Motorsport Plumbing Systems: Dry Sumps
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Dry Sumps
06.41
| 00:00 | When it comes to dry sumps, the oil plumbing varies dramatically from what we've just discussed in the previous module. |
| 00:06 | These, although used in some factory configurations, are used extensively in motorsport applications. |
| 00:13 | The advantages are substantial here, significantly increasing the oil capacity, providing consistent oil supply to the engine, and eliminating the risk of oil starvation at sustained high G forces, removing aeration that affects the oil's lubrication performance, and in some cases, a dry sump will allow the engine to sit lower in the vehicle, reducing the centre of gravity height. |
| 00:37 | In simple terms, a dry sump works by evacuating oil out of the engine, storing it in a remote reservoir, and then pumping it back through the engine. |
| 00:47 | Though there's a lot more to it than that which we'll cover soon. |
| 00:50 | First though, we need to understand that as the engine is actually drawn out of the crankcase, the crankshaft is no longer rotating in the oil storage as it does in a wet sump engine. |
| 01:01 | The advantage here is reducing what's referred to as windage losses, which is essentially resistance to the crankshaft rotation as it spins through the oil. |
| 01:10 | Removing this resistance with a dry sump system can result in modest power gains depending on the engine. |
| 01:17 | The other advantage of a dry sump system comes in reducing crankcase pressure, which in turn reduces the pressure differential across the piston rings, helping to prevent blow by where the oil makes its way past the rings and into the combustion chamber, lowering the combustion efficiency. |
| 01:35 | This can also allow us to reduce ring tension on the cylinder walls, lowering the friction force and further helping our power output. |
| 01:43 | The actual crankcase pressure, be it vacuum or positive pressure above atmospheric, will largely depend on the aspiration of the engine, being natural or forced, but we'll come back to this soon. |
| 01:55 | There's a fair bit more to the operation of a dry sump system that involves a range of different components, one of which is the plumbing. |
| 02:03 | So, let's cover that now. |
| 02:05 | Not all dry sumps are created equal, with the main differences being what's referred to as stages, which are essentially sections of the pump of which there could be anywhere between two and six. |
| 02:16 | In all variations, there will be a remote tank for storing the bulk of the oil and of course the pump which is usually driven mechanically by the engine rotation, either directly or off a drive belt. |
| 02:28 | The tank could include some form of plumbing to a drain point underneath the vehicle to help with oil changes as well. |
| 02:35 | The pump draws oil from the tank and supplies it to the engine through the pressure stage. |
| 02:40 | But before the oil gets to the engine, it'll pass through a remote inline filter and possibly also an oil cooler. |
| 02:47 | From here, oil will flow through the engine just like in a wet sump system and end up in the oil pan which itself will typically be a lower profile than a wet sump equivalent. |
| 02:58 | The oil will then be drawn out of the pan to pump through the scavenge lines, sometimes through scavenge filters in order to protect the pump in the case of an engine failure. |
| 03:08 | The number of these depends on the number of stages of the pump, but between two and four is typical, while there are often also scavenge lines for turbochargers. |
| 03:18 | It should be noted that some dry sump pumps designed for specific engines will have the pump integrated into the oil pan so the scavenge lines are part of the assembly and therefore don't need to be plumbed externally. |
| 03:31 | These dry sump kits are usually more expensive but save a little time and money as we don't need to make up scavenge lines. |
| 03:38 | Some pumps will have individual scavenge lines from the pump back to the tank, while others include a manifold on the pump that basically joins all the scavenge stages into one single line, substantially simplifying the plumbing. |
| 03:52 | All of these systems are going to have a pressure stage and some amount of scavenge stages, but the ventilation of the system is where we see the biggest differences. |
| 04:02 | As I mentioned briefly before, the type of induction, as in if the engine is naturally aspirated or boosted, will have a big impact on this. |
| 04:11 | Generally speaking, for wet sump, naturally aspirated engines, the crankcase pressure is just above atmospheric due to the small amount of cylinder pressure that will pass the piston rings during combustion. |
| 04:23 | And as we discussed, this pressure is vented out the valve cover. |
| 04:27 | For dry sump systems, the scavenging effect should be strong enough to create a vacuum in the crankcase, reducing the pressure relative to the cylinder, which can result in power gains if the piston rings are selected accordingly. |
| 04:41 | To achieve this though, the engine must be sealed, meaning no breathers in the valve cover. |
| 04:46 | Naturally, if we can't create a vacuum and the engine is sealed, this will be damaging and likely blow out the seals. |
| 04:54 | The ability to create this vacuum depends on the scavenging ability of the pump and the plumbing. |
| 05:00 | A vacuum regulator is also necessary on the scavenge lines to prevent the dry sump pump creating excessive crankcase vacuum if the throttle is released quickly at very high RPM. |
| 05:11 | Without the regulator, we could end up seeing issues like crank seals being sucked in. |
| 05:16 | The tank must be vented with breathers in this case, as this is where the extra pressure ends up. |
| 05:22 | But the tank should also be vented regardless to remove extra air pressure that is built up as the aeration is removed from the oil. |
| 05:30 | For low boost forced induction applications, this setup might also work as long as the scavenging effect can overcome the crankcase pressure, specifically at higher load and RPM where the blow by is most significant. |
| 05:44 | But for high boost applications, the crankcase pressure is almost always too great and will require ventilation even with a dry sump system. |
| 05:54 | The reason this is important for us of course is this all requires plumbing. |
| 05:58 | Before we dive deep into this plumbing, let's summarise. |
| 06:02 | Dry sump systems are very common in motorsport and these provide a range of advantages in both reliability and engine performance. |
| 06:10 | These systems can vary considerably in layout, but will involve a tank and a pump with a number of stages. |
| 06:17 | One of which will be the pressure in and out from the tank to the engine, usually through an oil filter and cooler. |
| 06:24 | Oil will be drawn from a relatively low profile oil pan through the scavenge stages of the pump and then returned to the tank. |
| 06:33 | Ventilation of the system needs to be considered along with the crankcase pressure. |
