I wrote this little primer on our past and present small block GX cylinder head offerings just so that everyone can make a little better sense of our switch in naming conventions and available models. We are open to suggestions for a naming scheme that actually makes sense to novice and experienced builders alike, so let us know if you have an idea.
The Discontinued Stuff:
"Stage 0"/Standard Shredder = Older version of our current "Level I" head with less hand work. Superseded by the current "Level I". Worked best with 1.2:1 rocker arms and CM or other .265" lift cams.
"RPM+" = Discontinued standard "Stage 0" casting with upgraded valvetrain for higher RPM operation designed for the minibikers that want to MPH it out on the top end. Flowed 80cfm @ .300" valve lift and did not have the valve seat and other work that our current heads have, but it did do 11,000rpms on a few dyno runs before it kicked a lash cap off. Might have been because the lash wasn't set to zero or they just do that, but we don't know. Either way, any of these engines will eat 80cfm before you ever get to 11,000rpms, so it was kinda silly, but it did it. We didn't see a reason to offer this head anymore because it can't even feed a 212cc at the RPMs that it was capable of. If you liked this head then you NEED a Level II!
Here is a video of that head on the dyno making an indicated 21.9hp. We've since added a couple of features to help our standard Level I head outperform this head without the extra cost of the hardware needed to rev that high.
https://www.youtube.com/watch?v=k-mpm8Cc0Hw
"Stage 1" = Older hand ported version of the standard 28.5mm Shredder head with upgraded valvetrain but lacking the latest seat cuts and other upgrades. Flowed 90cfm @ .400" valve lift and worked best with .308" lift cams and 1.3:1 rockers. This one did alright and made great average power but got beat on the top end by some of the major players, so it's dead now. Superseded by the awesome CNC ported Level II.
Our Current Lineup:
Level I = Standard 80cfm @ .300" valve lift Shredder casting with no port work done but still out flows a stock low velocity Predator or GX200 head by at least 15cfm. Has all of the latest upgrades and tricks to ensure it performs as advertised with the seats cut to proper depth for correct spring install height. Comes with 1.2:1 ratio rocker arms and works best with the .265" lobe lift cams like CM or Fire 265 and a 26mm PWK. For the $119 price it's a solid upgrade that'll wake up any stock head Predator or GX engine. Equivalent to the other guy's "Stage II" offerings.
Level II = CNC ported and extensively worked 28.5mm Shredder casting that now flows 100cfm @ .400" valve lift giving it a blistering 330ft/s throat speed. Seats are cut and enlarged and the hardware includes 40# dual springs with titanium retainers and light weight lash caps. This is as hot as it gets for a 28.5mm head, and when combined with a 308 cam, 1.35:1 rockers, and a 30mm PWK it will rip your face clean off. Supersedes the older "Stage 1" by dominating it in every way possible. Can be found outperforming the competition's "Stage V" 32mm offerings at a track near you.
How much flow do you need? This chart can be used as a loose guide to how much air flow a given size engine needs to make power at various RPMs:
