I have a 07 Softail Custom with stock engine . I have recently upgraded to V & H pipes and Hi Flow air filter. I am thinking of upgrading to a Harley ST4 1690 Race kit.
Can anyone with experience, suggest how much additional performance, torque, HP, ....... I can expect from this upgrade.
Thanks much.

 

I did a 103" kit with 251 cams MVA heads matching 10.5 piston and the 58mm TB along with the other parts to finish. I know this is not exactly what is available in a kit form from SE but it is what I ended up with. All these parts work together very well and they make a touring bike(I have a SG) extremely fun to ride, no ping either.Only about 400 miles so far no no dyno or no mpg estimates.