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Early/late cams

 
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2596
Location: MI

PostPosted: Thu Apr 29, 2021 5:58 am    Post subject: Early/late cams Reply with quote

Did the camshafts change in 77/77.5 or anytime between the earlier 24s and the 931?
Buckets?

Thanks..
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Mike9311  



Joined: 14 Dec 2004
Posts: 1678
Location: Chicago-ish

PostPosted: Thu Apr 29, 2021 11:31 pm    Post subject: Reply with quote

Hope this helps

http://www.924board.org/viewtopic.php?t=22636&highlight=amc+cam
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2596
Location: MI

PostPosted: Sat May 29, 2021 11:15 pm    Post subject: Reply with quote

“ Allright, I went out and measured them. The little one is 1.98" and the big one is 2.04". ”

2.04-1.98 is only 0.06” difference, which is quite insignificant sounding to me..

This wouldn’t tell the full story in possible differences in lift though.. The smaller diameter cam measured across the cam to the top of the lobe could even have MORE lift than the larger one depending on the base measurement at the narrowest part of the lobe..

Lift is maximum diameter - minimum diameter..Not just maximum diameter..


But... If early vs late cams had much differences in minimum diameter it would cause lots of problems swapping them, because the heads would have to be different to accommodate for it..
Such as cam journals a different height related to valve stem tops, valve stem length, bucket thickness, etc..
Something would have to be different..
I doubt they are much different in that regard..

Therefore so far I’m going to assume that early cams have a 0.06” smaller lift, which is basically nothing, is it not?
Is 0.06” even within the realm of meaningful?
I think no..

But what about angles and durations? Much more difficult to measure by the home gamer..

I’m not seeing this 46/47 # on this cam.. Where is that number supposed to be exactly?
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 1227
Location: Maysville, Colorado

PostPosted: Sun May 30, 2021 2:52 am    Post subject: Reply with quote

In 77.5 they changed the intake valves from 38mm to 40mm and also changed the cam duration a bit. Haynes manual has the details. That later cam seems to have been used on both the NA's and 931 for the remainder of the model run. I trashed my early cam as soon as I got a later one for fear of mixing them up so I can't supply any identification numbers for the early one. I do have turbo cam around if you need any numbers off it.
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Mike9311  



Joined: 14 Dec 2004
Posts: 1678
Location: Chicago-ish

PostPosted: Tue Jun 01, 2021 11:02 pm    Post subject: Reply with quote

I should scan the cams and put them to CAD. We would know everything then

Could even bring scanner up there some time this summer or borrow cam for a bit. Then bring it back

I was just there too

Edit: 0.060" is 1.5mm plus all that "duration" going through that 1.5mm
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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