Pumping Oil

In the last issue, I cited that there are many questions, side issues and problems that regularly occupy "Br time. On reflection, the following must be one of THE most popular, so more than a side issue is pertinent. Or more precisely, questions appertaining to their performance.

For many other engine types, tuning companies offer both high capacity and/or high pressure oil pumps. This is a very relevant, and indeed praiseworthy option to the standard equipment types. Especially when one considers such bizarre facts as original Ford/Lotus twin cam pumps only supply 40psi of oil pressure. Having owned a Mark2 Lotus Cortina I can support this fact. So why on earth do prospective ballistic Mini engine builders amongst the general public demand a high pressure/high capacity oil pump over and above those available as "OE" equipment? Especially as the oil pressure relief valve in an A series engine dumps typically around 30-40% of its pumping capacity straight back into the sump? AND can easily achieve oil pressures over 70psi in a reasonably well built A series engine? Both are more than adequate for supplying lubrication whilst in operation. Conversations with many of those aforementioned ballistic engine tuners illustrated a certain mis-interpretation of details outlined by other intrepid A series "queries".

It is true that in days of yore, there was one pump that supplied a better flow rate than other manufacturers of the time. The venerable "steel backed" Holburn Eaton manufactured type pump. In those days this was somewhat inconvenient as it was only available in star-drive. Therefore application to anything other than a 1300 type block was a pain - INCLUDING '5' blocks. However, it certainly did not improve PRESSURE. This phenomena is determined by other factors of the engine build (a separate and further article).

For the meantime we'll deal with flow-rate, and criticisms of why Mini Spares should manufacture their own more costly oil pumps. This is pretty simple on the face of it - time is money. The longer it takes, the more it costs (a fact that can be applied to just about EVERYTHING!). Automation, or robotics, has seen the requirement of human intensive jobs to be adapted for mechanical assembly to reduce production costs. I touched on this subject briefly in the first issue of Mini Tech News shortly after the introduction of our Sure-flow oil pumps. Since then widespread sales and useage against the OE type pumps we sell has proved their worth. Essentially quality is often compromised in the aforementioned process.

Right, so what does all this mean to flow rate? for a start, pumps internals with large manufacturing tolerances become grossly inefficient at high rpm. Particularly when the oil gets hot, highlighted further when cheap/inferior/incompatible oils are used (see separate story). To a point where a portion of the oil simply passes around the internals of the pump rather than the engine. Definitely not good.

As with all things, there is a vast amount of theory behind pump capacities, delivery rates, etc. There are even reference books available on delivery rates for differing pump sizes and configuration quoting all kinds of data. I know, I've seen and consulted them from time to time. But as with all things theoretical, they tend to ignore that phenomena you and I exist in - REAL LIFE. These factors of theory tend towards perfect world situations, ignoring such things as incorrectly sized and right-angled feeds. Not to mention some exceptionally inefficient designs of intake and exhaust porting (no - not the carb and exhaust ports)!

Now, how about some real life facts? Rotor configuration has much to do with it. You can have 4 into 5 (4 blades in 5 recesses - forget correct terminology here!), 5 into 6, and so on and so forth. Most modern engines have very high blade into recess numbers. Basically, the higher the blade/recess count, the less pulsing is experienced and therefore the better the oil supply. Another plus factor is that shallower rotor assemblies are more efficient, limited space being a situation forced upon modern car manufacturers where compactness is of premium importance. The shallower the rotor assembly, the more efficient each port (recess) is at filling and therefore delivering a more consistent flow of oil. Where's the relevance of this? Well, I have to confess to a certain amount of theoretical verses practical proof on this, so I'll just deliver a first hand, tried and tested situation. The introduction of the Metro Turbo saw the eventual use of the A series' first real high capacity oil pump. Why? Because the Turbo needs a constant, consistent flow of oil if it is to have a hope of anything like a reasonable life. But how necessary was it, bearing in mind the standard oil pumps' performance? Getting qualification of this kind of thing from Rover is a total non-event, so consider this .. .when the Group A Metro Turbo cars hit the circuits they only used the then available steel backed oil pump (4 into 5 configuration), and they used squirters to cool the underside of the piston crowns in their 220 bhp engines. Mostly it is because major manufacturers of production cars need to totally over-engineer everything to make it last considering the general public's reluctance to change the oil at required and advised points - not to mention the use of "cooking fat" instead of quality oils.

Where did this extra capacity come from? Rotor depth. Ah! So that's it? Well , it's not as clear cut as that. Remember what I said about rotor depths versus efficiency? Sure, they made the rotor deeper, but was it effective as flow rate to the same degree? I think not. After various discussions with professionals really in the know with regard to race engine application, theory and practice are very different. On paper, one configuration may look great. In practice in it's installation it can be worse than pathetic. However, I was given some guidelines to follow to assess pump performance without fancy and expensive equipment. Armed with this I decided to compare a couple of pumps. Not wishing to get in slanging matches with current mass producers, i decided initially to concentrate on our own pumps.

Testing our 'Turbo" pump against a "normal" sureflow pump proved very interesting. Both are almost identical externally - unlike the "OE" Turbo pump that is visibly different due to its deeper rotor configuration.

The results briefly were as follows:-

This shows that the Turbo pump gives a consistent 27% higher rate than the standard type pump. compared with other Turbo pumps for the A-series there is little difference between theoretical and actual delivery because of the design. Deeper rotors are subject to inefficiency for a given intake/exhaust port size as they do not fill to capacity on each revolution. A situation that worsens the higher the rpm is due to less available "filling" time.

Conclusion thus far: more rotor blades/recesses give less pulsing (not so important), shallower rotor set-ups per required capacity give far superior effective flow.

This has tempted me to make some special equipment to make very real life comparisons. I may even put my neck out to test and report on other pumps. We already know Mini Spares Sureftow pumps are better - dare we print by how much?

Keith Calver