That would only happen if you go too big on piping and reduce the exhaust velocity.
You're right but for the wrong reason. It's the vacuum effect, or exhaust scavenging, that affects performance. When done right, the outgoing exhaust pulses will form a vacuum that sucks exhaust out of the combustion chamber quickly, so more fresh air can be used in the next stroke. This is a hard thing to accomplish because there's so many variables involved. If there's not a strong enough vacuum, then exhaust isn't being pulled out of the chambers quick enough, so exhaust fumes will remain during the next cycle. A well tuned exhaust can act literally like a mini supercharger. I forgot the technical term but there's also pulses that will bounce back and right into the combustion chamber, and there's ways to control that as well. Exhausts can have these mini chambers built into them to catch these returning pulses.
You're missing a key piece in your argument: higher exhaust velocity is what creates that higher pressure delta and scavenging. Matching the pulse timing to piping size and length is critical to optimizing scavenging because of the effect on velocity. Smaller diameter piping will increase exhaust velocity at the expense of mass flow due to pressure drop, which is fine at lower RPM (where flow rates are lower) but will become overall detrimental to power at higher RPM.
I'm not really sure how there was gain with stock manifolds but headers can't be all that different. I can say from experience that it is a hell of a lot louder running catted headers and Borla S-type. That was my combo on my 2016... almost wake the dead loud.
Thank you for the kind words. I hope you're enjoying the Power Pack 2.
As mentioned in the article, removing the restrictive resonator with an X-pipe is probably where the biggest power gains of a catback comes from. I would be surprised if there was a significant improvement of any axle-back on a car with headers and an x-pipe since the X-pipe location has such a big influence on the torque curve. Removing the cats is where you'll find the biggest gain, then probably the resonator. Most of the gains from headers come from removing the cats (long tubes don't make significantly more power than a catless stock header).
Thank you. I can assure you that the S-type has a distinctively different pitch than stock (active or not) in a 2018 Mustang GT. The Atak is very similar and a little louder due to a lack of the small pre-muffler resonators. Either way I think you'll be happy with your purchase. Be sure to post your feedback once it's installed!
As far as I can tell the review is for this SKU: BOR-140745CFBA.
