Techline-Nov.08-Oil coolers-Pt II: Heat Rejection and Pressure Drop (conclusion)

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Part II concludes here

Now that Marv and I have dispensed with the semantics and the fine lines between terminologies, in the everyday world most people take poetic license with the various terms and interchange them as I have done before. I can only say that the term heat rejection was not descriptive of what I thought was going on, namely dissipation. After going through all of this, I am now comfortable with the term heat rejection.

The turbulation inside the cooler’s passages that is so vital to oil cooling, and thus engine preservation, does obstruct the flow of oil somewhat. The accompanying charts, which are based on wind tunnel and flow bench analysis, demonstrate that the 10-row Jagg oil cooler is much more free flowing compared to its counterpart eight-row Harley-Davidson cooler. I think it important to say that on a stock H-D ridden normally, the increase in pressure drop on a single H-D cooler will not affect the bike’s engine longevity in any serious way. However, from a performance perspective, I cannot say that. Why wouldn’t a rider choose an oil cooler with less pressure drop over those with a higher pressure drop, all other factors being equal?

Jagg has conducted testing that demonstrates that the cooling properties of both Jagg and H-D oil coolers are equal, which you can also see in the accompanying charts. I asked Marv why three examples of heat rejection tables are needed. He replied, “There will be as many heat rejection results/comparisons as there are composites/sets of input variables.” Actually, Jagg tied the analysis together very well. There are three different gallons per minute (gpm) oil flow rate variables (0.793 gpm, 1.321 gpm, and 2.642 gpm) given in the first chart, the one labeled Pressure Drop. Jagg does a heat rejection analysis of each of these three variables in the three successive charts to tie the pressure drop and heat rejection analysis together.

According to an analysis published by Jagg, the Jagg oil cooler has three-and-a-half times less pressure drop than the comparable Harley-Davidson oil cooler. “At practical oil-flow volume, the performance of both subjects is virtually identical. More simply stated, it does not matter how well the oil cooler performs if it restricts adequate delivery of the oil to the intended areas of the motor. The Jagg oil cooler bests the competition again. It is important to note that this is a comparison of components. Future comparisons will detail the additional performance and flow advantage of the Jagg oil filter adapter’s oil flow theory and its effect on system pressure.”

The reader may have noticed that the Harley-Davidson oil cooler has eight rows or passages while the Jagg unit used for comparative analysis has 10. Furthermore, Jagg’s literature states that the cooling properties are equal. This begs the question; does this mean the H-D oil cooler is superior because it accomplishes the same cooling job with 20 percent fewer rows than Jagg? I put this to Marv Beals, who responded, “Without the entire picture, it could be misinterpreted to mean the eight-row cooler has better heat rejection characteristics. However, this statement and your question point directly at the heart of my entire focus … if the other products of our heat-rejection dialog are not considered (ie pressure drop), then the aim of the entire discussion is missed. One must consider the entire system. In other words, we could alter our turbulators to hold the oil in the cooler longer (create more restriction), thereby giving the ambient air that is blowing across the outside of the oil cooler a greater chance to reject the heat, but we chose to balance heat rejection with flow. Given that both oil coolers are intended to be installed on the pressure side of the oiling system, we can then state how significant it is that we are providing our heat rejection while still allowing the oil to go where the flow and pressure intend it to go. In other words, it doesn’t matter how cool the other guys can get the oil (and they don’t get it any cooler than we do, mind you) if this cooled oil is not getting where it needs to go in order to do its traditional cooling and lubricating duties.” In short, oil-cooling properties are irrelevant without including pressure drop analysis. We can increase cooling efficiency with fewer rows by restricting the oil and keeping it in the oil cooler passageways longer. On the surface, this sounds great. However, we are also restricting the oil’s primary function of lubricating by retarding its travel time to the parts that require the oil’s film strength to separate moving parts. Cooler oil not getting to where it is needed does not help parts that are starving for maximum lubrication.

Conclusion
Next month we’ll cover practical tips for an oil cooler installation, such as return or feed mounting, how to direct-mount a second cooler, and mounting two 10-row coolers. I’ll also discuss the negative vacuum principle, two-pass design, and the types of Jagg oil coolers available.

Donny Petersen
Tattoo Tony’s Heavy Duty Cycles
Toronto, Canada
www.HeavyDutyCycles.com