Ok so I have said and mentioned this before and there are even a few Manuals out there including Haynes, Chilton, and also another source by Nissan Redline. But the FSM states the usual 9.5:1 C/R.
Now I've been doing a little bit of piston research and there are 2 Different Combustion Chamber sizes in which Manufactures are measuring by.

The 46cc CC is being measured by: JE, Supertech, Weisco, and CP
The 43cc CC is being Measured by: Ross, Arias

To my understanding the Stock KA24DE pistons are the same between all the DE's S13 & S14 which IIRC have a Piston Volume of -20cc's or somewhere in that range. To my understanding w/ have 0 Deck clearence (correct me if I'm wrong) which is what all the Manf. state and use to Measure. Another Variable the Manf. use to Measure is the HG Thickness being .045" or 1.14mm.

Putting all these variables together gets me these Final Compression Figures:

43cc Head: 9.52:1 C/R
46cc Head: 9.17:1 C/R

Rounding those figures gives you 9.5:1 and 9.2:1

Somebody go measure the CC of an S13 and an S14 Head pls and verify something, this is driving me nuts. Another thing that makes me into thinking the S14 Has the Higher C/R head is that the Cams are smaller, the SVC was removed form the Intake, and the Head Cast Number is different. Also look at the Gasket sets, 91-94 are all the same 95-96 have there own and 97-98 have there own...

Link to the different Heads thread back awhile ago:
What's the difference ka24de s13 head and s14 head, Pics are here!! - Zilvia.net Forums

WTF is going on........

 

i heard the 95-98 ka heads flow better compared to the 91-94..which dissy do u use if you put a 14 head on a 13 block?

 

^You use the one according to your OBD System if it's in an S13, you use the 13 Dist.


I also heard that too, but I see no evidence as the Heads look Damn near Identical besides the VC Gasket...

I just want to know where that 3cc's come from, I'm beginning to think the S14 head is Milled a bit to make up for the 232 cams and up the C/R...
I would make logical sense as it makes a bit more power w/ smaller cams and an OBD-II Emissions system...

 

Head flow rates are the same.
Flame front propagation speed on the 95-98 is better. You can look at the reference numbers between the 2 heads they are in fact slightly different in quench area.
KA24de truck and altima engines are for sure 9.2:1 compression engines.
Redline claims that the quench area being slightly different from the 95-98 heads may yeild a slightly lower compression on 91-94 heads.
Also on some model years between 94-95 depending on the production date would use a different head. I believe that is why there could be so much confusion on the head types and CR ratio's for 240sx KA24de engines.

 

+1, i have read the same thing in several different sources.

 

Interesting, any links to these sources?

 

No, but I have a 95 head sitting in my garage right now, if some one has an OBD1 head we can take some measurements of the quench area, and head cast numbers.

 

I Do but I'm ~3000 miles away from my car until July

 

OBDI Head:

43cc

(Found in the bowels of my computer from my '91 engine)