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GX200 Turbo project

65ShelbyClone

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Is running a fuel pump + regulator required on a draw-through system?

A pump only if you can't get enough fuel to the carb. A regulator only if your pump produces too much pressure for the carb.

Trying to figure out if I need to have fuel pressure rise proportionally to intake pressure,

That's only necessary when the fuel metering device(carb or fuel injector) is exposed to boost pressure.
 

VC10786

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A pump only if you can't get enough fuel to the carb. A regulator only if your pump produces too much pressure for the carb.



That's only necessary when the fuel metering device(carb or fuel injector) is exposed to boost pressure.
Thank you, that clears things up a bit.
Since I have a draw-through setup, my fuel metering device(carb) is never exposed to turbo boost pressure.

So the only factor preventing my engine from running right is the jet size, correct?

I'm thinking, as the turbo spools, more suction/air flow is created in the carb venturi, which would automatically cause more fuel to be pulled through the jet, and should dynamically meet the engine's needs, assuming my jet is big enough to supply the amount of fuel it needs, right?

Right now I'm guessing that is my bottleneck, which is why I ordered an aftermarket carb with several larger jets sizes available.
 

65ShelbyClone

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So the only factor preventing my engine from running right is the jet size, correct?

In a nutshell, yes. Your air filter looks pretty small as well which will affect jetting if it's a restriction of any kind.

Jetting a draw-through turbo should be fairly straightforward even with a stock carb. I'm not sure hat kind of problem yours is having.

I'm thinking, as the turbo spools, more suction/air flow is created in the carb venturi, which would automatically cause more fuel to be pulled through the jet, and should dynamically meet the engine's needs, assuming my jet is big enough to supply the amount of fuel it needs, right?

Sort of, but it's not that straightforward. Velocity through the venturi is what causes a pressure drop that pulls fuel through the jet circuits. More velocity will pull more fuel until the carb has reached its maximum airflow capacity. Air and fuel flow stops increasing at that point and manifold pressure between the carb and engine starts dropping (or "vacuum" starts increasing). Now the carb has become a restriction and is limiting power.

Draw-through setups simplify the fuel system at the expense of having to use a carburetor that is usually too large and over-jetted for the engine when not under boost.
 
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