generally the old school rules of engine work apply awesomely to the A series and new school modifications work a treat too!
old school way: Theres no replacement for displacement so try to start with an A15 or A14 for the extra torque advantage. The three big gains are had in compresion, carburettors and camshaft so shaving the head and fitting flat tops will up the compression, fitting twin sidedraughts will let it breathe up high in the revrange and the right cam for your power range will tie it all together as long as you have some good competition valve springs and big end studs fitted.
Electronic ignition, thermo fans, oil cooling and a good free flowing exhaust will make her run even better.
New school way: You can also turbo the A series with great results so check out the tech section for ideas on how people go about this, be it a draw through set up or blow through or even a wild twin turbo set up like 1200rallycar has done, there is some amazing examples here that will make chossing between a tough N/A build or a off-it's-head shrieking, whooshing and whistling turbo screamer harder than you think
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