Can anyone tell my why I can’t or shouldn’t run the bypass regulator before the carbs? Aeromotive says it should only be installed after the carbs, as in this diagram.

I have run it right before the carb & it works great, for a street set up it would be better after for keeping the fuel cool.

So if the regulator was before the log, it essentially a dead head system? There seems to be many ways to skin this cat.

no its not a dead head, it is still returning the unused fuel.

Not sure about the porting in the regulator. If the flow area in the regulator is large enough to feed the carb without restriction, I can’t think of a reason it wouldn’t work fine.
That picture also says to return to top of tank.... so take it as more of someone’s recommendation than the correct way to use it.

I am running a bypass regulator on my EFI swap.

The bypass regulator I am using (Holley 12-886) controls the pressure at it's input and anything in excess goes out the bypass line. So my fuel rail is between the pump and the regulator.

If you plumb it any other way it does not work as designed.

Aeromotive probably knows how to properly plumb it.

You graphic's plumbing does not match the available ports in the picture you also posted. In the graphic I would bet those carb feed ports and the regulator inlet port all are the same internal to the regulator and in essence the carb in the graphic is plumbed exactly like Aeromotive says to do it.

Those graphics are straight from their website.

One graphic is for a log feed and the other is directly into to carb.

It would be interesting to see what size restrictor hole is in the return line port
I think all of the EFI system with high pressure, above 15 lbs., have the regulator after the fuel rails in the line returning fuel to the tank

I am running that set up. The way the fuel log picture shows is the simplest. The regulator just mounts to the fuel log, clean set up, no drama. My return goes back to a submerged port in the rear of the fuel cell.

It is my understanding that the regulator after the carbs help dampen the pressure spikes in the fuel log

It’s all just a bit confusing to me, as some call this set up a bypass system and others such as aeromotive call it a dead head system.
At this point, I’m leaning towards putting the regulator after the carbs.

That is a different regulator. for a dead headed system

The way it’s set up with the picture with the log, the regulator determines the main feed line pressure.
If you have the regulator set at 6psi, the whole main feed line is at 6psi.

With the regulator between the pump and the carb, the regulator only regulates the pressure between the regulator and carb....... independently of the main line pressure.

Any regulator with a return line to the tank is by definition not a “dead head” regulator.

That makes sense. So is one version better than the other for keeping the fuel cooler and the pump quieter?

Here is my set up.

Put the regulator after the carb.. it will flow fuel to keep the whole system cooler( much less
time for fuel to set and heat up

I don't run a return style regulator but I can see a benefit of the regulator being down stream from the carb. With it plumbed this way the first restriction in the system is the needled and seats in the carb, not the regulator. I would think fuel supply would be more consistent this way. Yes I know thousands and thousands of cars have been plumbed with the regulator first and have performed fine. Potato or potatoe? LOL

do you set the fuel pressure and float level with the car runnning or off?

Running, if using a dead head system.

If I was designing a fuel system for a fast carb car I'd probably use a high pressure pump and have the regulator before the carb. Then you have high pressure up to the front and low pressure after the regulator for the carbs. If you are using a low pressure pump then I don't think it matters too much. In that case I'd just follow the instructions and assume that the mfg knew what they were doing.

No since in reinventing the apple