[onovakind67]

EA3.0 comes up with an effective CR of 7.72, cranking compression of 195, and 10.8" vac at idle. Your compression will be closer to 10.5 if you keep a tight quench. I run my iron head 406 with 74cc chambers, 10.3:1 compression and a 224° cam on 91 octane gas.

 

[onovakind67]

Originally posted by rcatala:
I forgot to tell about the .005 piston to deck ,0.39 head gasket ,flat top 5 pistons valve relieve,74cc heads,may be this is the difference in DR ,THANKS ONOVAKIND67 ,all the help you and other can give me will be very helpful .

I can call AFR and may be ask them for a upgrade in the springs to install a xs282 ,244/252
.520/.540 lift

open close .@.015
35 67
79 31
but I am not sure about the powre rpm of this cam and a stock 400 crank
this cvam gives a DC OF 8.1 DYNAMIC COMPRESSION

If you look at the cam card, you will find that the advertised duration for the Comp XE solids is measured at .015" tappet lift. At .015" tappet lift and .016" lash the valve is already open, so using the 274 number to determine the valve closing point is misleading.

 

[onovakind67]

Wasn't there recently a large pissing match about DCR? In my opinion, it's an interesting thing to know but shouldn't be the driving force behind the parts selection. There are a whole lot of other things to consider about the effects of the compression ratio on the engine build that have to do with resistance to detonation, like quench, swirl, burn rate, cooling efficiency, scavenging, wave tuning, timing, octane, coatings, etc.

The XS274S cam should work just fine in your car.