Piston Ring Sealing: The Chi Of Free Horsepower

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Here’s how to free up more horsepower in your engine by finding balance
By Jeff Huneycutt

Honestly, we don’t know much about chi, crystals or any other new-age hokum. But we do know to shut up and listen when the horsepower experts talk. And lately, Driven Racing Oil’sTM Lake Speed Jr. has been talking about how to free up more horsepower by finding “balance” when you build your next engine.

And no, he’s not talking about yoga or meditation–although we’ve heard that’s good for you–instead, he means finding the right combination of parts and preparation to properly seal the combustion chamber floor. When most people think of the combustion chamber in a running engine, they picture the cylinder head and maybe the valves. But that is only the top of the chamber. The chamber floor consists of the top of the piston and the rings. It’s the piston rings which keep combustion pressure from squeezing down the side of the piston between the skirt and the cylinder walls, and the more efficient the rings are at keeping the rapidly expanding combustion gases from escaping the chamber, the more power your engine will make.

It’s a mistake, however, to think that the piston rings do all this by themselves. The rings depend on motor oil splashed up onto the cylinder walls by the rotating crankshaft to provide lubrication where the ring contacts the cylinder wall. Without proper lubrication, friction between the ring and the cylinder wall will cause irreparable damage within a matter of minutes. But the oil also provides a secondary benefit: It actually helps seal any small gaps between the edge of the ring and the cylinder wall, decreasing blow-by and improving horsepower. The oil, in turn, depends on the engine machinist to properly prepare the cylinder bores by honing a series of tiny grooves into the cylinder wall in a crosshatch pattern. It’s this pattern of grooves that actually helps trap a small film of oil so that the cylinder wall isn’t wiped dry every time the piston rings slide past.

“At Driven Racing Oil, we have great relationships with a lot of the top engine builders,” Speed says, “but we also work very closely with some of the top manufacturers such as Total Seal Rings and Sunnen. And by learning from each other, it helps us all understand what is necessary to help an engine make as much power possible while still maintaining great dependability. What is very clear is that the system that seals the combustion chamber from the cylinder is dependent upon several factors. In other words, the piston ring isn’t doing it all by itself, and the oil definitely isn’t doing it all by itself, either. You have to have a balanced system where the rings, the motor oil, and the cylinder wall preparation are all designed to work together.”

Lake points out that what may have worked in the good old days will likely leave you eating your competitors’ dust today. Ten years ago a set of high-tension rings 0.043 of an inch thick for the first and second ring were standard fare, and so was heavy motor oil. Today, low tension rings only seven millimeters thick are quite popular, but if you are running the same oil you were 10 years ago you are robbing those new piston rings of some of their potential performance. Performance oil technology has advanced just like hard parts. It goes back to that balance Speed talks about. And if your engine isn’t balanced you are losing out on either power or durability.

“The old school 0.043 piston ring has a lot of tension, or pressure, against the cylinder wall,” Speed explains. “So you need a thicker oil to keep the piston ring from scraping all the oil off the cylinder wall. But with the newer seven-millimeter ring, you don’t have as much tension, so if you keep that same oil, all you are doing is making it more difficult for the piston and ring to move up and down the cylinder bore, costing you horsepower. Modern oils with better resistance to heat and improved lubrication qualities like those in Driven’s lineup allow you to run lighter-weight oil than ever before while also improving protection.

piston rings“The same thing is true for the other corners of our triangle,” he adds. “For example, you can try to cut some internal friction by making the cylinder walls smoother by taking away the depth of the grooves in the crosshatch. But if the cylinder bore is super smooth and flat and you don’t leave any valleys in there, you are going to have to use a thicker oil. It has to be more ‘clingy’ than normal, otherwise you won’t have enough oil remaining in the upper cylinder bore region to maintain good ring seal. Because you’ve gotten rid of the valleys in the crosshatch, there isn’t any place for the oil to hang on to, so now you have to raise the viscosity to make up for it. But increasing the viscosity raises the internal resistance in the engine. Not only is it tougher for the rings to move through that film of oil in the cylinder bore, but it also makes it more difficult for the oil pump to push the oil through the engine. So the result of trying to create super-smooth cylinder walls to cut friction can actually raise friction in other ways throughout the engine and wind up costing you horsepower.”

CYL FINISH_1It turns out that the right combination of cylinder bore crosshatch and lightweight oil is even better for ring life than a smooth cylinder bore and thicker motor oil–so you can have the best of both worlds. The key to a good cylinder hone –one that allows oil to cling to the cylinder bores without causing unnecessary friction with the piston rings– is to cut “valleys” without any “ridges.” A good engine machinist will use a series of honing stones to cut the crosshatch into the bore and then go back with a finer stone and knock down any ridges the rougher stones created.

The idea is to make the engine run as efficiently as possible. There is only a finite amount of power in a drop of gasoline, but no one has ever been able to turn all of that chemical energy into mechanical energy. In fact, in an internal combustion engine, most of the energy is lost to heat and friction. The good news is that plenty of power can be found simply by helping an engine work more efficiently.

“A good ring seal is efficiency,” Speed says. “The fuel will make the power, all we have to worry about is getting that power to spin the crankshaft and not blow it down into the crankcase.”

Going back to the old school 0.043-inch thick rings, Speed points out that the formula to get this to work in a 350 cubic inch V8 with a 6,000 rpm redline making 400 horsepower is relatively simple. In a motor running 10W-30 motor oil, it is pretty easy to get the rings to seal up and run without issue. But there’s also plenty of power being lost to heavy components and friction between the rings and the cylinder bore.

piston rings3“Now let’s take that same motor as a baseline and try to build a nine or ten thousand rpm race engine,” Speed adds. “Those 0.043 rings don’t work anymore because that’s too much mass we are trying to move up and down the cylinder. So the rings get smaller and lighter, and the piston has to lose mass too. That leaves less contact area between the rings and the piston’s ring lands to help hold those rings straight. The thinner ring also means there’s less area of contact between the outside edge of the ring and the cylinder wall. On the one hand that means less friction, but it also makes it harder to get a good seal.”

So you can see just a few of the challenges that come with trying to build a high horsepower engine. It’s a lot tougher to find that right balance of factors than it is with the 400 horsepower engine. If the 400 horsepower motor is walking down the sidewalk, finding the right balance for a 10,000 rpm race motor is walking a tightrope. Getting that extra power with the same displacement is possible by increasing the efficiency–race teams prove it every weekend–but because components have to move faster while weighing less and still maintaining the same cylinder sealing capabilities, the precision required ramps up as well. “Hey,” Speed adds, “it’s pretty hard to fall off the bottom of a mountain, but it’s awfully easy to fall off the top.”

And it’s not just the oil guy stressing the importance of finding the correct motor oil to match the rings and cylinder bore crosshatch. Keith Jones of Total Seal Piston Rings says proper oil selection is critical to helping the rings do their job.

“No matter how much you want it to be true, there is no single ring that’s the best for every situation,” he says. “Whenever I talk to a customer, my first questions are always, ‘What are you doing?’ and ‘What’s your application?’

Sunnen Engine Honing“Take, for example, a twin turbo application,” Jones adds. “On a performance engine like that you can have cylinder pressures of several thousand PSI. But you have to remember that the cylinder pressure is trying to get behind the ring and push it right through that thin boundary layer of oil on the cylinder wall. If we choose an oil that’s too thin, that cylinder pressure is going to push the rings right through that boundary layer of oil and the rings are going to fail in no time. Too thick and you are wasting energy and causing other problems. You have to consider the cylinder wall to be a bearing surface just like the main and rod bearings because the ring has to be able to ride along the cylinder walls on a film of oil. You wouldn’t put a zero-weight motor oil in a Top Fuel engine because you know the rod bearings are going to come crashing right through that film of oil and into the crankshaft’s rod journal. It’s the same thing with the piston ring.”

When you pull out all the stops, it is actually quite amazing how precise modern machining methods can be when preparing a new block. Top-flight engine builders for NASCAR Cup teams and other professional racing organizations use equipment that allows them to be incredibly precise. The result: once the engine is fired for the first time, there is practically zero break-in required. That’s why you may hear that Cup teams break in their engines using the same synthetic oil that they race with. But just because they do it, that’s doesn’t mean it is necessarily a good idea for you and your new engine.

00106The equipment required–including diamond honing stones–to prepare a block to the NASCAR Cup level is incredibly expensive and simply out of the budget for most of us real-world folk. Instead, by using a quality break-in oil, you can protect the engine while helping the rings to seat as quickly as possible. Essentially, during those first few minutes of operation the engine finishes the final bit of machine work that Cup teams spend so many thousands of dollars to do themselves. The trick is to use a motor oil during the break-in process that helps the engine to break in quickly (seat rings, mate tappets to camlobes, etc.) while also providing optimum protection during what is a very stressful time for engine components.

“A lot of guys think that break-in oil is just about protecting a flat tappet valve train,” Speed says. “But our break-in oil is also formulated chemically to help a new engine seat the rings quickly without doing any damage to either the rings or the cylinder walls so that the engine winds up at the same place as the big-money race engine. There’s a lot more to our break-in oil than simply throwing in a lot of zinc to protect a flat tappet camshaft.”

One specific application where engine builders can often improve ring seal–resulting in both more power and longer engine life–is methanol burning race engines. Methanol is an alcohol and doesn’t have the same lubricating qualities as gasoline. In fact, methanol can actually be corrosive to metal surfaces, making it a tricky fuel to work with.

As a way of protecting themselves, engine builders working with methanol will often add a “top lube” or “upper cylinder lubricant” to the fuel itself. The idea is to help keep the upper portion of the cylinder walls from being washed clean of oil by the methanol by actually adding lubricant into the fuel itself. But this can cause more problems than it solves, Speed says.

In past decades a top lube may have been necessary, but modern motor oil formulations are more resistant to methanol and capable of properly protecting a methanol-burning engine. In fact, use of a top lube can actually harm the motor oil.

CAST RING FACE“Top lube is usually just two-cycle oil or something very similar to it,” Speed explains. “Since it mixes with the fuel, it can’t have additives in it, and it doesn’t lubricate as well as a good motor oil. But some of it will get blown past the rings and into the crank case where it mixes with the motor oil. Then it dilutes the oil as well as the additives in the oil so that it can no longer do its job as well. We’ve worked with engine builders before who have blamed us because they were seeing a lot of sludge in the bottom of the oil pan during teardown. We tested the sludge trying to find the problem and discovered that the motor oil didn’t contain any of the stuff that was making up the sludge. It was the top lube getting into the crankcase and turning into the damaging sludge.”

Speed also points out that top lube can also actually hurt ring seal. As we discussed earlier, the most critical moments for establishing great ring seal is when the engine is first fired up. In order for the rings to properly seat, there must be some friction to help the rings mate to the cylinder walls. That’s why a good break-in oil is designed to properly protect an engine while it breaks in without being too slippery. Adding a top lube to the fuel throws off that delicate balance established by the break-in oil to potentially greatly increase the amount of time required to seat the rings. Often, if the rings don’t seat quickly, the seal will never be as good as it could be.

Carb-Defender-single bottle-Web“Your goal should always be to achieve maximum ring seal to make the engine as efficient as possible,” Speed explains. “So the best thing is not to use a top lube. If you are worried about corrosion from methanol, use Driven’s Carb Defender, which protects the fuel pump, carburetor or injectors without adding lubrication to the fuel. And then run a quality break-in oil which will protect the cylinder walls from scuffing and helps the engine finish the honing process so that the rings will seat very quickly. Don’t add any lubricity to the fuel or even the oil during the break-in process.”

The message we got from both Speed and Jones is that sometimes it can be tough to figure out exactly which oil–and ring package, for that matter–is right for your application from reading catalogs or the internet. But that doesn’t mean you are forced to rely on guesswork. The best manufacturers of both performance motor oil and engine components are constantly finding ways to improve engine efficiency and want to help you reap those benefits. So give them a call and get busy building your best engine yet.

 

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