? more power? 3) should I ask the dealer to put one on my new WRX before I take it home?David
It is the section of the exhaust that goes from your catalytic convertor to your muffler (hence the name cat-back)
Potentially it "could" do both increase fuel economy (due to a more free-flowing exhaust) and make more power (also due to a free flowing exhaust)
Personally I would go for an aftermarket cat-back if you want the car to have a little more announced exhaust note. HKS, 5-Zigen, Blitz, Apex-i, etc.. all make very good cat-back exhausts that are designed to flow well. If you get an aftermarket one get one from a good manufacturer and not just the cheapest one you can find otherwise it may sound like all those annoying hondas out there with their coffee-can sized exhaust tips that sound like crap (I would avoid APC and Toucan Industries for exhausts). You may be surprised, the aftermarket may be cheaper than the factory installed cat-back (or the factory option cat-back). Also, I should note this is a very easy do-it-yourself project that you could easily do with some jack stands and a metric wrench (12mm if I recall correctly).
CAS
No, actually it is the entire exhaust system behind the cat......all that would usually be between the cat and muffler is a short section of pipe and maybe a resonator. Anyway I wouldn't expect much of an improvement on a stock Subaru. TG
Ok, so I wasn't 100% clear but I wasn't wrong either. To clarify I should have said it is the section of pipe going from your catalytic convertor to the end of the exhaust including your muffler. I think most people here seem to be able to comprehend what it was that I was trying to say, well most people that don't try and pick apart every single post for the smallest detail of clarity. You know, TG, I have defended you in this group in the past, but I am starting to feel that you really don't have a use here other than to criticize and make yourself feel all high and mighty because you came up with a marginally better way of explaining something than someone else did. If it makes you feel better about yourself rip me in this post, but be warned, I won't back down about what I said. And technically I answered his question correctly, he asked "what is the cat-back pipe", not "what is a cat-back exhaust system".
I disagree again, the stock muffler is extremely restrictive
Re-read my post, I wasn't ripping anyone or trying to appear any particular way....just trying to help the guy who started the thread. TG
Even a lot of high performance cars have a fairly restrictive exhaust system. I have a 1994 Corvette that responded very well to aftermarket headers and exhaust even though it was already putting out 300 hp/300 lb-ft torque.
A more normal car has even more restrictive stock exhaust and will certainly respond to a more free flowing exhaust.
From what I have seen on the WRX STi, it has all the exhaust flow that it needs. Now all I have to do is find a way to buy one of these.
I used to think that less restriction was always better, but people on this and other newsgroups educated me on the subject. Here is a post that I made on this ng after I was educated: I'm no expert either, but know only what I've read on this subject. On modern 4-strokes, there is generally considerable valve overlap (i.e., there are a few degrees of crankshaft rotation during which both the intake and exhaust valves are both open. This has to do with dynamics of the flow that improve performance at higher rpms (IIRC, this has to do with "scavenging"?).
Without some backpressure, the overlap would cause flow disruption at lower rpms, and low-end performance would suffer without that backpressure. With just the right amount of backpressure to optimize operation throughout the rpm range, the system is considered to be "tuned"; removing the backpressure "detunes" it. Of course, with a turbo charger, the turbo itself presents back pressure, so you would generally want as little other backpressure as posible in a turbocharged system.
There - that "exhausts" my knowledge on the subject. 8^)
Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")
I have done a fair amount of WOT racing in the Corvette and the free flowing exhaust was very noticeable. When you get to the power level of a Corvette or WRX STi, there is enough air flow through the motor to justify a very free flowing exhaust.
I would imagine that the motor in the WRX STi is flowing a high percentage of what my 5.7L Corvette does when they are both at WOT. I can't imagine what it would be like to own one of these high revving WRX's with a close ratio 6 speed.
You do want to watch out on a low power motor when it comes to picking an exhaust system. If you do not have enough exhaust velocity, you can end up with exhaust gases still in the cylinder when the exhaust valve closes. You will have reduced your power instead of increasing it.
[reordered for readability]
Tracy,
Why the proclivity for changing subjects to one word exclamations (typically negative). I've heard Billings was a nice place with nice folks.
Best Regards,
-- Todd H.
2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USAI guess I hang out with Llamas and sheep a little too much. Tracy Everett Glenn
That could very well tie in with the valve overlap thing (i.e., the exhaust valves being open into the beginning of the intake stroke). Higher exhaust velocity would mean smaller plumbing which in general would be referred to generically as a more restrictive exhaust (though it may give better overall performance, especially at the low end, for the reasons you state).
Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.