How many of you are running a DC JDM header wit the 2.5 collect wit a high flow 2.5 cat with a standard exaust like the Apexi N1 which is not 2.5?. Im getting ready to purchase my header and will be faced with this problem so i was wondering how the set up performs and what problems it faces.

thanks.

 

Any time you make a transition from a larger pipe to a smaller one, you increase your exhaust velocity, but decrease your cfm potential, which adds to back pressure.

So basically, having a stock exhaust on a larger header/cat is not going to give you much, if any, gains, since ultimately the engine is going to be limited by the cfm possibility of the stock exhuast, just like the stock engine.

 

my exhaust is not stock, i have the Apexi N1 Cat back.

 

well i dynoed saturday and didnt lose any HP.

 

You're not going to loose power, the system as a whole still flows more than stock. You will however stand to make a larger gain if you run 2.5" all the way back.

 

yea i will look to do that once i get into the motor internally