With this new elbow I have no lag anymore, it's great. I can slam the go pedal and hit 20-30psi right now and to make that even better I can't get the EGT's over 900 even with my tuner turned all the way up. I used to sit in parking lot's waitin for the turbo to come down to the 300 degree mark before I shut it down and it took a few minutes. Now it will drop in a matter of seconds.

I don't understand the science behind all this, that's why I was lookin for some discussion on it. I understand what your sayin in principal, but I'm seein a different outcome. It's all confusing for me.

Yes, your EGT's are going to go up and down quicker but your turbo is going to spool slower unless you had an extreme amount of back pressure to begin with.

Still lookin for opinions on this.

I know this is a hard topic for me to grasp as well and will argue everytime i go to my local tire shop with a guy who owns a powerstroke.. his argument is that a diesel engine is a air pump and his logic is the more air you can get in and out the better.. I on the other hand will look at it like DangerousD does and it all has to do with flow and back pressure.. i still have the stock hx35y on my truck with 4" exhaust and got great results with it, but i believe there is a point where to much will have a bad affect on the performance... with stock exhaust i saw two issues as far as flow and back pressure first will be the small 9cm exhaust housing and second was the stock exhaust 3 or 3 1/2 inch i don't remember what it is.. now exhaust is being pushed out of the turbo to small exhast diameter and then a very restirctive muffler.. we eliminate the stock exhaust and muffler and almost eliminates any issue with the exhaust being restrictive and back pressure.. no the only issue is the turbo.. then this starts a big domino affect that goes back to the amout of fuel that is added and adding enough air to match that which results in maybe adding a bigger turbo..

the only way to really tell is on the dyno stock exhaust versus 4" then 5"
at what point are you killing performance, spool up, then we go into what are we using out trucks for all out comp or daily driver WOW I'M DIZZY NOW "give:

I aint know brainiac, let's understand that right off the bat. But I have had a 4" exhaust, that I noticed a huge improvement over stock with and the stock turbo. When I installed this new elbow on the turbo my spool times went way down, my EGT's dropped a little bit and the smoke affect went down which I am happy about. In theory I also agree with what DangerousD said, but I am experiancing the opposite. That's why this thread.

I thought the same thing when i did my axhaust but if you think about it it should help regaurdless of the elbow. Think about a ballon. When you blow up a b day ballon it is less restrictive and goes up easier then a water ballon that isnt made to hold as much. I dont know if I am the only one that understands this the way I am saying it here. Even with the stock elbow if the system behind it is freed up it will let the gases go through it faster.

Restriction (or more properly - pressure) is a result of many things - wall friction, bend radius, ID transitions, muffler type, overall exhaust construction. Gas moving from a 2" ID to a 3" ID experiences a pressure drop which may help exhaust flow depending on the transition from 2" to 3", the placement of the transition, and engine tune.

1. A poorly designed and built 3" exhaust would be worse then a properly designed and built 2" exhaust.
2. A properly designed and built 3" exhuast would be better then aproperly designed and built 2" exhaust.