what will fuel pressure be?

[97gsxturbo97]

Im trying to understand how this works. I will never do this so dont worry about that it just so I can figure this out. What would the fuel pressure be If I threw on a walbro 255lph fuel pump with a stock fuel pressure regulator? I dont need an exact number.

 

[1992awdlaser]

It varies. From the few people I have heard of doing this and then hooking up a fuel pressure tester the pressure was in the low 50's.

 

[97gsxturbo97]

I ask this because im trying to grasp how the system works. I come from mustangs and I installed a 255lph pump in a foxbody mustang. I didnt need to change the stock fuel pressure reg. The excess fuel would be sent back to the tank via the return system. I thought all modern day cars have this type of system? So if I install a walbro 255lph fuel pump in the eclipse I will have to buy a aeromotive fuel pressure reg in order to get the fuel pressure down to the stock 43.5 PSI. Is that what I need to do? Thanks for your help.

 

[1992awdlaser]

These cars have the same return system design as the mustang. Some cars have returnless sytems like newer neons.

This is what happens with these cars:

When you put the 255 in you are obviously going to be flowing more fuel to the rail then with a stock pump. To compensate for this extra fuel and to keep the fuel pressure correct the regulator bypasses more fuel back to the tank. But the regulator can't bypass enough fuel to keep the fuel pressure in check. As a result of this the fuel pressure will go up. This is why you need to install an afermarket fpr to turn the fuel pressure back down.

Also, since you have a AWD 2G you will want to drill the siphon tube that is in the tank out to 1/8". The 2g awd's have a saddle tank and the siphon is what helps gas get from one side to the other to keep it level in both sides. Don't drill it out any larger though or you will lose the proper ratio of fuel coming in to create a good enough vacuum to suck any fuel out of the driver side saddle.

Here are some pics so you know what it is.

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[TunaTalon]

The stock DSM FPR returns excessive fuel to the tank via a return line just like the aftermarket AFPR's. The difference is in flow capacity. The 255 lph pump will just pump more than the stock FPR is designed to handle.

The 2G DSM has a well balanced fuel system. At about 270 BHP the T-25 is at max, the 450 injectors are at max, and the stock fuel pump is at max. To get more power the 2G needs a full fuel system upgrade, and that of course requires some aftermarket fuel control.

Of course when you get more power the clutch will be a limit, and so it goes until your wallet is the limit.

 

[97gsxturbo97]

These cars have the same return system design as the mustang. Some cars have returnless sytems like newer neons.

This is what happens with these cars:

When you put the 255 in you are obviously going to be flowing more fuel to the rail then with a stock pump. To compensate for this extra fuel and to keep the fuel pressure correct the regulator bypasses more fuel back to the tank. But the regulator can't bypass enough fuel to keep the fuel pressure in check. As a result of this the fuel pressure will go up. This is why you need to install an afermarket fpr to turn the fuel pressure back down.

Also, since you have a AWD 2G you will want to drill the siphon tube that is in the tank out to 1/8". The 2g awd's have a saddle tank and the siphon is what helps gas get from one side to the other to keep it level in both sides. Don't drill it out any larger though or you will lose the proper ratio of fuel coming in to create a good enough vacuum to suck any fuel out of the driver side saddle.

Here are some pics so you know what it is.

You must be logged in to view this image or video.

You must be logged in to view this image or video.

Ok thanks for the great info. Now I was also reading about this and was wondering is it absolutely 100% necessary to do this. I will not be able to get away with just a 255 pump and aeromotive reg? I need to drill out that piece? Also Who determined that 1/8 was the size needed?

 

[1992awdlaser]

Some cars are fine without doing it and some are not. It is your choice of whether you want to take the risk of needing to pull the pump back out. The siphon can be a restriction that raises the fuel pressure also. That is why I suggest drilling it. Everybody I know that has done this used the 1/8" bit.

 

[97gsxturbo97]

Is the siphon easily accessible when I pull the pump out or do I need to drop the tank.

 

[1992awdlaser]

It's located right next to the fuel pump. If you take out your assembly you should be able to see it easily.

 

[97gsxturbo97]

ok ok so this thing is basically like a splitter and there will be rubber lines running to each side of the fuel tank to siphon the gas?

 

[97gsxturbo97]

Are the hoses that attach to this splitter a restriction at all? Also Should I do a fuel pump rewire when I install the pump. I heard the 255lph is so powerful that the voltage gained from the rewire will not be noticable or really do anything. I want to do everything all at once.

 

[1992awdlaser]

The hoses won't be a restriction.

Yes, you want to rewire the pump. The purpose of rewiring the pump is to keep constant voltage going to it at higher rpms. If you don't do this it will limit how much fuel you can flow up top.

 

[97gsxturbo97]

ok final question, Should I do a rewire just to the relay or all the way directly to the pump? I heard going all the way to the pump isnt necessary because the voltage drop will be insignificant from that point on. Do you recommend that I go all the way since I will be removing the pump anyways?

 

[1992awdlaser]

http://www.dsmtuners.com/forums/articles-electrical-wiring/96412-fuel-pump-rewire-kit.html

Just follow that and you should be good.