My Hemi car has a Carter electric + the hi-perf mechanical. It will run with just the mechanical, but it has 1/2" fuel line and the mech can't keep adequate pressure in a line that size after a couple miles. So I run both. Regulator after the mech pump, with a gauge. With a smaller line it might be OK, but I can't say for sure. Granted, the mech would have to pull through the vanes of an "off" electric pump, but mine will do that for a while until the pressure finally drops.