I have a 2006 sportster XL1200L , I've added Exhaust, mikuni carb, sportster cnc ported heads , and screaming eagle hi- pro cams, all else is stock and my compression is 9.7:1, and dyno'ed at 88 hp-77tq. In order to save a few $$, I'm considering decking my heads, instead of buying new pistons, to get to 10.5:1. My 2 Questions are this.

1. GENERALLY, What can I expect to realize in power from this increase in compression? 5% ? 10%? 20%?

2. will this increase affect both hp and tq equally?

 

It push up the hp and torque both.
Cams intake closing number will dictate what compression.
Best to seek a piston when needing to move your compression substantcially.
Scott

 

First of all welcome aboard from Texas…. secondly and last listen to Hillside he does this for a living. also when you shave heads you get into custom length pushrods and more down time for the bike

 

True about the pushrods, but you can buy adjustable ones.