Ok, I'm working on my 20b swap and I was just wondering... what kind of fuel pressure should I run?

Thanks,
Jesse

 

I'm wondering about that too, for when I take the EFI plunge.

 

mine idles around 35psi getting boost it sometimes jumps to 60psi ....just make shure it doesnt drop

 

This is a generic fuel pressure question.

You need to know several things.
*What is the flow rate of your fuel pump at high pressure levels?
*What kinda fuel injectors are you using?
*What is minimim pulsewidth you can use on your fuel injectors?

Not all fuel pumps are made the same.
You need to know how much pressure your fuel pump can handle before it tanks.
This ends up being your ceiling or maximum fuel pressure you can use.
Remember, the stock FPR (and most aftermarket FPR's) are 1:1 ratio - 1psi of boost will cause a 1psi rise of fuel pressure.

We've found that ND top-feed fuel injectors will handle up to 60psi to 70psi of fuel rail pressure safely.
The stock fuel injectors are side-feeds in primaries and top-feeds on secondaries.

Depending on control (i.e. aftermarket stand-alone EMS), some ECU's will have limitations on how low you can jack the pulsewidth down, mostly due to resolution.

Okay, so we should keep under 70psi, due to the limitations of the stock ND top-feeds.
If you're shooting for 15psi of boost, we need to add this to the base fuel pressure.
Between 35psi and 40psi is a good starting point.
Just to make sure, we need to check max fuel pressure = 40psi + 15psi = 55psi.
Make sure your fuel pump can handle the fuel delivery at 55psi!!!

In general, high fuel rail pressure promotes better atomization of fuel delivery...to a point.

Remember, the higher the fuel rail pressure, the harder the fuel pump has to work.
Running at higher fuel rail pressure might kill your fuel pump prematurely.

I know Jeff20B is going NA, so shoot for 35psi to 40psi anyways.


-Ted

 

How long do you think this pump will live at let's say 43.5PSI?

http://cgi.ebay.com/ebaymotors/ws/eB...me=rvi%3A1%3A1

 

Since 2 of my friends run Supras, we decided 2 Walbro pumps would work fine. Would this be considered overkill?

RETed, nice explanation.

 

I'm probably going to be running 2 aeromotive a1000's. I also have a tec 3, 3x850cc injectors and 3x1600cc injectors. I'm not sure about the amount of boost yet.

 

Thanks for your help btw!

 

RETed, if I use both stock rails, will I even need a pressure regulator?

 

Nope.
The stock FPR will just see "0" manifold at WOT, and rail pressure should stay around 40psi.
That's what we're doing.

I was thinking about your problem with the damaged stock FPR.
If you're still thinking about using this, you can lop off the damaged FPR and weld on or adapt a barbed fitting.
Then you can use any of the aftermarket FPR's out there that can easily adapt to hose ends.
This might be the most easy and least messy option if you haven't found a replacement fuel rail by now.


-Ted

 

I already sort of tried that. It turns out the whole rail is damaged. The whole thing went crooked. I chopped off the FPR in hopes of maybe fixing the rail, but the metal is too thin to work with.

I haven't actually tried finding another secondary rail yet. I guess I'm sort of hoping to get another stock one so I won't need an aftermarket regulator. The only downside is making room for it. I'll have to cut a hole in the firewall. To give you an idea of how much room I've got to work with, you know that flat machined section on the LIM with the two studs? Well, the LIM will fit the car with the studs removed. The flat part is about 1/8" away from the firewall if I remember right. The secondary rail is above that. I hope it won't interfere with the heater core. I don't think it will since I have some sound deadening material abount an inch thick. I'll have to test fit the LIM with the rail to find out for sure.

 

Jeff20b: I don't need my stock 20b fuel rails. If you pay the shipping, you can have it.

 

bladz311, you have a PM.

 

Ted or anyone else. It looks like there is a small nipple for vacuum reference on the FPR of the secondary rail only. It also looks like there is a temperature sensor on the primary rail. Is the nipple on the secondary FPR for manifold vacuum, and is the sensor on the primary for temp sensing? Is the temp sensor even necessary for me to worry about?

Which direction is fuel supposed to flow? Does it enter the primary and flow up to the secondary? Then exit from the secondary FPR and go back to the tank? I guess I just need to know which nipple of which rail gets which fuel line. Thanks.

 

The Walbro 255 LPH fuel pump just arrived.

 

Why go with 2 pumps that are known for premature failure?? For relatively the same money check out Product Engineering. Other than the Weldon pumps i haven't seen any pumps come close to what these do. Heres the link to them....
http://productengr.com/Fuel_Pumps.htm

 

Yep, you got all of that figured out correctly.
Nope, you do not have to worry about the fuel rail temp sensor.
I only know of MoTeC that can do fuel temp mapping - another variable to worry about that you don't need to take care of for now.


That is correct.
FPR always ends up being at the tail end of the fuel flow diagram.


-Ted

 

Thanks for the info! Ok, I'll connect the seconday FPR to the return line, then run a short line down to the primary rail, then connect the feed line to the other primary nipple. Where should the vaccum sensing nipple be connected to? The primary dynamic chamber along with the MAP sensor? I think I'll hook the brake boost to the secondary chamber because the secondary TB butterflies close before the primary does.

I'm glad I don't need to worry about fuel temperature for now.

Can I use standard neoprene fuel line like the kind on spools at the auto parts store (itls got a braided sleve inside)? Or do I need special 200PSI burst strength or something like that? I'll be sure to use metal line under the car. Man, I'd love to use 3/8" fuel line on the fuel pump with a Fram G3 in front of it, then 5/16" fuel line up on the rails.

Maybe if I'm lucky, my Rat's Nest will have some undamaged fuel rail hoses still on it.

 

I like to connect the FPR vacuum line to anything *after* the throttle body.
This way the FPR also sees vacuum, so it'll run at a lower fuel rail pressure at idle.
Theoretically, since you're using a stand-alone EMS ECU, you have absolute control over fuel delivery at the fuel injectors, so you really don't need to connect the vacuum line...


I'd highly recommend getting "fuel injection" fuel hose for your application.
We had carbed fuel line for one of our cars by mistake, and it literally fell apart in 6 months due to the 30+psi of fuel rail pressure.
Although this car was turbo'd, it really didn't see any boost due to a bad turbo, but the fuel lines did crack like a ****!
Carb fuel line is really only rated dafe up to 10psi to 15psi.
Running it at EFI pressures is asking for trouble!
Even if your NA is not running anything higher than 35psi to 40psi of fuel rail pressure, it is still recommended to get the higher rated fuel line.


-Ted

 

I'll probably still do it because people recommend a manifod vacuum sensing FPR.

Where can I find "injection ready" fuel hose?

 

The local auto parts store should be able to get that for you.
Make sure it says for fuel injection use and rated up to 100psi minimum (it is typically stamped good to 150psi to 200psi).
This stuff is typically priced around $5/foot, so it is pricey!

Makes sure the hose is stamped for 100psi minimum pressure, as we've gotten carb crap that the sale-idiot insisted it was good for fuel injection.
We will only buy stuff that has a pressure rating stamped on the side.



-Ted

 

I'll ask at my local auto parts stores.

I bet the owner(s) of this car spent a pretty penny on a run of EFI hose from the pump to the engine bay. I hope I don't have to do something like this. Scroll down a little. http://www.cardomain.com/memberpage/416517/8

 

bladz311, are you still around?

 

I'm gonna go out and try to find some injection pressure capable fuel line. I'll try to run some steel brake line or something just as cheap under the car so I don't have to do what is pictured in the link above.

 

I picked up 60" of 3/8" brake line and 60" of 3/8" injection capable fuel line.

Ted, does the return line have to be able to handle high pressure? Or will any old carb line work? Something tells me I can use carb line since there's like no pressure after the FPR, but I figured I'd better ask to be on the safe side.