Jaguar models were available with different compression ratios to suit different markets.
The normal was 8:1 but 7:1 and 9:1 were also available. (8:1 and 9:1 only for the
early Marks 1's). The /7 /8 or /9 suffix gives the compression ratio of a particular
The 7A prefix was used for both the Daimler V8 engines in the 2.5 V8 and
the 4.2 liter Jaguar engines in the Jaguar 420 based Sovereign. Number of cylinders
and engine configuration should be a clue in this case!!
The XKE series 1 4.2 had a new engine number series for the 2+2 model
introduced during 1966. This number series appears to have started at 7E 50001. The OTS
and FHC models engines are in a separate ranges starting at 7E 1001. It appears that the
engine numbers approximately match the chassis numbers
The XKE Series 1.5 also had a continuation of the 7E 5xxxx range for the
The XKE Series II 2+2 model engine number range starts at 7R 35001
Note After Dec 1970 the letters H (High), S (Standard), or L (Low) replace
-9 -8 or -7 as engine number suffix
XKE Series III engines for both OTS and 2+2 model were in one range 7S
The original cylinder head fitted to the 3442 cc XK engine was
retro-designated the Type "A" and fitted to standard XK120 and XK140 models. The
"C" type head was developed in 1953 as an offshoot of Jaguars racing program
with the XK120C racing car. The exhaust valve size was increased to 1 5/8 inches and both
inlet and exhaust porting was increased in size. This head could optionally be fitted to
XK120SE models after this date and to XK140SE models. It is usually painted red.
The next development was the "B" type cylinder head, which was
fitted to most "standard" XK150 models. It retained the larger exhaust valves of
the "B" type head and the inlet valve angle was changed from 30 degrees to 45
degrees. Power output was unchanged from the "C" type head, but maximum power
was developed at lower revs making the unit more flexible. The "B" type head was
normally painted light blue or green on 3.4 liter engines and a metallic dark blue on 3.8
liter engines. According to Nigel Thorleys bood "Original Jaguar MK 1 and MK
II" the cylinder head on MK II models of 3.4 and 3.8 liter capacity (which also
used the "B" series head) were always painted blue and a photo in the book shows
the blue to be a light robins egg color.
The "straight-port" head was developed for the XK150S models and
as the name implies had the ports straightened for better gas flow. It was usually fitted
along with 3 SU carburetors, a 9:1 compression ratio and a lightened flywheel. The
straight port head was usually painted a pumpkin orange color. This was also
the cylinder head fitted to Series 1 and Series 2 E-Types.