OOTB Stealth vs Prepped Stealth?
Better flow, duh. :D
Sorry
Well actually, the better flow is incidental to the purpose of prepping the heads. No head coming off a production line is always ready to go OOTB. So we bring the new heads into the shop, disassemble, flow them and inspect each part. The springs are all measured for pressure (if they are going to be reused), the valves are inspected and checked for roundness (many valves are discarded and new ones procured because we find a lot of the valve stems around the lock groove are marred during the assembly by whoever slaps these heads together), valve guide clearance is checked, the valves are back cut, we use one intake and exhaust valve to do a rough performance valve job to the head and set the valve installed heights to + or - .001". Then the heads are turned over to Cody (my son) and he does the port, bowl and combustion chamber clean up. He returns the heads to me and I do a finish valve job and flow them again. Any big flow discrepancies are noted and corrected by going back to the porting bench and then back to the flowbench to be measured again. That being done we cc the chambers and mill the heads to correct the ever present wavy block surface. The heads and all components are cleaned, valve stems & guides are lubed and the springs are assembled to the correct installed height. The clean heads are bagged, boxed and shipped. And just
incidentally.....the flows increase from what we find OOTB.
Reusing all Stealth components, this service is $600. At a dead minimum the stamped 7 degree locks should be replaced with machined locks as they are what tears up the stem and lock groove. I have come to believe that 10 degree locks are
not the best solution with the light spring pressures these heads come with. These machined 7 degree locks are a whopping $29 a set. Well worth it when you don't have to file the valve lock groove to prevent it from scoring the bronze guide as you remove the valve. Any other replaced components are of course an additional cost.
440 Source says in their instruction that their springs should be used with lifts of .510" or less.
It's best with new heads to just buy the heads from 440 Source and have them shipped directly to us. It saves shipping one way as 440 Source will ship their heads for free.