Lots of wrong information.
This subject has me so confused! I have now read through the whole thing.
I feel like in one breath guys are saying post turbo exhoust tuning is irelavent to scavenging, then explaining the effects of it in the next breath!
If the anwser is in here, it lacks the "why" explanations, and and or the disproof of opposing theorys.
One thing i tend to coclued when opposing theory our fought to death is, both sides are right or wrong, and theres more to it.
I like that aboosted brings up the point of load as an important variable. But why? Is exhoust velocity less or more? Is it safe to say waste gate, cam timing, spark timing , oporating rpm, power made, and ...(aka tuning) all play a role in this discussion? Would it be possible to manipulate a 4" cat back to make lowend torque also?
Its a bit frustrating when these topics turn in to i know more then you debates. Here is an important fact. largely in part by way of header tuning the Mazda "sky active" is making race engine compression on pump gas. Why i bring this up is to make the point that if you asked the most brilliant mind in the field to accomplish that on a mass produced application in the year 2000 it would have been deemed impossible.
My point is no one know every thing or even close to it. When at the track i have seen many turbo exhoust setups varying across the subjected spectrum. Same for exhaust design on production turbo cars.
If i was trying to play the know it all role my posts would lack "?" Marks and "to my understanding" just here to contribute and learn.
Now for facts i have that could start some good talking points:
My first mod was a 4" cat back. I felt allmost nothing. But i used the stock mid pipe to cat back flange. (2 1/4 +/-) after cuting the flange back as far as i could (3"+/-) the but dyno felt it as well as mpg. (Stock tune)
I think hart throb clamed 50/30 ish with just there cat back.
To my understanding one of the site vendors noticed a small torque loss with a 4" vrs 3" tuned right?
Catless downpipes lost power almost everwere with superchips tune, and is amazing every were with one custom tune and is amazing mid and up top with another. (4" cat back my truck)
Hoping we can spend more time debating the subject, and less proving who know more then the other. Im guilty my self at times i know its tough, but at the end of the day its the internet and we should all be taken as simple opinions that in conjunction may come to a conclusion or help a viewer, and or our selves come to an extremely educated conclusion. Sizing up each other dos nothing for any of us.