Double check my fuel system logic

[UofA_ZCar]

I have been reading about fuel set ups for a few weeks now and believe I have it figured out. That being said I was hoping some of the guru's would just confirm that I am on the right track and/or comment on any thoughts. I'm putting an L28T in my 240Z and hope for between high 200's and 350HP.

 

Tank: Stock with a sump welded in.

 

http://www.summitracing.com/parts/CEE-4040/

 

All lines (AN and new hard lines) would be -6AN / 3/8. According to grumpysperformance.com that size line (both feed and return) can support up to 375 HP.

 

Fuel Pump: Walbro 255lph with -6AN adaptors. Flows 67.3 GPH and according to my calculation 350 max HP X .17 = 63.7 GHP needed.

 

http://www.fuel-pumps.net/500.html

 

FPR A Return-Style regulator. I found the one in the link below but any other suggestions would be great as I haven't spent too much time reading on regulators.

 

http://www.diyautotune.com/catalog/sx-performance-15404-an-fuel-pressure-regulator-p-300.html

 

Injectors: I found the formula below and it shows I need 338cc injectors.

 

350 X 0.55 = 192.5

 

193/6 (number of injectors) = 32.17lb injectors

 

32.17 X 10.5 = 338cc injectors

 

My Questions

 

1) Why do the sumps have two fittings? I know the feed goes from there but does the return also?

 

2) Assuming the return doesn't go to the sump.... I would just weld a steel AN fitting to the gas tank in place of the original return nipple correct?

 

3) To attach a an AN fitting to the new hard lines I us a "sleeve" and "AN" nut correct?

 

4) Is my injector calculation correct and if so could you recommend common injectors people use (I admit I have not searched this yet, but everyone needs a little spoon feeding now and again )

 

Thanks in advance for any help!

[rossman]

1) One for the supply and one for the return

 

3) Yes and you need to flare the tube

 

4) Based on this calculator, I'd go with a larger injector. RC or Precision make good ones.

Edited May 16, 2011 by rossman

[UofA_ZCar]

Thanks! So in the max HP scenario:

 

(350 x .60) / (6 X .80) = 210 / 4.8 = 43.75 lbs/hr per injector

 

43.75 x 10.5 = 460 cc/min per injector

[rayaapp2]

Some people run dual pickups and pumps in parallel for certain applications. Depending on how they are routed it could be that one has a return or can be used as a return.

 

+ 1 on the RC Engineering Injectors. Ive been happy with RC injectors on 2 of my cars and one for many years now.

 

Personally I also would recommend the Bosch 044 fuel pump over the Walbro 255 unit any day. Costs a little more, but seems to actually work as designed and last longer that way. Again just my personal opinion.

 

And as rossman said "3) Yes and you need to flare the tube". I made that mistake with my tank when I first put the AN stuff together having never messed with Aircraft/Navy fittings before in my life. Make sure you flare it... or it leaks and/or comes apart. Wish I had, had that advice.

[TimZ]

Thanks! So in the max HP scenario:

 

(350 x .60) / (6 X .80) = 210 / 4.8 = 43.75 lbs/hr per injector

 

43.75 x 10.5 = 460 cc/min per injector

 

I agree on using the higher BFSC for both the injector calcs and the pump requirements.

 

Also, on the flow for the Walbro pump, that appears to be the flow rating at 43.5psi, which is lower than what you'll be needing at max boost. Here's a link to some Walbro flow charts - you should use the flow rating for the base pressure plus the max boost pressure you'll be running...

 

http://www.gnttype.org/techarea/fuelsystem/walbroflow.html

[UofA_ZCar]

Thanks for the replies.

 

Here's a link to some Walbro flow charts - you should use the flow rating for the base pressure plus the max boost pressure you'll be running...

 

http://www.gnttype.org/techarea/fuelsystem/walbroflow.html

 

 

Please bear with me as I'm learning all this fuel delivery stuff as I go. How do I figure our what my hase pressure will be?

[Tony D]

Base Pressure is the pressure used by the injector manufacturer to calculate the flow---some it's 3 bar, others 36psi. This is also referred to as 'STATIC' fuel pressure. That would be the pressure you see on the fuel system with the key ON and the car NOT running, this is your 'BASE' fuel pressure setting.

 

As soon as you turn on the car and start running, the vacuum signal to the FPR (18" Hg -- roughly 9psig) will decrease your static pressure by roughly that amount. When you go to boost, the Delta-P across the injector has to be the same as 'static' so the injector is giving it's rated delivery, so you have to add boost pressure to it otherwise at some point you could literally blow boost back down the fuel rail!

 

For instance:

Injector is rated to flow at 550CC's at 3 Bar Static Pressure. (LETS JUST SAY 3 BAR is 45PSI FOR THIS DISCUSSION!)

FPR is manifold-referenced, 1:1 Ratio (meaning for any action on the sensor input to the FPR, it moves pressure that way.

 

At idle, with the above example, you would show 45-9=36psig

At 10 psi Boost you would have 45+10=55psig

 

Follow?

 

In the same way, you can take injectors and 'tweak' their delivery as well, say you have a 3 bar rated injector of 450cc's, and don't want to buy those 500CC or 550CC/min units. By taking the static pressure from 3 bar to 4 bar you directly increase the flow rating of the injector in a similar ratio. Those 450CC injectors at 3 bar are flowing more like 550 or 600cc/min injectors (this is in injection handbooks, this is a WILD approximation, check it out if it interests you...I digress!)

[Wedge]

Just some heads up if you want a Bosch 044 fuel pump i got mine on amazon for under 200$ check it out. Good luck

[UofA_ZCar]

Thanks for the replies. I have a much better understanding on how the injectors and FPR function from your post Tony......thanks.

 

In the future when I get it all in the car and get in working I'm sure I'll have more questions.