In terms of your questions as to why modern cars specify lighter weight oils, its because (in general) they have tighter tolerances between the components than our old Z's. Heavier weight oils simply won't flow through the small spaces as well. Viscosity is a term for RESISTANCE to flow, thus heavier oils would cause the oil pressures to rise too high in a tighter engine and not provide enough lubrication.

Of course, because of varying climates, you would switch to a higher weight oil (in the case of a hotter climate) to keep the pressures in check, and to aid higher temp running performance. I've read of some Aussie guys who race their L6 motors with 70W.

the whole thing is a balance, really. I can't see either pressure or volume being more important. You tailor the oil weight, pressure and volume to suit your engine and what you intend to use it for.

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-Chris

No, your argument makes sense.

My Turbo Buick bud argues that the oil filter bypass will allow a good oil flow, but very little pressure. He figures if the pressure was more important than volume, they could have designed it the other way around.

I tend to think that a low pressure might not be able to reach all the areas it needs to. Not sure why I even introduced this question, but it seems to fit Phrog's 'pump' thread.

Of course, you could have a good pump and full oil, but drift your Z so hard that the oil walks away from the pickup, causing the pump to cavitate, causing the bearings to run dry, causing the rod to fail, causing AJs block to...... well, never mind.

Clay, do you still have a picture of that ventilated 260 block?

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1970 240Z

Lighter weight oils also significantly increase fleet fuel economy, which is another big reason that the latest cars are designed with "thinner" oils in mind. CAFE standards need to be met. It's a numbers game.

As an aside, the only way to increase head pressure is to increase the flow rate of an equivalent weight fluid in an equivalent flow path. That means increase volume. You cannot increase the pressure of the fluid without trying to stuff MORE of it into the same space.

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-Dave
76Z Turbo'd
72 In Progress---DONE!

True.

This is also why the DL Potter spring kit I showed *should* make higher pressure, because it prevents the pump from bypassing fluid for a larger range. You don't *need* these springs for mild everyday use, of course. However even if you had a high volume pump pushing fluid, unless it has the proper pressure spring, its not going to do any good. It will keep pumping the same amount of fluid, but its bypassing x amount of that back to the sump.

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-Chris

I increased the oil pressure in both my truck and my 240, took about 5 minutes each. For $19.95 I will tell you how.

Added a handful of sawdust??

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1970 240Z

Now that iz old school!