Topic: Rocker Ratio

[vannyvtwin]

I was watching a video from Crane cams. He says you can increase the ratio of the rocker by increasing the length of the pushrod.

I'm having a hard time getting my head around this.

Maybe someone can help explain this a bit. I keep thinking this would just close up the lash and not be helpful...

[redline]

Rocker Arm Ratio is the length of the valve side of the rocker arm to the center (or pivot point) of the rocker arm divided by the length of the Cam or Pushrod side to the center of the rocker arm.

Dont see how increasing the length of the pushrod changes the fulcrum of the rocker? But hey, get that pushrod long enough, and you have constant overlap!

[fordman21]

As mentioned, the rocker arm ratio in itself is what it is, that can not be changed. But the total valve lift can be affected buy the pushrod length . It depends where the rocker arm travels in the arc, that will change the rocker lift ratio. The idea was right, but maybe not the best choice of words.
An example would be: two identical engines with 1.6:1 rocker ratios. One has an optimal pushrod length with perfect geometry acheiving maximum valve lift. The other engine has too long of a push rod making the rocker spend more time at the bottom of the arc going sideways on the valve tip(in a lower arc) rather then up and down in the arc like the other engine.

[slideways]

Hey Ryan, in a motor where you have to run stock rods and rockers is there any perfect length i can shoot for with a mic? I have a friend that worked up a jig to rank my rockers in order of valve lift so we can have the most aggressive ones on there and still be legal. Now i'm wondering if i can shave the pushrods or hand pick the longest to get what i want.

Thanks

[fordman21]

Sure, they are probably all very close but you can choose the best push rods to get what you need. You will have to put a dial indicator on there and see what is the best, then try to find more like it. On the vanny you can probably tune the length by drilling the push rod seat in deeper on the lifter if need be, or the rocker boss height on the head can be slightly milled down. You will have to do some playing. Also the length of the tip of the valves above the keepers can be altered to give you what you need as well.
On the vanny's when you get milling the heads and changing the base circles on the cams it gets everything out of wack. I used to have longer stem valves and raise the springs and use different pushrods to correct everything on my engines, it was worth the effort and noticable on the top end. Not to mention that it cut down on a lot of wear. I had to weld two valve covers together and make a taller valve cover.