I got a 1999 Pontiac Grand Prix GTP and upgraded to a 1-3/8" radiator. The radiator listed in this post will bolt directly in a Grand Prix with a couple slight modifications that anyone can do. The install is straight forward and easy, one of the those most simple mods you can do and one of those most benifical too, especially for you intercooled guys.
Here's what I got...
I went to my local O'Reillys Auto Parts store and got me a new aluminum Proliance Radiator PN: 432387. If for some reason they cannot access this PN (they should have no problems) the radiator is for a 1998 Chevy Monte Carlo, 3.8 Liter V6 N/A, and there will be 3 choices for the radiators... a 5/8", 1", and a 1-3/8" HD listed on the computer. If its not in stock it'll most likely be at the local HUB, you should get it the same day most likely. Before buying the radiator, take you tape measure and double check the core size! The first one they got for me was 1", but the sticker had the correct PN on it. They got another one and it was correct, double check this before purchasing! The radiator cost me $186.99 and w/ tax that came out to $202.65. It comes with a LIFETIME Warranty which is worth its weight in gold IMO. If something fails on it, a replacement is a few hours from me at all times. This is important to some people, especailly those with daily drivers.
I just did a write up on how to install/modify it to fit here: http://www.grandprixforums.net/f73/c...rade-3697.html
Don't go with stock when you can get a nice upgrade for the same price and only need to do very minimal and painless modifications.
Hope you guys enjoy this upgrade!