Question about lift at the cam vs ratio rockers

[daveblank]

Forgive me, I was reading a post earlier & had to get back to work. Now I can't find it & my searches on the subject are giving contradicting answers.


The post i saw earlier said that high lift at the cam was hard on the case. I have seen the descriptions on some Engle cams say that they will cause wear to the lifter bores.

Which is better, high lift at the cam with 1.1:1/1.25:1 ratio rockers or low lift at the cam with 1.4:1/1.5:1 ratio rockers? For example I found 2 cams that would be very close
#1 .420 lift @ cam .525 @ valve with 1.25:1 256dur @.050
#2 .378 lift @ cam .529 @ valve with 1.4:1 256dur @.050

Please educate me. Would one actually be harder on the case/lifter bores? What about the rest of the valve train(springs, valve guides, push rods, etc)? Would one way vs the other dictate more or less valve spring pressure? I would think not because it would be the same total lift & the same RPM potential. Any other considerations?

NOTE - I'm not asking for cam recommendations, I'm just trying to clarify what I read earlier & make sure not to prematurely wear my new case.

[modok]

By basic logic...
the high ratio setup would put less stress on the lifter bore, since it uses a smaller diameter circle of the lifter to achieve the same valve motion.

But in practice, it's a little less clear.
I really think it's the intensity that wipes out lifter bores.
Cams that accelerate very rapidly from the lash ramp to peak velocity, the lifter contact very quickly moves outward before the lifter is moving much.
While, cams that accelerate slow, the contact moves out more gradually and the lifter is moving faster by the time it ramps up to peak velocity.
IMo it's a lot like how rings wear most at the very top where they stop, because when the ring stops it's not riding on a film, and lifter the same way. You try to accelerate fast, that puts a lot of force on the lifter when it isnt moving much.


So it should be simple, but.... in order achieve the same exact valve lift curve, a cam for higher ratio would have to have a higher intensity to match, perhaps not by the usual rules of thumb we compare with, but it would be true the lifter would have to reach peak velocity at a lower lift and with a proportionally higher force on it.......so
THEN AGAIN most hp cams do cheat by dwelling for a time at peak velocity, and with the ratio rocker cam you would not need to dwell as long to achieve the same overall performance.
So my premise of having identical lift curves is not really what you'd actually do anyway, but you could do that, tho you never would on any engine but this one with it's unlimited lifter size

But anyway, I'm pretty sure it/s the intensity that kills lifter bores mainly, specifically how rapidly the lifter accelerates. And it doesn't really have much to do with anything else than the ramps.
The vz and fk cams should be hard on the lifter bores, since they have fast opening ramps, but a k10 or 218 should be easy on the bores because they accelerate gently, and most popular cams are in the middle between these examples.

[Dusty1]

[daveblank]

That makes sense.

[BFB]

far as the VZ, not going to argue with what their intended use is but there's also guys that have run those cams in engines for years.
and maybe those racing the engines are torn down and rebuilt regular, but every race? maybe.. but regardless of frequency, them slinging the engine the rpms they do had as much to do with rebuilds if not more than just the cam its self. if the cam is that harsh and hard on the lifter bores that the engine needs rebuilt after every race then the case is going to need replaced or at least sleeved every race too, and I don't see guys using cams that trash their case just like that.
I just don't buy into that shit about the vz cams, there's a lot out there that have just as much or more lift than the vz's but you don't hear the negativity about them.
like the 218 mentioned, granted ramps could be different but it has .459 lift compared to the vz15's .435. how much can the ramps ACTUALLY vary between those two cams to make much of any difference at 6000 rpm? serious question.

so far, I have one engine out there with a vz15 and 10k miles on it, maybe y'all are right and it'll let loose tomorrow. we'll see...
got another with a vz25 that has about 4k , again, time will tell

as far as the original question, I always think the whole scenario is kind of off. ok sure, low lift w/ ratios might be easier on the lifters / bores but ratio rockers give less leverage and thus more spring pressure for the lifter side to work against than stock rockers. so then you might need to run heavier pushrods to take the force and then heavier springs to control their weight... so which is better or worse? like most of this stuff, its a give & take and there's not always a definitive answer, no right and wrong because there's so many variables.
_________________
"how am i supposed to torque the rear wheel nut to 250 ft lbs??? " - clonebug
An interesting thing happens in forums where everyone starts parroting the same thing and "common knowledge" takes over.
Most experts aren't.

[Brian_e]

It has way more to do with the lobe profile than the amount of lift. The VZ cams, and the CB Bigfoot cams are obvious compared to well designed gentle cams. You can see the difference just looking at the lobes.

Super aggressive cams have very flat flanks, and a very short opening ramp. Pointy nose as well. This hangs the contact patch on the lifter WAY out at the edge of the lifter. That’s is why lots of the aggressive cams need to use 30mm lifters, because they would run off the sides of a standard 28mm lifter.

This is also known by some as the intensity. The ramp rate of the cam is limited by the diameter of the lifter. Flatter flanks need larger diameter lifter heads to ride on.

When the contact is moved way out, it side loads the lifter pretty bad. I had a mag case get beat up pretty bad with a cb Bigfoot cam. The soft magnesium doesn’t help anything. That is why they are sleeved with brass or bronze to hold up WAY better. Once they are correctly sleeved they should hold up for quite a while.

Brian
_________________
So more or less the lazier and stupider you want to be, the nicer quality parts you need to buy.
-Modok

Narrowed beams, Drop adjustable spring plates, Bus disk brake and IRS kits.
www.type-emotorsports.com

Type E Engine Parts and Supplies
https://type-emotorsports.com/collections/engine-parts

[oprn]

[Dusty1]