How do'es a carburettor work with a turbo

Site Subscriber Joined: 23 Jan 2005 Posts: 502

The air going it to it is under pressure from the turbo.

But the fuel is gravity fed.

Is the ventury strong enough to pull fuel through.

Retroholic Joined: 23 Dec 2005 Posts: 3315

on a 5GTT it has a carb and fuel pump

Site Subscriber Joined: 23 Jan 2005 Posts: 502

So no float bowl.

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

all carbs have a fuel bowl and a fuel pump. Gravity feed systems were about pre model T!

All carbs work on a differential of pressure. The difference is normal atmo pressure 14.7 PSI and the vacuum the engine creates.

They are so damn complicated thankfully the multipoint efi system came about and made things extremly simple.

Fuel is pulled in by the engine air speed through the venturi, this draws fuel from the float bowl through the jets and out into the incmoning air, the accel pump actually squirts an amount of fuel in via a diagphram. It squirts in fuel causing it to run run rich preventing a stumble due to the sudden change in air speed. Some of us that have driven classics may know the good old no accel pump acceleration, you need to slowly accel to stop the car stumbling badly.

Enrichment valves are again diagphrams operated by spring pressure, when the air pressure is right the valve opens allowing more fuel into the throat enrichening the mixture.

Fuel is pumped to normal carbs at a max of about 5/6 PSI. Air pressure is 14.7PSI which is just over 1 BAR.

The float bowl is the resovoir so no need for higher pressur eor flow.

However thats for NA cars.

Turbo carbed engines are another matter.

Cars like the GTT have sealed carb bodies and uprated seals. The normal carb is vented to atmosphere, not so the turb carb, it has to basically be 'vented' to turbo pressure. GTT's do this with pipes from the lobster to the carb body.

Fuel delivery, on turbo carb engines there is a higher pressure basically efi pump. The carb has a rising rate fuel pressure regulator again like efi cars.

The fuel has to flow in sufficient quantity and pressure to overcome the turbo pressure. The turbo pressure is basically trying to shove the fuel back to the tank. So a rising rate pressure reg basically maintains the fuel flow and pressure to a pre determind value above the atmo/turbo pressure

The other way which tvr used back in the good old days was to have a normal carb, completely enclose it in a cast iron box this way the outside of the carb was subjected to turbo pressure thus it could behave normally and a higher flow and pressure fuel pump.

Thankfully today its far simpler, just need to map the ECU to fire the injectors and its done.

Site Subscriber Joined: 23 Jan 2005 Posts: 502

Thanks Chris.

Site Subscriber Joined: 07 Oct 2004 Posts: 2281

Chris should write a book!