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 Post subject: Rocker arm ratio
PostPosted: Fri Mar 14, 2014 3:01 am 
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Turbo Slant 6

Joined: Sun Aug 25, 2013 2:14 pm
Posts: 759
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Going thru old posts between the two slant sites and picking up info. I would like to understand rocker arm ratio.

Evidently it is 1.5 on the slant but there is a possibility of a 1.6.

Id like to understand what all that means and how it is measured in non-technical terms as it pertains to the slant if possible. Thanks


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 Post subject: Not too hard...
PostPosted: Fri Mar 14, 2014 6:54 am 
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Joined: Tue Oct 29, 2002 8:27 pm
Posts: 9714
Location: Salem, OR
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The rocker arm is a "see-saw"...the pivot and relationship between where the pushrod and the valve tip are located on the rocker and the pivot point at the rocker shaft determine the ratio, or multiplier for the lift from the cam lobe, and how the duration and cam events are perceived at the valve... (i.e. if the ratio is 1.5 at the rocker, the cam lobe at max height is .300 then 1.5 x .300 =.450 max lift at valve, if a set of longer rockers can be installed and setup properly then you can get more lift/and alter the perceived cam events a bit...so a set of RAS 1.6 rocker x our .300 lift cam would net a .480 lift)...all things not being 100% fair in the universe and how physics works, and mass production tolerances a couple things will happen...you may loose some lift due to the valve lash not being 100% perfect...also because our rockers were stamped mass production units they are not 100% perfect and land in the 1.465 ratio range (On my hipo engines I've pulled several engine's worth of rockers and put together a set or two that were "close" and not all over the board cylinder to cylinder.)

There really isn't a set of 1.6 rockers for daily driving, they are also $$$ compared to other improvements that can be done to the engine (these are really key if drag racing or doing an all out engine that needs a little more than the standard tricks can't provide).

-D.Idiot


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 Post subject: Re: Not too hard...
PostPosted: Fri Mar 14, 2014 12:19 pm 
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Turbo Slant 6

Joined: Sun Aug 25, 2013 2:14 pm
Posts: 759
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Quote:
The rocker arm is a "see-saw"...the pivot and relationship between where the pushrod and the valve tip are located on the rocker and the pivot point at the rocker shaft determine the ratio, or multiplier for the lift from the cam lobe, and how the duration and cam events are perceived at the valve... (i.e. if the ratio is 1.5 at the rocker, the cam lobe at max height is .300 then 1.5 x .300 =.450 max lift at valve, if a set of longer rockers can be installed and setup properly then you can get more lift/and alter the perceived cam events a bit...so a set of RAS 1.6 rocker x our .300 lift cam would net a .480 lift)...all things not being 100% fair in the universe and how physics works, and mass production tolerances a couple things will happen...you may loose some lift due to the valve lash not being 100% perfect...also because our rockers were stamped mass production units they are not 100% perfect and land in the 1.465 ratio range (On my hipo engines I've pulled several engine's worth of rockers and put together a set or two that were "close" and not all over the board cylinder to cylinder.)

There really isn't a set of 1.6 rockers for daily driving, they are also $$$ compared to other improvements that can be done to the engine (these are really key if drag racing or doing an all out engine that needs a little more than the standard tricks can't provide).

-D.Idiot
Thanks, this makes sense to me. Im going to assume when dissasembling a head for service I need to be looking for deep scoring on the rocker shaft as being an issue but how deep in un-acceptable?

Also should I be looking for ob-long holes in the rocker arms, are these generally measured for out of round-ness. Im assuming these are all things that can really play havoc with a valvetrain.

How about the tips of these rocker shaft where they ride the pushrods, is wear ever an issue there?


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