Engine compression ratio info

[BarracudaDave]

Just picked up an ebay reproduction operator's manual for my 70 Cuda.  Page 53 lists the engine specifications.  I was surprised to see the 340 engine listed as 10.5 to 1 compression.  I didn't think it was that high from the factory?
The other engines listed were 6 cyl at 8.4 to 1; 318 at 8.80 to 1; 383 2 barrel at 8.7 to 1; 383 4 barrel at 9.5 to 1; 426 Hemi at 10.25 to 1;  440 4 barrel at 10 to 1; and the 440 six barrel at 10.5 to 1.

[Chryco Psycho]

most of those figures were under ideal circumstances  & a bit optomistic but in the right area

[Aussie Challenger]

  Earlier 426 Hemi engines had 11.5 :1 & I heard some were even higher.   

[moparmaniac59]

As the "smog" engines came along later in the 70's the compression ratios dropped considerably. Take the '74 440 engine (no longer available in "E" bodies) as it only had an 8.2:1 Compression ratio as did the 400. The 318 dropped to 8.6:1. The six cylinder stayed at 8.4:1 and the 360 was 8.4:1.



                                                 Matt B.

[71chally416]

Every stock early 340 I've ever seen apart has an above deck piston deck height, so the 10.5 comp number for them is probably accurate.