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rocker arms?

This is a discussion on rocker arms? within the Internal Engine forums, part of the LSx Technical Help Section category; whats the difference between a 1.7 ratio and a 1.8 ratio non adjustable rocker arm on a stock engine? what ...

  1. #1
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    rocker arms?

    whats the difference between a 1.7 ratio and a 1.8 ratio non adjustable rocker arm on a stock engine? what does the extra .1 do?

    thanks

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    Pathelogical Liar BlackLT1Z28's Avatar
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    Increases lift that extra 10%.

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    member since may 2000 nhraformula's Avatar
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    save youre money and keep the stockers

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    well i was gonna upgrade to a chromemoly push rod cause the stock are junk and i figured i might as well put a set rocker arms while im there

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    Quote Originally Posted by ban-one View Post
    whats the difference between a 1.7 ratio and a 1.8 ratio non adjustable rocker arm on a stock engine? what does the extra .1 do?

    thanks
    The difference is very easy to figure using the easy math.

    a rocker arm with a 1.5 ratio should produce a net valve llift the is exactly 1.5 times greater than camshaft with .300 inch lobe lift should produce a max valve lift of .450 inch. ( 1.5 x .300 = .450.) Plug your numbers into that equation and you got your difference.

    However, due to manufacturing tolerances, deflections in the valve train, and the complex motion of the rocker as it sweeps across the valve tip, actual valve lift seldom equals theoretical value.

    Hopefully this helps

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    Quote Originally Posted by nhraformula View Post
    save youre money and keep the stockers
    i thought ls1's rocker pins fall out alot, into the oil pan.

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    King 0f n00bz shady milkman's Avatar
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    Quote Originally Posted by Hi-Po View Post
    The difference is very easy to figure using the easy math.

    a rocker arm with a 1.5 ratio should produce a net valve llift the is exactly 1.5 times greater than camshaft with .300 inch lobe lift should produce a max valve lift of .450 inch. ( 1.5 x .300 = .450.) Plug your numbers into that equation and you got your difference.

    However, due to manufacturing tolerances, deflections in the valve train, and the complex motion of the rocker as it sweeps across the valve tip, actual valve lift seldom equals theoretical value.

    Hopefully this helps
    damn hi-po thats some good stuff thats for the info.

  8. #8
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    Quote Originally Posted by Hi-Po View Post
    The difference is very easy to figure using the easy math.

    a rocker arm with a 1.5 ratio should produce a net valve llift the is exactly 1.5 times greater than camshaft with .300 inch lobe lift should produce a max valve lift of .450 inch. ( 1.5 x .300 = .450.) Plug your numbers into that equation and you got your difference.

    However, due to manufacturing tolerances, deflections in the valve train, and the complex motion of the rocker as it sweeps across the valve tip, actual valve lift seldom equals theoretical value.

    Hopefully this helps
    i think i understand so if i have a max lift of .600 the 1.5 rocker arm will lift the valve .900 of an inch? so which ones should i use on a stock motor that i dont plan to head and cam for a long time?

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    1.7 or 1.8 or will it even matter?

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    Quote Originally Posted by ban-one View Post
    i think i understand so if i have a max lift of .600 the 1.5 rocker arm will lift the valve .900 of an inch? so which ones should i use on a stock motor that i dont plan to head and cam for a long time?
    keep the stockers... they are good quality and have been known to hold up to some pretty serious HP. if you do end up doing a cam more than liely you will not want increased ratio rockers. Stick with the stockers bro.

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    Quote Originally Posted by ban-one View Post
    i think i understand so if i have a max lift of .600 the 1.5 rocker arm will lift the valve .900 of an inch? so which ones should i use on a stock motor that i dont plan to head and cam for a long time?
    The rocker arm ratio is multiplied by the NET lift of the cam lobe, not the gross advertised lift. I don't think any cam will have a net lift of .600".

    And keep in mind when matching up rockers with cams is the total gross lift. If you go too big, then you'll run the risk of a valve interfering with a piston. And that is BAD.

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    alright thanks alot yall have been a big help

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    well... while we are on the topic of rocker arms.... i often have something to say about them. I believe that some people buy rocker arms and dont understand that by installing higher ration rockers is changing your valve train geometry..... that aint good. This geometry is between the valve stem and rockerarm when the valve is opening and closing. These higher ratio's are causing the pushrod to rub against the side of the clearnce hole in head. I am not saying higher ratios isnt worth power... just that there are things you gotta do.

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    Senior Member mrr23's Avatar
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    Quote Originally Posted by ban-one View Post
    whats the difference between a 1.7 ratio and a 1.8 ratio non adjustable rocker arm on a stock engine? what does the extra .1 do?

    thanks

    the extra .1 changes the VALVE duration and lift. IE, a cam with .500 valve lift with 1.7 rockers will have a .529 with 1.8 rockers.

    .500 divided by 1.7 times 1.8 = new valve lift .529

    depending on what rocker you buy, you can see anywhere from 5-20 rwhp.

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    Senior Member mrr23's Avatar
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    Quote Originally Posted by Hi-Po View Post
    well... while we are on the topic of rocker arms.... i often have something to say about them. I believe that some people buy rocker arms and dont understand that by installing higher ration rockers is changing your valve train geometry..... that aint good. This geometry is between the valve stem and rockerarm when the valve is opening and closing. These higher ratio's are causing the pushrod to rub against the side of the clearnce hole in head. I am not saying higher ratios isnt worth power... just that there are things you gotta do.

    the geometery change isn't on the valve stem side, it's on the pushrod side. a 1.7 and 1.8 rocker are identical in every aspect except where the pushrod seats into the rocker. to increase rocker ratio, they move the pushrod towards the center.

    now, how is this causing the pushrod to rub the side of the guide holes in ls1 heads? i've been running the vinci/crane 1.8 accelerated lift rockers for over a year now. no wear to the holes in the head.

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    Senior Member mrr23's Avatar
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    Quote Originally Posted by nhraformula View Post
    save youre money and keep the stockers
    that's not what he asked.

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    Senior Member mrr23's Avatar
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    Quote Originally Posted by shady milkman View Post
    i thought ls1's rocker pins fall out alot, into the oil pan.

    some of the early years have this problem. don't know exactly what year it was 'fixed'. it still happens.

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    Quote Originally Posted by mrr23 View Post
    the geometery change isn't on the valve stem side, it's on the pushrod side. a 1.7 and 1.8 rocker are identical in every aspect except where the pushrod seats into the rocker. to increase rocker ratio, they move the pushrod towards the center.

    now, how is this causing the pushrod to rub the side of the guide holes in ls1 heads? i've been running the vinci/crane 1.8 accelerated lift rockers for over a year now. no wear to the holes in the head.
    i thought thats what i said....?? maybe not. i didnt re-read my post. you are correct...

    The wear wouldnt be on the head... on the pushrod is where the wear would occur.... i am not imply that a .1 increase would cause major wear... i was just stateing

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    Senior Member mrr23's Avatar
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    Quote Originally Posted by Hi-Po View Post
    The wear wouldnt be on the head... on the pushrod is where the wear would occur.... i am not imply that a .1 increase would cause major wear... i was just stateing
    you are correct that the head would wear if the pushrod came into contact with the pushrod. aluminum will wear over steel anyday. what you said was this:

    Quote Originally Posted by Hi-Po
    These higher ratio's are causing the pushrod to rub against the side of the clearnce hole in head.
    coming closer to the mounting point of the rocker, it would rub the part of the hole closest to that point, not the sides. good thing about the LS heads, they have enough room to not cause any interference.

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    well the stock ratio is 1.7 and i just figure if i am going through the trouble of swaping my push rods i might as well put a set of rocker arms on.

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