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You can remove far more weight by hollowing out the core of the lifter than cutting in a waist. I suspect the waist is cut to improve oil flow - e.g. a Cleveland which needs to more oil to the rear mains.
Roller lifters are bad idea on a tappet lifter cam. As has been alluded to, the base of tappet lifter is slightly domed. Which in conjunction with fact that the lobe on the cam has a slight taper across its face, caused the lifter to turn in its bore as it goes up and down. This means you get even wear across the cam/lifter = takes long time to wear out.
For a hydraulic tappet lifter cam lobe, the lobe is tapered all the way around the lobe as the lifter is in continuous contact, so is spinning all the time.
For a solid lifter, while the lefter is on base circle, it isn't always in contact - when cold you have the few thousandths clearance. So, the base circle is flat and then the taper is slowly added as the lobe provides lift to rotate the lifter, and removed as lifter comes back to base circle. As the acceleration is slight, wear is minuscule.
If you put a solid lifter on a hydraulic cam, you are suddenly starting the lifter and that rapidly wears either the cam, the lifter or both = pieces of them in oil and failure.
If you put a roller lifter on a tappet lifter cam, only a small portion of the roller is against the cam due to the taper on the lobe. This results in high contact pressures and quick failure of lifter, cam or both.
Swapping between hydraulic and solid roller lifter cams doesn't have wear issues, but there are usually issues with profiles not being compatible.
Back to solid lifters - they are simple, they are light but they require maintenance. Wear on cam lobe, lifter, pushrod, rocker, valve stem & seat all have to be manually adjusted for. Which requires you know what you are doing and is messy - you are removing valve covers on a regular basis which is asking for a leak.
Enter the hydraulic lifter - for a slight bit of complexity and weight, you eliminate maintenance. But there is a drawback when you start using an aggressive cam.
The same functionality that allows the lifter to over fill (pump up) and keep the valve off its seat - becomes especially bad when you rev so high you 'float' the valve and/or is the profile of the cam results in the valve bouncing off the seat. In either case, the hydraulic lifter 'sees' this as wear and fills up to eliminate it. Hence the anti-pump up lifter, which reduces the tendency.
A side effect of an aggressive cam is poor idle - lift and duration for high rpms are excessive for low rpms. What Rhoades lifters do is allow a little oil to seep out at low rpm, so cam effectively has less lift/duration and engine idles better - kind of the opposite of anti-pump up lifter, they under fill the lifter at low rpm. Then as oil pressure/speed increases at high rpms, the lifters let less oil out, allowing the cam to have its specified lift/duration.
So, without changing the cam - lift/duration/overlap - there really isn't an advantage to FE lifters. Now putting in FE Rhoades hydraulic lifters with appropriate cam could allow more rpms while maintaining existing low end performance - assuming the intake and exhaust would support it.
Roller lifters are bad idea on a tappet lifter cam. As has been alluded to, the base of tappet lifter is slightly domed. Which in conjunction with fact that the lobe on the cam has a slight taper across its face, caused the lifter to turn in its bore as it goes up and down. This means you get even wear across the cam/lifter = takes long time to wear out.
For a hydraulic tappet lifter cam lobe, the lobe is tapered all the way around the lobe as the lifter is in continuous contact, so is spinning all the time.
For a solid lifter, while the lefter is on base circle, it isn't always in contact - when cold you have the few thousandths clearance. So, the base circle is flat and then the taper is slowly added as the lobe provides lift to rotate the lifter, and removed as lifter comes back to base circle. As the acceleration is slight, wear is minuscule.
If you put a solid lifter on a hydraulic cam, you are suddenly starting the lifter and that rapidly wears either the cam, the lifter or both = pieces of them in oil and failure.
If you put a roller lifter on a tappet lifter cam, only a small portion of the roller is against the cam due to the taper on the lobe. This results in high contact pressures and quick failure of lifter, cam or both.
Swapping between hydraulic and solid roller lifter cams doesn't have wear issues, but there are usually issues with profiles not being compatible.
Back to solid lifters - they are simple, they are light but they require maintenance. Wear on cam lobe, lifter, pushrod, rocker, valve stem & seat all have to be manually adjusted for. Which requires you know what you are doing and is messy - you are removing valve covers on a regular basis which is asking for a leak.
Enter the hydraulic lifter - for a slight bit of complexity and weight, you eliminate maintenance. But there is a drawback when you start using an aggressive cam.
The same functionality that allows the lifter to over fill (pump up) and keep the valve off its seat - becomes especially bad when you rev so high you 'float' the valve and/or is the profile of the cam results in the valve bouncing off the seat. In either case, the hydraulic lifter 'sees' this as wear and fills up to eliminate it. Hence the anti-pump up lifter, which reduces the tendency.
A side effect of an aggressive cam is poor idle - lift and duration for high rpms are excessive for low rpms. What Rhoades lifters do is allow a little oil to seep out at low rpm, so cam effectively has less lift/duration and engine idles better - kind of the opposite of anti-pump up lifter, they under fill the lifter at low rpm. Then as oil pressure/speed increases at high rpms, the lifters let less oil out, allowing the cam to have its specified lift/duration.
So, without changing the cam - lift/duration/overlap - there really isn't an advantage to FE lifters. Now putting in FE Rhoades hydraulic lifters with appropriate cam could allow more rpms while maintaining existing low end performance - assuming the intake and exhaust would support it.
