Originally Posted by bonny99
Would raising the rocker ratio on a 1974 350 produce any horsepower gains?
Probably a little....considering what the base power output of a low compression smog motor is, don't expect much. (gains are always a percentage of the motors current output...which in 74 wasn't much at all.)
All a larger ratio rocker does is extend the cam a little and open the valve a little deeper into the heads. If the intakes and heads can actually flow any more is a different story.
Instead of putting money into just rockers, consider a new camshaft and heads. Bumping the compression up a little, or a better pair of heads will go a lot further towards upping the power output instead of just a set of rockers.
Before you get too far into this, measure the cam you have now. (degree wheel, dial gauge, and paper & pencil) This can tell you the lift and duration of the cam in the motor, which you can use to translate what the rocker change would bring.
Example, let say you have a mild grind (like a 248 grind) that has lobe lift of 0.2667 for a duration of 192 degrees...your typical stock emmissions grind. With 1.5 rockers, that works out to a valve lift of 0.4000". Change to a 1.6 Rocker, that will change you valve lift to 0.4267" and maybe added 2 degrees of useful duration. *YAWN*...that'* maybe worth 2 hp. And you spent about $70 bucks to get it.
Do a cam swap to a mild performance cam for about $160 and get a brand name cam that produces 0.450" of lift with 1.5 rocker and a 210 degree duration. Now you might extract another 15 to 20 hp out of the motor...more if you heads and intakes are up to the task of flowing the extra air. See what I mean, the cost per hp is cheaper going with switching cams vs. playing games with rocker ratios.