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Old 02-11-2011, 02:16 PM
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Solid lifters on hydraulic cam

I have just been asked a question from a friend and he wants to know why you can't run solid lifters on a hydraulic cam.I have been at rodding for years and this is the first time I've been asked this.I told him I wasn't sure but I think the metal is diffrent.I also told him I would get the answer to this.Any takers?

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Old 02-11-2011, 03:43 PM
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Metal isn't any different, both are cast cams with the same heat treatment, as are the lifters. The difference is that the hydraulic cam doesn't have the valve lash clearance "take-up" ramp ground into the lobe profile, to softly take up the valve lash clearance without pounding parts to death. Run solid lifters on a hydraulic cam and it will beat the valvetrain to death, along with the difference between durations caused by the lack of the clearance ramp will make the cam seem much bigger with solid lifters on a hydraulic cam.

Not something you want to try to do.

There are guys getting away with running solid ROLLER lifters on a hydraulic roller cam, but it is a special situation discussed with the cam manufacturer to get the cam profile compatible. They run the solid roller lifter with very little lash clearance, like .004-.006", real tight, so it comes as close to zero when running without actually being zero clearance and holding the valve off the seat when it should be closed.
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Old 02-11-2011, 04:36 PM
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Thanks for the reply, To put it in laymans terms am I to understand that the peak of the lobe is (fatter for lack of a better word) on the solid lift grind?
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Old 02-11-2011, 05:38 PM
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Quote:
Originally Posted by oldschool hero
Thanks for the reply, To put it in laymans terms am I to understand that the peak of the lobe is (fatter for lack of a better word) on the solid lift grind?
Sort of but not really. The main difference is starting up the side of the lobe, the shape is carefully computed to take up the clearance on a solid lifter valvetrain without smacking everything together like you hit it with a sledge hammer. It is not something you can see with the naked eye, ir even measure with a pair of calipers. It is a difference in rate of lift per degree of rotation, the lobe softly takes up the clearance on the solid and then gets to the job of accelerating the valve open faster than a hydraulic lifter can handle, but the key is that lash take-up ramp as far as differences between the two types goes.
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Old 02-11-2011, 05:42 PM
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Got it .The old dog just learned something new.Goes to show you can learn if you ask. Thanks again
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Old 02-11-2011, 06:24 PM
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Quote:
Originally Posted by oldschool hero
I have just been asked a question from a friend and he wants to know why you can't run solid lifters on a hydraulic cam.I have been at rodding for years and this is the first time I've been asked this.I told him I wasn't sure but I think the metal is diffrent.I also told him I would get the answer to this.Any takers?
You can do this, its that's there no point to it. Hydraulic cams, at least factory cams use a lot of ramp to keep control of the lifter. This is wasted time on a solid as it doesn't suffer from pump up so it can be jerked around quicker.

The problem would be running a hydraulic lifter on a sold lifter cam, it's going to have tracking problems with the shorter ramps and faster lobe shapes so it will pump up sooner than it would with a hydraulic cam though you can get around a lot of that by adjusting the rocker so the lifter is pumped up all the way and depends on the retainer bail to keep its guts inside. Again what's the point?

To either of these combinations I wouldn't want to bet on lobe or lifter life, they're having a tough enough time with today's low ZDDP oils.

As for mixing a roller lifter with a flat tappet cam, I really can't see this! The lobe configuration between these cams is totally different because the roller makes an instant contact patch with the cam that requires all the duration to be built into the lobe shape. For a flat tappet cam, the lobe wipes the diameter of the lifter as it passes over the top, so the lobe has much less surface, almost being pointy, as the wiping distance is much, if not most, of the duration. Add to that, roller cams and flat tappet cams are made from much different materials. The roller, because of the instant contact point, wants to unroll the metal of the lobe so the cam has to be either machined from billet steel for high performance applications with sudden and high lift rates or from a steel casting if the timing and lift are mild enough to resist this "English Wheel" effect. A flat tappet cam has a lot of contact friction spread out over a relatively large area, compared to the roller, with the lifter rotating about its body length axis. This wants to scrub the lobe away rather than reshape it so a material that helps reduce friction from these scrubbing actions and retains oil in its pores is desired and that turns out to be cast iron. So mixing roller and flat tappet cams and their lifters would be pretty short lived experiment.

Bogie

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Old 02-11-2011, 06:45 PM
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curious why your friend wants to know?

to produce a similar power curve, the duration and lift required for solid flat is much greater than dur and lift of hydraulic flat on mild performance build.
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Old 02-12-2011, 07:42 AM
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He is getting ready to put an engine together and has all the parts, then he heard my BB /solids run and likes the sound of it.The best thing he can do now is go with what he has or buy another cam and lifter set.One of those (Can I save a buck here) short cuts.
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Old 02-12-2011, 12:18 PM
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Quote:
Originally Posted by oldschool hero
He is getting ready to put an engine together and has all the parts, then he heard my BB /solids run and likes the sound of it.The best thing he can do now is go with what he has or buy another cam and lifter set.One of those (Can I save a buck here) short cuts.
The simple and probably most cost effective solution if he wants the clack of solids simply for the sake of the sound is to put in a set of Rhoads lifters. These are designed to give better idle vacuum with hot hydraulic cams they do this by leaking down at a high rate. At low RPMs they tick like a solid but take some of the rumpty-rump of the cam away. As the RPMs come up there isn't enough time for that much leak down to occur so they start to work like a regular hyd tappet and give all the duration and lift back to you. The leak down rate remains sufficient at high RPM that the lifter doesn't pump up like a convention hydraulic will if it looses contact with the lobe.

They really only pull about 4 to 6 degrees out of the duration at idle to the effect to the cam rumble isn't all that much. They can actually cut ET as the engine will have less ability to spin the tires out of the hole so the better bite really cuts the 60 foot time. Then the power curve comes up to max as the vehicle is moving and the tires have bite. All-in-all, a good combo to make a fast car that isn't so far over the edge that it's miserable on the street. These also help with the converter if it's running an automatic. The stall speed doesn't have to be so high, by reducing converter stall, the power transfer rate becomes more efficient earlier in the RPM band. But that's a discussion worthy of a book by itself and is a subject is largely miss-understood by the average torque converter buyer.

So the Rhoads are good way to get a solid lifter sound at idle and if this is a reasonably hot cam will restore some bottom end torque while increasing the upper end rev range.

Bogie
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Old 02-12-2011, 03:48 PM
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Thanks I'll pass that along to him.
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