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rear mounted regulator vs return system

 
Old 08-30-2010, 03:28 PM
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preston
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Default rear mounted regulator vs return system

I know all the big power guys switch the later returnless systems to a full return style with the regulator at the front. My impression is that this is more to overcome various issues with the system and line/pump sizing, and that adapting an existing return style aftermarket system is the easiest route.

But the trend with some of the non-vette cars that use big fuel pumps (both n/a and turbo) is to move the regulator back to the tanks with a long vacuum line, and then deadhead the line up to the fuel rails, ie a returnless system - although unlike the vette system the regulator is outside of the tank. THe point of this is to keep the big fuel pumps from overheating the fuel when the tank is low, long drivers, traffic etc. This isn't so much a problem with the pump heating the fuel as the fuel making the trip to the hot engine too quickly because of the large volume of fuel being moved.

The people I"ve talked to that did this report no problems even on the big turbo builds.

I'm just curious if anyone knows of any other reasons than above that most big power vettes move to a return system. Have people actually found performance problems with a returnless system ? Again I understand in stock form that the returnless system is not ideal for performance, I'm asking about specifically building a large fuel system that simply regulates and returns fuel back at the tank rather than bringing the fuel forward to be constantly heated by the engine bay.
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Old 08-30-2010, 03:37 PM
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The conversion to return system is due to the initial drop in pressure a returnless system has when fuel demand is quickly increased. Since the regulator is so far from the rails it doesn't react quickly enough to keep the pressure steady. It has to see the drop in pressure and then close itself to increase flow and then the long line from the tank to the rail has to re-pressurize.
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Old 08-30-2010, 06:06 PM
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It also will heat up all the fuel in your tank.
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Old 08-30-2010, 06:10 PM
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There is that too.
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Old 08-30-2010, 07:50 PM
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the problem i see with a rear mounted regulator is that there will be a pressure drop during the length of the fuel lines, a front regulator ensures that the motor sees its required pressure.

i have a tiwn intank setup with both walbros sitting in the stock canister, the fuel cools them and i dont go past 1/3 tank (rather be safe)

if you went with one external pump (cuts install cost) they are usually boost referwnced with a hobbs switch, basically the external pump only provides enough fuel to counter the boost pressure.

our cars like 60psi, but with 10psi of boost there is 10psi of pressure pushing against the fuel so your net fuel pressure drops to 50, this also explains why FI cars need much more fuel. whether you have an external pump or twins the hobb switch/ regulator says "hey the motor is seeing 10psi, better bump up fuel pressure by 10, so your pumps make 70psi, push through the resisting 10psi and the motor stays happy at 60psi, hope that made sense. once i figured it out 2-3 light bulbs went off
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Old 08-31-2010, 12:26 AM
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Originally Posted by 5 Liter Eater View Post
The conversion to return system is due to the initial drop in pressure a returnless system has when fuel demand is quickly increased. Since the regulator is so far from the rails it doesn't react quickly enough to keep the pressure steady. It has to see the drop in pressure and then close itself to increase flow and then the long line from the tank to the rail has to re-pressurize.
Originally Posted by MachineWorks View Post
It also will heat up all the fuel in your tank.

Well said.

<END THREAD>
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Old 08-31-2010, 09:07 AM
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First off it may seem like I'm against you on every thread (based on your belt alignment/dongle filter thread) and thats certainly not the case so I'll start with a

There are some mis-truths below though. A second pump, whether internal or external, on a hobbs switch or wired to be on all the time is not countering the 10 PSI of manifold pressure. It's just there to make sure you can maintain the ~58 PSI that the system wants. A single stock pump (expexially without a BAP) is not up to the task of providing enough flow to keep the pressure at ~58 PSI when there is a big fuel demand. It's true that at 10 PSI of manifold pressure you are effectively running 48 PSI of fuel pressure but we just tune around that by leaving the injectors open longer (this happens inherently when tuning the AFR provided the injectors are large enough). With two in tank pumps you will see ~70 PSI at idle because the regulator is being overloaded and can't divert enough fuel to keep the pressure at ~58 but as soon as you go WOT the pressure will drop back to ~58.

Ideally we would have a boost/vacuum referenced regulator but that would require moving the regulator at least ouf of the tank if not up to the rail (EG: return style).

Originally Posted by SinisterC6 View Post
if you went with one external pump (cuts install cost) they are usually boost referwnced with a hobbs switch, basically the external pump only provides enough fuel to counter the boost pressure.

our cars like 60psi, but with 10psi of boost there is 10psi of pressure pushing against the fuel so your net fuel pressure drops to 50, this also explains why FI cars need much more fuel. whether you have an external pump or twins the hobb switch/ regulator says "hey the motor is seeing 10psi, better bump up fuel pressure by 10, so your pumps make 70psi, push through the resisting 10psi and the motor stays happy at 60psi, hope that made sense. once i figured it out 2-3 light bulbs went off
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