Hi Matt;
As Tracy has said, it should be noted that a true modern automotive returnless design has a pump regulator assembly mounted directly in the fuel tank. I believe there is someone on this list that has also done this. That would be the best if not for the weight penalty of a pump/regulator for each tank. And while it is a small risk, it does also involve routing hi-pressure fuel through the cabin.
So mine isn't really a true returnless system, but since I'm not returning to a tank, I call it that.
As I have 6 tanks, I originally went with a header tank in my original fuel system as a simple way to manage the fuel. But it suffered from vapor lock. Venting it helped, but when doing circuits with a climb out every few minutes it still had excessive vapor issues. And by venting I always had to manage the facet transfer pumps to ensure it didn't go empty or full and pump fuel out the vent. So I added a valve to the vent that I could shut when in cruise. I looked into level management systems, etc, etc. That simple header tank was creating a very complicated fuel system which is dangerous.
Having 6 tanks to select from already adds a level of complexity, so I needed to eliminate the extra issues with the header tank. I was hesitant to remove it as I'd spent considerable time and effort to install that, but in the end it was the right thing to do. With that said, when I converted to a returnless system, I did make other changes that may have helped the header tank system, but I'm not going to second guess the decision to remove it.
Now my returnless system has low-press fuel routed through the cockpit, and as soon as it passes through the firewall it enters a large cartridge type fuel filter/water separator and then feeds 2 hi-press EFI pumps. The are mounted on the cool side of the FW, but unfortunately are still exposed to the heat of the engine/exhaust, but are shielded from direct exposure due to their location.
So the returnless system seems to work very well, with the exception of this heat soak that seems to be at worst about an hour after shutdown. Fuel pumps and regulator located on the cool side of the firewall should completely eliminate this.
At the risk of adding back some complexity I'm pretty much sold on the idea of a momentary-on push button operated solenoid valve to vent the header. The reason I'm not so adverse to this is that you have to make it vent by holding the button. It can't be inadvertently left on... as long as the button doesn't stick!
The regulator I'm using is from SX Performance 15404-3.
The fuel filter is a Parker Racor 120A with the R12S filter cartridge and I added the optional RK10109 metal fuel bowl kit and the RK30880E water-in-fuel detection kit. I use the vent port for my regulator return.
Todd --- going fishin...