i have posted this before around the question of how much hp/trq does the stock cat restrict vs replacing the stock cat with a test pipe. this is assuming a 3 inch turboback...does anyone have any dyno proof of gains had by removing the stock cat and using a test pipe? i have heard 5-7 hp then some say 15+hp and more.. if i am losing 5hp no biggie but if a 50 dollar part (test pipe) alone will yield 20hp or something i would consider... see my sig for mods..

 

I've heard 15hp if I remember correctly, could be mistaken.

 

i went from high flow to test pipe on my 8 with full AMS turboback. the butt dyno felt a gain, not huge, but it was felt. id say 5-10hp.

 

meow!!

 

The cat-back is not giving you any gains because the stock dp and cat are restricting the airflow. If you are going to go catless(which I reccommend and do myself) then I suggest opening up the turbo-back...

 

high flow vs test-pipe were almost exactly 10 whp different on my car, and that's a high-flow

 

I just recently went from a HElix HFC to catless and picked up 2 PSI of boost. That was the only change. So however much 2psi is worth?

The engine does feels a bit more responsive as well. I'm guessing that's due to the decrease in exhaust back pressure more than increase in boost pressure though.

 

Dude, first of all how do you buy a "turbo back" exhaust and still have a stock cat ? I mean i will give it to you, if the exhaust you got was as "small" (not 3 inch) as your original stock system you might want to start by throwing that thing in the nearest lake you can find. But if you mean that the only pipes you got that were new were after the stock cat then you need to upgrade the rest of you system with a true turbo back exhaust. Then if you want to fully commit i would say run the test pipe. I am not condining braking the law but that is the chance that you take running the test pipe. But that would be the least restrictive system.

 

Have you checked to see if the extra boost is safe with your current tune? Fyi.

 

Sometimes removing a cat creates boost creep which is the reason why you feel a gain on the butt dyno. You gotta see a real dyno sheet to see the gains.

 

I've been watching with my scan tool (it logs and graphs) and haven't seen any knock or timing being pulled. So, it seems to be. Fyi.

 

the benefits of a TP are much more than just the power, but its easier to accurately log AF ratios (unless the wideband is before the cat) and its just safer in general when running higher boost (makes the car less prone to knock by lowering EGTs)

 

It depends on what other mods you have..Turbo+stroker...etc...the more mods initially the more gains you have

 

I thought the loss was more of a percentage of power rather than fixed. Think about it, more hp=more airflow the more of a restriction it will become as more air tries to get through

 

no cat, it sounds ****.