Surge Tank Setup
For a big fuel system you have a few options, all of which require custom work. The most common is dual or triple in-tank pumps, but dual or triple hangers are hard to come by for the MKIII and you're still stuck with crappy Walbro pumps plus running tons of stainless line from the tank to engine bay. Another (possibly) even more expensive option is a fuel cell, but I wanted to keep my car stock inside.
Weighing all of my options and budget, I decided to go a route that's used on alot of rally cars-a surge tank. A surge tank is basically a reservior fed at low pressure by an in-tank pump that an external high pressure pump pulls from. Fuel pumps flow alot more at lower pressure so the tank stays filled even though the external pump is pulling alot of fuel from the tank under WOT.
In my setup the stock pump feeds a 2L tank mounted under the headlight:
I used -6 braided fuel line for everything with Summit swivel fittings to ease the hose routing. The stock fuel feed runs to the lower side of the tank creating a swirl effect to push air to the top of it (why they're sometimes called "swirl pots" across the pond) and the Bosch 044 external pump I have mounted on the inner fender pulls from the port on the bottom:
The pump outlet has a tee fitting on it and there are 2 feed lines that run to either end of the stock fuel rail. I had initially drilled and tapped the second feed but the threads didn't hold so I had the fitting welded to the end of the rail. One thing I learned is that the 044 (and any roller type fuel pump) don't like to be run dry so I had to add a check valve to prevent drainback when I shut the car off so that there is fuel in the pump at all times. I picked up a -6 Aeromotive valve from Summit Racing as well as an inline filter just to be safe:
The stock return location goes to an Aeromotive FPR and then back to the top of the surge tank. There is also a return line at the top of the tank that acts as an overflow feeding back to the stock fuel return line into the Supra's gas tank.
By my calculations I should have fuel avaialable for at least 30 seconds of WOT just based on surge tank size and pump flow rates. Should be good for my goal of ~500hp on E85, although my 680cc injectors are probably too small. I was hesitant to go any bigger because I'm still on the stock ECU (with SAFC) and want to be able to run regular gas as well, any bigger on the injectors and I don't think I'd be able to lower the base fuel pressure enough to compensate and not be super rich at idle.
The plan for now is to see how it runs with the 680s and go from there. I have a feeling it will be scary fast at it's current power level once I get it tuned so we'll see...
