Benefits of High Ratio Roller Rockers
Many TR6 owners are looking for a way to increase the horsepower output of their engine without sacrificing “street”-ability and reliability. Modifications such as compression increase, mild porting of the head, special valve grinds and installation of exhaust headers are a good start but to go beyond this the valve operating characteristics will need to be changed. Two factors that affect this are the shape of the camshaft lobe and the rocker arm ratio. Many people install a high performance cam but overlook the benefits of increasing the rocker ratio.
Choosing the right cam can be a difficult task. Valve duration must be kept within certain limits to maintain enough torque for street use. The object then, is to flow as much air as possible in the limited amount of time that the valve is open. To do this the valve must be opened and closed as quickly as possible allowing it to remain open wider for a longer period of time. The rate of speed at which the valve operates is measured in rate of acceleration and peak velocity. These values will vary from one cam profile to another but will always be within a specific limit to work with the stock diameter lifters. A very slight increase in these values will result in a considerable increase in performance. An effective way to increase the acceleration and velocity at the valve is to increase the rocker ratio. Increasing from the stock 1.46:1 ratio to a 1.65:1 ratio will result in a 13% increase in acceleration and velocity of the valve as well as a 13% increase in valve lift. This can result in a horsepower increase of up to 10% in a stock engine.
A more obvious benefit of installing roller rockers is that of reduced friction and wear. The stock rockers slide over the end of the valve stem putting a considerable amount of side pressure on the stem. This creates friction and wears the stem and guide. A roller rocker has a small roller that rolls over the end of the valve stem. This virtually eliminates side load on the stem and greatly reduces wear.
Another area of high friction and wear is between the rocker arm and rocker shaft. This is a problem area in the TR6 engine. Every used stock rocker assembly that I have inspected has shown considerable wear and galling of the shaft and rockers. Roller rockers with needle bearings installed on a new hard shaft will eliminate this problem. Reducing friction in these areas will also increase the horsepower output of the engine.
In summary, by reducing friction and increasing airflow, high ratio roller rockers will increase horsepower by as much as 10% without sacrificing streetability. For the best results choose a cam with the right duration for your type of driving, the maximum allowed lifter velocity, and conservative lift, then install high ratio roller rockers to increase the velocity and lift.