Thread: Series 2a petrol head

That is pretty much the case. The heads can be distinguished by the newer head having a square boss about 2cm across cast into the top of the head between the rocker cover and the carburetter. This should have an 8 stamped on it if it is an 8:1 head, and 7 or blank if a 7:1 head. Earlier heads do not have enough metal to safely shave more than about enough to bring it to 7.5:1.

If you increase it to over 8:1 you do run the risk that it may not be happy on standard unleaded.

But increasing compression ratio is the most fruitful engine modification you can make.

John

ok thanks mate, mine has the square cast into it with a 7 stamped into it. So if i run it on premium unleaded would it be safe to run around 8.5:1 in it? Thanks for your help mate.

does anyone know how much the head would need to be decked to get around 8:1 comp ratio? thanks

Originally Posted by army2a

does anyone know how much the head would need to be decked to get around 8:1 comp ratio? thanks

No, but I would expect anyone who is equipped to do this is also equipped to calculate the amount required to be removed.

John