5.9 Mag stock LB or rebuilt SB
@AJ/FormS
I like what you’re saying and I do like the thought of the high CR. Can I do that on 91 octane? 1200ft elevation, not much humidity to speak of and hot as hell. At least right now. Not that it would be driven in the summer too much.
Would you start with the rebuilt SB or the 96k mile long block.
I am at 930 ft. My alloy-headed 367LA has had cylinder pressure as high as 195psi, and the Scr has been as high as 11.3, yielding a Dcr of about 9.2.
Currently she is sitting at 11Scr and 185ish psi, with a bigger cam.
She has always run on 87E10, and has never required an octane booster.
This engine was disassembled and inspected for detonation/etcetera, 5 times, in it's first 5 years, from 1999 to 2004, with none found. She now has over 100,000 miles on it. and The tune was easy.
Your results may vary, it depends on your skills.
As for which engine to start with; IDK anything about Magnums, but
since hi-compression pistons are a pre requisite to these numbers, as are alloy heads; all yur gonna need from a core is the block/crank/rods/and covers. At this point, the only good reason to use a Magnum, is for the roller lifters.
Do you need 195psi? No.
but, once you've driven something like that, you'll never go back to 155...... which at 1200ft, with a 400hp capable cam, is not gonna bring you any smiles. Rather 185 or more is nearly as much fun.
If the short, has dished pistons, those will have to be swapped out.
If the long, has iron heads, those will have to go; you cannot run much over 160/165psi with iron heads.
Iron heads, costing you 30psi, will knock your V/P down the same amount, taking your low-rpm torque from feeling like a bigblock, down to feeling like a stout 5.2M.
With a hi-stall convertor, this is not that big a deal; and iron heads at a Dcr of say 8.0>8.3, would still be fun, but those dished pistons still gotta go, cuz 8.3 Dcr may require an Scr of over 10/1, depending on the Ica of the chosen cam.
BTW
your 1200 ft elevation is costing you about 6 or 7 psi over sealevel, which translates to the same amount of lost V/P, which translates to about a half a point of Scr. What that means is that 11.3@1200ft runs about the same as 10.8 at sealevel. That's like 10 or more horsepower at say 3200rpm. almost a full cam-size over the nose., also probably worth 200 rpm stall. I'm guessing.
The point is this, when it comes to making low-rpm power;
the number one rule is that there is no replacement for displacement; but
the number two rule is that once the displacement is fixed, there is no better alternative than cylinder pressure.
If you have a clutch, pressure is paramount because the vast majority of time will be spent locked into low-rpm by the roadspeed.
Read about V/P here;
V/P Index Calculation