Morris Minor Owners Club

My car has a 948 cc engine and matching cylinder head. I'm looking to fit a replacement, unleaded head and wondered if a 1098 cc head would fit. Are the combustion chambers larger? Is there much of a power advantage in fitting a 1098 cc head? Thanks.

The 1098cc cylinder head Pt No: 12G202 will fit the 948cc Minor engine without modification.
You will get a small increase in performance with the 12G202 head.
Before fitting the 12G 202 head would benefit from say a 0.030" skim to bring the 26.1cc combustion chamber back to the 24.5cc combustion chamber of the original 948cc cylinder head.

DeeRo wrote: ↑Fri Aug 28, 2026 5:14 pm My car has a 948 cc engine and matching cylinder head. I'm looking to fit a replacement, unleaded head and wondered if a 1098 cc head would fit. Are the combustion chambers larger? Is there much of a power advantage in fitting a 1098 cc head? Thanks.

I’m going to message you…

Yes, I wasn't sure if increasing the combustion chamber would affect the power output. Thought it might have an adverse effect. The idea of a skim is sound so how would power be increased with the larger head? Are the valves larger? Thanks for your reply by the way.

The 12G202 head has larger valves and better porting which makes the head more efficient so creating more power but not that much power.
Below is the details of heads used on the 'A' Series.
It lists valve sizes and head details.

Quite a significant increase on the inlet side then Phil. What about the width of the combustion chambers, just thinking about head gasket size? Any difference?

Just use a 1098cc Head gasket when using a 1098cc 12G202 head.