Volvo B20 Head Identification
On a weekly basis we get questions from customers about which head they have. Often they think they have an E head when they really have an F head , or vice versa. This is important, as the E head with its gasket gave a nominal compression ratio of 10 - 1, whereas the thicker F head, with its thicker head gasket, was rated at an 8.7 - 1 compression ratio. Identification and differentiation is really quite simple.
First method - measure the head from the gasket surface to the head bolt surface.
The factory specs for both the thickness of the head ( height of the head ) and of the head gasket are as follows:
B20 A head 3.41" -- head gasket .055 ( 1.4 mm ) unloaded --- .047 ( 1.2 mm ) loaded
B20 B head 3.39 " --- head gasket .031" ( .8 mm ) unloaded --- .028 ( .7 mm ) loaded
B20 E head 3.34 " --- head gasket .031" ( .8 mm ) unloaded --- .028 ( .7 mm ) loaded
B20 F head 3.42" -- head gasket .047" ( 1.2 mm ) unloaded - .039 ( 1 mm ) loaded
Note that measuring the head thickness only works if you are sure that the head has not been milled.
Also note that when reinstalling a head and computing the compression ratio that the original thickness gaskets are no longer available. Some are thicker, some are thinner, eventhough they are still listed under the original parts numbers.
Second method - identify the head based on the shape of the head above the intake and exhaust ports.
Photos will do better than a thousand words here so please examine the photos below:
A 72 - 73 F head is pictured below. The injector openings over the intake ports indicate that it was made for fuel injection and the flat over the #2 exhaust port indicates that it is a 72 - 73 F head.
The later, 74 - 75 version, of the F head is shown in the photo below. The flats over both the #2 and #3 exhaust ports are the key.
The next photo is of an E head. Note there are no "flats" above the exhaust ports.
An early carb head is similar to the E head, but with no injector holes and a step in the intake port for locating rings.