Head cc vs comp ratio

velardejose · Mar 30th, 2005, 11:05 AM

Hi
Just cced my 'old' e15 head (has no visible numbers on it) and my 'new' 15M head:
'Old' head: 23 cc
Hgasket 1mm: 4.5 cc
Piston dish: 14.5 cc
Total comb chamber volume: 42 cc

Swept volume per cilynder 399 cc

399+42=441
441/42=10.5:1 !!!
I was boosting a 10.5:1 cr e16 engine!! Next time I wil cc all parts myself...

I was trying to install a 15M head I have, and numbers would have been:
15M head: 17 cc
Hgasket 1mm: 4.5cc
Piston dish: 14.5 cc
Total: 36cc

399+36=435
435/36=12.08:1!!!

For a stock e16 cr (7 psi boost) project, I want a 9:1 cr
I am using a 2.5mm Headgasket
'Old' head: 23cc
Hgasket 2.5mm: 11.25cc
Piston dish: 14.5cc
Total: 48.75cc

399+48.75=447.75
447.75/48.75= 9.2:1 cr

Pls correct me if I'm wrong
Thanks in advance
I want to complete this 7 psi boost project at ~9:1 cr before lowering it to 8:1 for 14 psi boost

BeEleven · Mar 31st, 2005, 02:17 PM

Is that 12.08:1 the number for an E15 head swapped onto an E16 block with E16 internals? I tried calculating it earlier and got 11.1:1, but I guess I did it wrong. I'll be running that combo N/A....hope it doesnt blow up.

velardejose · Mar 31st, 2005, 02:21 PM

Car is way smoother than before, and no sign of pinging
I used that head with an e16 block with a 304 cam and dual carbs and had no problems

dburone · Mar 31st, 2005, 03:20 PM

When you calculate dynamic compresión ratio, or real compresión ratio, do you think about volumetric eficiency?
If you have a static CR of 9.0:1 it doesn’t meen that the pressure of the cylinder is like the engine really compressed that amount of air, because it doesn’t really fill the cylinder and pressure is less than 1 atm

Doesn’t this count?

velardejose · Mar 31st, 2005, 03:33 PM

Yep
But what the engine's specs say is this static or geometrical comp ratio and thats the starting point
Efficiency has to do with other factors as well as static cr, like air temp, a/f ratio, rpm and others