Same as anything els exhaust,high flo air filter,K,N? Then it starts to get real expensive,Heads yours should be o/k on that model, ported,1:7 "Cobra svo" roller rockers with std cam & change rocker covers or another cam?The usuall stuff.
More timing on high octane fuel,check preignition.Etc?
Probably the most cost effective mod you can do, as well as being a mod you should do, is exhaust / extractors. If you've got a series 2, then it's probably ok to keep the stock system. You could always do a cat-back job, and it wouldn't hurt the note either :)
It all depends on how much you've got to spend. Have you got a budget in mind for this mate, or just shopping around?
Porting usually makes a difference when other mods are done,thats when you'd put GOOD valve springs in etc.Depends on budget?Exhaust as others have stated is a good place to start,then all other mods co-ordinate with each other.A thing that doesn't get mentioned too is the efi pump I don't know what has what from eb to au inc G.T?But in U.S Mags they allways state to increase the pump hour rate.[install bigger pump]
If I tweaked another 5Ltr again I would try the 1;7 rockers with good valve gear,alot less hastle esp with your heads the Cobra's1;7 are pedestal mount?.You only have to take the valve cover's off too.Costs mega to replace cam,the heads have to come off for the roller cam followers hit the head and cannot come out to allow removal.Unless you do it yourself?oh radiator,air condensor,bumper etc Hassel.The 1;7s give ya more lift getting the valve open quicker too,so it vertually gives it more duration not much but some,o/k.Yes it does make a difference when all added up.Check out www.performancebrothers.com Mainly Ford or Mustang..Some answers there too.But remember the Mod [ohc]4;6 in latter models..
The AU I XR8 was supposed to be a 185kw. AUII from April 2000 was 200kw. Difference? GT40P heads (iron!), roller rockers, lighter pistons, different cam (perhaps EB GT or similar), different headers? They idle differently. Still could do with a lot more grunt though!
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