i think one goes up and down and the other one goes round and round or is it they both go up and down and round and round ...frank...
The difference is not as much the camshaft as the lifters. Hydraulic lifters act like little hydraulic shocks-they pump themselves up and become stiff, but can 'float' or pump down above certain RPM's (high). This keeps the engine revs down by lessening valve opening/lift. Mechanical or 'solid lifter' camshafts have lifters that do not vary the valve lift as hydraulic lifters do. Thus...they rev as high as the motor will want to go. For your next question about 'roller camshafts', they have wheels where lifter meets the camshaft lobes. This allows different geometry in lift specs, less friction and less energy is used as a result of being more more efficient. They are available in solid or hydraulic lifter versions. Seth
I'll go even further: Hydraulic cams are for ease of use. They follow the general shape of the cam lobe, but have the oil as a cushion on the parts so you don't have maintainence to worry about. The liability is when the fluid nature of the oil causes erratic valve motion in extreme use situations. Solid cams have no cushion. They follow the lobe of the cam and send that exact motion to the valves. Without the fluid nature of the hydraulic lifter, solid cams tend to react to the throttle much faster, have a wider power range, and can rev higher. A solid and hydraulic cam with the same specs, when compared, the solid will: Rev quicker, more throttle response. Have more vacuum. Idle smoother. Make more power. Rev higher. Have more low rpm power and torque by far. Solid cams must be respected though, they have no cushion to rely on when needed. They need to be adjusted in a way that accounts for expansion and contraction of the metal components. Stock solid cam cars, and old school rods, didn't have the good aftermarket valvetrain parts we have today, so they needed adjusting every time plugs and points were changed, which was about every other oil change. This has given solids a reputation for being high maintenance. However, with todays common speed parts like roller rockers and locking nuts, they just need to be tuned properly once, then checked on the rare occaision. They say about once a year or so with good valvetrain parts. Rollers are the same, they just have roller wheels on the bottom of the lifter instead of flat metal. This allows for a MUCH much more aggressive ramp on the cam. Flat lifters have sharp edges so if the cam tries to raise the lifter onto the ramp too fast, the edge of the flat tappet will 'dig into' the lobe of the cam. Rollers will lift much faster without damaging the lobe. There are roller cams that are so aggressive that the lobe almost looks like a figure 8. This is also the reason that roller cams need much stronger springs. The lift and lower of the valve is so aggressive that without strong springs they would just bounce and be an uncontrollable mess. The hydraulic and solid rules apply the same. That is why the factory uses hydraulic rollers. Solid rollers have no cushion, then have much higher pressures and more parts, so they can be dangerous to an engine if they are not respected. Dave
So in my 351 Cleveland with 4v heads and about 10:5.1 compression am I going to benefet from solid over hydraulic. The clevelands are high revving motors and I want to make some killer power. They made about 300hp and 400 torque in 1970 so that is where I am starting and I want to do about a .550-.600 lift. What do you guys think? -Andrew
If you've got money to spare, I would go ahead and have the internals zero balanced. I think it'd pay off in the long run - especially running high RPM's. Good luck.
For your application I wouldn't bother with a solid lifter stick. I would spring for a retro-fit hydraulic roller camshaft setup, though. You can achieve lots of lift while keeping the duration relatively short which helps a Cleveland do two things: A. Make great power with excellent throttle response. B. Be more tractable on the street. Most big hydraulic cams and "street" solid lifter sticks for a Cleveland have too much duration at .050" lift to be streetable. They're usually hard to drive, idle like snot, and don't make power until 4000 rpm. With a good hydraulic roller cam you can have damn good low-mid range throttle response and good upper rpm breathing. A good street Cleveland will not see over 7000 rpm anyway and the hydraulic rollers will usually be good to that rpm. Crane Cams has a few grinds that look pretty good. PM me if you need help picking one out. Oh yeah.....I wouldn't internally (or zero) balance a Cleveland engine unless it will regularly see over 7500 rpm runs. External balancing is fine for street Clevelands.
