2005 Grand Marquis
 

Hey everyone new member. I just brought my 05 grand marquis and I want to know how I can get up to 375 to 400hp with breaking the bank??

Without breaking the bank? Depends on what you define as breaking the bank.You are not going to accomplish it without an engine tear down.

Ok. Well I don't mind spending what I need since this is my first mod car. But what do you recommend as a good setup to achieve that kind of HP???

I don't wanna rain on your parade, but it appears that you have set your sights MUCH too high, as you are asking to get 400 HP out of 281 Cubic Inches, which equates to 1.42 Hp per cubic inch -- for a 2-ton, street-driven, 4-door sedan -- NOT bloody likely !!
Another factor to consider is the Transmission -- the stock tranny can't handle 400 Hp without extensive (and expensive) modifications.
To get that kind of power to the ground, you'll need a Trak-Lok limited-slip rear end, with at least a 3.73:1 ratio -- and a cast-aluminum differential cover that has jack-bolts for the carrier-bearing pre-load adjustment.
The stock wheels are MUCH too narrow -- you'll need at LEAST an 8-inch wide wheel, with appropriate-width tires.
When we wanna go racing, we often overlook all the obstacles to going really FAST, and wind up slow, broke, -- and disappointed.
Good Luck -- and let us know how it goes !!

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Custom Bumper Cutouts for Dual Exhausts make for better aerodynamics and they increase ground clearance, too.