Re: 6-71 blower tuning
Blown big blocks on the street like high initial but do not require a ton of total.
I would shoot for 20* initial and a total of 32-34* all in by 2500 rpm.
You can run more total if you install a boost retard type ignition.Say 38* at no load cruise..but pulls out a degree of advance for every 1lb of boost.
For example..if this combo could muster up 5 lbs of boost..timing would lay back from 38* to 33* with spark retard.
As for the pulley combo..how well the engine moves air thru it will dictate stacked up pressure in the manifold.You will need a vac/boost gauge installed below the blower and monitor it at wot/max rpm.
As big as that 6-71 is..its not ideal atop a free breathing 496.The 8 series would be better suited..buts lets work with what you have.
If the underdriven 6-71 suits your needs..dial in the tune up and enjoy the few lbs of boost she offers.When that gets old,flip the pulleys and run 10 over.Boost pressure will not be the issue..intake charge temp will be.
if you can stay out of detonation on pump swill,fine.If not..water/meth injection is an option as well as an e-85 conversion.
And yes..boost referanced primary power valves is a wise choice for a blown street unit.There are times when the the engine requires additional enrichment to the main well..but the blower is still pulling x# of inches of vacuum on the carb base.External referancing allows the power valves to operate as per design.
+1. George gives good advice on the timing. you are at 10% under drive which will only give you ~4.4 lbs boost with a 6-71 on a 496. Flip the pulleys around for 10% overdrive and make ~8.6 lbs boost. I wouldnt overdrive the 6-71 much more than that on pump gas. If you want more boost, than that, you should go to an 8-71 on that 496.
1973 RS Z28: 401ci Dart Little M, Littlefield 8-71 supercharger @14lbs boost, Callies Magnum crankshaft, Lunati Pro-Mod rods, JE pistons, 7.8:1 compression, AFR 227 Comp heads, T&D 1.6 shaft rockers. Reed solid FT cam (240/250@.050, .523/.542 lift, 112 LSA), QFT 750 carbs, Tremec TKO-500, Lemons headers, Moser 12 bolt, 33 spline axles & 3.42 gears