Series 2a petrol head

[army2a]

Hey guys, does anyone here have a later series 2 head to suit a 2.25 petrol? I'm looking at getting one decked but mines the older 7.1 which I have been told can only be shaved to get around 7.5:1 compression. Does anyone know if this is true and why? I've read that the later head would be ok to deck to get around 8.5/9:1?

[JDNSW]

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

[army2a]

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.

[army2a]

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

[JDNSW]

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

[army2a]

true, thanks for your help mate