Originally Posted by bmwrench
You can tell the 308 from the 336 by looking at them, but I have to have them side by side. There's a noticeable difference. You can also check via the dial indicating method at the lifter. Measure full lift and multiply by 1.39 (the rocker ratio) You can also get an idea by when then the motor starts pulling hard. With a 308, the motor begins making good power at about 4500 RPM. With a 336, about 5500.
Cam specs are pre rocker arm ratio. Cam specs are cam specs. Valve timing specs are valve timing specs. Rocker arm ratios vary. I would measure lift at the adjuster side of the rocker arm. There is no ratio there although the radius of the arm is slightly altering your reading. It will still be close enough to know if you have a 308 or a 336. Despite many reports to the contrary I think because of one erroneous internet writeup by Tom somebody, 336's DO have more lift than a 308. I think it is a bit over 1mm.
336's offer a lot more midrange with a lot of setups. Big port heads like the original poster's engine has can be a midrange problem. IMO, 336, late model raised port floor small port heads, 44mm intakes on STOCK seats that have the room for 2mm diameter larger valves, and 38mm mikuni's or Dells will get you a lot more than stock midrange and WAY more top end. Dual plugging and raising the compression will only make it all even better from idle on up as long as you don't go too far, especially right off idle and up through the midrange. I am running a 336, stock 42mm intake, small port heads, stock 8.7:1 CR, and 38mm carbs. I have a lot more midrange than stock. Going from 32mm Bings to 38mm Dells helped my midrange by quite a bit. I think my 336 makes more power than a 308 from about 3000rpm on. At about 5200 to 6200 it kicks in to stage two is making considerably more and above 6200 it kicks into stage three and is making a world of difference.
I am typing all this just to counter all the 336 stuff I read that in my experience is just not true. I had to listen to a bunch of 336 horror stories while I installed mine at a well reputed dealership. ALL of them were BS.