The stock cross pipe to the turbo is like 2.25 inch. I have heard someone say on here that small is good cause that keeps the exhuast moving fast into the turbo. But I was thinking about this and I am not sure if that would be tru. I need some more opinions on this. If I stepped up to a 3 inch crossover pipe (which would cost next to nothing to have made), it shouldn't really slow down the air going into the turbo. It would allow more air through the cross over pipe into the y pipe and up pipe. And if it is shoving more air into the y pipe doesnt that mean that it could even increase pressure going to the turbo?

 

What's the outlet size on the manifold? Go bigger than the manifold, it will decrease pressure, and slow down flow. If it's currently smaller than the manifold, matching it would be best as smaller would be restricting flow, and not allowing the volume through.

 

I believe that the pipe comeing off the maniflod on these trucks is 2.25". It then opens up to a 2.5" pipe going back where they meet under the truck ( on non-turbo trucks that is). I think that that down pipe off the turbo is also a 2.5" pipe and most were the smashed version.

 

I don't see how it could help. THe crossover is carrying only the drivers side exhaust over to the y-pipe where it joins the passenger side exhaust.

Perhaps, if you replaced the crossover, and the y-pipe, and the turbo inlet??? I donno

 

it wont help the outlet on the manifold is 2.5" the inlet to the y pipe is 2.5" the up pipe is 2.5" the exauhst on the N/As that both banks run to is 2.5" so I don't think a 3" cross over will help.

 

In simple terms, if a turbo is putting out 10 PSI, the exhaust back pressure is also 10 PSI.

So now consider the volume inside the cross over.
A gas like air or exhaust will compress.
So the bigger the container you are putting it into, the longer it takes to bring up to pressure.

So the first thing you would notice is more turbo lag.

Now go out and find two trucks with the same size motor but one with a much larger exhaust than the other one.
Have them both idling at the same RPM.

Now hold your hand at the end of each exhaust.

The smaller exhaust has more pressure and is moving faster than the larger exhaust.
So increasing the cross over size will also reduce the max boost the turbo can produce.

If you think about a positive displacement pump, like the cylinders are in each head, as long as the RPM stays the same, the volume of exhaust stays the same no matter how big the pipe it goes into is.

420/8= 52.5 cubic inches per exhaust stroke per cylinder.

If the pipe is 1 sq. in. in size, each exhaust stroke fills 52.5" of pipe.
If the pipe is 52.5 sq. in. in size, each exhaust stroke fills 1" of pipe.

Now consider 10 strokes per minute.
Exhaust in the 1" pipe is moving 525" per minute.
Ehaust in the 52.5" pipe is moving 10" per minute.