Horsepower. It is a simple recipe. It takes air, fuel and heat to create heat energy. That is then transferred into mechanical power through the piston, rod and crank. From there, it can be handled many different ways to put the horsepower to use.
We have covered many installs on injector upgrades, dual CP3s, bigger turbos, fuel systems-just about all of the bolt-on components that can help you increase the horsepower and torque of your engine. Over the course of the next year or so, we will be building engines and explaining how to build the power, what it takes and why we choose the components that we do.
One of the key elements in building power is understanding how to make it all work together harmoniously and efficiently. When it comes to an engine, the camshaft plays probably the biggest role in that. Now don't get me wrong. If the other components aren't paired right, it won't work either. But you can have all of the right components and still not be able to make the power because it cannot get into or out of the combustion chamber.
Knowing that we are about to embark on some serious horsepower buildups, we took a few moments to sit down with one of the lesser known, but better cam manufacturers in the diesel industry, Zach Hamilton of Hamilton Cams.
Hamilton Cams has been slowly building a reputation for increasing low-end power and reducing smoke while not losing the top-end power in Cummins engines. Their latest camshafts are the results of hundreds of hours of testing different grinds and trying different things to achieve the best results they can.
Before we get into types of cams and what to look for, let's start with the basics.
TERMS
Lobe Lift: Lobe lift, measured in thousandths of an inch, is the amount the lifter is being pushed up by the cam. Solid lifters relay this amount of lift up through the push rods minus the valve lash. A hydraulic lifter relies on oil pressure to fill and therefore, the lift isn't always the same amount being transferred up to the push rod.
Duration: Duration is how many crankshaft degrees the valve is held open. This can be measured a couple of different ways. Most manufacturers today start the duration when the valve has been opened at .050 of an inch. Advertised duration is measured when the valve is just opening at around .006 of an inch, which can be quite deceiving when valve lash and other play is taken into account. When comparing cams, make sure you check this measurement and make sure both cams are referencing the same points.
Ramp Rate: This isn't an industry term used to sell cams, but you will hear cam manufacturers refer to their cams as having a high ramp rate. Ramp rate is in reference to the time it takes the lobe to start opening the valve to when it reaches its maximum lift point.
Lobe: Lobe is the part of the cam that the lifter rides on. The lobe is the profile of the cam. There is one lobe per lifter (not necessarily one per valve).
Lobe Separation Angle (LSA): LSA is a measure of the angle between the centerlines of the lift lobes from the center of the cam. LSA is predetermined by the duration of the cam and isn't generally discussed when looking or comparing cam profiles.
Overlap: Overlap is the amount of degrees that the intake and exhaust valves are open together.
THE 4 CYCLES
Intake Stroke: The piston is moving downward, pulling in fresh air.
Compression Stroke: The piston is moving upward, compressing the air. How the fuel timing is set will determine when the fuel is injected, but it is injected before the piston has reached the top of this stroke.
Power Stroke: The air and fuel that have been compressed are now on fire and pushing the piston down.
Exhaust Stroke: After the air and fuel have been burned, the piston moves upward to push the exhaust gases out of the cylinder.
CAM TIMING TERMS
These may seem confusing, but remember that the cam only goes around once per two crank rotations. So, the 4 cycles are taken into account with one rotation of the cam.
TDC: Top Dead Center. This is the furthest point upward the piston will travel.
BDC: Bottom Dead Center. This is the furthest point downward the piston will travel.
TDCC: Top Dead Center Compression Stroke. This is the furthest point upward the piston will travel on the compression stroke.
TDCE: Top Dead Center Exhaust Stroke. This is the furthest point downward the piston will travel during the exhaust stroke.
BTDCE: Before Top Dead Center Exhaust Stroke. This is in reference to an event during the exhaust stroke before the piston has reached the top. This is usually in reference to when the intake valve starts opening.
ATDCC: After Top Dead Center Compression Stroke. This is in reference to an event that happens during the power stroke, usually in reference to when the exhaust valve opens.
Generally the exhaust valve starts opening before the end of the power stroke between 110 to 135 degrees (ATDCC). The power stroke ends at 180 degrees ATDCC. Opening the valve early helps remove most of the exhaust out of the cylinder and also uses some of the heat energy from the flame to help spool the turbocharger. Higher rpm engines will open the exhaust valve earlier, while lower rpm engines open it later.
If you have ever stood next to a truck that has sputtering in idle, that is generally caused from the exhaust valve opening early during the power stoke. The sound you hear is the actual sound of the combustion bursting into the exhaust manifolds.
With today's current emission laws, the valves are opening later to help promote a more complete burn and cool the exhaust gas temperatures before they are released into the exhaust manifolds.
On the intake side of things, the intake valve starts to open during the exhaust stroke around 10 to 15 degrees (BTDCE). This is to help create a low-pressure area in the combustion chamber which helps draw in the fresh air (referred to as cylinder scavenging). Pistons that need to be fly cut are cut to allow the valve to open more during this event.
Since both the intake and exhaust valves are open, this is called valve overlap. How long the valves are open will depend on how much overlap the cam has. On street cams, the exhaust valves almost always close at or close to 0 TDCE, so the overlap is usually a measure of how early the intake opens, not necessarily how long the exhaust valve is left open. "We watch this very carefully," Hamilton said. "If the exhaust back pressure is higher than the boost pressure, what is actually happening is the exhaust gases are pushed into the intake, which is never a good thing."
The intake valve stays open through the entire intake stroke and into the compression stroke. The engine setup will determine when the intake valve actually closes-which is measured in degrees before TDCC. Cams cut for high revving engines will keep the valves open longer to adequately fill the cylinder at high rpm. At low rpm this can bleed off valuable cylinder pressure, pushing it back into the intake. If the intake valves stay open a considerable amount of time while the piston is on its upward travel, the engine might bleed off too much cylinder pressure and have a hard time starting. This, combined with already-low compression engines, make ether a common sight at sled pulls. Remember, diesel engines are compression ignition, not spark ignition. These engines generally have a rough idle and will not smooth out until they start revving up. Tractor-pulling engines are a great example of engines that keep the intake valves open for a long time. They are very hard to start and require a very high idle to smooth out.
So what should you look for when looking for a cam? Well, it depends on what you plan to use your truck for.
Towing cams generally have an intake valve duration of 170 to 175 degrees of lift at .050 and the exhaust will be around 206 to 210 degrees. These are usually displayed like Intake 170@.050; Exhaust 206@.050 or 170/206.
Performance street cams will have a duration of 175 to 195 degrees of lift at .050 and around 210 to 220 degrees for the exhaust. Intake 175@.050; Exhaust 210@.050 or 175/210.
High rpm cams (usually P-pump engines) will have a duration of 200 to 230 degrees of lift at .050 and the exhaust will be around 220 to 250 degrees. Intake 200@.050; Exhaust 220@.050 or 200/220.
The amount of lift should be determined by how much the heads flow. Most cylinder heads start leveling off at a certain point of valve lift. That's the point at which the intake valve isn't a restriction and opening it further doesn't help much, if any. If a cylinder head has a port job, it might flow more at higher lift. In this instance a custom high-lift cam could be very beneficial.
The duration of the cam plays a huge role in the efficiency of the engine at a given rpm range. The above durations are only guidelines (good ones provided by Hamilton Cams), but the engine builder should discuss the exact engine specs with the camshaft manufacturer to be sure to get the right one.
SOURCES:
Hamilton Cams
www.HamiltonCams.com
512-804-9015