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Rockers, cams, and their effect on power

As such, 1.9 rockers are generally prefered for the highest power increases. Other ratios such as 1.8 are best mixed with higher ratios on naturally aspirated engines, and 1.7 ratio rockers are perfect for vehicles that already have a mild cam and headwork and are looking for a bit more power.

You've no doubt heard people mention what cam they're running or what ratio rockers they might have and wondered to yourself just what those items did and how replacing them helped the engine make more power.  We're here to explain in a very basic, very non-scientific way.  If you're new to engines this will help you understand how these components tie into your overall setup.

Q. How do high lift rockers/aftermarket cams make more power?

A. To understand this, one must first understand that an engine is basically a large air pump. The more air you can get in and then out, the more power you make. This is why devices like superchargers (get more air in) and headers (get more air out) make such a large impact on horsepower levels.

Let's look at a side cut-a-way of a "V" overhead valve style engine like the 3800.


You can see the cam is situated in the center of the block. The cam has lobes on it which open and close the valves as the cam rotates. The lobes accomplish this by pushing upwards on the pushrods which then act upon the rocker to open the valve.

Remember, to increase power we want to increase the amount of air going through the engine. To do this we can hold the intake and exhaust valves open longer and we can also open them further. There are two ways to accomplish this:

High Lift Cams - Simply installing a different cam with higher lobes will result in more lift (the distance the valve travels). A cam can also change duration (how long it takes the valve to open and then close) as well as several other variables. For the sake of simplicity we're going to keep this article simple.

High Lift Rockers - You can also get more lift by switching your rockers. The rockers are a basic fulcrum setup so moving your pushrod closer to the center of the rocker will result in less lift while moving your pushrod further from the center of the rocker will result in more lift.

Rocker lift is measured in ratio. Most stock 3800 rockers are 1.6 or 1.66 ratio. This means that the rocker tip moves 1.6 times as far as it's pushrod tip. So on a .250 lift cam lobe the valve lift is actually .400" for a 1.6 ratio rocker, .425" for a 1.7, .450" for a 1.8, and .475 for a 1.9. So you can see the jump from stock to 1.9:1 ratio is significant.