 Techline-Nov.08-Oil coolers-Pt II: Heat Rejection and Pressure Drop
Part II begins here and continues in the next thread
To cool the oil in his Shovel or Panhead, the resourceful biker of yesteryear would find a wrecked car and remove the transmission cooler. After using a few hose clamps and some extra oil line, he’d have a perfectly functioning oil cooler on his bike. This methodology still works well for those so inclined. However, we now have the advantage of the Internet, where a little research can easily determine which oil coolers, if any, are turbulated for better heat dissipation.
For whatever reason, Harley and many of its dealers have been saying for years that the Evo, and now the Twin Cam 88, do not require an oil cooler, or synthetic oil, for that matter. However, the factory did offer oil coolers as an option years ago. Back then, Harley used nonturbulated oil coolers (#62571-77, black; #62577-77, chrome) from Lockhart Industries Inc., formerly located in Paramount, California. These coolers came on certain Big Twin Shovelhead models: the 1977-81 FX, FXS, FXEF, FXS-80, and FXEF-80 (#62551-82, black; #62559-82, chrome); on the rubber-mounted 1982 FXRS, and the 1978-81 FL, FLH,
FLH-80, and FLH Classic (#62571-77A, black; #62577-77A, chrome).
How Much Cooling?
A good oil cooler will drop the engine oil temperature by at least 20 degrees F. How much cooling occurs will obviously vary with differing conditions. No matter how hard I try, I cannot remember where I saw this cooling claim many years ago. But here it is anyway: An oil cooler will lower the oil temperature about 22 degrees from 200 degrees to 178 degrees if you are traveling at 40 mph in 77-degree weather. Personally, I would be very happy if my engine’s oil temperature stayed at 200 degrees. I would be ecstatic at having temperatures as low as 178. In fact, I would have to say that a cooler was probably not necessary in these situations. Twin Cams do not run at these low temperatures. Our goal is to lower a Twin Cam’s cylinder head temperatures down to about 210 degrees. We can control detonation at this temperature, but not at 230-250 degrees and beyond. I’m comfortable that the above quote is probably accurate for the precise test parameters mentioned, but I would guess the figures apply to an Evo or even a Shovelhead using about a five-row, nonturbulated cooler and a richer air/fuel mixture than the present EPA-mandated one of 14.7:1. While descriptive and authoritative, the tested figures are for a specific (probably carbureted) engine, timed and tuned for that engine’s and rider’s needs, with a specific air/fuel mixture. The oil cooler was probably placed in one of a few possible locations with or without some air obstructions. I could go on, but while informative in a general way, these test figures will not have any relevance to your bike except to demonstrate that an oil cooler, any type of oil cooler, will lower oil temperatures somewhat to varying degrees depending on many factors. I do not feel the quote has much relevance for the Twin Cam, which removes heat via internal oil jets, which are directed underneath the piston crowns (domes). With a 60-percent increase in finning compared to the Evolution models, the Twin Cam also does a good job of dissipating the heat generated by the combustion process. However, this air-cooling system easily becomes overwhelmed.
The courteous and knowledgeable Marv Beals, the public face of Jagg Oil Coolers, will put the last nail in the coffin of this discussion. “We do not feel it is correct to provide a specific temperature drop unless it can be considered as a product within an overall equation. For example, someone can say his oil cooler can lower temperatures by 22 degrees Fahrenheit and not provide supportive input parameters that show how he arrived at the performance conclusion. What if that supportive data was an outrageous inlet oil temperature of 350 degrees and an ambient temperature of 32 degrees? That would be a poorly performing oil cooler that could only provide a 22-degree drop under those circumstances, but the consumer believes it can do a great job because he does not have the whole picture. On a daily basis, I provide experts in such diverse occupations as a NASCAR engineer and an industrial floor sweeping machine manufacturer with specific heat rejection data of our oil coolers.
This same data provided to the consumer does not assist with product education. It is universally and unequivocally misinterpreted as to how his specific cooler will perform in his specific environment. Jagg oil coolers are designed to allow your bike to maintain a standard temperature range.”
Stoichiometric Ratio
The Harley-Davidson engines that preceded the Twin Cam have less cooling fin area and retain more heat inside the engine. They also run a richer air/fuel ratio (AFR), one that’s below (richer than) today’s closed-loop EFI, EPA-mandated stoichiometric AFR of 14.7:1. Stoichiometric 14.7 (14 parts air to one part fuel) is considered the optimum air and fuel ratio for gasoline engines (theoretically) and results in complete combustion. Stoichiometric AFR is different for various fuels: gasoline is 14.7:1, diesel is 14.6:1, methanol is 6.4:1, and ethanol is 9.0:1.
The word stoichiometric is a mouthful, never mind spelling it correctly. How does someone come up with a name like stoichiometric? I assumed the fellow that figured all this out in the distant past somewhere lent his name to the concept. As it turns out, stoichio derives from the Greek word stoikheion, which roughly translates into element. The metric part sounds very familiar and identifiable as a classification of measurement. In a convoluted way, the answer comes from metric, then metron, and from there into the word measure. So, stoichiometric roughly translated means measure element. The subject gets more complicated, but understandable when explained properly. Stoichiometry is no fly-by-night, theoretical bull$#%@, as it rests upon three incontrovertible laws of physics: the law of conservation of mass, the law of definite proportions (also known as the law of constant composition), and the law of multiple proportions. I will mercifully spare you further discussion, although I am sure the word stoichiometric no longer seems so alien.
One last point to drive the subject home (since stoichiometry will become a mechanic’s household word in the future): chemical reactions combine in definite ratios of chemicals. Chemical reactions can neither create nor destroy matter. Furthermore, elements cannot change into another element like the old medieval belief that there was a way of changing lead into gold. Next, the quantity of each element has to be the same throughout the overall equation or reaction. To use a familiar example, the gases hydrogen (H) and oxygen (O) combine to form water with two hydrogen molecules bonding with one oxygen molecule: 2 H + O = H2O.
So, the stoichiometric ratio of the element(s) in air relative to gasoline is 14.7:1. How do we burn such a lean mixture of fuel? Heat is the short answer. Cylinder head design and mating piston dome shape assist greatly, but the bottom line is that the spark plug gap is increased to allow for a hotter spark, which is needed to ignite the leaner mixture. The hotter spark comes from a higher voltage coil. Gasoline cools but there is not much in a stoichiometric mixture. Air heats, and there is a lot of air in a 14.7:1 mixture relative to the cooling properties of gas. The factory has developed a fan (#91550-00C, chrome; #91531-00D, black) that installs on FLHTs and claims it lowers engine oil tank temperatures 20 degrees, measured at the oil tank.
Article continues in next thread. Check back issue for pix and extra information. |
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