Advantage of flat tapped cam over roller cam. (Page 3/3) La fiera DEC 24, 10:34 PM The other problem with ZDDP is that the more pressure it is exerted on it, the draggier it gets. Drag needs power to be compensated, so a loss of power is experienced when high pressures are put on the "high zinc oils". Will DEC 25, 04:02 PM quote Originally posted by theogre: And a big part of why is EPA and other gov's wants to Reduce Wast Oil. This is the crux of the matter... EPA considers used oil an "emission" and looks at what's in the used oil leaving the car to go into the environment. Thus the EPA doesn't like zinc and makes OEMs minimize it. Allen Cline told me the roller valvetrain in a C4 Corvette was worth 0.5 mpg when GM switched from flat tappets to rollers everywhere. They waited to do the same on the OHC engines because the lower spring loads made the gains to mileage in OHC engines much smaller. I've also previously read the bit about flat tappets accelerating valves off the seat more quickly than rollers--probably in a Vizard article. Note that's accelerating the valve *off the seat*, meaning just the first 0.020-0.050" of lift. The limitation to lobe size is really the relationship between the lobe's base circle diameter and the lifter diameter. OHC engines can get fast ramp rates because the tappets are generally larger in diameter relative to the lobe's base circle than on a pushrod engine. As Vizard notes, once the contact point of the lobe on the lifter advances to the edge of the lifter, the flat tappet cam can't go any faster without damaging both lifter and lobe. This is a key factor in lobe design. So while the flat tappet may be able to crack the valve off the seat faster than a roller lifter, the roller lifter will be moving faster in mid-lift and will achieve max lift sooner than a flat tappet will... and that's what gets air into the cylinder... opening the valve as far as possible as fast as possible and holding it open as long as necessary for the RPM. La fiera DEC 25, 07:45 PM quote Originally posted by Will: So while the flat tappet may be able to crack the valve off the seat faster than a roller lifter, the roller lifter will be moving faster in mid-lift and will achieve max lift sooner than a flat tappet will. I do not want my cam to go through mid-lift and max lift at a fast rate, I want it to go through it gradually or slower to mimic a "round/roller" cam lobe. The reason behind it is to increase air velocity. If done right and with the right intake and exhaust systems, 100+ VE or supercharging can be achieved. That's what I have done with the Supernatural system. The fast mid-lift and fast max lift will work for supercharged and turbocharged engines but not for NA engines like mine.