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With the heads and piston combo your running I'd figure you've got around 8/8.5 to 1 compression.Longer duration will kill the bottom end like you said it did.

Try calling comp cams their Extreme series has openings and closings that are supposed to help cylinder pressure.

I had the same problem years ago w/a comp magnum 292 cam,in a stock bottom end 350.Sounds like your following the same path I went down.

BTW,when I changed from a mld roller to a much bigger one I went from,220 cranking pressure to 190,and picked up over 1/2 a second.
 

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It picked up both NA and sprayed.

Dynamic compression,includes valve overlap,and duration.The number is usually in the 9 to 1 range(high compression race motor) or less,if I remember correctly.I had read some articles on this awhile back.

Static compression involves the piston at BDC vs.TDC.(what you see advertised)

The compression guage your using gives you a reading based on dynamic compression.You can't really tell the static compression with it.Too many variables cam,engine temp, air temp,starter cranking speed and the fact that rarely do 2 gauges read alike.

They make great tools for finding potential problems,ie drastic drop in all cylinders or more then 10% between them.

I try to check and log mine every couple of months to see if I've got something going south.
 
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