Fuel System - Part 1 - Hard Lines

The common approach when it comes to running the fuel lines for the AK builds is to use -6 or -8AN stainless steel braided hose from the tank, along the inner chassis rail to the engine and, in the case of fuel injected engines, similarly run a return line down the opposite chassis rail and back to the tank.  The fuel pump and filter are typically fitted on the supply pipe run and also fixed onto the inner chassis rail.

Although the AK fuel tank for a fuel injection set-up has a small sump to prevent fuel starvation under hard driving, a conversation with an AK owner at Stoneleigh a couple of years ago about his experience of fuel starvation, convinced me that I was going to go belt and braces on this and install a surge tank in my fuel system.

A surge tank is a small volume tank fed by a low-pressure fuel pump from the fuel tank; any excess fuel is fed back into the fuel tank.  The engine is then fed via a high-pressure pump from the surge tank.  This means that even if the fuel pick-up in the tank is uncovered, there is sufficient fuel reserve in the surge tank to provide an uninterrupted fuel supply to the engine.  An added advantage is that since the fuel between the surge tank and the fuel tank is constantly being recirculated this keeps the fuel supply to the engine cooler which is a big advantage, especially with the increasing ethanol content in fuels.

The surge tank will need to be installed in the boot of the Cobra and it made sense to me to also install the fuel pumps and filters in the boot rather than fixing them under the car.  Since I would need to run the fuel pipes from the fuel tank up into the boot and then back out again I decided to use run hardlines for the fuel supply and return lines along the chassis rails.  

I went with Goodridge HL836 lightweight aluminium hardline which I purchased from Merlin Motorsports.  This is made from Hycot aluminium; a precision-drawn aluminium tube with a black polyamide coating.

-6 Size Aluminium Hardline

Hardline Fittings 

I used my plywood brakeline template/ guide to help bend the tube to the correct profile.  The hardline diameter is 10mm which worked fine in a mini pipebender.  I made the pipes slightly longer than I thought I would need; these will be trimmed back when I know exactly where I will want to create the transitions to the braided fuel lines.

Hardlines bent to shape

These were then fixed into place on the chassis rails using some of my bespoke mounting blocks; the fixings on the offside chassis rail also being used to hold the rear brake pipe in place.

Supply and return lines fixed in place

Supply line will connect to a braided line at this point 

At the rear, two braided lines will run up into the boot

Everything seemed to fit into place quite nicely and I was very pleased with the final result.

You may spot from the pictures that this blog post is a little outdated given that the engine and gearbox are now in place but for some reason, I just never got around to writing up this instalment.  In hindsight, I was bloody lucky that the locations I chose for the brake/fuel line mounts didn't clash with the transmission as there was no prior consideration of this in my planning!! (Although I did crush the nearside fuel line when installing the gearbox which required the purchase of some additional hardline and a re-bending exercise - luckily I had kept the piece of plywood with all the bend guidelines on!)