1275 head porting

[downsey]

What is the typical horsepower gain with a ported 1275 head? and how noticeable is the extra power?

[bmcecosse]

Well it depend what you do - and who does it! Simple thing is to fit the larger inlet valve from the MG Metro - this is 35 mm against the standard 33 mm (both sizes approx). Open up the throats around the valves and open the turn round into the port as much as possible. This is the key area - the actual 'ports' are plenty big enough, it's the turn into the valve throat that causes the restriction. A full race 'Downton' head would make about 20 bhp difference to your engine - but to get the most from it you need to upgrade the camshaft/carbs/exhaust to suit. But simple stuff done yourself will give another 10 bhp without spending a fortune. Get a hold of Mr Vizard's book on the A series engine - plenty of bed-time reading in there!