For a long time now I have been Using Small Block Chev oil pumps I modify like I have yet to see anyone else do.
Most people seem to use at least one of the small ports as the Pumps come. This to me is highly restrictive and basicaly a waste of their potential in this application.
I block off both the original inlet and outlet of the pumps and bore a hole to take a 1" pipe fitting in the sides of the casings right where the gears are.
I use a 300W 24V scooter motor and can get 80l min on warm oil and have yet to find anything I can't pump that is still at least semi solid.
With no insult intended, I'd go freaking nuts hanging round pumping at 2gpm and a lot higher. I can get 12GPM ( 50L) running the motors on half power, 12V.
This is a demo vid I did ages back of an early pump in action. I improved a bit on it since
https://www.youtube.com/watch?v=8o52BYTEau4This vid explains the pumps construction a bit more.
https://www.youtube.com/watch?v=fkBIYcT6j8UI have yet to find a pump other than one powered by a petrol 5 Hp engine that will keep up with these. I did have one running off a battery lawnmower motor for a while and that was a ball tearer. They are good up to about 3000 RPM but you do need around 500W+ depending on the oil you are pumping to get them to that. Just because the motor is XXXX rated, don't expect it to be doing that under load!
The performance on thick oil is also very good, about as good as one could get I believe. If you can draw the semi solid fats into a hose, these things will do it and spit it out the other end.
I have a couple I use at home with AC motors. one is 1/3HP and the other is 1HP, both 2800Rpm motors. They work really well and move oil fast. I use these for transfering up to multi 1000L of oil at a time in IBC's and have pumped at least 60K L with these different pumps over the years.
The only problems I have had with the things is the occasional Blockage when I have sucked up cloth Napkins which Jam the gears. Most times I can simply wind the pump back by hand ( with great effort) and once free reverse the motor and blow out whats left. Few times I have had them wrap round the gears and had to take the back cover off the pump and clear them that way.
You cannot put shutoff valves on these pumps being positive displacement and as I araldite the relief valve closed, the pumps will either stall the motor driving them ( 1 HP no problem) or the hose bursts. they have to be started and stopped with the motor. Some people might like to put a DC PWM motor speed controller on them if they had need for lower pumping rates.
I have been doing this a while now and always looking for the holy grail with something better but yet to find anything that beats these SBC pumps modified this way that allows for their full flow capabilities.