Wow, guys, lively discussion! I have to add a couple of points though. It is not necessarily higher gauge pressure that is in play here. Fluid pressure before an orifice (restriction) is higher than after. So whether there is a restriction before the gauge matters. (Heath’s point) The real pump pressure may be at its outlet or even internally. The only true measure is the torque required to turn both pumps under the same conditions (same engine, same oil, same temp.) at low & high speeds.
A true hi vol pump achieves that added volume in one of two ways, either taller gears (U Tube) or larger (dia.) gears. Some small increase may be achieved through internal improvements. If done internally, the pump may require less torque. So how the Melling achieves higher vol. in the 4.0 pump is the question. I’m not sure you can gain 20% with only internal mods to a dimensionally stock pump. You can compare it to your stock pump. It is probably taller as the Chevy one seen in the video. Also, according to the video, Melling’s hi vol pumps have the hi press spring as well. I don’t think you want that. Whether you can replace it with the spring from your stock pump, I don’t know.
Pushing more oil through the system (up to relief press) will also increase the oil temp I believe.
Another question would be does a stock 4.0 really need or benefit from more flow?
I’ve never dealt with Hesco but they have been around a while & there may be a good reason they add a fitting to spray oil directly onto the cam/OPDA gears on their hi vol pump for the 4.0.
I agree with jkp’s assessments. That said, go ahead GMBNT42, try it. It may not be that much difference. Several guys have inquired about going this route (with a Hesco pump). Keep an eye on OPDA gear wear & keep us posted on your findings.