Dear Buglover,
Yes.=A0 The idea of using #4 as a restrictor to increase either flow or pressure has merit.=A0 But I do NOT think the purpose was to improve oiling of the main bearings.=A0 As you know, the main bearings are the source of pressurized oil for the connecting rods, although not on a full-time basis.=A0 The oil passageways in the rods and in the crank only align every 180 degrees, indicating that these bearings do not require a great deal of oil for proper lubrication. (Indeed, this is generally true for all plain bearings._
I think the purpose of the restrictor is to increase the flow of oil through the oil COOLER.=A0 As partial support for this idea is seen in WHEN VW began installing the #4 plug in this fashion, that is, the
1600 engine was known to have problems keeping itself cool, especially in tropic climates such as Brazil, whereas there's no history of lubrication failures.With the HVX mods the oil cooling system is modified in that ALL of the oil flows throiugh a low-restriction oil cooler (ie, the Mesa- type).=A0 In a vehicle, the flow to the oil cooler is usually governed by a thermostatic valve which by-passes the oil cooler until the oil temperature reaches approximately 180 degrees.=A0 In an airplane, the temperature is controlled MANUALLY.=A0 The pilot opens or closes a set of shutters which controls the flow of cooling air throuigh the oil cooler.=A0 Using manual control is a bit old fashioned but it removes a component from the system (ie, the thermostatically controlled valve) and gives the pilot the ability to pre-configure the cooling system prior to take-off (ie,=A0 OIL COOLER - OPEN ).=A0 With a big engine (and at least a quart more oil) you've got a lot of waste heat to manage.=A0 Prior to take-off you can get stuck behind some guy doing his nails and it may be twenty minutes before you're cleared for take-off -- plenty of time for your Oil Temp to creep into the red. Your take-off run will bring it down a tad but you're at full throttle and as soon as you begin your climb-out your oil temp will start to rise, Since the angle of the aircraft will reduce air-flow through the oil cooler, you'll want to keep your climb-out rather flat.
If you're just doing Bumps & Grinds out of some cow pasture you'd probably have the oil cooler in the circuit all the time.=A0 But if you're actually going to FLY somewhere, configuring the engine for optimum performance at your cruising speed & altitude is critical, since it effects how much fuel you'll burn... which dictates how far you can fly.=A0 Once you are at your cruising altitude your oil temp will tend to be too cold.=A0 So you partially close the shutters until it's back in the green.=A0 Ditto for a long descent, during which the engine will tend to cool off.
NOTE: Once you reach your cruising altitude there are a number of chores to do, adjusting the mixture control and oil temp to give you the best performance at the lowest rpm. These tasks are usually referred to as housekeeping. Once you've done the housekeeping, if you follow the 'official' airways, you can look forward to about three hours of boredom mixed with a few minutes of total terror, when your puddle-jumper is overtaken and passed by larger, heavier, faster airplanes, some of which think it's great fun to see how close they can come to your wing tip. However, with a GPS that fits in your shirt pocket you're no longer bound to the airways, allowing you to pick a route that takes advantage of the prevailing winds. But you'll probably do what most us puddle-jumper drivers do: simply follow the railroad track. :-)
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