What's holding them back? Valve sizes, chamber, etc... I'm asking because I'm considering picking up some heads with hammer's impact service done. Just a port and polish job and upgraded valves and springs but no increase in valve sizes. Just wondering if it's worth it or not, for better performing heads. Granted they'll be better than the stockers, but on the fence if they'll be that much better. Hit me with some feedback, please!

 

The impact will get you much better performance out of the 883 heads. That's what will be going on my bike with the upgrade.

The 883 heads have two big issues, the crappy valves and bad ports. The impact service works to unshroud the valves and clean up the ports. The headwork levels above that start getting bigger valves and better springs/retainers. You can hit close to 100hp with just the impact heads.

 

Thanks scuba!