RE : Hemis and pushrods

["dion fields" <noid@domain.elided>]

>>Is there some theoretical advantage to pushrod engines that 
>>I'm not getting here?

Paul,

PUSHROD PROs :
simple and cheap to manufacture.
compact in size.
light weight potential.
engineers are more free to design combustion chamber shape.
short timing chain lasts long time.
easy to produce hydraulic lifters.
most americans like low revving, torquey motors.
American manufacturers are already tooled up to make these.

PUSHROD CONs :
high valve train inertia - high rev use requires expensive valve 
    train parts.
cannot tune intake & exhaust cams separately, hence no 
    Variable Cam Timing or simple adjustments by enthusiast.
looks simple and old fashioned.

DOHC PROs :
low valvetrain inertia - high revving cabability.
can tune intake and exhaust separately, can utilize Variable
     Cam Timing.
look sophisticated and cool.

DOHC CONs :
big bulky engines ( the new DOHC ford 4.6 v8 is as big as an
     old Big Block !! ) .
if made with the same materials and methods as the pushrod 
     engine, will be heavier.
lots of cams - expensive to make and assemble.
timing belts need regular replacement.
engineers stuck with a specific shape combustion chamber,
    though the pentroof is good to begin with.
hydraulic lash adjusters, if used, make the heads even bigger, 
   are more more expensive to make to keep compact.
most americans like low revving torque-monster motors, whats
    the point of the extra complexity if its advantages are not used?

this is over simplified and biased, and i am sure i left a lot out.
but there are very good reasons that American auto 
manufacturers like making these "old fasioned " engines.  of
course, the OHC 4-valve thing has been around an extremely 
long time as well - heck, look as a Duesenberg !

now don't get me wrong, i love my ALFA Twincam, as well as
other trick high performance units.  but for vehicles driven as
appliances, i think a well designed pushrod motor can work
quite well and be very cost effective.

dion fields
73 GTV
88 honda hawk motorcycle ( 3 valve, SOHC )
los angeles


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