Quote:
Originally posted by mike2002@May 1 2005, 04:12 PM
for a 170hp car, 2.5 is ridiculously big. borla had a better setup with 2.25" mandrel, stock is 2" pressure bent. its my opinion that 2" mandrel bent is the best setup for a near stock car (like ours). but the companies know to sell the kits, people want bigger, the average person putting exhaust on there car will order the kit with the biggest pipe. 2.5" mandrel isn't needed unless you are running forced induction.
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i agree......if it was a 170hp 4 cylinder. but you have to take into consideration this is a 3.4 liter v6, a decent size engine. you need room for all that exhaust to fit into. thats why the 2" stock piping is too restrictive. upgrade to 2.25" and you maintain velocity and it opens it up a little for the top end. upgrade to 2.5" and you push the peak power higher into the rpm band but also could gain a few hp with the bigger, more free flowing piping. swap to a high flow cat and gain a few more hp. ditch the cat for a completely unrestrictive exhaust and gain even a few more hp. its all the little gains that add up. plus if you plan on further modding the engine in the future, you've already got a good size exhaust to support those mods.
as for forced induction, you want the biggest piping possible. the pressurized intake charge pushes the exhaust out of the cylinder during valve overlap so you dont have to worry about the scavenging velocity to draw it out. you just have to worry about free flow and no restriction, especially with turbos. any restriction or backpressure what so ever could slow down the turbine wheel and cause excessive turbo lag. 3" piping is a must for boosted applications. anything bigger would be better, but you'd have a tough time fitting it under the car and going over speed bumps without scraping anything.
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