LilYellowZQ8
12-07-04, 09:02 PM
Written by Jedi Master.
What is there to gain by using aftermarket rocker arms?
The small-block Chevy engine used stamped-steel rocker arms since its inception. They are light, strong, reliable, and adjustable. If you dont plan on changing cams this offers a decent gain comparable to changing to and aftermarket cam though they wont be as good since durations are not being changed. The reduction in friction along with better ratio accuracy is the main thing these offer.
The stock rocker arm ratio is 1.50:1, meaning that the rocker arm multiplies the cam lobe lift by a 1.50 factor. Thus a cam with a 0.300 cam lobe lift has a valve lift of 0.450 inches. A 1.60:1 rocker will provide 0.480 inches of lift at the valve on the same cam. Still, switching over to 1.60 ratio rocker arms is a good and relatively inexpensive way to get some more power (10 - 15hp) from your engine. Using 1.60 ration rockers require using a pushrod .050 longer to keep the geometery the same as stock. Using 1.52's dont so this is also and option. Replacing the stock rocker arms with aftermarket 1.50 rockers will make a difference simply because they have tighter than stock tolerances in the manufacture of the parts. Typically, the stock 1.50 rockers will have less than the specified ratio, which means less valve lift with some valves getting .450, a few getting .420, and a few others getting .400. These diffences alone could cause a loss of power.
Be aware also, that you may have to enlarge the pushrod guide slots that are cast in the cylinder head with larger than 1.50 ratio rockers. The pushrod may hit the end of the slot because the pushrod seat on the rocker arm is moved closer to the stud in order to obtain the larger ratio. Naturally you will have to take the heads off to do so.
What is there to gain by using aftermarket rocker arms?
The small-block Chevy engine used stamped-steel rocker arms since its inception. They are light, strong, reliable, and adjustable. If you dont plan on changing cams this offers a decent gain comparable to changing to and aftermarket cam though they wont be as good since durations are not being changed. The reduction in friction along with better ratio accuracy is the main thing these offer.
The stock rocker arm ratio is 1.50:1, meaning that the rocker arm multiplies the cam lobe lift by a 1.50 factor. Thus a cam with a 0.300 cam lobe lift has a valve lift of 0.450 inches. A 1.60:1 rocker will provide 0.480 inches of lift at the valve on the same cam. Still, switching over to 1.60 ratio rocker arms is a good and relatively inexpensive way to get some more power (10 - 15hp) from your engine. Using 1.60 ration rockers require using a pushrod .050 longer to keep the geometery the same as stock. Using 1.52's dont so this is also and option. Replacing the stock rocker arms with aftermarket 1.50 rockers will make a difference simply because they have tighter than stock tolerances in the manufacture of the parts. Typically, the stock 1.50 rockers will have less than the specified ratio, which means less valve lift with some valves getting .450, a few getting .420, and a few others getting .400. These diffences alone could cause a loss of power.
Be aware also, that you may have to enlarge the pushrod guide slots that are cast in the cylinder head with larger than 1.50 ratio rockers. The pushrod may hit the end of the slot because the pushrod seat on the rocker arm is moved closer to the stud in order to obtain the larger ratio. Naturally you will have to take the heads off to do so.