Advertised Duration on the original cam in a '67 327-350?
08-06-2001, 11:04 AM
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Advertised Duration on the original cam in a '67 327-350?
What's the value for "degrees advertised duration" on the original "151" cam that the factory installed in a 1967 Vette with a 327-350? Thanks!
08-06-2001, 04:01 PM
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Re: Advertised Duration on the original cam in a '67 327-350? (Stingrr)
at .050 the timing specs are IO 1.0,IC 41,EO 49,EC-7.0 dur 222/222 :chevy
08-07-2001, 09:23 AM
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Re: Advertised Duration on the original cam in a '67 327-350? (clem zahrobsky)
Clem, thanks for the info - would you also happen to have the value for degrees advertised duration? Seems that it's not listed in any of the online references like GMPP or their supplier, Crane Cams.
08-07-2001, 01:30 PM
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Re: Advertised Duration on the original cam in a '67 327-350? (clem zahrobsky)
The 342 degrees duration quoted by Clem was listed in Corvette News back in ‘65 when
the 151 cam was first used in the then new L-79.
Unfortunately, Chevrolet has used a number of measuring methodologies over the years,
but they rarely specify the details. The Cherolet Power Manual lists “crankshaft duration
at lash point” as 320/320, and I think I’ve also seen 306/306 specified.
The 342 number probably includes both the inlet and exhaust ramp in its entirety, and
“duration at lash point”can be misleading because of differences in acceleration profile.
When comparing cams, it’s best to use the .050” tappet lift duration numbers, but these
are not exact due to differences in ramp design. In particular, comparing a hydraulic and
mechanical lifter cam using the .050” tapper lift data is meaningless because mechanical
lifter cams have longer/higher ramps. The Chevrolet mechanical lifter cams look quite
aggressive because of their long/high ramps, but in reality they are milder than aftermarket
cams with similar .050” duration data.
Duke
the 151 cam was first used in the then new L-79.
Unfortunately, Chevrolet has used a number of measuring methodologies over the years,
but they rarely specify the details. The Cherolet Power Manual lists “crankshaft duration
at lash point” as 320/320, and I think I’ve also seen 306/306 specified.
The 342 number probably includes both the inlet and exhaust ramp in its entirety, and
“duration at lash point”can be misleading because of differences in acceleration profile.
When comparing cams, it’s best to use the .050” tappet lift duration numbers, but these
are not exact due to differences in ramp design. In particular, comparing a hydraulic and
mechanical lifter cam using the .050” tapper lift data is meaningless because mechanical
lifter cams have longer/higher ramps. The Chevrolet mechanical lifter cams look quite
aggressive because of their long/high ramps, but in reality they are milder than aftermarket
cams with similar .050” duration data.
Duke
08-07-2001, 04:01 PM
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Re: Advertised Duration on the original cam in a '67 327-350? (SWCDuke)
Thanks for the tips! I suspected the advertised duration values changed over the years, despite the insistences of some motorheads that the numbers have been constant for 35 years. No wonder that particular info is conspicuously absent in the current GMPP listings ;)
08-07-2001, 09:07 PM
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Re: Advertised Duration on the original cam in a '67 327-350? (Stingrr)
I remember seeing that cam listed as 270º @ .008 by one of the after market grinders. Most after market grinders use .008" for their "advertised" figures but GM used to measure from the point that the lifter first moved. As already posted, the advertised "total duration" figures aren't usually as reliable an indicator as are .050 figures. Two different cams may have the same total duration but have a 10º difference at .050.
