If you look at any 3 of them, except maybe the XR276HR10, you'll quickly spot a trend, and an unforgivable sin. The valve springs Comp used lose control around 4100 RPM. So why wasn't the testing stopped and the springs upgraded?
The only honorable thing Comp can do at this point is to admit their wrong, and redo all of it with 26981s in an L31 with an Edelbrock RPM Air Gap, and 1.625" long-tubes with collector extensions and a Holley 750.
The more of you who send this to Comp, the more likely they are to actually redo the whole mess.
Then you can see a new trend: everything with over 480 lift will crap out.
See, when you flowbench Vortec heads, if you open the intake valves past 480, the flow stalls a bit. You can hear it. And as you close the valves, the port DOES NOT recover.
But these are the heads anyone can get for $50 on half price day at any Pick N Pull or similar salvage yard in the lower 48 States.
You can run them used without taking them to a machine shop. I've done it many times. I suggest new valves, with undercut stems and 30 degree back cuts, and choose gaskets that are not thin steelshim nor MLS. If the heads are warped, the composite 0.051"-0.053" are most likely to seal well enough to hold 400 HP for another few years if daily driving.
You can run a 0.554" can if you pop for 1.3:1 rockers, but I never have and never will. A HR with a 214-224 intake is an excellent match for these heads on a 350, and I haven't seen any good HR cams with that duration and 0.554" lift. You can find many with that duration and <0.480"
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Yeah not sure what they used in some of their tests but sure didnt run like id expect.

there were a few low duration high lift profiles out there. Comps old magnum high lift line had decent numbers. Their xfi line goes down to 218/224 i believe in shelf cams but 113 lsa i dont love. Lingenfelter had the 211/219 that was mid .500’s with 1.6’s.

need to go custom to get short duration and anything higher. .550’s is all you really need in a sub 6200 ish rpm motor. Can go to 6500 in some setups too. Problem with higher lift short duration is they can sound alittle noisy or sewing machine like. Depending on the lobe

 

You must be looking at the GM Performance Mexican 062 heads flow. Those tank much over 0.400 lift. The stock old GM 906s that came on an OE 1997 L31 in my Express van did not drop off in flow until ~0.530 lift. The difference was 215 cfm @ 0.400 dropping to 210 cfm @ 0.450+ for the garbage Mexican castings vs 242 cfm @ 0.500 for the OE Canadian casting cast in 1996.

The engine in my 97 Express van exploded in 2004 at 57K miles from hydraulic locking #2 when the intake gaskets failed. I put a circa 2005 built mexican crate engine in it and immediately noticed it was probably 30 hp down on the factory engine. Not only that the garbage Mexican heads cracked in under 30K miles.

I have known for a decade before Cutter Performance found the same thing and made a video of it.

https://youtu.be/24fKnh3-9l0?si=jU-PspTAy6HGKPe_