Larger Exhaust Plus Stock Turbo=Worthless
 

From what I just found on my truck you can run a 20 inch exhaust, if you have a stock size turbo it don't matter, your still runnin the stock exhaust size. I just pulled the stock elbow off the back side of the turbo to replace it with the Megamouth Elbow and what a shocker. The hole on the elbow is even smaller in diameter then the stock exhaust was. Now going under the rule that we use for fuel, that your flow is restricted by the smallest passage way in the flow, then the size of your exhaust means absolutley nothing if you are running the stock exhaust elbow off your turbo.

I will get some pictures posted later in the evening on this to show what I'm talking about. It's scary when you see the restriction.

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This photo shows the end that connects to the back of the turbo. The turbo outlet itself is the same size and shape as the whole plate that you see there. So as exhaust is exiting the turbo, as you can see from the black coating half of the exiting gasses are hitting a dead end wall and having to recirculate before escaping. If the porting and polishing we do to the exhaust manifolds make that big a difference in performance, I can't imagine what this is doing to air flow.

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This opening measures 2 1/2 inches across for inside diameter. So no matter how big of an exhaust you are running, if you have the stock turbo and elbow you are running a 2 1/2" inch exhaust.:madd::madd::s::booo:

I suspect this also applies to the 1st and 3rd gen trucks also.

how much did you end up paying for that megamouth thing

I got it out of the classifieds on here, used. Think it was $150. They are $199 off the site new but it's a 6-8 week wait. He makes em up for each order and then they have to ship from Canada.

The elbow on the 3rd gens is nothing like that one. It has no "flat" area, it's a completely round unit that mounts with a band clamp, no bolt holes like I see in the one you show.

I'm glad to hear that they did improve on it cause this is crap.

And the 3rd gens are 4" now...

This is a fairly major issues, gotta be some strong opinions out there someplace about it. Somebody tell me I'm wrong in how I'm lookin at this and explain why. I'm havin a really hard time beleiving that with all the advancements we have made on these trucks that something this critical could go mostly unnoticed.

Thats not compleeeeetely true Dennis. Imagine having a pipe that is 20' long...the surface area on the ID of that pipe = X amount of restriction to flow. The longer the pipe the more restriction. The same ID pipe at 5' will have far less restriction. Now factor in the scavenging affect. When you try to force a liquid or gas from a large pipe, through an orifice, then to a larger pipe again you get a scavenging affect which increased the velocity. SO, this is why you see a 200-300* temperature drop in EGT's just by changing to a turbo back exhaust. BUT, yes...making the flange or orifice larger will move more liquid or gas and decrease velocity at the expense of lagging the turbo because of reduced backpressure. The restriction at the flange for a mildly modified truck is actually a good thing. :up: :bombin:

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.