On the subject of fuel systems, we'll also point out that you don't need to spend a fortune on pumps. The dual quads on the 8-71 actually reduce fuel-system demand since there is always twice as much fuel in reserve in the bowls than with a single carb. At this engine's power level, you could feed the carbs with a Holley PN 12-454-20 mechanical fuel pump ($99.88) to keep it simple.
Been waiting for the punch line? In the first test, in an attempt to match the low boost levels of the mini blower, we gave the 8-71 a 63-tooth blower pulley and a 47-tooth crank pulley for a drive ratio of 0.75:1 (25-percent underdriven) and achieved peak boost of 4.8 psi. That was good for 717 hp at 6,200 rpm and 674 lb-ft at 4,500 rpm. That's an increase of 56 hp, but note that we lost 24 lb-ft, even with extra boost. Since air inlet temps were not increased, the only answer is that it just plain eats more power to spin the larger blower. More evidence of that: We gained 1.8 peak boost, but only picked up 56 hp, or 31 hp per pound of boost. With the mini blower, going from 2 psi to 3 psi picked up 30 hp. The 8-71 doesn't gain a torque advantage until 5,100 rpm, when the smaller blower is probably starting to heat up.
That's interesting stuff, especially considering that the 8-71 displaces 436 ci versus the mini blower's 177 ci, which is why the big blower can spin so much slower yet achieve the same boost. At 6,000 engine rpm, our 8-71 was only spinning 4,500 rpm, where the mini blower was cranking a whopping 12,600 rpm. Perhaps that's why the big blower works better up top. But it makes a really compelling argument for the mini blower at low rpm and low boost.
The Glory Run
You didn't think we'd stop at 4.8 psi boost, did you? With a little guessing and gambling, we figured that the cast-crank, stock-block engine would probably stay reliable to around 750 hp, especially since we didn't think we'd have to lean on the blower too hard to do that. The more you crank up the boost, the greater the load you put on the crank snout. With a casting and a single keyway, we weren't thrilled about trying to stuff 8-plus psi into this thing. But we felt pretty good about 6.4 psi, which was delivered with a 63-tooth blower pulley and a 52-tooth crank pulley for a ratio of 0.83:1 (17-percent underdriven). That gave us a nice 766 hp at 6,200 rpm and 726 lb-ft peaking at 4,600 rpm. And, of course, the 8-71 was now in its glory, killing the mini blower at every point in the curve.
Not bad for a tame little tow-truck motor. Maybe you should go get a blower.