Curious what you guys run in place of the stock "cool-fuel" systems, looking for something reliable to comfortably feed a 500-550hp 509. I am not sure I can look at it the same way I would building a EFI fuel system for a car? If I go to a good inline pump and -AN lines with a quality fuel pressure regulator what do I use as a cooler? My plan is ditching the stock black MPI mag intake for a Holley multi-port EFI throttle-body system.

Your fuel tank can work like a cooler with a return system

I know Holley makes retro-kits to put the pump in the tank with a Hydra-mat, is that something to look into as well so the pump is also cooled by the fuel in the tank on top of running a return fuel system?

https://www.holley.com/products/fuel...e/parts/12-137

You can plumb in a small cooler right where the cool fuel is located if you want, but I personally don't think it is necessary with the fuel returned to the tank. I wouldn't bother with putting a pump in the tank. A Weldon or Aeromotive inline pump will work fine.

What Ive done on quite a few mpi setups is
1. Reuse stock water sepreator/fuel filter in stock mount as prefilter, if making boosted hp (700 to 900) , drill the stock 1/4npt out and retap to 3/8.I would just use it way it is for your hp goal.
leave filter and go to the pump
2. buy a appropriate marine rated efi pump, if it draws any kinda amperage, use your efi to trigger a relay vs directly power it as it taxes your efi wires
3. buy a small inline auxillary cooler like a cheap ps cooler with threaded npt fittings, go thru it to rail
4. Put a 10 micron inline after filter before fuel reaches the rail to keep any debris from ever reaching the injectors
5. Leave rail or rails and go directly thru your efi regulator back to the second inlet on factory filter like it does stock
6. as preference I use braided stainless teflon lined hose with non conductive outer coating and an to npt fittings at all the aforementioned components
I tuned a 280 powerquest when it was 90 out that had fuel returning to the tank with no cooler. We would sit at dock and make tuning changes on laptop, when we got on plane, it would lean out to 15-1 regardless of tuning changes. After we went down river a mile or so afr would drop down and stay down until it sat again, we were 100% sure it was boiling the fuel in the rail, Smitty

How whipple plumbs the fuel on the 525 whipple kits.

If your goal is 500-550hp, why not just replace the pump with one from a 500efi?

This is how I have my 584HP Holley EFI multi port 454's plumbed in my boat. I Tee'd my return before the fuel pump. I've had no issues


.

They run the return back through the fuel filter?

Similar to an automotive setup. And yes I will use the Holley to trigger a relay for the pumps and a direct feed from the batt through an appropiatly sized circuit breaker to feed the actual pumps.