My wife has a stock 03 trail boss and i have a stock 04 magnum 330 2X4. After reading about people changing their primary spring to get performance inprovements i decided to try it. I bought an EPI red and pink. Before i installed either my wife and i drag raced each other down the street out front. After several races it was a dead heat from a dead stop to wide open(about 45mph per speedo on my magnum). Same thing from a 10mph roll start. I changed the stock spring to the red and we raced again. In the first 100yds she pulled about 2 lengths and after that it was even to top speed, still about 45mph. I was suprised how much difference it made. This was the best way for me to test the difference since i have no tach or speedo on the boss. I havent tried the pink but i will let u know when i do.

 

try a polaris white spring

 

same as epi red