Adjustable or Non-Adjustable...

[Diogenes]

...that is the question.

At what point is an adjustable valvetrain required?

I ask because I am considering replacing the OEM valvetrain on my mild 390 (a "reworked" adjuster on a couple rockers). The heads are C6AE-U with adjustable. Cam is a Bullet hydraulic 286/286-10H, lift .524/.524, dur@050230/230. The installed pushrods are Melling MPR-78 with an OAL 9.157 in.

Is it best to keep the adjustable (rebuild/replace), or go with a non-adjustable? If switching to non-adjustable, do the pushrods need changed?

[pbf777]

     If I were buying for myself, or advising another (maybe that's what I'm doing here?  ), buy the adjustable!   

     Scott.

[Rory428]

Adjustable rockers use pushrods with cups at the top, non adjustables have balls at each end, so yes, the pushrods are different. A cam like the one listed would be fine with non adjustables, provided the correct length pushrods are used, but over the years, machine work, valve jobs, wear of components etc, custom length pushrods may need to be ordered , and if the valve heights are not all even, different lengths may be required for one engine. Personally, I have found that the factory style adjustable iron rocker arms are very sturdy and provided the adjusters have snug threads, are very good for maintaining lash or preload. I have used them on solid flat tappet cams over .600" lift, and 6500 RPM without fail. So although you don`t NEED  them for this application, the adjustable rockers will make setting the hydraulic lifter preload quick and easy, certainly much easier than having to measure, and order new pushrods, and then have to wait for them, hoping you measured accurately.

[Diogenes]

Adjustable rockers use pushrods with cups at the top, non adjustables have balls at each end, so yes, the pushrods are different. A cam like the one listed would be fine with non adjustables, provided the correct length pushrods are used, but over the years, machine work, valve jobs, wear of components etc, custom length pushrods may need to be ordered , and if the valve heights are not all even, different lengths may be required for one engine. Personally, I have found that the factory style adjustable iron rocker arms are very sturdy and provided the adjusters have snug threads, are very good for maintaining lash or preload. I have used them on solid flat tappet cams over .600" lift, and 6500 RPM without fail. So although you don`t NEED  them for this application, the adjustable rockers will make setting the hydraulic lifter preload quick and easy, certainly much easier than having to measure, and order new pushrods, and then have to wait for them, hoping you measured accurately.

Thanks, this is exactly the info I needed.

[blykins]

FWIW, I pretty much send out every hydraulic cam engine that I build with non-adjustable rockers.   If the customer is looking to save money, I will use the factory non-adjustables.   They will support 7000 rpm and 440 lbs of open pressure set up correctly.  If the customer wants "fancier" parts, then I'll send my roller tip non-adjustable rockers.   Measure for pushrods once and then never have to touch the system again. 

[RustyCrankshaft]

Another vote for non-adjustable on a hydrualic cams. I don't really see the need for adjustables on a hyd cam in most cases, especially on a street engine.

[jayb]

I don't run many hydraulic cams, but when I do I always use adjustable rockers.  It seems like a lot less hassle than measuring for and ordering special pushrods, and having to do that again if you freshen the heads and cut the decks, or decide to install or remove the rocker tins, or decide later to install a solid cam, etc.  On the hydraulic cams you never have to touch the adjustment after its set, so there's not really any maintenance requirement.  The only issue I've ever had with adjustable rockers is loose adjuster screws, which is a problem easily resolved with a locknut.

[TJ]

Slight thread hijack…of all the features in a rocker for street use, how important is a roller tip?  I went with that option because I’ve seen what non roller tip over many, many cycles does with relatively low lift and low-ish rpms. 

[Rory428]

Personally, I dont think the roller tip rockers help anything, until you get into larger lift cams, like closer to .600" lift. I have ran factory adjustable rocker arms with well over .650" lift, but at that lift, I have to think the roller tips would help to reduce side loading of the valve guides, but performance wise, I doubt you would see any improvement on an ET slip or dyno sheet. When I switched from iron rockers, to Erson rockers, which not only have roller tips, but also roller fulcrums, and the ET slip showed zero improvement. As for factory adjustable iron rockers with loose grip of the adjusting screws, I have had some rockers like that, and once I installed the .003" oversized adjuster screws, never had any issues again, even 20 years later. Like Jay said, I would much rather be able to get the lifter preload (or valve lash) where I want it , using the adjustable rockers, than deal with custom ordering, and waiting for them to arrive, hoping that you measured accurately, and all valve stem heights are identical. and also as Jay said, if you change heads, head gaskets, cam base circle , surface the block and/or heads, any minor differences can be easily compensated for with a bit of adjuster movement. Also easy to experiment with lifter preload or valve lash. Maybe if you have an assortment of different length pushrods on hand, the non adjustable rockers may be fine, but I like the ability to "dial in" the lifter preload or lash with the adjustable rockers.

[blykins]

Slight thread hijack…of all the features in a rocker for street use, how important is a roller tip?  I went with that option because I’ve seen what non roller tip over many, many cycles does with relatively low lift and low-ish rpms.

You get more net lift at the valve with a roller tip.  The movement is translated into a spot about .050" wide as opposed to around three times that with a shoe style rocker.   If you stick a dial indicator on the spring retainer and roll through a cycle, you'd be surprised sometimes at how much lift you actually lose to movement that's not translated into lift.  In some instances I've seen .070-.100" difference, which could cost a few horsepower with the right combination.

Jay had a point, for those of us who spend a lot of time "tinkering", which means trying different parts, tearing down the engine over and over again, etc., then an adjustable rocker would probably have a little more worth.   But I'll also say that there's a lot of engines I send out that shouldn't have any parts swaps or rebuilds or freshen-ups for a *very* long time.  In that situation, the non-adjustable rocker will show its worth as there are less "moving" parts or potentials for failure over the years.  Adjusters do break from time to time.

In addition, on the higher rpm hydraulic cams, less weight on the hindend of the rocker arm can be an advantage. 

I will also say, just as a complete and off-the-wall side note, that non-adjustable rockers can be used with solid cams as well.  It just takes a little more time during engine assembly/measurement to get things right, and of course if you do change anything at all, then you have to start over, but it is possible.  Lots of Cup and circle track engines out there with non-adjustable shaft mounted roller rockers on solid roller and solid flat tappet camshafts.  Any weight that can be saved in the valvetrain can lessen the necessary spring pressure requirements, which translates to less part wear and fatigue. 

[Lowrider]

Years ago after I lunched a 427 in my 63 Galaxie I picked up a warranty turn in 390 shortblock from a 68 Gt Torino. Only thing I changed was I put in a C8AX-C hydraulic cam in it. I used all the 427 upper parts, heads, 2x4 intake and adjustable rocker arms. Took some tinkering with the rocker adjustments but it ended up a trouble free setup. That combo was the most consistent engine I think I ever ran. That big old boat would turn a 13.1 every time. It had no problems turning 10.5 slicks. The only shortfall was I could never get it to run in the 12's. I think life got in the way before I got there.

[fryedaddy]

no one has mentioned the difference in ratio 1.76 vs 1.73

[blykins]

no one has mentioned the difference in ratio 1.76 vs 1.73

My rocker arms have a 1.76 ratio, but in all honesty, the difference is pretty miniscule.  On a .360" lobe lift cam, the difference would only be .010" at the valve.