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ITB Fuel distribution

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I am putting an EightStack system into a GT40 replica. The throttle bodies are modeled after Weber 48IDA's with the fuel inlets center, outboard facing. Curious if there are any advantages or disadvantages in the fuel distribution. I am thinking one of three approaches

1) Series: one single loop around the perimeter - fuel in on one side, branching to each ITB, ending at the pressure regulator, and then the return

2) Parallel Y: Fuel comes into a Y fitting at the rear, down each side and then terminating at the regulator and return

3) Parallel 90: Fuel comes in at the back and 90 degree fitting to the legs that feed each side, then terminating at the regulator and return.

The system will be injected so will run about 43psi and max out around 500hp

Fuel loop options

Any one system or variant stand out as being the preferred way? Suggestions or ideas.

I can visualize some theoretical preferences but curious if any really stand out.


What you've called parallel Y has never failed me, so I generally go that route.

The other options sometimes work, sometimes result in issues. In your application they may all effectively result in the same great outcome though as there are many factors involved.

I err on the side of what gives me the greatest likelihood of success unless I'm in a situation where I want to test alternatives to learn about the outcome.

To add a little science to this, my testing has indicated the additional hose length inherent in the parallel Y system is part of the benefit, acting as a damper that has worked better than actual damping devices in testing. That does assume you use fuel line that's not hard line, doesn't have a hard internal sleeve.

As with Mike, Option 2 would be the way that I would lay it out as well. Mike and I have similar experiences in working with Subaru flat engines, the Series style feed is what Subaru uses, and it causes issues when you ramp up the power.

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