Turbo Installations to Petrol Carburettor Engines
Our primary method of aftermarket turbocharging a carburettor 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 onto the turbo's compressor housing. With this setup, 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 the correct tune. Most OEM carburettors can be used draw-through but create a lot of cost to tune correctly.
For engines 2 litres 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 a reduction of the engine's compression ratio, which allows efficient ignition timing and boost pressures up to 9 9PSI without water injection when using the best quality petrol. Blow-through systems with and without intercooling have less potential to pre-ignite, which means some engines will operate on original compression specifications. When water injection is used on a draw-through 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.