rocker arm ?

[srpntlair1]

I am trying to understand the difference/ advantages of rocker arm ratios. stock 1.5 VS. roller tipped 1.7 what does the difference do and what changes besides rockers need to be done to accept them?

[Ghoste]

Think of the ratio as using a longer lever, it'll effectively move your valve a little further and give you more lift.  The only change to use them is to install them and then to make sure that you aren't going to have so much lift that valves strike pistons but if you ar putting it on an otherwise stock engine, you shouldn't have to worry about that.  There can be other cons with high ratio rockers but let me ask this, why did you choose the 1.7?

[srpntlair1]

I didn't choose them I did a search for roller rockers and saw a set with a 1.7 ratio and was just curious. but basically if I had say a stock 484 lift cam with 1.5 rockers in essence with 1.7 ratio it would make it seem like a higher lift ie 504 cam....

[aifilaw]

quite simple.

let's say you have a 484 lift cam, that's 0.484 lift at the valve. Divide that by the stock rocker ratio (1.5) and you get the lift at the cam lobe: 0.32266666666666666666
Apply 1.7 ratio rockers to the same cam, multiply 0.3226666666 by 1.7 and you get your new lift at the valve:
0.548533333333333

So, if you plan to do such a thing, first question would be, do your heads flow well at 0.55, any better than they do at 0.484... if they are stock cast iron heads, the answer is no. With some work, the answer is yes.
The second question is, will this hit my pistons... simple answer (without checking valve geometry based on cam and crank movement) is a dummy check.
Remove the valve spring, move the valve in exactly 0.5685 inches, rotate the entire assembly aruond and past piston at TDC... if clearance then you should be fine.

Other issues you will run into is increased wear on the valve tip, valve guide, et cetera and the increased ratio of the rocker... obviously the rocker is built at a 1.7, so it should be able to handle it... but can the valve springs?

[Animal]

Piston to valve clearance is critical @ the O/L period (15* before & after TDC on ex/in stroke) not critical @ full lift as the piston will always be chasing the valve..................unless the valve timing is wayyyyyyyyy out o whack.

A checker spring would come in handy.

[firefighter3931]

High ratio rockers accelerate the valve action....this can be good and bad depending on the application. It's important to match the proper valvesprings to keep the valvetrain stable at higher rpm. Failure to do so will result in valve float and spring surge....which will result in breakage. 

On an oldschool grind like the MP purpleshafts the 1.6 rocker is a good choice but on a newer fast rate grind like the Engle/VooDoo/Comp xehl profiles i would stick with a 1.5 ratio. 

The 1.7's are a poor match for anything but a race build, inmo.


Ron