Someone please tell me where I'm going wrong with my logic.
The fuel pump runs untill it reaches a certain pressure, then shuts off.
The only place to put a fuel pressure gauge on a tbi setup, is between the fuel pump and the fuel pressure regulator.
The gauge should only be telling me the pump output pressure, reguardless of what I try to adjust the fuel pressure regulator to.

Now if the regulator holds back the pressure in the line untill it gets to certain level, then sends the excess pressure/fuel to the return line, that could pose another issue. If I put a higher pressure pump [say 35psi] and try to get the regulator set to 25psi, the pump would run continously.

I want to use regular 350 injectors at a higher pressure to feed a 400sbc, but I think I should find out what pressure the regulator is set at as a baseline.
Then I could modify the regulator and see how much difference in pressure I can get, and what exact pressure works best.

Can anyone lead me through the fog on this one?


Bob

 

Your getting pressure and volume confused. Take any pump and just let it pump to atomosphere and it'll make 0 psi. Now cap off the outlet and it'll pump up to some arbitrary number. In order to make pressure you have to have a restriction in the system.....which is exactly what the regulator is for.

What you need to be concerned about is whether your pump can supply enough volume to support a certain pressure at the volume you need. A stock TBI pump has a hard time keeping up with a stock motor let alone higher than stock FP and increased fuel demands of a bigger motor.

In short, get a walbro 190 and be done with it, it'll supply enough volume to support more HP than TBI is capable of making.

I hate to sound like a broken record but don't even try to do this swap if your not going to do DIY chip tuning. You'll never get it to run very well and you'll leave a LOT on the table.

 

I've ordered the moates autoprom tonight.
I've learned enough from reading on this site the past year to work up the nerve and cash to try to tune.
You guys are so helpful to everyone, I figured I can do it with your backup help.
I read a post that said increasing fuel pressure may be a better solution than bigger injectors. I understand there are a lot of variables involved, but that was the gist of it.
To get more fuel in the cylinder in the split second the injector is open, a higher pressure, or bigger injectors are needed. Of course, keeping them open longer with prom tuning works also, but all three methods have there limits.
By reading what the pressure is before I start messing with it will allow me to go back to the starting point if I get lost. I'm just wondering what fuel pressure I'm reading between the pump and tbi, and how to tell what pressure the injectors are getting.
thanks
bob

 

is this helpfull?

http://www.users.bigpond.net.au/ben_...ctorsizing.xls

note the variables you can play with.

 

the injectors will see what ever pressure your pressure gage shows.

so you know, the fuel pump on a fuel injected motor runs continuously when ever the motor is running.

 

Thanks Ronny, but I dont have excel so I cant see the file.

Thanks DENN_SHAH, this is more like the info I want.

So the regulator controls the line pressure upstream, and when max pressure must release it to the return line.

So measuring pressure anywhere in the fuel line will show how much pressure the injectors are getting, is that
correct?
Its seems kinda simple when explained that way. I was over thinking on how it may have worked.
Thanks for the help
Bob

 

Fatbob, you still sound a little confused. The pressure regulator dose just that, it will maintain a preset pressure at all times unless the fuel pump is going bad or you have a restiction between the pump and regulator. If the regulator is factory set at 11 or 12psi the the injectors will see the same pressure, you could see a pressure drop at throttle tip in, but it should come back up. Any excess pressure the pump makes is bleed off into the fuel return line. Hope this helps

Steve

 

Another thing.. the Fuel Pressure regulator is on the Return line basically. So anywhere from the fuel inlet on the throttle body back to the fuel pump in the tank will read how much pressure your injectors are seeing. The fuel pump will supply the volume to the throttle body and the excess is pumped back to the tank through the fuel pressure regulator where pressure is raised to allow the injectors to open and close allowing the fuel to be released into the engine letting the car run. Quoting from some other good TBI thread "THe pump supplys the volume, the regulator maintains pressure"