Quote:
Originally Posted by Telly9987
So Im taking my car into my shop and she's going up on the lift for the first time in the AM. Im debating what to remove. Both resonators AND the cats? Just the cats? Just the resonators? X pipe or H pipe? So many options and configurations....
I feel that without cats, and 2 sets of resonators there has to be a dip in performance. Everyone always wants to straight pipe everything and have everything wide open BUT back pressure is here for a reason (by profession I tune race bikes). I see it on my dyno all the time with lack of pressure or too much pressure effects power and mapping should be adjusted. On our teams bikes for the past 2 years we have introduced butterfly flapper valves BACK into our systems with tune-ability to control angle and adjust pressure. EVT is a whole map I focus on with my riders to help with throttle smoothness and responsiveness..
Really torn here....
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AFAIK losing back pressure is always beneficial, it's the lack of efficient exhaust scavenging & resulting drop in velocity that results in a drop in performance. The turbos/turbines already regulate the "scavenging" needed. For turbos, less back pressure means the turbos can push higher boost if tuned for it - hence why you have to go catless / high-flow cats for higher power when tuning.
You should ask yourself if you like the stock tone. If yes, then try removing the secondary cats - this will add the most volume without introducing much rasp - this may get a bit bass-y though based on experience with S55. If you remove the resonators, then you'll probably want to add an X or H to merge the pulses to fill out the sound and help reduce rasp. As an anecdote, one guaranteed way to make S55 sound worse (yes I said WORSE) is to run unmerged straight pipes back from the cats.