FWIW, I am wondering if you calculated that with the small dome that piston has?
Yessir.... and it is good to ask the question. KB makes certain assumptions on their CR number listings. I get their numbers if I assume a Magnum standard block height (rather than a standard LA block height) and a .039" thick head gasket.
BTW running some quick numbers, that flat dome is probably around .040"-.045" high above the compression height; it takes that to make the -1.2 cc head volume with typical eyebrows. That does not quite jive with the KB notes but the numbers say what it needs to be. So OP, if you have assembled the short block, maybe you can confirm that the pistons stick above the block at TDC? Like around .030" for an LA block...?
No not yet. However to maximize 1/4 mile and tuning possibilities with timing and id like better flowing heads if I could gain little safety net at the same time it'd be nice.
Taking your xe274 cam, and doing a DCR computation, that ends up at 7.95, with the cam installed dot-to-dot... i.e., with the cam mfr's standard ground in cam advance. Your cranking pressures ought to be around 160 psi, not awfully high, but where you need to start paying attention to everything that could lead to detonation.
FWIW, I've run 10.3 SCR and 8.3 DCR with iron heads on 93 pump at around 1000-2000'; 165-ish cranking pressures at 1000' so a tad higher than your setup. No issues that I could not manage; could not use regular, and I needed to stay conservative on ignition advance. That engine did have mild quench to help fight detonation, which you won't have with the open chamber heads. Put almost 100k miles on it.
(BTW, you don't need as much ignition timing in general with higher CR's, though more advance is usually better for open chamber heads. As I understand things, the higher peak cylinder pressure and better peak timing that you achieve with timing advance comes with the higher CR's to some degree.)
As an exercise, I've computed up some 63 cc Edelbrock closed chamber heads with these pistons. (ProMaxx lists 65 cc's as an option but I don't know of they are still strictly closed chambers. You might inquire.) Put in a .065" thick head gasket to work with my assumed piston height above deck of around .030" (Needs confirming! If I am wrong, all this is wrong.) and get to .035" quench gap. (It is not a prefect quench gap with that dome not going to the edges of the piston top, but it still ought to provide some quench effect.)
With all that (and assuming my thoughts about the piston dome are right... did I say that needs confirming? LOL), the SCR is now
10.6 and DCR is 8.5. Hmmmm.... a few more tweaks, like a .070" head gasket, and a 279 duration cam, like a Voodoo 703, and the SCR is 10.4 and the DCR is now 8.25. Getting pretty safe now with quench and AL heads, though you still need to take the proper care.
BTW, are you stuck with the 91 octane there in Tulsa? And do you have an LA block?
