The Stovebolt Site Forums The Shop Area Engine Shop Oil pump - high presure, or volume, and why?

Hope the title does the question justice.
I've had this discussion (and argument) more times than I can recall. At this point
I'd have to say the jury's out on this for me.
I'm more inclined toward high volume, for an engine build up. But I'm still on the fence.
So. Which is better for something intended as a weekend warrior, high Volume oil pump,
or high Pressure, and why?

Thanks!! I'd love to hear your opinions!

--Chris

For what engine?

Since it's theoretically possible to lubricate an engine properly with zero oil pressure, I say "neither". If I supply every bearing in the engine with one drop of oil every time a drop finds its way past the bearing and drips back into the oil pan, the pressure will be zero. The fact that pressure builds up at all indicates the oil pump is delivering more oil than the engine really needs. The trick is to be sure that everything that needs oiling gets enough, so a pump should flow slightly more volume than all the pressure-lubricated parts require. Running any pressure above 20-30 PSI at hot engine cruise RPM is just wasted horsepower. Since pressure is controlled two ways- - - -bearing clearance and relief spring pressure, running just enough volume to lube everything is the goal I try for when building an engine. On engines with hydraulic valve lifters, keeping enough pressure built up to keep the lifters from bleeding down and making the rocker arms rattle is also important. Running a pump capable of supplying several times the oil volume (or pressure) needed by an engine for adequate lubrication is an exercise in stupidity.
Jerry

@panic
Ya know. I thought about adding that it was for my '64 292. But then thought to myself. What's the difference?
The best principal remains the same. Doesn't it? Maybe not. It's for my '64 chevy C20 long stepside, that's running
a 292.

--Chris

Thanks, Jerry!
That makes all the sense in the world. You just made me feel a bit better about not being able
to come to a conclusion -- because I was trying too hard. The answer is *neither*!
That's what I get for getting myself sucked into all the market hype. I'm usually quite
good about naming snake oil, when I see/smell it. But got duped this time around.

Thanks again!

--Chris

The obvious exception is when building a race engine. Since the average high performance engine has 2-3 times the bearing clearance of a street engine when it's built, and it's not expected to last very long, it's necessary to run an oil pump capable of keeping all those big clearances filled with oil. Most of the round track engines I've built over several decades were totally worn out with less than 1,000 miles on them, if they lasted that long before hand grenading. I built them with more clearance brand new than a 100K mile street engine would have. They were producing at least three times their designed horsepower and running way above their max RPM, so loose clearances were an absolute must to keep them from tightening up and seizing prematurely.
Jerry

If I can, I choose volume over pressure. Both might take the same hp to turn the pump, but I like the extra volume of oil over the higher pressure of possibly less oil. I have seen to many oil pump driveshafts and gears worn out by high pressure oil pumps. A friends 455 Buick twisted the pump shaft right off with 85 psi oil when it was cold. Never heard of any damage from high volume pumps. Heavy oils do the same type of damage to gears and shafts.

the pressure comes from resistance to flow (volume) so a "high pressure" pump would merely be one that puts out more volume, the other factor would be the pressure relief setting of course. You can't make a low volume pump "high pressure" without limiting discharge flow. If it is putting out more oil than can be rejected by the various losses throughout the engine you will get higher pressures. And one of the main reasons for so much oil flow to racing engines is to pull heat away from the bearing surfaces, the actual lubrication requirement is quite small.

HRL, correct me if I don't have this right but rule of thumb has been 10psi/1000RPM. Is that still safe to assume. I remember the older Detroit Diesel's, 7-8psi at hot idle and 35-38 psi wound out. I agree with you, more pressure/volume is wasted energy.

I have had 216 Chevy engines that held 11psi at highway speeds and zero at a hot idle that ran for years. High pressure pumps are hard on drive gears, both cam and distributor, and high volume pumps give the oil less time to lose heat before being back on hot metal again. Now with that said about regular engine we HAVE to run 200psi hot on our blown tractor engines if they are at maximum boost---45psi. They have a dry sump system with 24 quart capacity and a Gilmer belt driven external oil pump with three scavenger rotors and one pressure rotor. The screens in the return port on the oil tank kept showing both metallic and copper particles, a sure sign of bearing problems. We tried different bearing materials and clearances ranging from 0.015 to 0.006 without success. A drag racer friend that ran a blown fuel car clued us onto going to ultra high oil pressure and the problem was solved. All our wet sump engines run in the 40psi range without problems so what we have theorized (not proven) is that the extreme oil pressure is so high that there is a pressurized oil cushion (that can't escape) between the rod journal and the crank pin that cushions the firing impulses. Whatever is happening it took us from a rebuild after every show, with a maximum of three pulls, to six shows before rebuild.

@Evan
So the trick with ultrahigh oil pressure, is to use disposable cam, and distributor gears.

Seriously, tho. Good data. Thanks for taking the time to share it!
Those tractor pulls sound kinda "spendy". :O

--Chris

The unlimited class tractor pull engines I've worked with had a lifespan measured in minutes at full throttle at best- - - - -some of them were scrap iron after (or during) one pull. One notable example was a "426" hemi I helped build that ended up at 547 cubic inches once we filled the block with epoxy and bored the cylinders out for flanged sleeves that left a stripe of epoxy showing down the front and rear of all the cylinders. My guy won the first three pulls he entered, running fuel injection without a blower. Then he got greedy and installed a 40% overdrive blower without reducing the static compression ratio. He (almost) made a full pull at Hazel Green Alabama before the engine blew the crankshaft out the bottom in three pieces. The cylinder walls held, though!

Rattle and Snap plantation in Columbia Tennessee ran two jet black International tractors, "Black Widow" and "Old Rattler". I'll bet Evan has encountered one or both of them somewhere along the tractor pull circuit!
Jerry

Have run with "Old Rattler" on numerous occasions. I'll bet that the blown one with high compression was unbearably loud.

When he passed me at the 200-foot mark just before the engine scattered, he was hauling the mail and I could feel the ground shaking under my feet! The engine hand-grenaded at about 250!
Jerry

I realize this is completely off topic, but at a county fair one year, the Army had one of their tanks on display, and just for kicks they brought it over to the truck pulls and hooked it up to the sled. Could have pulled it sideways for all that it mattered. The last 50 feet he actually let off the throttle a little bit. That was kind of cool.

Yep, pulling is all about weight and traction, and that tank had all of that covered big time! Plus, if he was running some sort of turbine engine, the horsepower was there as well!
Jerry

Steam traction engines will also walk away with the sled at a tractor pull, it's a slow walk. Not many HP, but they have the weight and traction.