cam selection/head flow

in my experience with amc from the factory they use strait duration for smooth idle but most of my motors I build they like split duration   

Most of the dyno testing that I have seen has been primarily done on the old small block Chevy which had worse exhaust to intake flow percentage than AMC. This should mean that a split duration cam should be more beneficial to the Chevy than to the AMC V8.

   The dyno charts of the split duration cams usually picked up maybe 8 to 10 horsepower above maybe 4,500 to 5,000 rpm compared to straight duration cams, and lost almost that much under 3,000 rpm. Most of these tests were done on hot street combinations with headers. It seems to me that a split duration cam does the same thing as a slightly bigger straight duration cam would.....loses power on the bottom end, and gains it back on the top.

Cam timing events have less to do with real head performance than most think.
I strongly suspect these people posting here are aware of that.

The exhaust event is times to give the maximum scavenging that
is inclusive of opening early enough to purge all exhaust gasses and
create the important vacuum boost to the intake event.
The intake typically requires less timing to be optimum at the same desired engine speeds.

True no matter what balance you have in the ports.

Nearly half of the flow through an un supercharged engine is caused
by the pull of the exiting exhaust pulse.

This is why "tuned" headers make more power than a better flowing manifold or shorty headers.

I agree with JTSLLC1. Now that the secret is out of the bag. AMC for years have had a better flow out of the exhaust than most sbc ever had. The headers have a direct connection to scavageing than most people realize. It all depends on cam events and intake charge velocity. I stick with what runs best and not try to jump all over the place with what other people run. Your combo may not work well in another engine almost identical. There is always a little difference in any engine combo.

Pontiac engines all used cams with longer EX. duration to help the poor flowing ex. ports. The 340 Mopar had 8 Deg. more ex. duration with more lift for the same reason.