Bert, what car? Approximate weight? Trans/converter? More 1/4 mile or 1/8 mile? Significant street driving?
Then I can answer that. As much "detail" as you're willing to share. What style rear axle?
X 2 on the "X" pipe. A lot of our Pontiac guys use Pypes. I've heard good and bad. The X-pipe definitely makes power, though.