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3. Turbo Installations to Petrol Carburettored Engines

Our primary method of aftermarket turbocharging a carburettored petrol engine uses the carburettor in a draw through function, usually with a constant depression CD Stromberg 1¾" side draught unit mounted through an adaptor with V band clamp directly on to the turbo's compressor housing. With this set up a journal bearing turbo with a carbon compressor seal is required. The 1¾" CD adapts and tunes very effectively on power outputs up to 250 engine HP, with two units in parallel used for power above 250. Examples can be found in the Retro Turbo Equipment section. Small Square bore vacuum secondary holley type carbs adapt well when modified to give correct tune. Most OEM carburettors can be used draw through but create a lot of cost to tune correctly.
For engines 2 litre or less the Blow through Solex-Renault carby works very well and drives like good EFI. For engines above 2 litres we have used the XE-XF Falcon Weber with modifications. If good fuel mixtures can be created both draw through and blow through systems can be successful.
Our draw through carburettor turbo installations always include reduction of the engines compression ratio which allows efficient ignition timing and boost pressures up to 9PSI without water injection when using best quality petrol. Blow through systems with and without inter cooling have less potential to pre-ignite which means some engines will operate on original compression specifications. When water injection is used on a draw though system with the liquid entering at the carburettor inlet, damage is not caused to the compressor wheel blades.
Photos of some draw through equipment layouts are in the Retro section. Power gains up to 200% are achievable with correctly set up and tuned engines with draw through carburettor systems.
Purpose made 4 Barrel Blow through American carburettors for large displacement engines are now on the market.