[DeTomaso] Fuel Pump Advice

[Julian Kift]

Most folks using an external electric fuel pump are drawing fuel from the bottom of the tank via the drain plug port. Electric fuel pumps don't like running dry and are typically not self priming so require a head of fuel over them. This leaves your current fuel pickup to be used as the bypass return, you'll want to remove the sock filter though.


Speaking of which you should consider installing a rollover valve on your tank vent line, Hall sells a unit that bolts right in place of the stock vent.


http://hallpantera.com/cgi-bin/p/awtp-product.cgi?d=hallpantera-inc&item=22057


Internal bypass pumps are normally pressure limited pumps i.e. they have built in self regulation and can be used with a static regulator (non bypass), so not ideal for high HP applications as you have identified.


As the pump is going to have higher capacity than you are drawing most of the time, the problem with Teeing the return back to the pump feed is that you risk fuel constantly recirculating and heating leading to vapor lock in hotter weather. I'm pretty sure there must be other reasons not to do it related to pump performance in a closed loop system.


You could opt for an in tank pump, which provides the option to use the existing fuel pickup and is always primed (well unless you run out of fuel!) but may suffer from fuel slosh/surge at low fuel. Typically in tank pumps have a baffle or the tank is designed with a low point/sump for the pump to sit in.


Julian

________________________________
From: DeTomaso <detomaso-bounces at server.detomasolist.com> on behalf of Rob Dumoulin <rob at dumoulins.net>
Sent: Friday, December 30, 2016 5:09:32 AM
To: Pantera - Mail List
Subject: Re: [DeTomaso] Fuel Pump Advice

Update based on feedback I received.  Thanks to everybody.

   - Using a Bypass-style regulator is recommended, especially at my HP
   range.
   - Add a 100 Micron fuel filter before the pump, regular one after
   - 7 PSI is what I should target as inlet pressure to the carb
   - An oil pressure cutoff switch is important
   - An inertial cutout switch is a nice addition
   - A momentary (manual) or timed primer circuit is recommended

What are my options for the bypass circuit?

   - Add a return port to the gas tank (Not a desired choice for me)?
   - Add a T before the fuel pump and recirculate warm fuel
   - Use a pump with an internal bypass (Is this a good option)?

Can I use the tank vent line somehow and vent the tank some other way?

On Thu, Dec 29, 2016 at 1:07 PM, Rob Dumoulin <rob at dumoulins.net> wrote:

> My Titus block build is about to start and it was realized that the block
> was not machined for a mechanical fuel pump like I expected.  Call it blind
> faith vs. Murphy's Law.  The engine will be in the 600 HP range with an 800
> CFM carb.  Any suggestions for a trouble-free electric fuel pump that can
> be wired for safety into an oil pressure sensor shutoff?
>
> Rob
>
-------------- next part --------------
   Most folks using an external electric fuel pump are drawing fuel from
   the bottom of the tank via the drain plug port. Electric fuel pumps
   don't like running dry and are typically not self priming so require a
   head of fuel over them. This leaves your current fuel pickup to be used
   as the bypass return, you'll want to remove the sock filter though.

   Speaking of which you should consider installing a rollover valve on
   your tank vent line, Hall sells a unit that bolts right in place of the
   stock vent.

   [1]http://hallpantera.com/cgi-bin/p/awtp-product.cgi?d=hallpantera-inc&
   item=22057

   Internal bypass pumps are normally pressure limited pumps i.e. they
   have built in self regulation and can be used with a static regulator
   (non bypass), so not ideal for high HP applications as you have
   identified.

   As the pump is going to have higher capacity than you are drawing most
   of the time, the problem with Teeing the return back to the pump feed
   is that you risk fuel constantly recirculating and heating leading
   to vapor lock in hotter weather. I'm pretty sure there must be
   other reasons not to do it related to pump performance in a closed loop
   system.

   You could opt for an in tank pump, which provides the option to use
   the existing fuel pickup and is always primed (well unless you run out
   of fuel!) but may suffer from fuel slosh/surge at low fuel. Typically
   in tank pumps have a baffle or the tank is designed with a low
   point/sump for the pump to sit in.

   Julian
     __________________________________________________________________

   From: DeTomaso <detomaso-bounces at server.detomasolist.com> on behalf of
   Rob Dumoulin <rob at dumoulins.net>
   Sent: Friday, December 30, 2016 5:09:32 AM
   To: Pantera - Mail List
   Subject: Re: [DeTomaso] Fuel Pump Advice

   Update based on feedback I received.  Thanks to everybody.
      - Using a Bypass-style regulator is recommended, especially at my HP
      range.
      - Add a 100 Micron fuel filter before the pump, regular one after
      - 7 PSI is what I should target as inlet pressure to the carb
      - An oil pressure cutoff switch is important
      - An inertial cutout switch is a nice addition
      - A momentary (manual) or timed primer circuit is recommended
   What are my options for the bypass circuit?
      - Add a return port to the gas tank (Not a desired choice for me)?
      - Add a T before the fuel pump and recirculate warm fuel
      - Use a pump with an internal bypass (Is this a good option)?
   Can I use the tank vent line somehow and vent the tank some other way?
   On Thu, Dec 29, 2016 at 1:07 PM, Rob Dumoulin <rob at dumoulins.net>
   wrote:
   > My Titus block build is about to start and it was realized that the
   block
   > was not machined for a mechanical fuel pump like I expected.  Call it
   blind
   > faith vs. Murphy's Law.  The engine will be in the 600 HP range with
   an 800
   > CFM carb.  Any suggestions for a trouble-free electric fuel pump that
   can
   > be wired for safety into an oil pressure sensor shutoff?
   >
   > Rob
   >

References

   1. http://hallpantera.com/cgi-bin/p/awtp-product.cgi?d=hallpantera-inc&item=22057