350 SBC Build / considering Roller ROckers - what Ratio? - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-23-2010, 11:42 AM
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Lots of intresting stuff. One thing Im gleening from all this is that it seems that a higher ratio rocker has the same effect on the valvetrain as simply adding the equivalent amount of lift and a more aggressive ramp profile. So simply adding 1.6 rockers to a stock cam would be far less demanding on the rockers themselves and the rest of the valvetrain then adding them to an already aggressive cam. In other words, any ill effects of going to a higher ratio are going to be proportinate to what they are being added to. And likewise, the extremes that one needs to go to to guard against said ill effects (fulcrum rockers, behive springs, etc.) are also going to depend greatly on the bumpstick in question.

Just a thought to throw out there for anyone considering going to a more spendy valvetrain. It may be expedient or it may not..

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Old 07-23-2010, 02:05 PM
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Pontiac RA-IV 1.65:1 rocker arms.

The Pontiac 1969-1970 Ram Air 4 engines used 1.65:1 rocker arms and they were used on the same camshaft with 0.470" valve lift that was used in the 1968 Ram Air engines but with 1.5:1 Rockers. That was an economic move by the engineers so they would not have to have another camshaft made with 10% more valve lift in order to achieve the desired 0.517" valve lift that the dyno-room said to use with the improved 1969-1970 Ram Air IV heads.

Pontiac used 1.65:1 rocker arms prior to the Ram Air IV engines with the 1963 421 Super Duty engines. In fact, the camshaft used in the 1963 421 SD engines had the similar specifications as the 1968 Ram Air and 1969-1970 Ram Air 4 cam but it was a solid flat tappet cam with less cam lobe lift. All Pontiacs that used 1.65:1 rockers also used 7/16" rocker studs due to the increased side-load on the rocker studs. The high performance Pontiac engines used some sort of drip rail to lubricate the rocker arm pivot balls. That is a sore spot with those type rocker arms in a high performance application.

The two reasons I used full roller rocker arms is: 1.) Reduce the excessive side load on the valve stems and prevent excessive valve guide wear that always accompanies high lift camshafts, 2.) Reduce operating higher temperature that accompanies pivot ball rocker arms compared to full roller rockers and guard againt galling the pivot ball due to lack of lubrication. Grooved rocker balls are marginal at best in a high performance application.

The reason I used beehive / ovate valve springs is because they will accept 0.500" valve lift with 310 lb. open pressure without having to machine the thin valve spring seats of the 4.3L V6 heads in order to accept taller high load valve springs so the rocker arms would not hit stock center bolt valve covers. Those are reasons enough for me to use that type equipment regardless what the sharp pencil boys say.

I have had pivot ball rocker arms burn up and seize, bending and breaking pushrods when the lubricating oil from the push rods was being tossed over the pivot ball at sustained high RPM. The valve covers I was using when the failures occurred did not have drip rails. Drip rails often have to be removed before some high lift cams are used. Pontiac Ram Air IV heads use individual rocker arm drippers divert oil to the rocker balls to lubtricate the failure prone pivot ball type rocker arms in high performance engines. Those "drippers" had to be bolted to the tops of longer 7/16" rocker studs so the high lift rockers would not hit them.. All "real" high performance engines should always use full roller rocker arms and they should be stainless steel full roller rocker arms that are that are rebuildable. Use stainless steel full roller rocker arms that are rebuildable and not the goofy roller tip, ball pivot rocker arms. .

Last edited by MouseFink; 07-23-2010 at 02:33 PM.
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