Turbo porting... all bull?

[skint]

I've noticed that quite a lot of after market turbo upgrades port the turbo. As far as I can see, this is where the turbo housing is polished up to remove any faults in the castings and make it easier for the air to pass over the surface.

On a 2nd level, I think some porting actually removes a degree of metal to allow more space in the turbo.

I can see my the 2nd level (which I think it proper porting) starting to make a little bit of difference but wonder whether it's really worth it? Is it something that would give marginal increase in response and maybe 1-2bhp?

Anyone knows the score here or have experience ?
Cheers!

[Lotsayellowsnow]

It seems that porting the turbine's housing without increasing the size of the turbine itself might allow air to travel past the fan blades without pushing them/being pushed by them- leaving "dead" air to cause turbulence. If you took the turbine out of its housing, it would move hardly any air because there is no housing to guide the air across the fan blades. I would think that at a certain clearance, the turbine would just spin more freely and effectively move less air.

An engine creates the most power the furthest possible from vacuum in the intake. In a normally aspirated engine the pistons create a suction. Porting the intake ("bigger holes") helps balance with atmospheric pressure (reduce the vacuum in the intake) - but in forced induction the turbo creates pressure- even further from vacuum... Extra dead-space in the turbo is esentially a "hole" and since we want more pressure, we wouldnt want a "bigger hole" to help balance with the atmosphere- pressure escape.

Polishing makes sense to me- decreasing the fluid friction between the air and housing- but porting without increasing the diameter of the fan doesn't... PROFESSIONAL PLEASE!

If I'm right, a bigger form turbo (T28, TD04) is necessary for a bigger housing...

If you wanna increase hp a couple from the intake side- try bigger intake piping and a more free flowing intercooler.