Hey,
I had this in another thread but no one seemed to notice soo... which diameter of pipes for a cat-back system creates the best HP gains 2.25 or 2.5 ???

COLE

 

I run a 2 1/4 i could have gone with a 2 1/2 but i did not want to loose to much back pressure. I also dont have any cats its just a straight pipe from the exhaust manifold rite to the muffler it sounds awesome. Good gains with the intake and all some thing like 10hp maybe more i still need to get a header tho.

 

Oh no! Not that back pressure thing again.....

 

well... lets talk about that back pressue thing... which diamter of pipe would give me the most backpressure with the most HP gains

 

why don't you do a search and stop beating dead horse

 

depending on who you speak with on this board you'll either get suggestions of 2" or 2¼". Are you running N2O or anything like that? Backpressure is your enemy. You want a high flowing exhaust system with good "exhaust velocity" If you plan on using the bottle 2¼" is what i'd get. Or if you have plans to run some wild cams you could go with the bigger diameter. BACK PRESSURE IS THE ENEMY!!!

 

I too have posted this before...and will do it again....

your engine is a complete system....from the tip of the intake filter to the tip of the muffler....you can just start bolting stuff on and you may or not really see any gains...most likely you will....but to varying degrees....

for you to get the most bang for you buck....put together a plan....this will require a lot of research....and you actually may find that the answer is not out there....

you need to match your intake to the cams to the header to the exhaust to the muffler......and if you have any sort of forced induction that fits in there too......

what you buy today just as an exhaust system may be fine for now if you are running everything else stock...but start adding other things and you may find it inadaquate....

as far as back presure....yes it will rob SOME power....but NO back preasure is just as bad.....its a delicate balance.....and probably the only people with the REAL answer to this...is a shop that carries not only all the pieces and parts that you would want...but one that has a Protege and has done extensive R&D with it and all the parts and many many varriations of those parts and done MANY MANY dyno runs to have data to back everything up...

BUT....guess what? I am not so sure that a shop like that exists for us.....after all....we have a hard enough time just finding a company to make parts for our cars...much less a shop that has dedicated those kinds of resources to one of OUR cars.

:{D yeah I know....this probably didn't really help you....for there really wasn't a pat answer for your question.

 

Brullen Exhaust in Toronto has put on a couple cat-back systems for some peopel with P5s. It took them about three days of testing to setup the first one and from their testing I think they got about +5 HP gains with 2.25" pipes.

Although I am considering 2.0" pipes when I get mine done (quieter? ) because there are a lot more restrictions up before the cat. Unless the guy advises against it. He seems to really know his stuff when it comes to exhaust systems. Gave our club about an hour long talk about it!

http://www.brullenexhaust.com/