Thread: 1st GM Product Purchased

So after owning 9 Fords, I have moved over to the dark side. I picked up an 03 GTP with 84k. It is extremely clean and has only been through one winter. I am mainly a mustang guy and have been into cars for about fifteen years.

While doing some research to determine how best to modify the GTP, I keep finding posts about people being concerned about Knock Retard. I know in the early mass air days, you could make some modifications and the computers would be able to "learn" and adapt to the new modifications. You usually had a limit to the modifications you could do before the car ran too lean. (exhaust and air intake) With most new cars, if you even put an air filter on them they need a tune to avoid running lean. I have seen many people talk about scanners and being very concerned about KR.

So my question is, if you get the car custom tuned, do you need to worry about KR? Are these cars any different than any other fuel injected vehicle when you go to modify them? I would like to put some headers, Downpipe and then possible go with a pulley. I would plan to dyno tune the car if I put on any of these mods. I can't imagine why these cars would be different but with so many people being concerned, I figured I'd ask. Maybe people are rolling the dice, but I would never imagine putting a smaller pulley on a vehicle without a tune. Even with the headers I would be concerned.

Is there something I'm missing?

Thanks

Give this thread a read and it should answer most of your questions. http://www.grandprixforums.net/threa...00-Powered-Car!!
Also check this thread out as well. http://www.grandprixforums.net/threa...ommon-problems

i wouldnt be too concerned with the KR if its stock. sure, it might knock a little, but with a big ol 3.8 pulley on there, it shouldnt be enough to worry about.
headers and a custom tune you will probably be able to run a 3.4" pulley. that is a very common setup on these cars.

I'll be honest, they don't really need a tune to run most mods. If you changed injectors or like the MAF and throttle body itself, sure you'd want it tuned. Or if you messed with the cat converter and did a egr delete with a header install.

They run rich from the factory, around 11ish and go a tad richer as time goes on. They do it to keep it safe, they knock from the factory but even doing exhaust mods could not get rid of it all. Anything after the converter is not a issue flow wise, so wasting money for bigger exhaust would not be a wise purchase.

But with modding, you do want to monitor things. Thats why we say you need something to watch KR etc etc, because if you did add more boost you would want to make sure it's safe. Figure if you had 2-3º of knock with 6-7 psi and you added boost and are running 9-10 psi and see the same knock, that 2-3º with more boost pressure is more harmful and you could chip a piston.