Overhead cam direct acting lift limitations

[MadBill]

So far this is only my 'out of the box' thought, but a friend of mine has a bunch of 4 cam/4 valve BBC-based Batten engines and his various cams have either way too much duration or 'dunce cap' shaped lobes plus sub-optimal lift.
My thought is to bond rectangular 'feet' onto the faces of shortened buckets. They would self-align against adjacent bosses and provide a much wider contact face for higher valve velocities...

[UDHarold]

With a valve spring bucket 1.38" in diameter, you divide by 2(.690") and subtract your clearance from the edge(.690"-.020"=.670"), then divide by 57.3. Your answer should be .011693"/* max velocity. A higher design velocity gets closer to the edge of the spring bucket----How brave are you?
Finding out this number is most easily done using various cam analysis software, such as CamDoctor, etc. Trying to measure it with a degree wheel is nearly impossible. Most cam designers should be able to give you this number on any given design---For instance, all my current solid flat tappets for the SBC/BBC .842" diameter lifter are at .007041"/*. My old .960" diameter mushroom designs were around .00807"/*. Most of my roller designs are in the .0085"/*-.0095"/* range.
Velocity numbers are only important in flat tappet solid and hydraulic designs, acceleration numbers are important in roller designs.
The highest lobe lift I have designed a DOHC bucket follower for has been .575", and yes, it did not run off the tappet.

UDHarold

[CamKing]

I was told by cam grinder that some of their profiles are 70% on the bucket- any idea what that means?

I have no idea.
As long as part of the lobe is riding on the top of the bucket, it can't catch the edge. (I normally design the cams to run out to .008" from the edge.)

Camking, Harold- how big a lobe could you get on a 24mm bucket?

How big do you want??
As you increase the duration, you can increase the lift.
As you increase the aggresiveness of the profile, you can increase the lift.
You could stay in the 240's @.050" and get over .400" lift.

How much lift and duration do you want?

[preston meyers]

With a valve spring bucket 1.38" in diameter, you divide by 2(.690") and subtract your clearance from the edge(.690"-.020"=.670"), then divide by 57.3. Your answer should be .011693"/* max velocity. A higher design velocity gets closer to the edge of the spring bucket----How brave are you?

Thanks for the minor education there. I am getting a better understanding for sure.

As far as how brave am I? I'd venture to say rather brave when it comes to trying out new engine parts. That being said I don't think there is a need to be all that brave in this case. I'm looking for a max lift in the .500 range on the 38mm bucket. From what I have seen this should be more than feasible.

[GJ]

I worked on 3 2RZ heads and the stock lift is .340 lift . They all bought cam with around .410 lift . They go outside the lifter bucked (solid buckets ) so we had to grind on the head so the cam rotates . We tried one with a shim bucket and it looks scary when the shim slightly lift on one side . But they all ran and made over 800 rwhp . I need to check how much lift I go with these ( coil bind etc) these thing flows alot over .400 lift . Stock they flow 250 cfm @ .340 lift . Ported and 1mm over valves they flow 280 cfm @ .340 lift , 300cfm @.410 lift . I then just pressed it until it hits the seal (didn't check the lift) and it flowed 335 . Thats alot for a 4 cyl head . Well the valves are huge and the ports are big too . I wanted them to try bigger cams but I need to check if they make bigger solid buckets so I could machine it for it to work on these heads .
GJ

[CamKing]

They go outside the lifter bucked (solid buckets ) so we had to grind on the head so the cam rotates .

That has nothing to do with where the cam rides on the bucket.
You can have a cam that never gets close to over riding the edge of the bucket, and still have so much lift that you have to clearance the head and/or cam cover.

[bobqzzi]

I was told by cam grinder that some of their profiles are 70% on the bucket- any idea what that means?

I have no idea.
As long as part of the lobe is riding on the top of the bucket, it can't catch the edge. (I normally design the cams to run out to .008" from the edge.)

Camking, Harold- how big a lobe could you get on a 24mm bucket?

How big do you want??
As you increase the duration, you can increase the lift.
As you increase the aggresiveness of the profile, you can increase the lift.
You could stay in the 240's @.050" and get over .400" lift.

How much lift and duration do you want?

Well, at this point what I'd want to know is how little duration you could get away with for 11.7mm lift (a figure at .040"/1mm would be ideal) and how big (small) you would need to make the base circle.

Also- as the cam engages the lifter, it starts with a very narrow point of contact (Or maybe I am completely misunderstandning this- please correct me) and as we go up the lift curve the point of contact widens until the entire width of the lobe is in contact with the lifter- aren;t the edges of the lobe "off the bucket" at initial contact?

[CamKing]

Also- as the cam engages the lifter, it starts with a very narrow point of contact (Or maybe I am completely misunderstandning this- please correct me) and as we go up the lift curve the point of contact widens until the entire width of the lobe is in contact with the lifter- aren;t the edges of the lobe "off the bucket" at initial contact?

Not unless you're running tapper on the lobe.
We normally don't run tapper on the overhead cams.

[CamKing]

Well, at this point what I'd want to know is how little duration you could get away with for 11.7mm lift (a figure at .040"/1mm would be ideal) and how big (small) you would need to make the base circle.

To get under 287 @ 1mm would take some work.
As for the base circle, I'd need to design the lift curve first.

[djr48312]

I worked on 3 2RZ heads and the stock lift is .340 lift . They all bought cam with around .410 lift . They go outside the lifter bucked (solid buckets ) so we had to grind on the head so the cam rotates . We tried one with a shim bucket and it looks scary when the shim slightly lift on one side . But they all ran and made over 800 rwhp . I need to check how much lift I go with these ( coil bind etc) these thing flows alot over .400 lift . Stock they flow 250 cfm @ .340 lift . Ported and 1mm over valves they flow 280 cfm @ .340 lift , 300cfm @.410 lift . I then just pressed it until it hits the seal (didn't check the lift) and it flowed 335 . Thats alot for a 4 cyl head . Well the valves are huge and the ports are big too . I wanted them to try bigger cams but I need to check if they make bigger solid buckets so I could machine it for it to work on these heads .
GJ

So normally the "rule" is max lift == bucket diameter / 2 - .060" .

The .060" is for clearance from the edge. Here you are saying that yes it is possible to have lobes go past the edge, and this would be a good thing for situation which need more lift. What are the downsides? Is there going to be a durability issue?

[gruntguru]

If it's not possible, how feasible is it to put in larger lifters

Much easier to have a spherical "dome" the lifter face. Only disadvantage is, the smaller the radius of the "dome" the shorter the contact line of lobe on lifter.

A cylindrical dome would avoid this problem but would require something to stop the lifter rotating.