1.3 ratio rocker ?????

[David wulf]

I'am building a hemi predator with RTC 6 head , it's getting a dyno 308 cam . With this cam and rockers what would my lift be . I have no idea how to figure it out .
Next ?? Will this be too much lift for this set up ?
Next ?? I'am also building a red clone with a black mamba and champion rockers, would I be better off using the 1.3 's in my clone mamba combo ? And putting the champions in my brothers predator with the 308 dyno .

 

[ole4]

If the Dyno 308 is really .308 lift then with true 1.3's you would be right at .400 lift. You would probably have to lower valve spring pockets to prevent coil bind and would need some stiff springs. I don't know what the dual spring setup stock coil binds at, have to go look at my spring chart in the shop. Also valve to piston clearance would have to be checked. black mamba with 1.3's works fine I use that setup on a few engines with 26lb springs and it's good for at least 7500 but I do check seat pressure and make sure I have 25 to 26 lbs of seat pressure with some thin shims when I assemble the head.

 

[SnakePliscan]

Whats rocker ratio anyways?

Cam lift x rocker ratio. so 0.308 x 1.3 = 0.4004
Rocker ratio is measured on ether side of the fulcrum (stud), if their the same its 1:1 make the push rod side 1/2 the valve side and youve got 2:1 ie the valve side moves twice as far as the push rod side. make the p/r side 0.769 and the v/v side 1.00 and youve got 1.3 to 1 ie. 0.769 x 1.3 = 1
That relationship applys to the rockers motion aswell, call it a motion multiplier.
In engineering a rocker is a 1st class lever, it can have underdrive and overdrive depending were the fulcrum is located other than the middle. in a motor its a overdrive deal. some overhead cam engines put the fulcrum at one end of the rocker the cam to one side of the middle and the valve at the other end thats a 3rd class overdrive lever, same as a broom that you sweep the floor with. (2nd class lever if your wondering is a wheelbarrow, the wheel is the fulcrum.)
High ratio rockers are nice because you can snap a valve open way faster and put more area under the curve at high rpm than any profile you can grind into a cam lobe alone.