Oil Pumps For Street Stock Race Engines

On a stock-type oiling system in a Street Stock level race engine, the softball-sized iron nugget buried at the bottom of the engine is the part that keeps it alive. The right oil pump can make your engine live longer. It can also free up horsepower that can be used at the rear wheels.

There are several oil pump performance variations available for stock power level engines. The first is the stock pump. It began its job when the engine was fired up at the automaker's plant. It is really a reasonable oil pump, in most cases, for stock engine classes. It may have fed lubricant to the engine for 100,000 miles (or more). Like other parts in an engine, it can wear out, and it's inexpensive insurance to replace a stock pump.

The next variation is a high-volume pump. This is sometimes referred to as a "high-pressure" pump. Actually, these two descriptions are not equivalent. The high-volume pump is designed to pump a higher volume of oil at the same pressure. In doing so, it may raise the oil pressure because a higher volume pumped into the same oil gallery space will cause a pressure increase. The intent of this design is to increase the oil flow. Increased flow is necessary in an engine where the working clearances of the bearings are larger. A point to remember is that the engine's bearings are oil-cooled.

All stock-type pumps have a pressure relief valve. This is necessary because cold, thick oil at start-up, or another restriction such as a plugged oil filter, can cause a serious problem. Once upon a time, long ago, I only had to blow two oil filters off of an engine before I found out that the relief valve was stuck. The relief valve prevents damage to the pump drive system by releasing any excess oil pressure back into the oil pan, instead of trying to force it through the engine's oil distribution channels. Because this drive system includes the camshaft and ignition drive on most stock engines, an overload on the oil pump can cause complete engine failure. A stripped cam gear from a seized oil pump is not a pretty sight. With a high-pressure pump, the relief valve will release pressure at a higher point than a stock unit, but it will still only have the volume of the stock pump.

Stock Oil Flow

I spent some time with two engineers from Melling Engine Parts, Mike Osterhaus and Cal Rydjord (sounds like Richard), discussing oil pumps for stock power level engines to get their tech advice. Melling is the largest manufacturer of new and replacement performance oil pumps in the United States.

Beginning with the stock pump, Rydjord felt it was adequate for most engines in stock-type racing classes. He pointed out that most Street Stock and entry-level race car engines have a stock, or possibly rebuilt, bottom end. Usually, the bearing clearances are stock. Therefore, even to 7,000 rpm, a stock pump has sufficient volume and pressure to supply oil to the engine.

Rydjord also offered his exception to an old adage. "The rule of 10 psi oil pressure for every 1,000 rpm is not really necessary. At one time, given tooling and manufacturing of the day, this may have been necessary. Today, while safe, it is overkill. Winston Cup engines live with only 50 pounds of oil pressure at 9,000 rpm."

To illustrate the extreme of reducing oil pressure, Rydjord related a story of a Pro Stock drag racer (upward of 1,200 hp) who, when needing a few more hundredths for a tight race, adjusted the dry sump oil pump to run with less than 40 pounds of pressure for the last half of the quarter. The less work the pump had to do, the more power went to the rear wheels. Subsequent teardowns revealed no damage to the bearings. This is not meant to imply one should arbitrarily reduce oil pressure, but to show that oil pressure by itself is not the end of the story.

High-Pressure pumps

Our discussion then moved to high-pressure pumps. These are really stock-volume pumps with a stronger spring backing up the pressure relief valve. This means that an oil pump must raise its pressure to a higher level before the relief valve opens and dumps oil back into the pan. If this extra pressure is not needed, then the engine is using horsepower to pump oil to a peak pressure that is unnecessary--thus resulting in less power to the wheels. An additional loss is that windmilling the unneeded oil back into the pan aerates the oil and raises its temperature. A higher oil temperature can also affect the engine by raising the water temperature.

Rydjord pointed out that the use of a high-pressure pump would not affect the idle oil pressure. It would only show up at an rpm where the pump capacity overcomes the pressure relief valve. He said that although each engine might be different, the relief valve would probably start to open around the oil volume that could be used at 3,500 engine rpm. So, consider that too much oil pressure wastes horsepower.

I asked Osterhaus about using high-volume pumps in stock level racing engines. He responded, "The stock pump can take care of the bearings on most stock or near-stock engines. There are two good instances where a high-volume pump should be used. In a case where the bearing clearances have been opened up, allowing more oil to flow through, the higher-volume [pump] would be a benefit. This situation is not as prevalent now as in the past. Most engine builders seem to tighten up the bearing clearances now. The other situation is when an oil cooler, or some other restriction, is added to the oil system. Then, additional flow is needed."

In my experience, I use a high-volume oil pump whenever I use an oil accumulator. The high-volume pump can refill the accumulator faster while still having enough capacity to supply oil to the engine. In case you haven't heard me say it before, I think an oil accumulator should always be used on a circle track race engine with a stock pan.

Use A Big-Block Pump?

Osterhaus and I had spoken before about the use of a big-block Chevy oil pump on a small-block engine. My long-held opinion was that the big-block pump was costly overkill. I had thought it pumped too much oil, therefore heating up the oil, and was thus unnecessary on a stock-type engine.

Osterhaus pointed out that the smallblock Chevy pump had 7 teeth on each of its gears, whereas the big-block unit had 12 teeth per gear. It was his opinion that the greater number of teeth of the big-block pump would smooth out the flow impulses of the pump. He noted these larger impulses from fewer teeth (of the stock, small-block pump) could affect the Chevy distributor because they are on the same drive. The impulses from the pump could randomly affect timing (creating spark scatter) to any given cylinder by a small degree.

But Rydjord noted, "I've never heard any specific complaints about these impulses affecting the ignition. But, yes, there would be a difference in the severity of the impulses between 7 and 12 impulses per camshaft revolution (half crank speed). I really don't know how much difference it might make."

When asked about the capacity of the Chevy big-block pump, Rydjord said, "The standard Chevy big-block pump has about 10 percent more volume than the small-block pump."

Lastly, I for their opinions on how far the pump pickup should be above the floor of the pan. Both stressed the proper space to be no less than 3/8 inch to keep enough flow, to no more than ½ inch to prevent uncovering while cornering.

Stock Conclusions

Stock oil pumps, in new or good condition, are adequate for many lower division race engines. Use a high-volume pump when an oil cooler or an oil accumulator are plumbed into the oil system. High-pressure pumps can overwork the oil and cost power. The Chevy big-block pump may be a good alternative. Keep the oil pickup screen 3/8-½ inch off the bottom of a stock pan.