Camshafts??????????
yeah I was wondering.......what are the physical differences between a solid camshaft and a hydraulic camshaft? I was thinking that only the lifters were made differently but I also assume, there has to be some difference in material inside the camshaft also. someone enlighten me.

Also......in regular stock cars (all makes and models) what cams do they usually come with. I would figure hydraulic unless there is some other type of camshaft I have no idea about.

another thing about cams........what is actually causing the radical idle is cars with racing cams? Is is the lobe seperation or the duration? or both? Im leaning more towards the duration. I dont think "lift" has anything to do with idle performance.


Engine Compression?????????
Say the engine is already in the car and running and everything.
What can you do to figure out the compression ratio your motor has? Is there a certain tool and precedure you can go about this?

anyones input would be greatly appreciated. thanx.

JD

 

The cores used for hydraulic and solid roller cams are similar. Since the sixties, small block Chevys have come from the factory with hydraulic cams. The switch from solid tappets was even before my time! Hydraulic roller cams became standard on small block Chevys in ~'87. So, prior to that the cams were hydraulic flat tappets. There were some exceptions. The original LT-1, for example, used a flat tappet solid type of lifter. A factory "hot rod", as were some other optional engines in the muscle car era.

Lots of things contirbute to the idle quality of a cam, primarily overlap. This largely a function of both duration and lobe separation. I never was one to pick a cam based on "sound", which seems kinda popular here. But FWIW, a cam with an early exhaust valve opening event will sound "mean" but not necessarily have a crappy idle and poor vacuum, which race cams do suffer from.

Lift does have some influence on idle quality, as it indirectly effects how "steep" the lobes are. More lift (for the same duration) implies steeper lobes. Steeper lobes provide more duration along the early part of the lift curve, which increases the amount of flow which occurs during the overlap phase, even though the overlap (measured at zero lift) is not changed. However, the current trend in cam design is more lift per degree of duration. This is precisely because of what you imply: more area under the lift curve = more hp without a significant sacrifice in idle quality, vacuum, drivability, emissions, etc. The problem with more lift per duration is that this increases the stress on all the valve train parts. High spring pressures and premium parts are needed, which can get expensive. For example, I am upgrading my valve train this year and will end up with ~$1,100 in parts (at wholesale prices).

You should do a search on "dynamic compression ratio". This has been discussed a lot recently over in Advanced Tech. Good luck in your quest to become a "cam guru"!

Rich Krause