Chiptuning addresses and links
Jet Performance http://www.jetchip.com/
Ronald Heidl http://www.poweredbyheidl.de./
Split Second http://www.splitsec.com/
Websites of interest:
928 Australia, Landsharkoz: http://www.landsharkoz.com/tt/ttchips.htm
I have run into this post on Rennlist:
There are some suggestions that a slight increase in fuel pressure, coupled with the chips, takes care of some of the pinging/detonation issues. I started with the recommended chipset, and then a different set after experiencing some of the pinging/detonation issues myself with SoCal pump gas. New chips solved the problems for me.
I have the adjustable rising-rate fuel pressure regulator sitting in my box of things.
The chips I have are supposedly for the GT rather than the S4. Dave Roberts brokered the swap with Autothority, and might be able to help with that info if it's important. It's quite unlikely that you'll find any pirated GT chipsets floating around, so you may end up paying the full price for the GT's --IF YOU NEED THEM--. Try a set of S4 chips in your car before you go hunting for the GT chips. The S4 chips seemed to have slightly better performance, and I would have kept them except for the hot-day pinging issue.
BTW, I still have that RR fuel pressure regulator sitting in my parts collection. one of these days I'll put it in, and reinstall the controller chips to see how it does.