You don't need to know as you hit a combo, probably through loooong experience, that was not too high or too low for your application; you 'just know'. Without that, folks can read something like the Crane cams catalog and follow their SCR recommendations with particular cams. That is the same idea, keeping DCR in the best range, just without the computations. I just started down this road with the OP since he mentioned a high SCR, and wanted to see if he was getting into a dangerous territory, detonation-wise.
For an entirely different engine, or starting from scratch with less experience, or going for certain applications with no catalog info, one had better compute it IMHO. I'll never build another N-A rally car engine without knowing where I am heading for DCR; a mid-high 7's DCR minimum will make the torque curve wider and that is very critical for a rally car engine.... unless you have a factory team 6 or 7 speed trannie with electronic paddle shifting! I've done the high 5's DCR type, that struggled to have a 2:1 usable RPM torque range, and also a low 7's DCR engine, with a solid 2.75:1 usable RPM torque range; the higher DCR 1.6L would outperform the low DCR 1.9L in that application (both with 4 speeds manual trannies, 3.73 or 3.91 rear gear, no OD).
On the street cruising scene and driving scene, low-mid RPM torque is important and that comes with good DCR. But, with drag racing, low DCR can be overcome to some degree with high stall
TC's and clutch slipping. And I've come to think more and more that circle track applications will be mostly track-dependent; you had better have a good 2:1 RPM range at Martinsville, no time to shift gears. But at Pocano, top end speed near 200 mph is key, so you sacrifice RPM range to get higher peak torque/HP and then use the gearbox in the corners to make up for a narrower RPM range.
As for the OP, if he is emphasizing drag racing, then a high DCR is perhaps less important, as with that engine size, maximizing DCR and low-mid RPM torque just makes the traction problem harder. If he CAN solve the traction challenges off the line, then more torque will be better but if you can't use it, then it may be a waste of effort. So that is another reason IMHO that fretting over a higher than 8:1 DCR may not be all that useful.
