Mick
Whilst you may be able to buy a bigger engine say 1275cc it will not put out as much power throughout the rev range as it would if the Shorrocks CB75 super charger was fitted.
The supercharger as you know will fill the combustion chamber more completely than a normally aspirated engine at all revs and the more you can get into the cylinder the bigger the bang and the bigger the bang the more power generated.
A basic 1275cc engine in unknown condition will cost these days in the region of £250 - £350. If it is a MG Midget especially a standard bore thick flange 1275cc Midget block - the block will fetch a minimum of £250 (I have just sold one for £280) not withstanding the rest of the parts. Midget engines in good condition are in the region of £500 - £700 dependent upon condition.
These are a selection of the minimum parts I would expect to fit to a normally aspirated engine to increase its power and keep its reliability:-
Road/Rally head - Mini Spares MSE6........................£640.00.
Camshaft 286 - Mini Spares...................................£184.00
Cam followers - Mini Spares.................................. £13.04
Duplex - Mini Spares...........................................£28.86
HIF38 SU carb - 'e' bay currently.............................£40.00
Inlet manifold - 'e' bay currently.............................£15.00
LCB ex manifold - 'e' bay currently...........................£92.00
Uprated clutch...................................................£150.00
Distributer to suit camshaft....................................£60.00
Gaskets and consumables.......................................£30.00
Those are the parts that spring to mind and of course it may need shells, rings ect and so on to keep it reliable.
The cost soon start to add up.
You may be able to get the parts off 'e' bay cheaper but unless you know the quality you may be buying a pup.
A de-compression plate to reduce the overall compression may be needed if the supercharger is fitted as too much pressure is as bad as not enough pressure.
Fitting a supercharger is an easy way to gain instant power but the engine must be able to withstand the extra cylinder charging and that is where the reliability comes into it.
When I worked in the BMC garage we supplied a new 970S Mini Cooper fitted with CB75 supercharger. Whilst the power was superb it was not that reliable so the supercharger was soon removed.
Regarding the w(h)ine mines a red.
Phil