...anytime you want better performance and better valvetrain stability with reduced friction. I recommend roller rocker arms for every application.
You may be able to use .525" lift with a set of factory lifters, but the key is to check the rocker tip and the contact patch between it and the valve stem tip. Look for interference or galling. Remember that most factory cams were tiny at about .080" to .100" less lift than what you're considering. The parts in the valvetrain were never made for the levels of stress you'll find at higher lifts. Consider the difference in spring pressure between a spring open at a height of installed height less .430" and a spring open at installed height less .525". The total pressure is going to be a lot more! Is this what you want to trust to a factory stamped steel rocker arm? Do you want to subject your valve tips to that kind of thrashing?
Use a set of roller rocker arms to put your engine into a safe realm. Roller rockers reduce friction and make power. Your budget and what you want to accomplish should be the deciding factors.
The other thing that people forget is that rollers actually have a higher reciprocating mass than standard rockers. Rollers don't "give" you any extra power, they are just more reliable within the power band that you have. They are designed for continuous high rev, high load applications as they do not fatigue or flex like standard rockers can.
I've got YT Rockers on my car and did notice that they quietened the valve train down a bit, but there certainly weren't any other noticeable benefits on the DYNO or otherwise. In fact, they can actually place greater stress on pushrods because this can become the gretaest area for flex and stress absorption.................so I had to go Moly one piece just to make sure. Rollers are also less tolerant to valvetrain geometry variances. You need to ensure that the valve stem tip to roller tip is spot on and that you choose the correct Rocker ratio as this can vary your cam lift. As per the guys from Yella Terra :
Rockers increase the lift of the cam by having unequal lengths from the pushrod cup or adjusting screw to the fulcrum and from the fulcrum to the tip of the valve.
Most rockers have a theoretical ratio of 1.5 to 1.7:1 that is the rocker increases valve lift by 1.5 or 1.7 times the cam lobe lift.
If your cam has a lift of .375" with 1.5:1 rockers, the lift at the would be .563" and .600" with a 1.6:1 rocker. Remember with solid lifter cams, valve clearance must be deducted from theoretical available lift.
Rocker arm ratio changes are frequently used to test the benefit of a higher lift of the valves without resorting to the more substantial camshaft changes.
Competition engine builders frequently experiment with changing inlet or exhaust and possibly both rockers, to establish if power gains are possible with different ratios.
An increased ratio will open the valve faster, lift it higher and close it faster, but won't effect the cam timing. The increased acceleration and deceleration of the valve from a higher ratio could lead to valve float occurring at a lower rpm.
The big advantage to the roller rockers is that they will greatly reduce valve guide wear. My brother ran 0.545" lift with factory rockers for a couple of years. When the heads cam off, the guides were knackered.
the lifter looses contact with the cam lobe and 'floats'. This is bad in numerous ways, not the least is that if the vvalve stays open a tad too long becuase it's off the lobe rather than following it, the valve can hit the piston. No two is that when the lifter comes back down it bashes against the lobe rather than slides against it.. which is bad as it wears the lobe quickly.
It will feel like it's breaking down ... I haven't ever had it backfire but as the valve timing changes it could well do that. It will lose power too.
I run .525 lift with standard rockers no problem. But I am aware it will flog out my valve guides more quickly.
Are you running a cam with this much lift boss351c or thinking about it?
Standard Cleveland valve springs will not work with a cam with this much lift.
At the increased RPM, the valves will "float"or bounce because the standard valve springs are not strong enough to hold the valves in their seats.
Roller rocker will not help this situation, you must have springs to match the cam.
As xacoupe said, valve float feels like the motor is breaking down,ie missing and losing power.
I do it at least once a night when I race, pulling my column auto past drive into neutral. I get some pretty good back fires also!
I would be going a set of Rollers anyway for a performance engine, hell even a pretty standard rebuild. Just an added mesure of security i guess.
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i cant remeber what sorta springs i got (i think they're double valve springs) but my problem with the car is that when under full throttle anything above 5000rpm it starts to breakdown and if i keep my foot into it i blow flames out the carb. this wont happen every time but a couple nights ago at the track it just wouldnt run and i had to go a bit easy on the throttle to get a clean run which only produced a 13.3 @ 105mph. Ive had this problem ever since the build was done but its slowly getting worse. My best time was the first time i went out on the track with 12.6 @ 109mph and a 1.8 60ft, since then i rebuilt the c10 trans put a 750dp, reset springs and put tramp rods on and took a 2inch spacer off and put on a nos plate (which i havent run yet due to problems). One other thing that could be causing this might be the fact that the carb has had the power valve taken out of it and the rear jets we used were as high as 76, my mate thinks that since it hasnt got a power valve in it u have to run way bigger jets in the rear to compensate ... what do u guys think????whats the benefit of not having a powervalve in the carb?
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