Rockers 1.5? 1.7? Whats the difference?

[Don]

I've seen posts describing the different sizes of the rockers. While I have a basic understanding of the rockers that lift the valves allowing air/fuel into the cylinder, I couldn't get a straight answer on the different sizes. When asking a local mechanic, I was given a blank stare combined with a what are you smoking? My first guess would be that it would push the valve open more? If I'm understanding this correctly, what are the advantages of the different sizes? I'm also assuming that the stock rockers are metal to metal and hence the reason to replace with the roller rockers as they roll down the metal when opening the valves creating less friction?

Reasons: I'm flirting with the idea of replacing the internals on my creampuff and figured I would educate myself as to what else should be replaced along with the pistons heads, piston arms and crank shaft.

 

[PhoenixGTS]

On 1.5:1 arm a 0.10" movement in the pushrod would = a 0.15" movement of the valve. On a 1.7:1 arm a 0.10" movement in the pushrod would = a 0.17" movement of the valve. Higher ratio = higher lift for given pushrod movement.

 

[Cal Cobra]

Good comparison Phoenix, but .02" doesn't seem like enough that it will buy you anything.

I always thought being open a little more would have benefits, but now that it's put in perspective I see why most dyno runs with roller rockers are negligible at best as to HP gains (although I would still think it's a lot easier on the valve train, and what the hey the tappets/cam are already roller, might as well go all the way).

Cal

 

[01sapphireGTS]

Don: If you are thinking about replacing your "Rotating Assembly", (ie Crank Shaft, Connecting Rods, Pistons, Piston Rings, etc...) You should really think about talking to a reputable viper tuner. That's an area where you can make poor choices that still cost a lot of money, which is obviously very bad.

I would suggest purchasing a balanced rotating assembly from someone reputable and then it is "right" instead of having some local guy spin and balance it for you. It may be a situation where you just send your block to that tuner and he will assemble it for you, thus fitting all the piston rings etc getting the weights perfect.

I would also talk to the tuner about rocker arms versus a different camshaft. It may be better to just get a cam with a profile you are looking for and not mess with higher ratio rocker arms. You have a lot of choices, please explore them.

BTW, rocker arms don't "lift" the valves. (Although everyone knew what you ment). The camshaft has lobes that are elyptical. The lobe lifts the camshaft lifter assembly, thus lifting the pushrod, thus lifting the inboard side of the rocker arm, simultaniously depressing the outboard side of the rocker arm, thus depressing the valve. So the valves actually get "pushed or depressed" into the head's combustion chamber awaiting a compression stroke and spark. Then like John Madden says "Boom".

Let us know what you end up getting...

 

[Don]

Thanks for the explainations and information!

 

[joe117]

"but .02" doesn't seem like enough"

He was just using that number as an example.
The extra lift is more than .02"

But you are right, the rocker mod from 1.5 to 1.7 isn't going to turn your engine into a monster of power.

And the downside is the 1.7 puts much more pressure on the pushrod side of the valve train.

There are limits as to the lift available without going to a 1.7 ratio.
The cam heel to base circle is only so tall.

 

[pedro]

Stay away from Mopar T&D rockers because your heads will need to be sent out to have the boss mild down $$$$$$$$$.roe racing has better ones that you will not have to have your heads mild???Go with 1.7

 

[HOdbleFman]

Stay away from Mopar T&D rockers because your heads will need to be sent out to have the boss mild down $$$$$$$$$.roe racing has better ones that you will not have to have your heads mild???Go with 1.7

With T&D's you do not have to remove the heads for proper valvetrain geometry. Go with the T&D's or Jesel. From experience, I don't recommend the other brands.

 

[pedro]

If you use the alignment tool that T&D give you your valve stems will be to heigh and you will need to shave your boss down !I had problems with valve cover not fitting rockers will hit cover and your geometry are not correct go with Jesel they cost more$$$$$

 

[ViperJohn]

If you use the alignment tool that T&D give you your valve stems will be to heigh and you will need to shave your boss down !I had problems with valve cover not fitting rockers will hit cover and your geometry are not correct go with Jesel they cost more$$$$$

All you have to do is remove the baffles in the valve cover to enable the T&D's to clear.