During my junkyard diving this weekend, I came home with a 360LA Roller Cam engine out of a '92 Ramcharger (530096921 casting). I've had an '89 Roller Cam 318 sitting in the corner of the garage for a while that's intended for a Volare swap, but I couldn't pass up the 360 roller motor for $200. It's high mileage (184k), but turning it over by hand didn't reveal any issues, and borescope inspection appears to be the original factory setup (not a rebuild).
Now to my question, did these late LA roller motors use the old 9.599" LA motor deck height, or had they already transitioned to the Magnum deck height (9.585" from what I've been able to gather)? Some threads I found spoke as if the LA roller motors had already gone to the shorter deck height (I found reference to 9.577-9.578" as the blueprint spec for these years). Has anyone else measured deck height on a stock 360 LA roller motor? What am I dealing with here? How about factory piston relief size?
I know, Chrysler blocks are all over the place, and the only accurate way to tell is to pop off the heads and measure how far the factory slugs are down in the bore, and compare that to their compression height upon disassembly. I'm just trying to do a little planning ahead, and determine whether this block is worth fooling with right now.
Discussion on why I'd like to know deck height:
I'd like to use commonly available +10 or +11cc dished pistons for a Magnum engine to work well with the EQ Magnum heads I have, but if this block is at the LA deck height, that will likely take significant milling to maintain any sort of decent quench. Alternatively, I could look at something like the Icon 742 (10.1 CR with zero deck and .039 headgasket), but that's an expensive set of pistons for what I'm trying to do. I'm not having any luck finding other pistons in the +9 to +11 cc range at the LA deck height. I think KB107s (+5cc) will result in excessive compression with the 64cc iron heads (10.6CR with zero deck and .039 headgasket), while something like the KB362 (+19.4cc) would be a little low (9.1CR with zero deck and .039 headgasket). I'd really like to shoot for 9.5-10:1 static compression and .040" quench, for use of regular pump gas at 5500+ elevation.
I think of the three listed above, the KB362 is likely the right answer, but it would be better to be able to use a Magnum type replacement piston, both for the ideal piston relief size and for cost. However, if the LA roller block is at or near the old 9.599" deck height, that's going to take a lot of milling to get down to zero deck. For example, the Speed Pro H655 is a +11.23cc piston with a compression height of 1.612". For a 9.599" deck height, that would require .074" of milling to get down to zero deck. A 1.675" compression height piston like the Icon or KB would only take .011" of milling to get down to zero deck, and would actually be almost at zero deck in a 9.585" deck height (.003" out of the hole in a perfect world). I don't know what "deck height" the commonly available LA intakes are set up for. Is there a rough number of how short the deck height can be before milling the intake also becomes necessary?
I'm probably focusing too much on quench, but I really would like to run on regular pump gas while still having enough static compression to work with a decent sized cam. Proper quench is about the only way I know of to do both without going to EFI. Maybe I'm overthinking all of this.