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Old 12-11-2005, 05:01   #1 (permalink)
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Benefits of Mechanical cam over hydraulic

Just wondering what the specific benefits of a mechanical cam are over a hydraulic cam?

Efficiency? Less wear? Costs in associated valve train components? Are they intercangeable using same valve train components?

Any help/advice appreciated

Cheers, Cheyne
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Old 12-11-2005, 07:37   #2 (permalink)
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Re: Benefits of Mechanical cam over hydraulic

There are many here that can give you elaborate info on that and I am sure they will be along shortly.

As in an automatic transmission there is a certain amount of slipping that occurs in the torque converter and that is a parasitic loss of power. There is a similar loss with hydraulic lifters in the fact that not a complete 100% of the cam lobe motion of lifting the lifter is transferred. With a mecahnical cam and lifters 100% of that motion is transferred to the pushrod. Due to the slightly harsher motion the cam grinder has to consider this when designing the cam.

There is a basic principle.
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Old 12-11-2005, 09:07   #3 (permalink)
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Re: Benefits of Mechanical cam over hydraulic

Quote:
Originally Posted by CJR09
Just wondering what the specific benefits of a mechanical cam are over a hydraulic cam?

Efficiency? Less wear? Costs in associated valve train components? Are they intercangeable using same valve train components?

Any help/advice appreciated

Cheers, Cheyne
The primary benefit of a mechanical cam over a hydraulic cam is that you can rev the engine higher without valve float with matched components.

There is virtually no difference in cost between a hydraulic cam and its components and those of a mechanical cam with one exception. Oftentimes a mild to moderate mechanical cam will require dual valve springs whereas a mild to moderate hydraulic cam will often use single valve springs. There is a slight difference in cost for the two springs over the single springs...and it would be very noticeable if you were using a half-million sets per year, but one or two sets every two to three years and you'll never notice the $20.

A properly match valvetrain won't wear more or less given the camshaft is equal in design except for one thing. If the mechanical cam is driven at a higher RPM than the hydro cam, then it will wear springs more quickly since they are working at a faster rate. Also, since mechanical cams usually require much higher spring rates and installed/open pressures than hydro cams, then there is certainly more tension involved. The higher tension springs will wear (lose tension over time) more quickly than the lower tension springs. This is why the factory installs whimpy camshafts and buttery springs and then has a redline at 4800-5400 RPM on old pushrod V8s.

The two types of camshafts are rarely interchangeable. Certainly the lifters will never exchange. The springs are unlikely to suit. Sometimes things like retainers and pushrods will swap, but I'd measure both to be sure. Usually a smaller diameter single spring is used in modest hydro cam installations where a larger diameter spring is used in the mecho cam installations. Sometimes this is done to accommodate fitting a dual spring configuration without special head machine work. Sometimes this requires fitting a spring "cup," which fits into the existing machined spring seat and is shaped to accommodate the inner and outer springs.

There are just enough differences that it is probably a far better thing to just think of the two types of cams to be completely different in every aspect and treat them as such. Use a mechanical cam when you want your engine to run beyond about 6400-6800 RPM...or if you want a cam profile that isn't made in a hydro, but only a solid.

Much of this discussion is based on flat tappet camshafts, but relates nearly equally to roller tappet cams, too. The biggest differences between flat and rollers are that a roller can handle a much steeper cam lobe ramp design than a flat tappet...and, you don't have to break-in a roller cam.

As for an argument that suggests that some cam lift is lost using a hydro versus a solid? It is not a "valid-enough" argument to seriously affect operation. How much lash does one give to the mecho versus how much "play" is in the hydro plunger? Let's say that the difference is .003" or as much as .008". Does anyone think that much difference is that important in a street car or even a sometimes strip car? The highest tolerance machined component in a pushrod V8 engine is the hydraulic lifter. It will be within a few ten-thousandths of as designed. That would be something like 0.0015-0.0017 ± 0.0001.

With a mechanical camshaft you can use lash as a finite tuning instrument--to a very modest degree. With a hydro, you're pretty much set at taking up the slack and giving a bit of preload and playing with what you've got.


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