A camshaft upgrade is an outstanding way to add some horsepower numbers to your dyno sheet and shave some numbers off of your ET, but going bigger isn’t always better in regards to camshafts. Understanding how lift and duration change flow and horsepower numbers will help you make an informed selectionus, and Russs Yoder from Erson Cams has joined us to explain the bare-bones basics of lift and duration.
The easiest way to explain camshaft lift is to think of it as how far the valve opens to its furthest point off of the valve seat. Camshaft duration can be simply explained as how long the valve stays open off of the valve seat. These two very simple movements are ultimately what establish how much horsepower can be made with a camshaft, and making adjustments to these two items will change a lot within an engine.
Yoder explains how the camshaft plays into this concept with a simple analogy.
“Camshafts are similar to your cell phone — they’re constantly updating the software to make them better, and a camshaft is the same thing, in a way. The bottom end of the engine is just a big air pump, so all it does is just move air around. The camshaft is the software controlling your valve moments, so if the valve timing and the amount the valves are open don’t match what the heads, valvetrain, or induction system like, the engine won’t make as much power as it should. Camshafts get updated like cell phones so they are smarter and make more power.”
If the camshaft is the brains of the operation, how do you make it wiser to your combination through lift and duration? When you look at how lift versus duration works, it becomes clear that there needs to be a proper balance between the two for the engine to function at its full potential. With today’s modern engine building technology, you don’t need to guess on numbers or just select a camshaft based on how well it works for someone else.
Knowing your flow numbers is important to getting the right camshaft lift. If you make any changes to the cylinder via porting, that needs to be considered when selecting a camshaft.
“Whether or not you have enough lift or too much lift depends on the airflow of your cylinder heads. It doesn’t do you any good to put a .700 lift camshaft in something that has a head that quits flowing air at .500 lift. The opposite applies if you only put a .500 lift cam in an engine with heads that flow more air — you’re leaving a lot on the table because you’re not getting the full potential of the engine,” Yoder says.
Getting the right duration needs to be approached slightly different, according to Yoder.
“Duration wise it’s more relevant to RPM range. The less duration the camshaft has, the more torque an engine will make; the higher the duration, the engine will make more top-end horsepower, but not as much torque. One of the reasons they don’t make as much torque is because when you’re increasing the duration timing, it increases overlap, and that basically decreases low RPM cylinder pressure. The only way to get that cylinder pressure back in the engine is to spin it to a higher RPM level. With higher durations, the valves are staying open longer, therefore they can pull more air in and make more power.”
Unless you’re a trained professional it might be a challenge to get the right lift and duration when you’re ordering a camshaft. Yoder shares how he goes about helping customers get the most effective camshaft for their engine package.
“When I talk to a customer, I ask if they have the flow numbers on their heads, have they ported them, and if they have been ported, do they have the flow numbers. The reason is that it’s critical information to help me get the best cam for them based on the application. Just knowing that information can help me ensure we’re maximizing what’s there to get all of the horsepower at our disposal.”
Getting the lift and duration right on a camshaft is what will take it from just sounding good to making solid horsepower, and taking the time to speak to a camshaft pro will make that process much easier and assist you in building a powerful engine for your application.