Someone posted a dyno some time back that showed a 5 hp gain. Not bad if you are taking the turbos off anyway and running the grinder yourself. I bought an extra set for $100, and I'll port them if I ever get the time.

 

Looks like I should pass.

Christian

 

sorry, but i have to disagree... restricting a turbo from getting exhaust energy (turbo manifold side) or expelling exhaust gasses (exhaust system side) never helps spool. Turbos hate exhaust pressure.

I'm not saying that properly porting out a stock turbo manifold will be noticeably beneficial. I'm just saying that the concept of restricting a turbo engine's exhaust to gain spool is unheard of.

 

No argument on the ultimate desire to improve air flow through the system and that you would not specifically work to increase back pressure by restricting the exhaust, but the fact of the matter is the spool time for turbos is directly related to the time it takes to build enough pressure to turn the turbos. There are a number of ways to help "build" the pressure. Smaller turbos have a smaller volume of space and therefore spool quicker. Often the reduction of lag will result in less power at the top. Hybrids try to strike a happy medium. For example Zero clearance turbos decrease the space between the blade and the housing thus reducing the amount of lost pressure...therefore pressure builds faster and less lag.

 

Creating the right amount of exhaust energy to spool any given turbo can be useful in perfecting your turbo's spool characteristics. I believe that building a "perfect" exhaust manifold for that particular turbo is key (I'm intentionally ignoring the post-turbine exhaust side as I think we both would agree that the best performance exhaust system for any turbo is having no exhaust system at all).

In other words, if it's an OEM turbo manifold, it may have some kinks and jagged edges that impede exhaust flow (in some cases the piping is too small to allow optimum flow - probably not in the 996TT's case for k16 turbos). In such cases, cleaning up a turbo manifold like this may see some gains/spool improvements - depending on how bad the design was to begin with. There's probably not a whole lot to gain from working on the 996TT manifold when dealing with stock k16s. But I believe that if you port it out to the point that you're experiencing a negative performance impact, it's not because it wants X psi of pressure, but because it's taking far too long for the gasses to get down into the turbine. Any poorly designed manifold could fall victim to this, but I see where you make your point that this is where more "pressure" would be beneficial. I just don't like calling it pressure I guess... I look at it as optimized exhaust flow. I think we're in agreement though. ya?

 

You could buy the ****ty chinese made headers like I have and just hope you have
made some mad power...

MK

 

Yes Tuna, Absolute agreement...well said.

 

I doubt even 5hp. that would be generous.