Rocker Arm Ratio

[SoulSurvivor]

what does the 1.6 and 1.5 rocker arm ratio mean? And which adjustable one should I use for my rebuilt 340? And...how do I adjust them. It seems confusing and i don't want premature cam wear or failure because I don't adjust the pushrods correctly.:read2:
Thanks gang,

Doug

 

[340sFastback]

The 1.6 ratios will give you more valve lift then a 1.5 ratio rocker when using the same cam.

As far as adjusting the rockers it depends if you are going to run a hydraulic or solid cam. For hydraulic lifters here is a pretty good write up on how to do it:

http://www.moparts.org/Tech/Archive/motor/14.html

Solid lifters use a similar approach except you leave some lash (slack) in the adjustment instead of taking it all out plus some like on a hydraulic.

 

[410 valiant]

You get two advantages with the 1.6 rockers. They give you more lift from the same cam and decreases the angle of pushrod to lifter angle. The lift is the best part and the angle improvement is slight.Good luck

 

[moper]

The ratio is the ratio of camshaft lobe lift to actual lift at the valve. Stock mopar is 1.5, ona fixed shaft. The true ratio of the stamped steelies are closer to 1.45 than 1.5... Aftermarket rockers come in up to 1.8, but they are not really budget...lol. Because it's a ratio of lift, meaning a range of movement over time (in degrees of rotation) when you go with a higher ratio arm, it will not only lift the valve open further but also open it faster, open it earlier, and close it later. Changing rocker ratio can mess things up with fast ratio cams if the valve springs are just able to do the work at the 1.5 ratio. So you want to make sure theres enough spring to control the movement, and the ratio is changed on the pushrod side, so you will want to enlarge the pushrod holes to avoid the pushrods hitting the heads. (especially with RPMs...)

 

[ramcharger]

Keep in mind that the force it take to open the valve from the cams point of view is increased by a factor equal to the increase in lift. There is no free ride.

 

[daredevil]

ramcharger are you trying to tell him the larger ratio needs more spring pressure?

 

[ramcharger]

The higher ratio is just a bit harder on the cam/lifters/pushrods is all. Let's say you are running 300 lb springs at max lift. The cam and lifter see 450 lb with a 1.5 rocker and 480 lb with a 1.6 rocker. Keep in mind that that the Ford Boss and 351 Cleveland series engines run a stock 1.73 ratio rocker. I built a 351C years back that used to like to spit out pushrods at 5k rpm like clockwork. Kind of a built in rev limter, lol! The problem stopped when I installed hardened p rods. Premium hardened pushrods are a must with higher than stock ratios IMHO. Lesser pushrods won't necessarily bend and break but I feel that they will deflect at higher rpms given the odd push rod angles our sb mopars have.

 

[bobscuda67]

The ratio is the ratio of camshaft lobe lift to actual lift at the valve. Stock mopar is 1.5, ona fixed shaft. The true ratio of the stamped steelies are closer to 1.45 than 1.5... Aftermarket rockers come in up to 1.8, but they are not really budget...lol. Because it's a ratio of lift, meaning a range of movement over time (in degrees of rotation) when you go with a higher ratio arm, it will not only lift the valve open further but also open it faster, open it earlier, and close it later. Changing rocker ratio can mess things up with fast ratio cams if the valve springs are just able to do the work at the 1.5 ratio. So you want to make sure theres enough spring to control the movement, and the ratio is changed on the pushrod side, so you will want to enlarge the pushrod holes to avoid the pushrods hitting the heads. (especially with RPMs...)

Are you saying that the duration is increased by switching to 1.6 rockers? If so, how much? It seams to me the valve starts to open when the lifter hits the cam ramp and it starts to move, it doesn't matter what ratio rocker arm you have.

 

[SoulSurvivor]

OK. I purchased a set a 1.5 stainless adjustable rocker assembly.(what makes these things so expensive?) 1.5 because the lift on the cam is just 477/480.
You guys scared me with all the 1.6 talk and from what I gleaned off of your comments 1.6 was not neccesary. I figured I'll stay with the factory ratio. Now what? Besides the link above on the adjustment is there ant tips on adjusting? I would be lost without the wealth of info here. Hopefully pistons, valve springs and push rods don't go flying all over the place when I fire her up for the first time:dontknow: