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Lash ramps for solid cams
Posted: Sat Nov 30, 2019 5:04 am
by MELWAY
Let’s talk about different ramp designs for solid cams
A lot of people talk about tightening lash right down to help solid roller lifter life on rollers cams for street use
I have heard that there are different designs in how the lash ramps can work. Constant velocity etc.
I know for example the old crane F series flat tappets call for .026” and are pretty noisy at that. I have always tightened them to .018-.020. And they seem much more quiet
Is it a true advantage to component life by running tighter lash
Re: Lash ramps for solid cams
Posted: Sat Nov 30, 2019 8:12 am
by My427stang
I doubt there is a big difference in reliability and longevity between the correct lash and less than that amount, but I certainly think that if you aren't on the lash ramp because you are too loose it is really rough on things.
So better tighter? Within reason IMO, but tighter certainly won't hurt anything if you have clearance and is a bit quieter
Re: Lash ramps for solid cams
Posted: Sat Nov 30, 2019 8:53 am
by F-BIRD'88
Visualize the effect of a hockey stick contacting a puck with different length stick swing-stroke from the puck.
Re: Lash ramps for solid cams
Posted: Sat Nov 30, 2019 8:55 am
by F-BIRD'88
Then also consider if that the cam card hot lash spec is right near the end of the lash ramp verses a lash setting that is s bit further back from the edge.
Considering if the lash is or becomes beyond the lash ramp, onto the opening flank the contact acceleration is much higher.. Shock force is much higher..
Roller bearings do not like shock force.
Re: Lash ramps for solid cams
Posted: Sat Nov 30, 2019 9:20 am
by My427stang
F-BIRD'88 wrote: ↑Sat Nov 30, 2019 8:55 am
Then also consider if that the cam card hot lash spec is right near the end of the lash ramp verses a lash setting that is s bit further back from the edge.
Considering if the lash is or becomes beyond the lash ramp, onto the opening flank the contact acceleration is much higher.. Shock force is much higher..
Roller bearings do not like shock force.
The question was about transferring the logic to an early flat tappet. Same principle of course, but for a flat tappet it you have time to get the lifter spinning and moving, earlier is likely not significantly better IMO
That being said,spinning earlier before acceleration, less lash before velocity change, can't hurt if the valve stays closed. I run mine tight too. 489 EFI FE I run at .014 cold, works out to be about .019 hot, with a .028 cam card spec. I do it mostly because the engine likes a little more seat to seat, but it's a bit quieter.
Heck I even closed up the intake side on my Cummins 6.7, I just went to minimum spec on the exhaust side because Iw as a little concerned with reports of exhaust valve cooling without enough seat time, but drove the intake a bit tighter and it was pretty happy, especially with the "all of the map" lash from the factory
Re: Lash ramps for solid cams
Posted: Sat Nov 30, 2019 11:24 am
by CamKing
There are multiple types of lash ramps( constant Velocity, Constant Acceleration, Constant Jerk, etc).
One of the most critical points in cam design is the velocity at the lash point. Since the majority of the mass in the valvetrain (valve, spring, retainer, rocker) isn't moving, below the lash point, the velocity of all that mass is zero. That means the velocity at the lash point controls how big the acceleration spike is when all that mass starts to move, and when it stops moving. It's that acceleration spike at the opening that stresses and flexes the valvetrain, which is not only hard on parts, but can cause valve loft. The acceleration spike at the closing point is hard on the valves and seats, and can cause valve bounce.
If you are having any issues, tightening the lash will lower the acceleration spikes at the opening and closing points, if the velocity is lower at the tighter lash points. This will be the case with every style lash ramp, except Constant Velocity. With a constant Velocity ramp, the acceleration spikes will be the same, no matter where on the lash ramp, you set the lash.
Re: Lash ramps for solid cams
Posted: Sat Nov 30, 2019 12:50 pm
by PackardV8
MELWAY wrote: ↑Sat Nov 30, 2019 5:04 am
Let’s talk about different ramp designs for solid cams . . . . Is it a true advantage to component life by running tighter lash ?
Some random thoughts:
1. Why would we buy a cam from a cam grinder who had no clue as to what was the ideal lash for his lobe profile? If Mike Jones says, it's .0xy", I'm going to believe he knows best.
2. Tightening the lash effectively increases the low-lift overlap. If the displacement is sufficiently large, it may not make that much difference, but on small displacement, more overlap has a much more noticeable downside.
3. Aluminum heads, rockers and rocker covers transmit much more valvetrain noise. Those of us who grew up with old arn are always unpleasantly irritated by how much more noticeable is the same profile when run all in aluminum.
Re: Lash ramps for solid cams
Posted: Sat Nov 30, 2019 9:37 pm
by MadBill
CamKing wrote: ↑Sat Nov 30, 2019 11:24 am
There are multiple types of lash ramps( constant Velocity, Constant Acceleration, Constant Jerk, etc).
One of the most critical points in cam design is the velocity at the lash point. Since the majority of the mass in the valvetrain (valve, spring, retainer, rocker) isn't moving, below the lash point, the velocity of all that mass is zero. That means the velocity at the lash point controls how big the acceleration spike is when all that mass starts to move, and when it stops moving. It's that acceleration spike at the opening that stresses and flexes the valvetrain, which is not only hard on parts, but can cause valve loft. The acceleration spike at the closing point is hard on the valves and seats, and can cause valve bounce.
If you are having any issues, tightening the lash will lower the acceleration spikes at the opening and closing points, if the velocity is lower at the tighter lash points. This will be the case with every style lash ramp, except Constant Velocity. With a constant Velocity ramp, the acceleration spikes will be the same, no matter where on the lash ramp, you set the lash.
<EDIT>
The DaveMcLain thread below pretty much covers it.
How is the design decision arrived at amongst the various ramp philosophies? Given that a constant velocity ramp always produces the same (relatively high?) stress signature at the moment of zero lash impact, whereas most/all the others might have much lower shock loads but be very lash-sensitive? Stated another way, shouldn't cams with constant velocity ramps produce the same valve gear noise and perform virtually identically -except perhaps for the minute lift difference and perhaps some slight overlap effects over a wide range of lash settings- as long as the zero lash point is somewhere on the ramp?
Re: Lash ramps for solid cams
Posted: Sat Nov 30, 2019 11:15 pm
by Stan Weiss
Remember length and height of the ramp will changes the numbers at the end. For illustration purposes these all have the same length and height. Also remember that the ramp must flow into the actual cam ramp.
The first graph goes from constant velocity to constant pop.
The second graph they are in reverse order going from constant pop to constant velocity.
Stan
ab-lash-ramps-lift.gif
ab-lash-ramps-vel.gif
Re: Lash ramps for solid cams
Posted: Sat Nov 30, 2019 11:56 pm
by MadBill
Isn't there one missing? I thought the sequence was : displacement-velocity-acceleration-jerk-quirk-snap-crackle and then pop; seven in all, ignoring displacement?
Re: Lash ramps for solid cams
Posted: Sun Dec 01, 2019 12:10 am
by Stan Weiss
Bill,
I may have them miss named but the graph / data is correct.
Stan
Re: Lash ramps for solid cams
Posted: Sun Dec 01, 2019 12:43 am
by Stan Weiss
The word constant means just that but does not tell you a hole lot about the ramp. If I increase the length of the constant acceleration ramp from above but leave the height the same I can have it have just about the same velocity as the constant velocity ramp at its end. But notice if I tighten the last on the constant acceleration ramp my velocity at valve contact drops.
Stan
ab-lash-ramps-vel2.gif
Re: Lash ramps for solid cams
Posted: Sun Dec 01, 2019 2:53 am
by bob460
CamKing wrote: ↑Sat Nov 30, 2019 11:24 am
There are multiple types of lash ramps( constant Velocity, Constant Acceleration, Constant Jerk, etc).
One of the most critical points in cam design is the velocity at the lash point. Since the majority of the mass in the valvetrain (valve, spring, retainer, rocker) isn't moving, below the lash point, the velocity of all that mass is zero. That means the velocity at the lash point controls how big the acceleration spike is when all that mass starts to move, and when it stops moving. It's that acceleration spike at the opening that stresses and flexes the valvetrain, which is not only hard on parts, but can cause valve loft. The acceleration spike at the closing point is hard on the valves and seats, and can cause valve bounce.
If you are having any issues, tightening the lash will lower the acceleration spikes at the opening and closing points, if the velocity is lower at the tighter lash points. This will be the case with every style lash ramp, except Constant Velocity. With a constant Velocity ramp, the acceleration spikes will be the same, no matter where on the lash ramp, you set the lash.
What type of lash ramps do the "HARDKORE Cam Series" have Mike?
Re: Lash ramps for solid cams
Posted: Sun Dec 01, 2019 8:50 am
by CamKing
bob460 wrote: ↑Sun Dec 01, 2019 2:53 am
CamKing wrote: ↑Sat Nov 30, 2019 11:24 am
There are multiple types of lash ramps( constant Velocity, Constant Acceleration, Constant Jerk, etc).
One of the most critical points in cam design is the velocity at the lash point. Since the majority of the mass in the valvetrain (valve, spring, retainer, rocker) isn't moving, below the lash point, the velocity of all that mass is zero. That means the velocity at the lash point controls how big the acceleration spike is when all that mass starts to move, and when it stops moving. It's that acceleration spike at the opening that stresses and flexes the valvetrain, which is not only hard on parts, but can cause valve loft. The acceleration spike at the closing point is hard on the valves and seats, and can cause valve bounce.
If you are having any issues, tightening the lash will lower the acceleration spikes at the opening and closing points, if the velocity is lower at the tighter lash points. This will be the case with every style lash ramp, except Constant Velocity. With a constant Velocity ramp, the acceleration spikes will be the same, no matter where on the lash ramp, you set the lash.
What type of lash ramps do the "HARDKORE Cam Series" have Mike?
Our HARDKOREcam series, is a series of Tool Steel cams. The profiles we grind on them, can be any of our profiles.
Most of our profiles use either Constant Velocity ramps, or a Constant Velocity/Jerk hybrid I developed.
Re: Lash ramps for solid cams
Posted: Sun Dec 01, 2019 11:56 am
by CamKing
Stan Weiss wrote: ↑Sat Nov 30, 2019 11:15 pm
Also remember that the ramp must flow into the actual cam ramp.
This is probably the main reason for using different types of lash ramps.
If the first and last steps of the cam lift ramp are too fast, a Constant Velocity ramp may not be the way to go.