oil pressure fluxuates just a bit

oil pressure fluxuates just a bit

Postby grumpyvette » September 3rd, 2011, 10:49 am

"hey grumpy??
I just broke in my new 496 stroker big block chevy
My combo is 496 mahle 18 cc domes, AIR FLOW RESEARCH 265 cc heads, isky ez roll solid lifters, with a comp cams xr286r solid roller on billet core, air gap port matched to heads and hp 1000 made 625 hp and 623 ft lbs at 6200 with 32 degrees timing and the oil pressure goes up to 65 psi then starts bouncing between 60-65 psi if I run the car on a hard acceleration test run, the cars got a 6 quart oil pan and a tall oil filter that holds almost a full quart by its self any ideas"


thats rather common in big block engines run in the higher rpm ranges if a stock oil pan or anything close to a stock 5-5 quart capacity oil pan is used, its mostly an oil control issue in most cases on a 454-496 bbc, if your not running a good windage screen that promotes rapid oil flow back to the sump,its USUALLY not really about the amount of oil as much as controlling the rapid return of oil to the sump so its constantly covering the oil pump pick-up.
just some info, you might need,
depending on the oil pump used, rpms and clearances a chevy V8 will generally push some where between 2 and 6 gallons a minute thru the oil passages, your average oil pan sump holds at most 3 quarts ,while the engines running, and theres generally about 2 or a bit more quarts in the upper engine, (lifter gallery, heads)while the engines running, so when you induce high inertial loads is common for the oil pump pick up to become uncovered even in a baffled oil pan for a few seconds as that 2-3 quarts in the sump slams forward and back in the sump, because remember , lets say your engines only pumping 3 gallons a minute, and theres got to be at least 2 quarts in the sump to keep the oil pump pick-up covered under high inertial loads, its only going to take a few seconds at most under those conditions to suck air into the oil pump. obviously having a baffled 7-8 quart oil pan has advantages under those conditions as theres a good deal larger (SAFETY MARGIN) in the amount of oil present over the oil pump pick-up is you use the higher capacity BAFFLED oil pan with its better oil control and larger sump capacity,, windage screen combo

in some applications adding an oil accumulators a good idea
yes its annoying but its usually not instantly damaging to the engine, but over time it can cause wear. without a effective windage screen the longer stroke, can cause a good deal of problems with oil being whipped around in the lower engine being turned to a froth,
At high-rpm, about two-three quarts of oil are on top of the engine (out of the pan), and there is always close to a quart in the filter, and oil passages, leaving one more quart in the pan in a typical five-quart system,, on a high performance big block, a 6 quart oil pan is FREQUENTLY ONLY BARELY adequate under mild driving conditions, A vehicle used for high-performance (high-rpm operation) driving should have a larger 7-8 quart baffled oil pan with a windage screen.

pressure is the way that you commonly measure resistance to flow rates, obviously the bearing clearances can,t rapidly change back and forth so its more than likely caused by an intermittent oil flow into the oil pump, or a lack of consistent oil around the oil pump pick up, because air in the oil allows the pressure fluctuation, a constant supply of non-compresses able oil would not,it could be something simply like the oil bye-pass valve sticking at times
now obviously Id need a bit more info,about the oil pan,design, windage tray design your using,or lack of a windage tray, and where, and when during the run the oil pressure fluctuates, but the first thing Id personally try is adding a quart of oil to see it it changes anything.
if oil pressures bouncing between 60psi and 65 psi it might indicate the oil pumps sucking a bit of oil froth, (air/oil mix) caused by the rapidly spinning rotating assembly or oil rushing away from the oil pump pick-up due to inertia during either acceleration or braking inertia. it may be cured with adding an additional quart of oil, it may be a defective gauge or it may be the oil pump pick-ups either mounted too close to the oil pan floor or its come loose.
It might be an issue with oil return drainage being restricted, I know guys that have used common metal window screen , and epoxy on blocks as a shrapnel screen the holes are far to small and it restricts oil flow, your far better off using the perforated metal with the 1/8" minimum hole size or a muck courser screen grill size

reading thru these links should help








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