[1968GTO421]

Originally Posted by Half-Inch Stud

HYD Flat Tappet Cam sizes for the Street/Strip 455 and 4.25 stroke stuff & IRON HEADS:

High Compr, > 93 Octane to race, about 93 Octane to Street (with light ping on some weather); 245/255 110 LSA. Ref Lunati SPC1-320 or 30705.

Theory by Dave Vizard for the ideal cam (455 & 2.11" valve); 242/237 106 LSA, 102 ILC, but ya gotta custom that. Probably ping with pump gas.
Lunati 30707 238/242 110, less ping, Crane Fireball H-294 238/248 110 LSA for less ping than Vizard.

Optimal Cam for Street/Strip, heavy 10:1 92 Octane; 234/244 112 LSA Ref Wolverine 5059, Old Faithful, Tomahawk TH-02 HF, REF Jim Hand mid 11s Wheels-up 4300 Lb Wagon.
Crower 60211 236/242 108 LSA is close enough here.

Optimal Cam for Street/ Strip, med-light, 89 Octane; RA-IV copies 231/240 cut to 113 LSA Lunati 10703, Crower 60919, REF Cliff Ruggles 11.3 ETs. with Flat-footed street driving

PMD RA III H-cam 9795744, the Smallest Cam i would ever dare 224/236 119 for best of all Street but might ping on 87-89.

MY OPINION:
I prefer SLOW ramps (ADV Dur - 050 Dur > 60*) for safe Lifter-cam follow, least ping.
Medium ramps are ADV Dur - 050 Dur = 50-60: i dunno, just have good spring pressure.
FAST ramps are ADV Dur - 050 Dur < 50* ; lifter-cam disconnect with hi-rpm and weak springs.
I remain fearful of HYD Rollers with IRON HEADS due to fast ramps, yet just fine for Alum Heads.

I am amazed that Comp Cams made the Flat Tappet XE series of 050 Dur 206/212 through 250/256 with FAST FAST ramps. I think the term "Lifter Crashing" was coined by XE lobes. I suggest XE lobes provide enough Ping to overcome the crashing noise! Seriously who uses XE lobes and likes the Reliability and Performance?

Not a 400 engine guy but i think this list is a guide for 3.75" Stroke if 10* of the 050 Dur is removed from the above list. 400s are a wonderful engine, someday...

As for this Thread, HYD Rollers with aluminum heads works but i shudder to think about the ping when using the HYD ROLLER with Iron heads of same 050 durations.

Thanks Mark, good info here.
I think this site relates to the part that I boldfaced:

http://members.uia.net/pkelley2/Overlap.html

Especially at the bottom where it mentions overlap and driveability.