flathead question

[chevy 37]

I worked on a 48 ford flattie and had it bored .040 over with edelbrock heads. Running 2 98's. Question is that the most oil pressure I can get is 30 lbs. which seems to work with this engine. I was told that the later engines used a heavier spring on the relief valve. Does this work since looking at the spring it is heavier and will I need to use this? 30 lbs. is not much and I like to get it up to 50 if possible.

[Itoldyouso]

All the major engine manufacturers have rethought oil pressure in recent years. We old rodders are used to stretching relief springs and shimming them to get 80 lbs oil pressure, but the new thinking seems to be that proper volume is more important than high pressure.

30 lbs is probably fine for your flathead, but if you want a little more insurance you might consider one of these high volume Melling pumps. Not cheap, but cheaper than having bearings fail.

http://www.thehotrodcompany.com/shop...&filterkey=oil

Don

[Bob Parmenter]

You're fine Bart. More pressure doesn't mean more lubrication. Pressure is a measure of resistance to flow. It's oil flow that lubricates, not pressure. Now, if you normally run 30 pounds, and then it suddenly drops to 0, that's an indication that flow has stopped since there's not resistance to measure anymore. THAT is the value of pressure readings.

[chevy 37]

Thanks Don and Bob. Bob the engine runs fine at 30 lbs. All the newer flatheads I've run 52-53, at 60 and 70mph, the oil pressure would be around 50 and drop to 5 at idle. This engine runs fine and at 70 the pressure is 30 and at idle 5. Just a big difference in pressure between the older and newer model of flattie's. Just had me wondering. Bart

[Rrumbler]

As Don and Tech both noted, pressure in an oiling system for rotating machinery is not as important as the availability of a ready and constant supply of lubricant. Once a crankshaft, or any rotating piece of machinery is moving, supported on an adequate film, surface tension and film shear take over, and as long as there is lube available, the rotation will pull it into the space between the bearing and the shaft. A good example of this is large rotating machines like really big motors and generators: most have external auxiliary oil pumps that are capable of rather high pressures. The pumps are started before the shaft is turned, so as to pump high pressure oil into the bearing space and "lift" the shaft off of the bearing surface, then the machine is started. After the machine reaches it's operating speed, the oil pumps are turned off, and slingers or dippers pick up oil from the plenum, or reservoir beneath the bearing and deposit it around the bearing edges where it is drawn into the clearanced space and provides a ready cushion of oil for the shaft to rotate on. Some of the machines I used to work on had armatures that weighed over 100K lbs, and they worked just fine in this fashion. In a reciprocating engine, the power pulse is in a tangent direction to the rotation of the crankshaft, but it is quickly converted to rotational force, and is not a significant factor, especially in multi-cylinder engines; the more cylinders, the more the pulses will be distributed around the rotational axis of the shaft. That is why a V8 is smoother than a straight six, and a V12 even smoother.

[IC2]

The HD gas turbines that I used to be associated with in various capacities ran, depending on the version 5100 - 7100 rpm, generating thousands of horsepower driving anything from a fairly small(relatively speaking) compressor to a 500 megawatt generator had a 25psig system with, depending on what system, ounces to hundreds of gallons per minute of oil flow.