We’ve discussed oiling systems a bit lately, encompassing both wet and dry-sump variants. While talking about them is great and all, many of you are visual creatures, and you want to actually see the results of switching from a wet sump to a dry sump. While it’s hard to show you what’s actually going on in a running engine that is pulling significant positive and negative Gs at high-RPM. One thing we can show you is dyno graphs.
Ben Strader at EFI University has a knack for explaining advanced concepts in an easy-to-understand manner. So when he tackles a subject that can be as complicated as a dry-sump oiling system, we tend to listen. It’s no secret that all it takes is a relatively small hiccup in the oiling system to turn your engine — whether it’s mostly stock or completely custom — into an expensive paperweight.
We all know that oil is the engine’s lifeblood. But for as important of a role as it plays, the oiling system tends to get very little attention from the average enthusiast. Thankfully, EFI University likes to test things on the dyno and get real-world results on things that a lot of people just guess at.
“We got to wondering, what’s the real difference between a wet sump and a dry-sump oiling system,” says Strader. “First we have to start out with explaining what the physical differences between the two systems are.”
“When your engine gets oil to lubricate all the parts, most of it makes its way up to the top of the engine and drains back down into the pan by gravity,” Strader explains. That part is very similar between the two systems, as a dry sump doesn’t alter the oil flow path within the engine itself.
The Wet Sump
As we have discussed previously, the reason a wet sump is called a “wet sump” is that all of the engine’s oil not currently being used by the engine is contained in the oil pan. The pickup tube is for the oil is submerged in oil held in the sump, hence the “wet sump” name.
“A disadvantage to the wet-sump system can be found in the oil pump itself,” says Strader. “Looking at a standard gerotor pump like you’d find on an LS, it’s a crankshaft-driven pump. It’s a nice design because it keeps the oil pump nice and compact, while still being able to move a lot of oil in a short amount of time. The downside comes when you start building high-performance engines; high engine speeds can cause the pump to move too much oil”
While on the surface, moving too much oil through the engine might not seem like such a bad thing, however, it can be. “While the pump has an internal pressure relief valve to prevent too much oil pressure in the engine, but at high-RPM, that becomes a problem,” Strader says.
“First of all, we’re doing work that we aren’t getting any benefit from. Secondly, [pushing large amounts of oil through the pressure bypass on the pump] tends to aerate the oil by recirculating it constantly. We really want to avoid that on a high-RPM engine.”
One of the other weaknesses of a wet-sump system appears in high-G situations, be it acceleration, deceleration, or cornering. “If you uncover that pickup, you’re going to suck air into the system, and air doesn’t exactly lubricate the system well,” says Strader.
The Dry Sump
“A dry-sump oil pan differs dramatically from a stock wet-sump oil pan,” Strader starts out. “Basically, what’s happening here, is that we take the engine’s oil supply — which was held in the pan of the wet-sump system — and we’re going to take it off-site and store it externally in a tank.”
In addition to external oil storage, a dry-sump system also uses an external oil pump. “The pump is driven by a belt from the crankshaft. One of the first advantages of that, is we can now control the pump’s speed,” explains Strader. “We can speed it up or slow it down by changing the size of the pulleys. The stock oil pump was driven directly off the crankshaft, it was always turning the same speed as the crank.”
Strader points out that the next difference between the two styles of pan is the difference in volume, with the dry-sump pan holding almost zero oil. “The instant the oil comes out of the engine and hits the oil pan, it’s scavenged by the oil pump and placed into the off-site reservoir,” Strader says. “That keeps all the oil from splashing around and keeps us from having to use a windage tray and creates a great advantage.”
In addition to the efficient handling of the oil, the dry-sump system is also providing the benefit of pulling a vacuum in the crankcase itself. “A lot of people forget, that if we’re moving 400 cubic-inches of air through the engine, we’re displacing that same amount of air in the crankcase. That pumping loss takes work, and costs us horsepower,” says Strader.
“Because the pump is evacuating that pan, and the air in the crankcase, it reduces the pumping loss and increases the power available to the crankshaft to send to the tires. Secondly, by creating a vacuum behind the rings, it increases the pressure differential between the combustion side and non-combustion side, creating better ring seal.”
On The Dyno
Theories are great and all, but Strader has built his brand not on just theories, but on putting those theories to the test. For this test, he uses a standard LS3 engine, with a few aftermarket goodies, like a stroker crank to make 416 cubic-inches. The first test was to run the engine on the dyno with a completely stock wet-sump oiling system.
After that, Strader removed the factory wet-sump system and replaced it with the Dailey Engineering five-stage dry-sump system (without even pulling the engine off the dyno), and then ran the engine on the dyno again, with zero other changes to the engine. “There were no tuning changes, no differences in fueling or spark or anything like that,” says Strader. “We just wanted to see if there was a power benefit to the dry-sump system.”
After compiling the data from the two dyno sessions, there was a distinct trend seen on the data. “It’s pretty interesting in that with zero changes, the engine made more power from the beginning to the end of the run,” reveals Strader. “From 3,000 rpm to 6,000 rpm, on average, the engine made 17 lb-ft more torque and 14 horsepower more… Everywhere. Some places made more than that, some made a little less, but there was an increase everywhere.”
In addition to power, Strader also recorded crankcase pressure on the dyno pulls to be able to illustrate how hard the scavenge pumps are working. “We had no pan vacuum with the wet-sump system all the way across [the RPM range],” says Strader. “With the dry-sump, we had about 6.5 inches of vacuum at 3,000 rpm, and by the time we got to 6,000 rpm, we had almost 10 inches of crankcase vacuum in the engine. That improves the ring seal and helps with the windage, and that’s where that extra power came from.”