After changing four oil pumps...
After changing four oil pumps in one day, we really have to thank the unsung Chevy engineer who first developed the one-piece oil pan gasket. The Dart SHP, one-piece rear main seal engine and Fel-Pro gasket made these pan swaps much less painful.
While everybody knows what the oil pump's job is and why it's there, few enthusiasts consider the lowly bubbler as a possible engine tuning resource. We've come to appreciate that it takes power to pump that oil, and as lubricants have improved over the last 10 years, we needed to know more about pressure, volume, and viscosity. Westech's Steve Brule proposed a flogging of four Milodon small-block Chevy oil pumps on a 372ci small-block Chevy. While somewhat mild, this small-block cranked out nearly 500 hp through two grueling dyno days of constant flogging with never a whimper. Even more impressive was the small-block's excellent consistency. If you're looking for a rock-solid small-block crate engine, the SHP is an excellent choice.
What we learned was that while there are not huge differences in terms of power, there are areas where small improvements can be realized with a careful approach to the combination of pressure, volume, and oil viscosity. Our tests showed us that big-volume, high-pressure pumps of years past may not be the hot ticket for all street engines. If after you read this story it suggests that 80- to 90-psi oil pressures that backyard engine builders used to brag about are now about as useful as last month's pine tree air freshener, then we've done our job.
The Dart SHP short-block came...
The Dart SHP short-block came preassembled, which made bolting together the rest of the engine easy once Brule degreed the cam and verified the piston-to-valve clearance.
Our Test Mule
A small-block Chevy seemed the perfect engine for this oil flogging, so Westech assembled a great test engine that started out as a Dart Special High Performance (SHP) 372ci iron-block short-block assembly. Instead of using the typical 383 approach, Steve Brule at Westech selected a big-bore/shorter-stroke combo consisting of a 4.125-inch bore and a 3.48-inch stroke. The Dart SHP short-block came assembled with a set of flat-top hypereutectic pistons and a cast crank. On top of this, we added a set of Dart Pro 1, 200cc intake port aluminum heads and a Comp XR294 hydraulic roller camshaft. The baseline testing on this engine pushed the peak torque up to almost 450 lb-ft at 5,100 rpm and peak horsepower to around 477.
Oil Pump Test
With the engine ready to go, Westech fitted the dyno with an extremely accurate oil flow meter that was located in line with a relocated K&N oil filter. We first compared flow rates with and without the K&N oil filter to determine what kind of restriction it represented. The flow changed an average of 0.2 gallon per minute with straight Lucas 30W oil, or slightly more than 3 percent, which we felt was not going to affect our testing. This first test also established the procedure where each test started within 1 degree of the same oil and water temperature every time to maintain testing accuracy, since oil and water temperature have a big impact on engine performance. Brule also wanted to ensure that ignition timing would not change with all the different pumps, so the distributor was never moved. This required Brule to snuggle up to a hot engine while dodging the Lucas equivalent of a 30W rainstorm.
We tested four different Milodon...
We tested four different Milodon small-block oil pumps, from a stone-stock piece to a high-pressure, high-volume Rat motor unit. The two largest-volume pumps also employed larger 3/4-inch-diameter pickup tubes with 5/8-inch tubes for the smaller pumps.
Once Brule waded through all four pumps, the results followed a somewhat predictable path. Most surprising, however, was the performance of the stock pump. The plain Jane version not only high-fived the horsepower race but also (to no one's surprise) achieved the lowest pressure. The stock pump's pressure curve was also the opposite of the rest of the high-volume pumps. Given more time, it would have been interesting to modify this pump by adding a small washer to the pressure-relief spring, which may have improved the pressure curve slightly without compromising power. Another surprising result was that the big-block pump was not the big power loser we had predicted. The Rat pump did produce the highest average pressure but managed to require slightly less horsepower compared with the high-volume small-block pump.
It's also normal to see that as oil pressure increases, volume decreases. But in this case, the pump size changed. The variable between the stock, high-volume small-block and big-block pumps is we were testing increasingly larger pumps. It might also be suggested that the larger big-block pump with its greater number of gear teeth might create a more stable pressure curve that increases flow without having to work nearly as hard. This would minimize the temperature rise. The greater number of pump teeth would also help stabilize pressure. We also considered reducing the pressure on a big-block pump to see if that might improve its performance, and what would happen if we combined those changes with a less viscous oil like the 5W-20. As usual, it seems our test created almost as many questions as it answered. We didn't really expect to see major power differences, but it was surprising to see how well the big-block pump performed compared with its small-block brethren.