Could you give us a little theory lesson here?
Any of the rest of you who know about these things feel free to chime
in.
Arch,
Sorry about the vernacular. Short & long refer to duration.
Basically, duration is how long the valves remain open. Lift is how
high they open. Overlap is when both the exhaust & intake are open at
the same time. The old rumpity-rump 60's muscle cars that used to get
our testosterone going had loooong duration camshafts in them, viturally
nil vacuum at idle and hence vacuum reservoirs (and switch pitch
converters). Early hot-rodders raised the idle speed as a band aid to
cover up this lack of vacuum problem. There's more to it than this but
I believe these are the basics.
Some of the newer camshafts (past 15 years) have dual patterns, that
is the intake & exhaust duration are different. Usually it's the
exhaust duration that's longer of the two events. The newer roller
camshafts take advantage of very steep lobe angles on the camshaft to
open & close the valves quicker getting in return the advantages of a
longer duration camshaft by allowing the valves to remain open
wider-longer without the penalty of overlap. This can't be duplicated on
a hydraulic lifter camshaft because of the diameter of the base of the
lifter. (It would literally run into the side of the lobe because of the
steep lobe angle.) Virtually all of the new pushrod engines use roller
camshafts.
There's tons more to elaborate on camshafts but it gets into reversion,
swirl, valve size, maximizing combustion chamber quench & on & on. Not
the purpose of this post.
Like Arch said, if any of the rest of you can add, chime on in!
Steve Ferguson
San Diego
Any of the rest of you who know about these things feel free to chime
in.
Arch,
Sorry about the vernacular. Short & long refer to duration.
Basically, duration is how long the valves remain open. Lift is how
high they open. Overlap is when both the exhaust & intake are open at
the same time. The old rumpity-rump 60's muscle cars that used to get
our testosterone going had loooong duration camshafts in them, viturally
nil vacuum at idle and hence vacuum reservoirs (and switch pitch
converters). Early hot-rodders raised the idle speed as a band aid to
cover up this lack of vacuum problem. There's more to it than this but
I believe these are the basics.
Some of the newer camshafts (past 15 years) have dual patterns, that
is the intake & exhaust duration are different. Usually it's the
exhaust duration that's longer of the two events. The newer roller
camshafts take advantage of very steep lobe angles on the camshaft to
open & close the valves quicker getting in return the advantages of a
longer duration camshaft by allowing the valves to remain open
wider-longer without the penalty of overlap. This can't be duplicated on
a hydraulic lifter camshaft because of the diameter of the base of the
lifter. (It would literally run into the side of the lobe because of the
steep lobe angle.) Virtually all of the new pushrod engines use roller
camshafts.
There's tons more to elaborate on camshafts but it gets into reversion,
swirl, valve size, maximizing combustion chamber quench & on & on. Not
the purpose of this post.
Like Arch said, if any of the rest of you can add, chime on in!
Steve Ferguson
San Diego
