Best mods to a V6;
Do all the bushes(castor bushes/big ones at the front will improve braking so much more in an old Commo for the least amount of effort and money)
King springs front/rear + Shocks to suit springs(anything lower than stock will need to have the camber fixed, get some adjustable castor bushes for the front, not entirely sure on the rears but I believe there is a camber correction kit available. They make special shocks for the shorter springs if you choose to lower)
New rotors for the front, possibly rear(not sure on JC's thoughts on drilled/slotted)
MACE chip or similar(cheap, easy to fix, gear changes are a bit smoother)
If the drivers seat is cactus, get a new/2nd hand one first
Dash mat(not "cool", but it's a damn fine way to spend $40 if you plan to drive when the sun is up)
Heard some things about the CAI, better to just cut the snorkel open and leave it as is, save yourself $300
Regular services, oil every 5000km or so in the city, fuel filter every 5-10,000km, air filter whenever it's dirty
Spark plugs/new leads if they are stock
Do all the hoses ASAP if they look a bit soft, and do the heater tap before it corrodes and cooks your engine(be careful of the 2 hoses leading into the firewall, heard they can damage the heater core and make it leak if you pull too hard etc)
Transmission service if it's got a fair few km on it
Drain and flush the cooling system, keep the glycol about 50%:50% water.
Bigger tyres, 245/45 17's are a nice size, slightly wider than stock for a bitmore grip. Downside is the rubber is more expensive. If you're keeping the steels, chuck some Bridgestone "Supercats" on and call it a day.
Cat-back exhaust, cheap off ebay. Easy to install, just remove the rubber mounts(you'll need a screwdriver for the little clip and possibly a rag to slide them off. Or cut them off, they are only $5-8 each). Extractors are optional, mixed reviews about them.
Probably more, like 1.9:1/1.98:1 roller rockers, check the power steering and replace it if it's leaking badly, etc. They have enough power to have some fun in, good fun on dirt roads. If you want a V8, buy an unregistered one and use it as a track car, not too much point driving an 8 in the city. On the highway they get slightly better economy than the 6 from memory, but it's your money. The Commodore loves the extra steering + throttle in and out of corners, just need to be quick with the wheel. The whole "handles like a boat" thing comes from either **** drivers or it being too low with bunk camber lol
