Rocker arm ratio question

moving from a 1.5 to a 1.6 ratio rocker adds how much lift?

Example .400 with a 1.5 will become .440 w/ 1.6 because of the 10% increase?

It can't be this easy...

Your math is wrong. You will see an increase from .400 to .426 not .440!

Take the base lift of the cam and multiply by 1.5, then multiply that same base lift number by 1.6. DONE!

...assuming that the 1.5 rockers actually were 1.5, the 1.6 rockers actually are 1.6, since the ratio does change over the course of lift. And also the deflection in the valvetrain, and this and that and the other...

It's close enough for a quick estimation of course, but if you GOTTA know then you have to measure, since some 1.6 rockers are closer to 1.55.

Hope you have baffles in your valve covers– I have 1.6 in my truck and the breather leaks oil like a sieve.

Like jimbbski said, you have .400 total lift with a 1.5 rocker. Divide .400 by 1.5 and you'll get .2667 (roughly) that's the actual lift of your cam lobe.

Now multiply that by 1.6 and you'll get .4267 (roughly) your new theoretical lift with a 1.6:1 rocker.

Hot Rod or Car Craft just did a huge test of something like 20 different rockers; stock, steel, cast, chinese, american. They posted the advertised ratio and actual ratio. Most of them actually have more than their advertised ratio to compensate for deflection and deformation.

But, the easy way to find your valve lift is take your current lift, divide by 1.5, then multiply by 1.6.

Thanks! This thread let me calculate what my cam really is.

.471 intake
.474 exhaust

Gnarly. I like.

Also, despite what the magazines will tell you, you also pick up some duration in the process. In my application, a .1 degree increase in ratio is worth 2-3 degrees.

So a .22 ratio increase would be 6-7 degrees more duration? Interesting.

Right... it changes duration at the valve because it reaches 0.050" lift sooner. It makes little difference in seat-to-seat values since the cam hasn't actually changed, but its whole point is to increase the area "under the curve" of the flow.

Comp Cams makes a 1.52 roller tip rocker that works very well. Magnum Rockers

http://www.compcams.com/Products/CC-'Steel%20Stud%20Mount%20Rockers'-0.aspx