Techline-October08-Oil Coolers - Pt I - Adversary is Heat (conclusion)

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Article concludes in this thread.

Oil Coolers
My bike does not usually ping, and it has 10.5:1 compression. I have always highly recommended using an oil cooler on all Harleys (except the water-cooled ones). I strongly advocate their use on hot-running Twin Cams. Now the coolers I have used on the Twin Cams do measurably lower heat, but I have never been happy with how much. That is, until last year. Bob Wood of Wood Performance, who has a great knack for simplifying the complicated, said that I need two 10-row Jagg coolers on my Twin Cam. Yup! You need 20 rows of Jagg oil cooling to lower the temperatures sufficiently in the heads to prevent detonation. Well, isn’t this interesting? I needed to install two of the biggest and most efficient oil coolers on my bike to control detonation. Bob says that head temperatures need reduction to 210-220 degrees F, particularly in high-compression engines. I followed Bob’s advice, and all I have to say is that it works, and works well.

Before going any further, I would like to deal with the words row and core. Jagg refers to the tubing in an oil cooler as rows, while other people in the industry, including riders, refer to it as cores. To be specific, and for our purposes, core generally refers to the cooling matrix of an oil cooler, which is comprised of all the tubes, fins, and the header plate together. Core sometimes refers to a whole oil cooler without specific mounting or specific application hardware. However, we should use row or passage to refer to single or multiple directional tubes as part of an oil cooler.

We’ll first discuss turbulation, which is an oil-mixing technique that increases oil cooling. Then I will discuss a design phenomenon called oil pressure drop, which we wish to avoid in our oil cooler purchase, especially when running two big 10-row coolers in tandem. The two concepts are related but separate. However, both turbulation and pressure drop are very important; we want one but not the other.

How do you choose an appropriate cooler? For the most part, visual inspection can determine oil cooler efficiency. First observe the length of the cooling oil passages encased by finning. Then look at the number of fins, and the area of finning as a cooling surface, with exposure to air, air temperature, and motorcycle speed. The internal construction of the cooler’s passages and any restriction causing pressure drop is discernible by other means, like sophisticated wind-tunnel and bench-flow analysis. Some coolers have turbulation, which mixes the oil inside the cooling passages to allow maximum oil exposure to the cooling effects of the finning. Two oil coolers offer turbulation that I am aware of: Jagg and Harley-Davidson. Jagg used to manufacture the Harley-Davidson oil coolers until the factory sourced them elsewhere. Read what you will into this situation, but certainly Jagg was the first of the two to turbulate its oil coolers. However, turbulation or mixing the oil is not a big secret, nor is the process complicated. It’s common sense derived from a logical thought process.

Laminar airflow into an induction throat is good as more volume moves in an orderly fashion. Turbulent intake air is not as good as it moves slower, thus reducing flow volume. The opposite principles are true for cooling oil. The goal is to mix laminar flowing oil that only cools on the outside edges near the row surfaces by putting minor obstructions in the way of the oil flow. We want to disrupt laminar flow in order to bring middle streams of hot oil in the center of the rows to the periphery, where attached cooling fins can dissipate the heat, thus cooling the oil.

For most of my mechanical life, I have made the assumption that oil cooler rows, which I incorrectly referred to as cores, are round and tubular. I guess some do have this design, much to their cooling detriment. Some diagrams even depict the rows as round tubes even though their coolers use a flattened row profile. The goal is to mix or turbulate laminar flowing oil, which would normally only get cooled on the outside edges of the oil stream near the row surface, by putting minor obstructions in the way of the oil flow. Turbulation disrupts laminar flow in order to bring the middle of the stream of hot oil to the periphery where attached cooling fins can dissipate the transferring heat, thus cooling more of the oil. However, the very necessary turbulation inside the passages that is so vital to oil cooling, and thus engine preservation, does obstruct the oil somewhat. How much is what we need to know so we can choose a cooler with the least pressure drop. Excess pressure drop may malnourish some areas of the engine with inadequate lubrication. Jagg was the first to turbulate its oil coolers. It also remains in the lead for the best combination of
turbulation with the least pressure drop.

In a two-pass flow configuration, the hot oil must enter and pass through the length of the cooling tube(s), make a 180 degree turn, and make a second pass back the length of the cooling tube(s), thus making two passes. There are two major reasons an oil cooler may have a two-pass configuration. The first is for plumbing configurations where the inlet/outlet location is important for space or design considerations. The second is performance. The performance reason requires a more in-depth explanation. Low gallons-per-minute (gpm) flow-rate systems, such as with Harley-Davidson applications, respond well to a two-pass flow orientation in an oil cooler that offers low restriction. The reason is that it gives the cooling medium greater opportunity for heat exchange into the atmosphere by slowing the oil down just a little. However, two-pass flow orientation is employed best when considered in the overall flow system. Contrarily, a cooler optimized for performance within a system with a single-pass flow configuration can gain a good deal of heat exchange by further slowing the oil’s flow and creating a two-pass flow configuration, but it will do so at the expense of significant pressure loss. Therefore, a two-pass flow orientation is the best total system if it uses turbulation without much pressure drop. Consideration of the total system is necessary, as the best results derive from cooperation between differing factors of maximizing cooling and minimizing pressure restrictions.

Jagg’s #4600 offset oil filter adapter is necessary for mounting oil coolers on Twin Cams. The optional #4700 offset oil filter adapter with thermostat is also available for those wanting an automatic shut off/turn on valve set to 180 degrees F. Either billet aluminum construction adapter installs between the engine and oil filter for quick and easy access to the engine’s oil supply. Moreover, the #4600 or the #4700 are required for oil cooler installation on Twin Cam bikes and are optional for fuel-injected Big Twin Evos.

Many adaptor plates do not flow the oil through the oil filter first. The design of Jagg adapter plates specifically flow oil through the oil filter before the oil cooler, resulting in less restriction because the oil is warm and thus less viscous. This is important for the Twin Cam because of the oil filter’s placement on the pressure feed side of the oiling system. The Jagg adapter offers less pressure drop than any other oil filter adapter due to this purposeful directional flow characteristic. This flow path, which goes through the filter first, contributes to the total system of turbulation combining with less pressure drop that makes the Jagg cooler advantageous over competitors at this time. The short version is that the correct volume of cool oil delivers strength to both separate and lubricate the mating components of all moving parts inside the engine with an oil film.

Conclusion
Next month, we’ll continue talking about oil cooler characteristics.


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