Is there any difference in gear/body size between the M55 and M55HV pump, or is it just a stronger relief spring?

I have been all over the Melling web site and all I have found is the difference in the springs.

I would "think" the HV pump would have a larger pump cavity so as to provide the additional 25% oil volume they advertise.

The body and gears of the hv pump are 1/4 inch longer than the non hv pump. That’s is what creates the extra volume.

Some interesting stuff. I have been watching his videos since he started.
He has just posted a bunch of videos on oil and oil flow, in his last one he made comments about the melling pumps for small and big chevys. Gerold Brand

Dave

HV pumps also have a 3/4" inlet.

Invest in a billet pump and forget these type.

The oil pump besides the oil in your engine is the most important thing in it. Took me 20years and 4 engines to stop being cheap and put a good billet pump in my motors. They will last several motors and well worth the extra when you stop and think about it. No pickup to weld on, have it crack next to weld etc. Your relying on a low dollar part for your entire engine.

I agree, invest in the billet pump assembly.

One of the primary issues with any volume pump is the oil pan sump capacity, it's really easy to drain the sump, that leave you pumping air to the critical areas. In short, not ideal.

Bob

Moroso billet and never look back

DO NOT install a M55 in a performance engine. The casting is weak and WILL break.

I agree with others about the billet pumps. I love my Melling Shark tooth. Same holds true for them about volume. Longer gears for the higher volume pump is all.

https://melling.com/aftermarke...ps/billet-oil-pumps/