is there a web page somewhere that show hp gains or speed gains for different mods?

 

Not that I know of, but I wish. That would be one big and helpful database.

All I can tell you to do is search it the mods on here and make and estimate, also some manufacturers make estimates on their parts. Either way its hard to tell with each individual car, only way to get the true figures for your car is by running it on a dyno or the track.

-Dustin-