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Rocker roller and ratio question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by txbartman, Nov 7, 2001.

  1. txbartman

    txbartman 1/2 ton status

    Jun 1, 2001
    Likes Received:
    Plano, TX
    I am building a 350 usign the basic GM Crate 350 (250HP model) I am doing a few things to it to increase performance, but don't want to void the warranty. One thing I am considering is installing roller rockers. Per Four Wheeler or 4WOR (don't remember which), that is a simple way to gain some efficiency from the engine (makes sense to me). The specs for the engine say: Valves: 1.940” / 1.600”. Does that mean the the ratio for the rockers is 1.6?

    The article also said that you could "trick" your engine into thinking you had a bigger cam by installing rockers with a greater ratio. I can't change the cam as it will void the warranty, so this seems to be a good compromise. What ratio should I go with? Should I just stay at the same ratio and live with it? Will I need taller valve covers? Will this swap force me to do something with the valve springs, pushrods, or anything else as well?

    Y'all's help is GREATLY appreciated.

    Check out <a target="_blank" href=http://tx85gmcguy.alloffroad.com>My Jimmy</a> with all her projects!
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Jul 23, 2000
    Likes Received:
    E-town baby!
    1.60" is the diameter of the exhust valve. Stock rocker ratio is 1.5 to 1. If the stock cam has .300" of lobe lift the rocker increases that to .450" at the valve with stock rockers. Same lift with 1.6 to 1 rockers and the lift seen at the valve is .480".

    1.6 is about as much of a non-stock ratio as you want to go with...and it shouldn't cause any clearance issues. I believe you should be able to just bolt em up and adjust them and call it a day.[​IMG] As for how much hp you'd gain...there are lots of claims made but a dyno is the best way to know for sure. I'd expect 10-25 hp gain with roller tipped 1.6 to 1 rockers.


    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
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  3. Andreas

    Andreas 1/2 ton status

    Feb 17, 2000
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    The 1.94"/1.6" part is the valvesize. 1.6" is actually bigger than stock GM (which is 1.5"), so it´s a good thing [​IMG]. Your rockerratio is probably 1.5:1. Cam manufacterers almost always spec their lift with a 1.5:1 rocker in mind. So, if you f.ex se a cam with .450" valvelift you divide that with 1.5 and end up with LOBElift. .450" divided with 1.5 is .300". To find out what happens with any other ratio you multiply the LOBElift with the new rockerratio, in this case 1.6. So, .300 times 1.6 is .480"

    Rollerrockers comes in different prices, material and design. The cheapest option is going with a rollertip rocker (comes in both 1.5 &amp; 1.6 ratios). They only have a wheel a the tip of the rocker, not where the stud goes. Rollertip rockers doesn´t need any tall valvecovers.

    Then there´s full rollerrockers, which has the wheel at the stud (along with the tip). They are made of steel or aluminum and needs tall valvecovers.

    Higher ratio increases the lift, not the duration. The roller "feature" reduces friction and frees a few hp. So, a full roller 1.6 ratio rocker is a good thing, if you can afford it[​IMG] They´re expensive!!!

    Find out what cam is in your engine now (the lift), divide it with 1.5 then multiply it with 1.6. If it comes out under .500" you don´t need new valvesprings. I´m thinking a standard GM crate engine cam has a valvelift around .400", so you should be safe[​IMG]


    406cui of pure sh*t[​IMG]
  4. 502Burban

    502Burban 1/2 ton status

    Jun 8, 2001
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    Southern California
    Some other things to keep in mind: To run "true" roller rockers with the extruded aluminum body and roller bearing at the trunnion, you will need to install (if you don't already have them, of course [​IMG]) screw-in studs. This requires machining of the heads.

    Also, you _will_ need taller valve covers for clearance. The body of the roller rockers is larger and will hit your stock covers. All things considered, you can probably get better power increases for your $250 than you would experience from the roller rockers.

    Don't get me wrong, though. I run Crane's roller rockers on every engine I build, and luv 'em.

    '73 GMC Suburban - 502DFI
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  5. chevyracing

    chevyracing 1/2 ton status

    Sep 8, 2001
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    If you use true roller rockers guidplates are a good idea too. I have roller tip rockers in mine and they do just fine. They are not noisey and don't need adjustment with hydraulic lifters.


    Like to go sloppin' 'round in da mud in a rapid fashion....=) [​IMG]

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