"Plumbing" question when connecting Spectra EFI tanks to EZ-EFI

Dear V-8 Buick EFI gurus,

I've been getting conflicting advice as to how to set up the fuel system in my trusty wagon to work with the EZ-EFI system that Jim is putting on my super-deluxe engine. My instincts tell me one thing but I sure would appreciate a confirmation. The normal way to set up the fuel system is shown on this diagram on page 9 of the EZ-EFI instruction manual:



However this refers to using the EFI fuel pump that can be bought along with the EZ-EFI system. The EZ-EFI system runs optimally at about 42 PSI of pressure.

Now the problem. I would like to use a Spectra Premium replacement tank with a built-in EFI pump. This pump is designed for multiple applications and can run as high as 80 PSI.

Now my attempt to dredge up my old physics knowledge makes me think that the recommended EZ-EFI setup will still work fine. My argument is that the single pressure regulator in the diagram above is effectively acting like a "dam" and allowing the water to "spill over" once the pressure of 42 PSI is reached. The Spectra pump may be capable of higher pressures, but it doesn't matter. Beyond 42 PSI, the gas will flow straight back into the tank.

However, I've also been given the following suggested "plumbing:"



In this scheme a bypass regulator is added before the throttle body to prevent the pressure exceeding 42 PSI. From my point of view, this just cannot be right - but I don't know this stuff.

So which scheme is actually the right way to connect a EZ-EFI throttle body to a Spectra EFI pump?

Inquiring minds want to know!! :idea2:

Cheers, Edouard :beer

 

Go with diagram #1. You only need one pressure regulator. I'd have to dig up a picture, but essentially mine is plumbed like diagram one except my surge canister is in place of the gas tank.

Fuel Tank/surge canister --> Fuel pump capable of 90psi --> Fuel rails with injectors --> Fuel pressure regulator to 43psi --> back to fuel tank/surge canister.


That second (first in line?) regulator adds unneccessary complications PLUS it limits the ability of the vacuum referenced fuel pressure regulator to do it's job. OEM's run a vacuum fuel pressure regulator for a reason, and until recently with PWM fuel pumps, always had a higher than necessary pump to them. There are good reasons for that, namely reliability in fuel pressure.

 

I agree schematic #1 is correct-go with it. The only problem might be if the upgraded fuel pump flows more than the pressure regulator can handle you won't be able to get the pressure down to the 42 PSI that you want, but that will be evident when you start the system up. Not a likely scenario. Mike D.

 

Don't you want to send the correct 42PSI to the throttle body instead of adjusting it after it has already gone into the engine? I would think the regulator would be effective only before the fuel is used.

 

It would only be a problem if the inlet size of the fuel pressure regulator was smaller than the fuel pump fuel line, and even then it would have to be substantially smaller. It works this way because fluid isn't compressible so pressure changes (ie regulation) are nearly instantaneously the same through the whole system, even immediately after the fuel pump.

 

Thank you-- I did not know that. I'm an irrigator, and we regulate pressure all the time, and we do it before it reaches any outlets.

That still seems weird.

 

I guess I should clarify that it only works that way for by-pass style regulators. If it's an orifice tube type or non- by-pass type regulator, then there is definitely matters before or after. Your irrigation ones are probably not by-pass type, in which case you'd be correct in having them mounted before hand.


Here is my set up. Fuel pump is off the picture, but the arrows show the direction of flow and the blue arrows are after the regulator. The regulator is circled in yellow. The pump is supposedly rated at 90psi if dead headed, but I've never had it turned up over 60psi.

 

Thanks for the clarification! I need to learn more about EFI. My trucks just work, and my old cars have always been carbureted.

 

Thanks for the reassurance! (Re: Spectra EFI tanks to EZ-EFI)

Dear SilverBuick, GS Mike, Frank, and V-8 Buick gasoline "plumbers," :grin:

Hurray! I thought that was right!! :TU:

I have an even better solution . . . . I ask Jim which regulator he uses when he installs EZ-EFI units and . . . . make sure I use the same regulator!!

Thanks fellows. Mostly for my own reassurance, still when you get too much advice o No: . . . . sometimes you need a little help!! :Smarty:

Cheers, Edouard :beer

 

Actually #1 is not correct either.
The SilverBuick has it correct. The fuel rails need to be plumbed in parallel.

If they are in series, the first rail being fed will cause a pressure drop in the second rail under heavy load.


Paul

 

I still cannot wrap head around how the pressure regulator after the fuel rails and on the return line lowers the pressure to the rails/throttle body/injectors Seems ass backwards to me. Maybe I just do not have a grasp here but on my hi volume race pumps I have to regulate my pressure down for the carb. That said is the pressure regulated on the return line keep the pump from sending 90 psi to the rails?

 

That wouldn't work either, since the return just dumps into the tank and the pump is not affected.

 

Yes, except that the return line pressure will vary because the volume of fuel an electric pump is supplying is more or less the same volume, so if the injectors or carb are consuming a large amount of fuel then the volume going out the return is less and consequently will drop in pressure.

 

I saw your post over at the FAST forum and started to reply last night but the wife grabbed me for some honey-do list items and I forgot. Anyway....

Pop the hood of any moden factory fuel injected car and I believe you will see an after the injector requlator setup. This keeps fresh cool fuel to the injectors all the time and the pressure is bled off at the back end and excess fuel returned to the tank. The fuel constanly re-circulating like this helps to cool the fuel pump too. I'm using an Aeromotive compact style regulator on my setup as it was recommened to me by a few tuners I had spoken with. I kind of agree that running both rails in parallel might be ideal but it I doubt it's worth the hassel on this system. Besides, thinking back on my hydraulic theory should it matter as long as our pump maintains enough volume and pressure? The reason you run a regulator before the carb (especially on mechanical pump applications) is because the needle/seat/float system in the carb has a habit of not appreciating the pressure surges it (they) would see with a bypass regulator system.

I think you will find that the pump in the Spectra tank is only good for about 350HP. Your easy upgrade would be one of the Walbro 340 pumps that will get you to about 450-500HP or use one of the Aeromotive 340 pumps should be good for about 550-600HP. I am running a pump for a Turbo Supra I got from Racetronix (Turbo V6 guys seem to like Racetronix) but it took a fair amount of modification to the pump hanger to get it installed and then it just BARELY went back in. There is a new Walbro pump that Racetronix is lisiting that should be good for a LOT of HP but I'm not sure on it's fit-ability. From what I've read over the last couple of years I'd probably go with the Aeromotive pump but that's me. All of these pumps will push about 80psi (you would need that much pressure with a turbo to overcome the positive pressure in the intake) so you have to use a regulator. I'm not a fan of any returnless pump systems and unless MSD has some special magic I don't see why they went that way on thier new FI system. The old pro-jection guys that were on the forum here used to complain about problems with their modulated pumps. Besides, the system with a pump in the tank (with a sock on it) and bypass regulator go 100K (+) miles on your modern car, why mess with what works???

One last thing, as I said in previouse messages I would NOT use anything for fuel line except the stainless braided teflon. Don't cry about gas fumes if you use the other stuff. I will post an I told you so message!

NOTE: My install (pictured below) feeds to the front of the throttle body, exits the rear, enters the regulator then exits regulator to return to the tank. If I were doing this over I think I'd have ran the lines through the frame up by the radiator then come up along the front passenger side of the engine like a SBC. My instal works fine though and has given me no problems (probably saved another 10 feet of line too!). I have the lines clamped to the floor pan and coming up by the heater/AC box along with some extra heat shielding just to be safe. Note the regulator is attached to the TB with a simple aluminum bracket. I originally had the regulator on the firewall but found it made some noise. As I have mentioned in other posts I learned a LOT from reading other discussion boards especially the C3 Corvette forums. Some of those guys seem to be working on unlimited budgets so you can learn from them the 4 $500 attemped things they did before they fixed the problem for good!

regards

 

Try looking at it this way. Let's say the return line regulator is set for 43 psi.
When the engine isn't running but the fuel pump is, the return line regulator will bypass whatever fuel it needs to back to the tank
to maintain 43 lbs of pressure.

As you can see, the regulator must have the ability to flow all of the fuel pumps rated flow back to the tank
in order to regulate the pressure when the engine is not running or at an idle.

This means anything on the fuel line between the pump and the regulator sees 43 lbs of pressure whether it's a carb or EFI fuel rails.
When the carb or EFI system takes fuel from the line between the pump and the regulator, that simply subtracts from the amount of fuel the regulator has to bypass and the line pressure stays at 43 lbs.

Paul

---------- Post added at 08:48 PM ---------- Previous post was at 08:34 PM ----------

Hydraulic theory applies for static conditions only.
As soon as you introduce flow, there is a pressure drop along the line.
The pressure drop is a function of flow rate, pipe diameter and length and a few other parameters.
If fluid is being taken out along the way there is an additional drop.

Paul

 

]

Hydraulic theory applies for static conditions only.
As soon as you introduce flow, there is a pressure drop along the line.
The drop is proportional to flow rate and line ID.

Paul[/QUOTE]

That sounds reasonable, so if I had a gauge on the front of the TB I might see a couple extra PSI than what is coming out to the regulator?

 

Just like some others have said....put the regulator after the fuel rails and all will be perfect.

 

As long as the fuel pump can significantly out flow the injectors the regulator at the end of the line should be able to maintain pressure all the way to the end of the rail. Now will that mean the first couple injectors are seeing a little extra pressure? Perhaps, but since the fuel is going into a common plenum (TBI style) it probably doesn't matter as the computer will adjust fuel to compensate for the difference to make the same AFR.

I often wonder if I'm loosing fuel pressure at WOT on my setup (too small of a fuel pump) and have tuned around it by simply openning the injectors longer. I'm thinking of installing a fuel pressure sensor to datalog and find out for sure. Until then my only evidence is at WOT, 6,000rpm, I can run an overly rich 10:1 AFR at 75% duty cycle, so I have room to add more fuel even though I really need to dial it back. I'm running a stock Ford fuel pump with 5/16th line diameter uzzled:

Is it right? No. Will it work? Yes. Will it hurt something? Not likely, especially in a TBI application.

 

That was my next question!! (Re: connecting Spectra EFI tanks to EZ-EFI)

Howdy Paul, John, Frank, SilverBuick, Ken, and V-8 EFI "plumbers"

Darn it Paul, you get getting ahead of me!! I thought I should only ask one question at a time!!

Okay, wasn't sure about this one. I was sure that this was needed if you were going sequential EFI. In that case there are multiple injectors and I thought you could have a resonance phenomena at some RPMs where a pressure drop would propagate from the upstream rail to the downstream rail thus "starving" an injectors for another cylinder.

Still, I wondered if this could happen when there are only two injectors?

However, I can think about this another way. There may be only two injectors, but they are supplying all the fuel that the 8 injectors of a sequential system. So the upstream injector will cause a huge pressure drop. Again if you are at the resonance RPM, the second injector will open at the moment the pressure drop propagates over it. If you have the "Y" arrangement, that causes the pressure drop to flow over two paths disrupting the resonance. So I agree with Paul and SilverBuick . . . . I just hope I didn't muddy the waters in my explanation!! :grin:

Bummer dude!! :grin:

Okay, I'll have to check on this one. My goal isn't to actually generate a lot of horsepower. The car is supposed to be a tow vehicle and not use too much gas while doing it! The existing pump might handle the job just fine. However, the computer simulations of the previous incarnation of the engine were at 400 hp, so that would make the pump a little weak for the job.

Okay thanks for the advice and photo. Jim has sent me photos of an install he has done. So now I have a few ways to think about this.

Thanks everybody!! This car wouldn't have a chance to ever run again without your help!! :TU:

Cheers, Edouard :beer

P.S. Thanks Paul for making the diagram!! :TU: That's what I'll use as my reference and I know it was a pain to tweak the FAST illustration - as I did it too! uzzled:

 

[Hi-Jack]

Any idea when we'll get to see pictures of this "green" 455? And what the final cam spec's turn out to be? :Brow:

[/Hi-Jack]