Re: [AMC-List] Continuing Saga of Doc the Jeep, Part II.5

["Swygert, Francis G MSgt 436 CES/CECM" <Francis.Swygert3@xxxxxxxxxxxx>]

The Comp Cams cam I have lists its duration as 252
deg. If the stock cam had MORE duration, why would they advertise this
cam as having increased torque and power from the stock unit? It also
makes me wonder what the profile of the stock 4.2 cam used in '82 was,
and whether I would have been better off to have kept it and simply
degreed it myself rather than buying a new cam when I rebuilt the
engine?

------------------------

You were likely better off to replace the cam. Lobe centers, lift, and
overlap may be different. The duration just tells you how long the valve
stay open from when it opens until it closes. Some cams have the lobe
centers further apart than others, which increases overlap. You have to
compare all the specs -- just one being different could make a
noticeable change in engine performance. You know, like 4* of timing...
;> 

4* is less than one tooth on the gears, that's why the offset key. On a
Corvair flat six one tooth is 14*, on most engines it's 16* (according
to a Hot Rod tech article, so that probably means most big 3 V-8s). The
AMC six should be in the 12-18 degree range per tooth, don't have
anything hand to check that with, and I'm not sure that info is in the
TSM. Knowing that it's 12*+ should help though! 

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