If oil is the lifeblood of your engine, then the oil pump and lubrication system are indeed the heart and circulation system of your big-block Chevy. For power levels up to about 500 hp, there’s really not much that needs changing, other than to ensure that your parts are up to spec, and that the lubricant you are using is the right choice for your parts combination.
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For the high-performance and racing markets, there are two choices in oiling system designs: wet sump and dry sump. All original equipment big-blocks were wet sump systems, so-called because the reservoir of oil is contained in the sump portion of the oil pan, and the oil pump pickup is submerged in this (hopefully) continuous supply of life-giving lubricant. Dry sump systems are the high end of the performance spectrum and they utilize a belt-driven external oil pump with multiple scavenge sections, which pull oil from several points in the engine and pump the evacuated oil to a holding tank. In addition to providing a much larger oil capacity, the tank allows any air in the oil to separate, delivering an uninterrupted supply of non-aerated oil to the pressure section of the pump.
The benefits of a dry sump system are many first and foremost, the engine receives a continuous delivery of oil under all conditions, whether accelerating, braking, cornering, or whatever. Second, the scavenge sections pull excess oil away from the turbulence of the rotating assembly, freeing up some horsepower by reducing the drag of engine parts “swimming” through a pool of excess liquid. Third, the scavenge sections are so efficient that they can pull a vacuum in the crankcase. This helps free up more horsepower and prevents oil contamination from getting past the piston rings and into the combustion chamber, where it could cause detonation, oil-fouled spark plugs, and other problems. Finally, because there is no need for a deep sump in the oil pan, dry sump oil pans can be much shallower that wet sump pans, giving car builders the option of positioning the engine lower in the chassis for a lower center of gravity and a lower hood scoop height for reduced aerodynamic drag.
So what’s the downside to dry sump systems? Instead of spending hundreds of dollars for an upgrade in performance, you’ll be looking at a bill for thousands of dollars, making dry sump systems the choice of all professional racers (when legal), but not a very cost-effective item when you calculate power gained per dollar spent.
Stock big-block Chevy oil pumps have been available in two configurations: standard volume or high volume. The difference is merely the length of the spur gears inside the pump housing; standard-volume gears are 1.135 inches long, and high-volume gears are 1.300 inches. Either design fits any standard big-block rear main cap. Note that Mark IV and Gen V/VI oil pumps are slightly different, so be sure to specify which version you want. Mark IV pumps do not clear the inner rear main cap bolt of a Gen V/VI engine, but Gen V/VI pumps can be used on Mark IV engines. The GM Performance Parts pump (PN 19131250) is standard on their 572 crate engines and is a good choice for any high-performance Mark IV or Gen V/VI big-block, when used with a pickup that matches your oil pan.
So why does everyone seem to think that all high-performance engines need a high-pressure, high-volume oil pump? It used to be standard practice to open up the main and rod bearing clearances in a high-performance Rat motor beyond the stock .0025- to .003-inch clearance, and to use a high-viscosity oil the belief that it gives more protection to the crank. Such practices increase the amount of internal hemorrhaging (leakage) in the lubrication system, and do indeed require an increase in oil pump volume.
Today, we can enjoy the benefits of better lubricants, especially with synthetic oils, and tighter bearing clearances actually provide better bearing life because the hydrodynamic wedge of oil, which supports the crankshaft when the engine is running, is stronger when the clearance is only .0025 to .003 inch. The general rule for high-performance engine oil pressure is 10 pounds per square inch for every 1,000 rpm.
Stock Chevy oil pumps have the pickup tube pressed into the pump body, and they have been known to fall out when subjected to the vibration of a high-RPM engine. All high-performance Chevy pumps should have the pickup tube secured by tack-welding the pickup to the pump body, or by a tab from the pickup tube that is bolted to one of the pump cover bolts. Using both methods is a very good idea, and most aftermarket pan manufacturers offer pickup tubes with mounting tabs to match their oil pans. Be sure to remove the relief valve spring before welding the pickup to prevent damage to the spring. Chilling the pickup tube in your freezer and heating the pump body by setting it out in the sun before pickup installation also helps the job along. Be sure to test fit the pan and pickup clearance before tack welding everything together. Recommended pickup-to-pan clearance is usually 1/4 inch, and don’t forget to add the thickness of the pan gasket.
Some pump manufacturers machine anti-cavitation slots and pressure balance slots into the pump body and cover to lessen the chance of cavitation at high engine speeds. Cavitation is a vacuum that occurs in a fluid when it cannot flow fast enough fill in the void behind the rapidly moving gears. This is not needed for street high-performance engines, and is not recommended for street use by most pump makers.
Fluids, such as motor oil, prefer to be pushed under pressure than sucked through a lengthy section of tubing, so keeping the pump pickup as short as possible is a good thing. Taking that concept to extremes, some aftermarket oil pumps for big-block Chevys use spacers between the oil pump and the rear main cap to submerge the pump into the sump portion of the pan. This may require a longer pump driveshaft, and the pump must be carefully matched to the oil pan depth to maintain the correct pickup-topan clearance. These extended pumps don’t fit most stock oil pans and must be used with aftermarket competition pans designed for the job.
Many of these extended pumps are machined from billet aluminum, and some use gerotor gears instead of common spur gears. Gerotor gears deliver a smoother supply of oil pressure without the pulsing that is characteristic of spur gear pumps, and the gerotor design greatly reduces the chance of cavitation at high engine speeds. Many dry sump oil pumps also feature gerotor pressure sections for the same reasons.
The stock Chevy pump driveshaft is a simple mild steel shaft that is driven by the camshaft via the bottom of the distributor, so that the oil pump rotates at 1/2 crankshaft speed. It uses a plastic bushing to hold it in place on the oil pump during assembly and to keep it inside the engine block when the distributor is removed. Heavy-duty all-metal driveshafts are available from the aftermarket and GMPP (PN 3865886) and should be in every high-performance Rat motor.
Until your power expectations exceed 500 hp, it’s quite likely that your original oil pan works just fine, as long as the pump is right for the engine. Remember that the first rule of oil pan selection is that it must fit on your car, and many large-capacity oil pans do not clear stock crossmembers, steering and suspension components, or other obstacles on the dark side of your ride. If you have the room, the Corvette 5-quart pan (PN 14091356) is a good first step up from the standard Mark IV passenger car 4-quart pan. It includes a windage tray and requires four main cap studs (PN 3902885) for mounting the tray.
Remember that oil pan capacity is listed without regard to the extra quart of oil in the filter: if you have to add 5 quarts of oil after an oil change, you have a 4-quart pan. Gen V and Gen VI engines were never offered in the Corvette, but there are plenty of large-capacity pans available for those engines, such as the 6-quart pan (PN 10240721), but it does not fit an early Chevelle or Camaro without modifications.
Fortunately, there are many excellent aftermarket pans available for Mark IV and Gen V/VI big-blocks from Hamburger’s Performance Products, Milodon, and Moroso for any application from street to all-out racing, and specialty oil pan manufacturers such as Dan Olson Racing Products, Jeff Johnston’s Billet Fabrication, and Stef’s Fabrication Specialties.
Competition pans include such features as crank scrapers to shear excess oil off of the spinning crank and rod assembly, built-in windage trays to shield oil in the sump from the turbulence of the spinning crank, and kick-outs on the right side of the pan. A kick-out provides an “escape route” for the oil thrown off the spinning crankshaft and channels the oil back to the sump more efficiently than a straight-wall oil pan.
Choose a pan that fits your car with as much capacity as possible to keep the oil cool. The number-one priority of your oiling system should be to keep the engine supplied with oil, and big boxy pans make it harder to control oil slosh during braking and cornering. Consult with the oil pan manufacturer for application guidance; they’d rather sell you the pan you’ll be happy with than some exotic pan that’s wrong for your street car.
Oil Filters and Adapters
1965 through 1967 big-blocks used a metal canister and pleated filter element, and all 1968 and later Mark IV engines have an oil filter adapter with an integral bypass valve for use with spinon oil filters. Gen V and Gen VI engines use a spin-on filter with the bypass valve installed in the block, and these bypass valves are a source of much misinformation. Their function is to bypass the filter when there is a pressure differential caused by a clogged oil filter. It’s possible that the valve also bypasses the filter during cold start-up when the oil is thickest, so some racing engine builders remove the bypass valve and plug the hole with a pipe plug. This positively ensures full filtration all the time, but may blow out the filter if you rev the engine before it is fully warmed-up. I prefer to leave the bypass valve in place and use a filter, such as the excellent K&N (PN HP-3002) that is large enough to keep up with the oil flow demands of the engine.
There are single and dual remote oilfilter adapters on the market, which can be very handy for plumbing custom vehicles, boats, etc., that have interference issues with the stock oil filter location. Very-high-end racing motors, such as the GM DRCE, have the starter on the left side so that an oil pan with a full-length kick-out can be used, and these require remote oil filters.
Pan Evacuation Systems and Vacuum Pumps
Production big-blocks relieve crankcase pressure and blow-by through breathers and a positive crankcase ventilation (PCV) valve in the valve covers. The PCV valve is connected by a rubber hose to a port under the carburetor, which draws the crankcase gases back into the engine where they are burned off. Racers discovered years ago that reducing the crankcase pressure produced power gains. The first systems to capitalize on this effect were pan evacuation systems that use a probe in the exhaust headers connected to the valve cover breathers to create low pressure at high engine speeds. This was a step in the right direction but it was not nearly as effective as a dry sump pump, which could create a much stronger crankcase vacuum.
Several decades ago, Competition Eliminator drag racers, who could not use dry sump systems because of class rules, started adapting the OEM belt-driven smog (Air Injection Reactor, or A.I.R.) pump to pull a vacuum in the crankcase and were rewarded with gains of up to 20 hp. That doesn’t sound like much, but on a competition engine with every possible modification already done, another 20 hp was like finding gold in a coal mine. In addition to freeing-up some horsepower, vacuum pumps do a good job of “housekeeping” by reducing oil buildup in the combustion chambers from leakage past the piston rings and valveguides, plus they reduce any small external oil leaks from pan gaskets, valve covers, etc.
For proper vacuum pump operation, the engine must be well sealed, and a vacuum relief valve is necessary to prevent excessive vacuum. If crankcase vacuum makes more power, how can you have too much? In a wet sump engine, there must be some pressure in the oil pan to push the oil into the oil pump pickup, and excessive crankcase vacuum lowers the oil pressure. Also, too much vacuum tends to rob the piston pin of splash lubrication; so many engine builders increase wrist-pin-to-pin-bore clearance slightly with a vacuum pump. Since vacuum pumps do such a good job of controlling the oil on the cylinder walls, low-tension oil rings can be used for reduced drag and even more horsepower. Wet sump engines should be limited to 18 to 20 inches of Mercury, while dry sump engines can get by with 24 to 26 inches because the pressure section in a dry sump pump is ventilated with normal atmospheric pressure through the oil tank breather.
There are companies that still modify the GM smog pump for racing engines, but most modern vacuum pump producers whittle their pumps out of billet aluminum, which gives them greater latitude for improving the design and features of the pump. Modern vacuum pumps are available in a variety of sizes suitable for different applications; you don’t need the massive flow capacity of a pump designed for an 800-cube Pro Mod motor on your bracket-racing 454. Most common are the three-vane pumps, while four-vane pumps pull more vacuum at lower engine speeds. Vacuum pumps are available from Aerospace Components, GZ Motorsports, Moroso Performance Products, Star Machine, and others.
Accumulators, Coolers and Accessories
Oil Accumulators are simple cylinders with a floating piston that store oil under pressure, providing a reserve supply that is automatically released when oil pressure drops below a safe level. If oil pressure suddenly drops because of hard acceleration, severe cornering, or hard braking, the air pressure immediately pushes oil into the engine’s oiling system to prevent damage to the main bearings and other engine components. Most accumulators have a manual valve between the supply line and the storage cylinder, so that you can close the valve before shutting off the engine and store oil under pressure for pre-lubing the engine prior to the next startup.
Oil coolers should be used any time your oil temperature nears 240 degrees F; conventional motor oil can start to break down at that temperature. Most highperformance street and drag race bigblocks don’t need an oil cooler; the engine is not operated at full throttle for more than 10 or 12 seconds at a time, and if your oil pan has increased capacity, as recommended, your temp should remain below that level. Road race cars need them, but not too many big-blocks are forced to turn left and right with regularity.
There are exceptions, of course: you might want to build a killer Rat motor for the Silver State Classic, in which “sortastreet” cars are driven at high speeds for hundreds of miles, and trucks absolutely need oil coolers. There are plenty of Rat motor powered trucks used to haul your favorite toys to and from the playground. As mentioned in Chapter 2, late-1960s and early-1970s highperformance blocks with four-bolt main caps are already drilled and tapped for oil cooler lines just above the oil filter pad. If you want to plumb a cooler into one of these blocks, order a bypass valve (GM PN 5575416) and install it in the rear hole. If your Mark IV block doesn’t have the factory oil cooler provisions, it’s no problem; there are plenty of aftermarket adapters that can be sandwiched between the block and the oil filter to accommodate cooler plumbing.
All Gen V and Gen VI blocks are drilled and tapped for the factory oil cooler lines in the oil pan rail just ahead of the oil filter. All production Gen V/ VI engines come with oil cooler bypass valves already installed. If you are not using a cooler, you need to plug the two threaded holes in the pan rail surface, and remove the bypass valve directly underneath the filter fitting. If you want to plumb an aftermarket oil cooler, replace the bypass valve in the oil filter pad’s offset hole with GM PN 25161284, which has the higher pressure differential necessary for the added restriction of the add-on cooler.
So what are oiling system accessories? The first thing that comes to mind is a magnetic drain plug, the best under-10-dollar part you can buy for your Rat motor. If you see “fuzz” on the magnet while changing oil, don’t bother putting fresh oil back in; you need to drop the pan and find out what’s going wrong. Similarly, Moroso makes a magnet and epoxy kit for cylinder-head oil drain-back passages that catch broken valvetrain parts, such as valvesprings and roller bearings, before they find their way deeper into the engine and cause real damage. Many companies also offer screen kits that can be epoxied over the large openings in the lifter valley for the same purpose.
A FilterMag is a strong magnet that clamps tightly around the oil filter to trap small ferrous particles inside the oil filter, which seems like an incredibly smart thing to do. To really take advantage of that feature, you should cut apart the used oil filter from any new or freshly rebuilt big-block to check for debris, and a good oil filter cutter makes that job much more palatable.
Motor oils can be divided into two categories: conventional mineral-based oils and synthetics. Conventional oils have been used for decades with good results, and their attributes include good performance under normal conditions, ready availablility, and relatively low cost, which can be important if you plan to change oil frequently (for instance, if you are using alcohol for competition and change the oil after every weekend of racing). Conventional oils are recommended to break-in a new or rebuilt engine, since synthetics are too slippery to allow some parts, such as piston rings and cam/lifters, to properly seat-in.
Synthetics are superior to mineralbased oils in every other aspect, providing better protection under severe conditions. They free-up more power in your big-block in two ways: first, they reduce the friction of metal-to-metal contact, such as with rocker arm to rocker pivots, timing chain to sprockets, etc. Second, because they offer better protection at full-floating junctions, like the main and rod bearings, a lower viscosity may be used, and that reduces parasitic pumping losses and windage losses.
Is there a downside to synthetics? Yes. They cost as much as three or four times as much as conventional oils, and they are good at finding little leaks and turning them into big leaks. If your old two-piece rear main seal is dripping a little bit now, it’s going to become a real problem with synthetic oil. That’s another reason that Chevrolet switched to a one-piece rear main seal on Gen V/ VI engines.
Standard automotive motor oils have severely reduced or eliminated zinc (ZDDP) from their formula due to environmental concerns, and it is the zinc that provides the high-shear lubrication necessary for the overstressed junction between the cam lobe and flat tappets. These new-age lubricants have been responsible for a rash of cam/lifter failures in older vehicles as well as in high-performance engines using conventional lifters. High-performance bigblocks need motor oils that have been specially formulated with zinc and/or other wear-reducing additives, especially if you are using a flat-tappet cam and lifters. Many cam companies, such as Comp Cams, offer their own brand of highperformance and break-in oils, which are highly recommended for use with flattappet camshafts.
Written by Tom Dufur and Posted with Permission of CarTechBooks