When or does less lifter weight have greater advantage vs using larger lifter wheel diameter by having an advantage with a larger diameter lifter?

"Hyd" normally means limited rpm peak, so a lighter lifter would seem to be an advantage, but a larger diameter (heavier) lifter with its larger wheel seems to have its own pluses. My application is road race/track car, no competition. Its got a 4.25" crank, so high RPM is not a goal. Current SB motor under construction has .842" lifter size bores, 50mm? cam. I will be using a bushed/non needle roller Hyd lifter. Not sure 100% they can be opened up yet anyway, or the meat of this question, is it worth it, and why?

The language is terrible but I think I get the just of your question.
It's a tough one. The larger diameter is said to provide greater control of the wheel following the cam. It also is said to provide greater reliability as the cam lobe impact will have less side load on the lifter bore. Most of the lightening has stemmed from unwanted high RPM harmonics. I would imagine that lighter metallurgy in anything spinning or going up and down would free up some HP. It will certainly loosen your wallet. I would say the larger diameter would be more beneficial in your deal.

Run the biggest wheel you can get.

Sorry it was tough question for me to frame properly.

Maybe I should have asked what is the weight difference between big and small diameter lifters and does it really matter?

Thanks

A large wheel on a very radical lobe (concave opening flank) requires a larger base circle, or the wheel will partially bridge the depression.
A larger wheel used on a cam designed for a .750" will not have the same effect as a higher rocker ratio (linear), but instead have accel and vel changes throughout the lobe's duration, extending the duration at both ends (very slightly) and varying along both flanks but zero at full lift.
To understand what's happening: a flat tappet always follows the highest point on the cam lobe regardless of its rotation. A roller always follows the closest adjacent point of the lobe (tangency), and this will vary with the roller diameter. The difference can be plotted, but the programs TIKO are proprietary.

Weight doesn't really matter. Use the biggest diameter body you can get with the biggest wheel. That's about .810-815 on a .904 body.

Quick math: assuming square corners and 3/8" width wheel, the largest wheel that will fit down a .904" hole is the height of a triangle with .904" diagonal (hypotenuse) and a .375" base: .822". Slight roller corner radius increases OD slightly, duh.
wheel diameter = (tappet ID^2 - roller width^2)^.5

Anyone use the ISKY Rev Kit? Would one help in this application?
http://iskycams.com/cart/index.php?main_page=product_info&cPath=49&products_id=1798

A bigger wheel is better, Pro Stock runs a 1" + diameter wheel for a reason. Trying to save weight on the push rod side will be a fruitless exercise, over the valve is a different story. Stiffness and rigidity wins, hence why we see lifters around 1" in diameter with 1/2" + diameter push rods.
That said, your camshaft profile will have been designed with a wheel diameter in mind, find out what that is.

With a big rocker, the pushrod side weight becomes even less important vs. valve side.

Pretty simple, IMHO. Many combos run a hydraulic .904 lifter with great succsess. Brian at IMM, (ou812) has this deal figured out to 6500 rpm on Magnum motors. I am running his setup in a 408 and it makes VERY good power for what it is, and great torque for coming off corners.

This won’t answer the original question, but I have a set of jesel .937 keyway lifters. Without any assistance from a scale, it is easily noticed the weight difference between a .904 tie bar set of lifters compared to two of the larger .937 lifters. Although some of this weight is in the tie bar, rivets, and extra height, the general body on a standard roller lifter is thicker all around.
The jesel lifter doesn’t need the additional height. The bodies are much thinner tool sleel. And the pushrod contact cup is can be installed for offset of the pushrod.
It is clear that jesel did put in effort to lighten the lifter.

Would my understanding of kinematics mean "important" by a simple factor of the rocker arm ratio being used?

From a simple observation, for the same lift rate and height at the valve, the help would come in the form of reduced ramp speed and lift required on the pushrod side. But because often the same cam lobe would be used, now the added rate of valve, retainer, locks, rocker and spring opening speed and total lift will add to the needed spring rate.

Pushrod weight value is inverse to the square of the rocker ratio.
2:1 rocker = 1 ÷ 4 = .25:1 ratio vs. valve weight

Got it.

I'm with you on this one.

Let me be controversial: if you don't care about weight, a taller tappet (at least from the lobe to the pushrod seat) weighs more than the length deducted from the pushrod, but it makes the pushrod much more rigid. Even 1/2" is worth something.
If the pushrod is 10" OAL, and the inserted eds are 1/2" each (the tube is 9"), taking 1/2" off the length has the same effect as increasing the diameter about 1/16": 16.6%.

One of the "secrets" to the LS: high cam placement makes very short pushrods.