Hey Zach,
I hate to kinda put you on the spot, but and maybe I have asked this question before, we have four first gens with over 260K on the lowest one and have never added zinc to the oil when we change it.
Are the factory cummins cams better when it comes to wearing than what a Hamilton grind is???? These trucks are not stock, but, have never had the valve springs or cams changed.
In your expert opinion, suppose I wanted to rebuild one of these first gens and see the benefit of an aftermarket Hamilton cam, would I be better off spending the money on a roller cam rather than paying for zinc additive the next 250k + miles?
Don't mind being put on the spot at all. Wear is all relative to each setup, it just is not as easy as making a blanket statement on OEM vs. Hamilton. Our cams are made by a Cummins supplier so the quality of the ductile chill cast core is as good as OEM. If we had the OEM 12v 1.10" tappet and the OEM .715"-.865" lobe width with the OEM profile vs the OEM profile on our 1.45" tappet and our 1.040" lobe width, then yes I would say wear would be much less, because of the higher surface area to support the oil film. The reason you cannot compare the two combos is that we have higher lift, profiles which experience higher spring pressures on top of sharper nose angles from increased lift. Below is the equation we use to calculate the load on the pushrod and the tappet, factoring for the average cylinder pressure, seat pressure of the springs and the rocker ratio.
792,000xBHP/C.I.x rpm=avg cyl pressure
325hp at crank = 273 at the wheels= 275psi 600 hp at crank=504 at wheels= 509psi. 750=630hp at the wheels=636psi 1000=840hp at the wheels=848psi 1200=1008hp at the wheels=1018 psi
24v with stock valve size, 1.34:1 rocker and 110# springs (exhaust)
275 hp=273psi x 2.65sq in= 728 lbs +220lbs spring press. X 1.34 exh. rocker ratio is 1271 lbs.
504hp= 2102 lbs force on pushrod
630= 2553lbs on pushrod
1000=3306 lbs on pushrod
1200= 3909 lbs on pushrod
12v with stock valve size, OEM spring pressure and 1.69:1 rocker(exhaust)
275 hp=273psi x 2.46sq in= 671 lbs + 80lbs spring press. X 1.69 exh. rocker ratio is 1269 lbs.
504hp= 2259lbs force on pushrod
630= 2779lbs on pushrod
1000=3660 lbs on pushrod
1200= 4367 lbs on pushrod
Also, In the past I almost never saw cam or tappet wear. We advised customers that they could use old tappets if they did not want to go to the trouble of changing them out. After oils changed around 2008 or so, we started seeing more wear and started advising customers to change tappets every time the cam was changed. Although this is only anecdotal evidence to run higher zinc oils, I don't think it should be ignored. If you run higher lift, higher spring pressure setup, I would run additive or Higher zinc oils like Joe Gibbs DP-40. I suggest oils with zinc and phosphorus at or above 1500PPM.
Also something to note, I recently pulled the cam out of my 2014 dodge with only 7,500 miles, and found a lobe wiped on the first cylinder and a tappet that was severely concave. This is with the Large 1.5" tappets and the 1.250" lobe width. Absence of zinc and phosphorus is a recipe for lobe failure in my opinion.
On the calculations, plug in your seat pressure, rpm, rocker ratio and C.I. etc and see what pressures your cam experiences.
On the question of roller cam vs flat tappet, since the low lift is much slower with the roller profile compared to a flat tappet with 1.5" follower, you would see a performance decrease going to a roller profile, although you would see a longevity benefit. In my mind the cost does not justify the benefit. $700+ on rollers, machining of $600+ custom pushrods at $250+ and a new cam at $600+. $2000+ pays for a flat tappet cam or two to be changed out.
