I received a few emails asking why I used Feuling 1-piece HP Pushrods on my 117 build
Eliminate pushrod flex, reduce valve-train harmonics and increase valve lift
Fixed Length 4130 Chrome moly one piece pushrods with swedged formed ends. Heavy duty 7/16 diameter tube with 0.165 wall thickness, precision concentricity, heat treated with a black oxide finish. Intake and Exhaust length pushrods are stock replacement lengths and designed to work with the factory base circle camshaft dimensions. These pushrods work with all Feuling stock and SE Milwaukee Eight camshaftst
Due to the unstable nature of this 4 valve engine design with 1 rocker arm activating 2 valve springs Feuling=left® highly recommends running one piece pushrods over quick install adjustable rods to maintain maximum cam/valve lift and reduce valve train harmonics and associated hydraulic lifter issues quick install pushrods are said to be easier to use, however they cannot compare to a solid pushrod for strength and durability
#4087 HP+=left® 0.165 Wall
When to go big, choosing pushrods
Here's an excerpt from the attached link regarding pushrod demands. While referring to autos, it still illustrates the stress on a pushrod in a high performance scenario.

One item to keep in mind here is that while weight is always a concern, it is less of an issue on the lifter side of the rocker arm since this side of the system’s total mass is only subjected to the acceleration dictated by the camshaft lobe. The issue of mass times acceleration that generates force becomes far more critical when multiplied by rocker ratios of 1.7:1 or higher.

We keep talking about loads, so let’s look at exactly what the pushrod is experiencing. A typical Pro Mod motor might need around 300 pounds of closed valve spring pressure and 1,400 pounds of open valve load. While that number alone is impressive, it’s somewhat conservative when you consider that if the rocker ratio is 1.7:1, then the pushrod must be able to easily withstand a load of 2,380 pounds (1,400 x 1.7) – or roughly equivalent to supporting the weight of the entire race car on that small column.

But these are just static loads and do not take into account the physics of the force = mass times acceleration formula. If we take what is commonly assumed to be conservative valvetrain acceleration rates of 100 g's at an equally conservative 6,000 rpm, this jacks the load to nearly 240,000 pounds. These are instantaneous loads but what’s really scary is when deflection does occur loads can spike to well over 1,000 g’s. That’s when the numbers become very immense.

This is the reason for such large pushrod diameters and wide wall thicknesses when dealing with large displacement engines with ridiculous spring loads at equally outrageous engine speeds

 

The large pushrod diameter isn't always the answer and I would have to see where switching from one brand to another really makes a change. I think that sometimes over-kill comes into it all. I have run various pushrods in the M8 and have found no measurable change in Power or Torque just from changing them. The issue is with the sever angles they all have to work at in a M8 there is just so much more to it all that meets the eye. Use a good quality pushrod and you will be fine for most M8 applications. What I can say it that as you add weight to the valvetrain system you have to control that weight properly and some of the valve springs we see people using on the M8 are really and issue. IMHO the pressure on these is way to high for the engine components being run. That puts excessive wear mainly on the cam and lifters and let's face it that not one of HD's strong parts. In a TC you had one valve and one spring acting on the rocker arm and lifter, the M8 on the other hand has two valves and two spring acting on the rocker arm and lifter. One of the main features in a 4 valve head is that it reduces the mass of the valvetrain so that you can reduce pressures and have better control over a wider range. The pushrod, lifter and rocker arm are very much the same in the M8 as a TC when it comes to mass with the M8 being slightly high on the rocker arm only. The problem comes with some of these heavy springs being used, is people forget you have two of them in a M8 so all the forces are over doubled for a very slight increase in weight and that's not necessary.

The TC with a much heavier and larger valve in the 110 engine use to kill the lifter all the time, so many aftermarket people figured out to reduce the spring pressures to stop killing them and there were no problems when doing so. Now we have a much smaller and lighter valve in the M8 and the spring pressures are right back to where they were on the TC 110 heads. Sure if your going to build a high RPM big Hp engine you need some of it, but for most M8 current builds of a Stage IV or less it's not necessary and actually hurts.

 

this is why my valves are sucked into my seats to much spring pressure

 

 

It comes dwn to the compromise.
If you want fast you do real narrow seats near the top of the margin.
No, they do not last as long. But is the 1000 little things that make an engine run great rather then just OK.
SO-
You have to be knowledgeable; as to what you are asking for.
Hardley EVER will the best performance mods give you the best in longevity.