Compression Ratio Confusion

[billy g]

I'm showing my ignorance here, but what should the compression ratio be for a '74 2002? Everything is stock as far as I know. Only mod would be a Weber 32/36 carb which should not effect compression, right? I've tried searching here and elsewhere and the answers range from 8.1:1 to 9.5:1. Does anyone have a definitive CR? Thanks.

[visionaut]

Regular ol’ USA 2002 would be 8.3:1…

 

The History & Reference section is good readin’.

[John76]

'74-'76 US carb models had to reduce compression to comply with the emission requirements. Lower compression lowered combustion temperatures which reduced NOX. The two-stage EGR systems also cooled the intake charge.

8.1:1 is the specified CR for "most" '74-'76, but some had 8.3:1 with the E-12 head. All had "baby grand" domed pistons except the 49-state '76 with the E-21 head had flat-top pistons. The CR difference with the domed piston cars is the recess between the top of the piston and the head. No recess = 8.3:1. Recess = 8.1:1.  Additional emission controls (air injection, thermal reactor, advance/retard distributor) determined the presence or absence of "the recess".

Your stock '74 came with a regular exhaust manifold with no air injection, 2-stage EGR, and possibly a vacuum retard distributor.

Sooo ... my semi-educated guess would be 8.1:1 for your '74 US spec manual car.

 

John