Knocking 340
I dont even know how to equate that to CR. :D
OK here; maybe this will help;
Cr is Compression Ratio. You take the entire volume of the cylinder with the piston at the bottom, and compare it to the entire volume when the piston is at the top.We call it Scr because it is a Static Compression Ratio number, nothing is moving . It is usually defined as;
(CV+cv)/cv where CV is the swept volume and cv is the chamber volume.
A stock 360 has a CV of 737.21 cc and a cv usually of around 105.3cc so then
(737.2 +105.3)/105.3=8.00/1 SCR or Static Compression Ratio.
But; the engine while running never has an intake valve that closes with the piston at the bottom, and compression building cannot begin until the intake valve is actually closed and not leaking.
In a performance engine, this point is often with the piston nearly halfway up the cylinder. Most performance cams will fall into the range of 60 to 70 degrees after the piston has left the bottom.
This is very bad news for the 8/1 engine, and the shorter it's stroke, the worse it is.
Lets take that 360 and say the intake valve does not close until the effective stroke is reduced to 2.58. Now the swept will be 531.2cc.. and the same chamber is 105.3 so once again;
(CV+cv)/cv = Dcr this time so
(531.2+105.3)/ 105.3=6.04 Dynamic Compression ratio . This is a decidedly un hi-performance number. With iron heads we like to target about 8/1Dcr.
So how can you get to 8/1 from 6/1 ? Principally, you have to shrink the size of the total combustion chamber; in this case a lot. 78cc is about the easiest to get so lets try that, still with the 2.58 Effective stroke.
(531.2=78)/78=7.8 Dcr, now yur getting close.
With a lil more machine work, you can get your chamber to 75.88cc and so
(531.2+75.88)/75.88=8.00/1 and there you go. Mission accomplished.
Now, from here, you have to go find a cam, with an ICA that will produce the effective stroke of 2.58, which is the only Ica that will produce the 8/1Dcr with the 75.88 total chamber size, in a 360, lol.
