Originally Posted by Bonhorst
I am thinking about getting some 1.6:1 roller rocker arms. The question i have is will they be compatible with the stock springs, and will the increased push rod angle cause the push rods to contact to pushrod holes. i will also be installing oem style roller lifters. also would i be better off just going with 1.6:1 lifters for the intake and leaving the exhaust at 1.5:1. here are the numbers for what i have in it right now. if i did the math right i think it should bring the intake lift to about .613
-Cast Pistons, (dished).
-Hydraulic flat tappet cam, (.383 intake / .401 exhaust) and a 112-degree lobe separation. (stock GM cam that comes in the crate motor)
-Cast Iron Cylinder heads with a 76cc combustion chamber. (Non vortec design)
You can't run OEM style roller lifters unless the block has provisions to mount the spider that holds the dog bones which align the lifters. The spider takes three bolt bosses cast in the center over the main oil galley (Chevy Small Block) others are similar but the oil galley may not be on the centerline. This also takes raised lifter bores as OEM lifters are about a half inch taller than flat tappets so the raised bores keep them steady and the oil relief inside their bores. The block for a roller cam is also different under the timing cover and cam gear is a thrust plate to keep the cam from engaging in front to rear movement which will quickly wipe out a roller lifter. This requires bosses in the block to accommodate drilled and tapped holes that hold the thrust plate in alignment to the cam centerline. This then drives a narrow cam gear and chain unique to the factory roller engines. The roller cam has a different shape lobe that is not compatible at all with a flat tappet lifters and vise-versa, the lifter type must match the cam type.
1.6 rockers increase lift and a term called Cam Intensity by about 6 percent over a 1.5 rocker. That's 1.06 times .383 or .401 which is .406 and .425. At .613, you didn't do the math correctly. Also, incase you were thinking it, the length of the lifter doesn't affect lift at the valve. A shorter pushrod is required to allow the valve to close when a longer lifter is used. The two things that control lift at the valve is the height of the lobe above the cam's base circle and the ratio of the rocker arm. Everything else in that chain just transfers motion, doesn't alter it.
Push rod length is one of the last things done. It is selected to achieve the proper sweep of the rocker on the valve stem tip. This will depend upon the cam lift, the rocker ratio, any changes to valve installed length as in a long stem valve or a deeply sunk seat, plus the actual build up height from the center of the cam to the rocker arm. Milling the heads, decking the block, messing with the head gasket thickness are some of the bigger things that affect the sweep. Go to the Comp site for a great description http://www.compcams.com/Technical/FA...inGeometry.asp