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MG MGA - Cylinder Head ID

Been on Barney's site looking at cylinder heads.I have ahead with the same casting # as section B in MGB Heads but it has 18 X on top at the back. Is this head a bolt on for a MGA block? Bob

Look at the flowspeed site
dominic clancy

Thanks Dominic

To my knowledge, MGA heads were marked "15" and "16" at the rear respectively. Various later heads go straight on, one of my MGA's has an MGB or Austin 1800 head marked "18 O"). These heads are supposed to have better breathing but it seems to make little or no difference to the performance of an MGA.
Barry Bahnisch

Thanks Barry


If you fit a cylinder head from a 1800 MGB to a 1600 MGA engine surely you have drastically reduced the compression ratio?
Is this why you got no more performance?
The piston crown shape and combustion chamber volume would have to be looked at.

M F Anderson

Mick, I have pondered this myself but the answer may well be that the combustion chamber size is the same, or almost so! Even so,I doubt whether "drastic" is the right term, perhaps "marginal" may be more appropriate given the small difference in displacement? From my observations, very few MGA's seem to have their original heads, many have MGB replacements.
Barry Bahnisch

MGB later 18v heads have the inlet valves moved outwards. Hence the later heads have different rocker pidistools... (sp)

Thus even on a standard 1798cc MGB block, if you fit an 18v head you have to make cutouts into the block surface. Asuming your cam has enough lift.

i.e. if you put the head on without inlet valve springs and hold the inlet valve by hand it will not drop into the bore if you let go.... just hit the block on one edge.

Thus if you over rev the engine the inlet valve can hit the block...

Plus gas flow would be hopeless.

From Memory... please correct me.. 18 "X" heads is an australian thing and this is the same as 18v heads.... but my knowledge is getting thin now. Better ask Peter Burgess on this one.

Mark Hester

1500 and 1600 heads are about 38/39cc, 1622 and 18G* heads are about 42/43cc chamber size. 18V heads are again about 38/39cc. So, 18V head on MGA will give the same CR. However the 18V head gets its chamber size by having a shallower chamber, which is why valve cutout notches are required. Bore size, valve sizes and cam lift determine size and number of cutouts required,The valve center lines are not moved; the offset rocker stands is for different reasons.

FR Millmore

This thread was discussed between 20/05/2011 and 23/05/2011

MG MGA index

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