TTI will give a stock or mild build up to 20 extra horses easy. Do not undersell the TTI headers. Go with straight through mufflers and shortened exhaust system and you will get an other 20 to 30 more horses especially if the pipes are 3 inches but 2 and half will work good too! I once had 1 an 3 quarter going into 3 inch with 4 inch tips out the sides in front of the rear tires. I f you have at least 391 gears or better and a 3 or 4 speed manual transmission and you can get them to fit 1 and 7/8 inch headers will also work.