I find two types of 997 headers. One is "short primary" into "pyramid collector" ala X51. The second is the "long primary" which you see from most major manufacturers. Here the tubes from the heads are long and gracefully arced. Are both considered "equal lenght"? There are obviously different design goals. I am looking to replace the oem cast iron but am more interested in midrange than top end. I would like to use the standard muffler can and cats. Can anyone shed some light on this for me? Gerry

 

Here you go - not specific to Porsche but a couple of good articles about the basic theory.

http://www.burnsstainless.com/TechAr...harticles.html

Ian

 

Hello Ian. I look at the two types of headers and wonder. They obviously should affect engine performance differently. Note this as per the article(which I so far have only scanned with sleep in my eyes): "long headers-> low rpm power. Short->high rpm power". This is interesting and relates to our conversation of last week. The X51 headers may not help the loss of low end. Someone else recently posted that he replaced oem system in C2S and realized how much power long primary aftermarket headers had cost him on the road. It may be necessary to reflash (ugh) to gain benefits across the rpm band with exhaust changes.To be continued. Thank you for the input. Cheers, Gerry

 

The OEM on the 997/997S is NOT cast iron.