It's probably safe to say that every professional engine builder has a set of engine oiling guidelines that have evolved over years of evaluating parts' wear patterns and overall component wear. Equally valid is the likelihood that not all non-professional engine builders have had the benefit of such experience over time. So it's on that assumption that we'll lay out some basic thoughts about race engine oiling that can benefit the garage engine builder. We won't get to them all in one bite but, hopefully, you'll collect some helpful takeaways from this month's discussion.
First of all, we're all familiar with the differences between wet- and dry-sump systems. However, it's important to point out that even in the best of applications, oil temperature control differs between the two. Of the critical factors in a racing engine oil system, temperature is high on the list. And even though you can include use of an oil cooler, wet-sump systems (by their design) generally operate with less oil volume, and that by itself can affect oil temperature. Of course, dry-sump systems have an oil cooler and the sump tank as well, so you automatically get the temperature controlling benefits of a greater oil volume. And by the way, if you choose or are required to run a wet-sump system, the chances are there'll come a time during braking, acceleration, or oil movement on banked tracks when the pump pickup will be uncovered. Including the use of an oil accumulator addresses problems associated with these on-track conditions.
Properly plumbing the remote oil tank in a dry sump system is critical to ensuring the oil
Next on the list is the fact that oil, at some point, is likely to become contaminated by dirt, fuel, coolant, and even air, believe it or not. Overall, each one or a combination of these can and will have an effect on both parts longevity and power. So it's important that we figure out ways to either prevent or reduce their contribution to oil contamination. The basic areas of concern are a good paper air filter element, air filter assembly that's sealed to the carburetor (or injector bodies), an initially clean oiling system and plumbing, and clean oil. As basic as all that seems, it's surprising how often one or more of these sources for contamination don't do the proper job.
And in this category, there's one more little item that Smokey shared with me on several occasions. Paraphrasing his comments and deleting the expletives, many filter manufacturers tend to filter the oil too finely. Logic would tell us this is OK. However, he said, when this occurs the attending pressure drop across the filter causes less oil flow to be available (flow rate reduction). So then you compensate for that with a corresponding increase in pump pressure, leading to an increase in oil temperature and more by-passed oil. The bottom-line is a net loss in power. You might want to take old Smoke's advice and not over-filter the oil in the first place.
He also had an opinion about filter area and plumbing size, as you might expect. In this regard, he always advocated using filters that allowed convenient and frequent internal inspection and plumbing that leaned toward the larger fittings and hoses. His penchant for "inspectable" filters was based on the belief that access to filter element material and frequent inspection are ways to head-off premature engine failures. He also liked to use wire mesh filters in place of other types. And before we leave this particular set of issues, he also believed that a single, large filter was superior to multiple, smaller ones. Placing filters in line tends to create a restriction, compared to a large (single) unit, and we're back to the consequences from increasing oil pressure when a restriction is created. Finally, as I recall, he simply said you "can't get too big" when it comes to filter size selection. 'Nuff said.
If you're in the process of choosing an oiling system, there are a few points to keep in mind during the selection process. For example, if you plan on using a dry-sump system, have some discussion with the manufacturer, concerning sizing. It's important to not zero in on a system that's too big for your particular application. Why can that be problematic? Well, big pumps require higher amounts of power to drive than smaller ones. Pump over-sizing also introduces a risk of increasing the amount of air that gets into the system. And, the last time I checked, aerated oil doesn't do a very good job of cooling and lubricating parts. Don't forget, oil pumps generate a fair amount of heat in the oil they circulate.
Let me give you an example of this observation, from personal experience. Some time ago, longer than I care to remember and while I was herding the R&D cats at Edelbrock, we built one of the first "spin machines" while in the development of the company's version of small-block Chevy rocker arms. Essentially, the "machine" was a bare block, wet-sump pump and pan, camshaft, valvetrain for one cylinder, cylinder head, and a 10hp externally-mounted electric motor fixture to drive the cam, valvetrain, and oil pump. Why we decided to include oil temperature measurement in the project, I don't recall, but we did.
Here was the interesting twist. After "spinning" the valvetrain for approximately five minutes at a speed comparable to roughly 5,000 engine rpm, oil temperature approached what you'd observe in a running engine…by measuring oil temperature on the discharge side of the pump. Of the factors demonstrated, it clearly pointed out the influence of oil pumps on oil temperature and the advisability of not over-sizing this component in a racing engine, independent of whether the system is wet- or dry-sumped.
In the interest of condensing as many additional oil-related features and recommendations as possible, as we wrap this up, I chose to return to the wisdom and experience of Smokey as he accumulated observations over time. Again, for example, he believed that if you hang any oil system drivers, pulleys, or other components on the nose of the crankshaft, make certain you balance everything as a unit in order to prevent premature parts wear or failure. He also included fans, alternator, and water pump pulleys in the mix as well.
He also had some recommendations about oil pressure vs. engine speed. As an example, his rule of thumb was to provide about 10 psi of hot (operational) oil pressure for every 1,000 rpm. Of course, virtually any increase in oil pressure (particularly at the higher rpm) can be associated with a corresponding loss in power. And, as a reminder, don't forget oil temperature can also rise. In that regard, a pretty good rule of thumb for operational oil temperature is a minimum of 200 degrees F, with an upper limit around 240-250 degrees. It's also wise to consult with the appropriate service technicians or oil supplier of your choice to make certain there are no special considerations to keep in mind for their specific product, like what you might expect with synthetic oils that can operate at much higher temperatures without any associated problems. Just make certain you also discuss temperatures at bearing surfaces when sump oil gets into the higher heat ranges.
Last thoughts? Never start a dry-sump race engine on cold (or ambient temperature) oil. The same holds for a lack of oil pressure. Were he here today, I suspect Smokey would tell you to make certain you've pressurized the oiling system (not by cranking an engine without spark) with heated oil. And never start an engine with a combination of no oil pressure and low temperature oil, unless of course you enjoy rebuilding engines and have an infinite supply of funds…neither of which is likely in the mainstream of possibilities.