HV vs Std Oil Pump Info

Another FWIW post... my son and I were drilling out the exit passage in a new Melling HV SBM oil pump today and decided to practice on an old standard oil pump from a '68 273. Afterwards, we did some comparative checks on the 2.

1. Rotor height: Std .829" ; HV 1.034"
That's a 25% height increase for the HV pump, and that agrees with the advertised 20-25% flow increase. That increase due to rotor heights would be the flow change into little or no restriction, so is not necessarily the increase in flow into an engine with no output pressure change.

2. Castings looked pretty identical inside. Lube for the shaft is a little different and more generous for the HV pump. This older std pump has a square o-ring cover seal and the new HV has none.

3. Relief valve pistons looked the same but the HV pump's step that is the rest stop for the valve is a bit further back, and puts more preload on the spring. But the location of the fixed end of the spring does not change, so I don't think that preload has any effect on the relief pressure by itself.

4. Springs looked identical but the spring wire diameter on the HV pump measured .069" and that on the .066". That works out to about a 20% stiffer spring rate. The fixed end point for the spring is at the same place: the plug.

With the stiffer relief valve spring, it looks like this pump will indeed push a somewhat higher pressure and push more oil into the engine than a standard pump, even with no engine changes. And, with the larger rotor height, it ought to continue to do this down to a lower RPM. (But I did not check the location of the relief port to be sure.)

I don't think the load change on the engine will be any higher than the 25% of rotor height.

Again, FWIW.....the floor is now open for comments, refutations, fist-fights, etc. LOL

Pix of older std pump inside followed by HV pump inside: