I know there is a formula somewhere, or will a Walbro 340 support 700 FWHP through stock lines? Or do I need dual intank pump setup? And on a dual pump setup do you need to run a new return line? I dont feel the need for a custom fuel setup for a 650/700 hp normally aspirated setup, or do I? What is the limit for stock lines? I will have 42lb svo injectors and as of now a walbro 340 with the harness kit.


David

 

Depends on your BSFC . If I were shooting for 700FWHP I would just do a dual intank GSS340. You *may* get by on one pump, especially with a boost a pump, but really the two fuel pumps and a y-block are dirt cheap compared to what you have in your motor, so why worry about it. Stock fuel lines (return, etc.) will be fine. If you feel the need to upgrade in the future you can just use your feed line as a return and run a new feed line - but you shouldn't have to do that.

As for injectors - if you are shooting for 700FWHP Na you are probably going to be turning some significant RPM. You don't see it brought up a bunch, but RPM has as big of an effect on injector sizing as horsepower does - you can support more power at a lower rpm as you have more time to inject the fuel. The same power level at a higher rpm will require a bigger injector. (assuming the same BSFC).

I would just buy one of LJ's acceleronics boxes and throw in some 72 low-z injectors - sure, they will be overkill, but they will idle/drive better than the big high-Z injectors that you will probably need.

If you will not do the impedance converter box just go ahead and get the 55 lb/hr siemens high impedance injectors from racetronix - no sense in taking a chance of needing more injector later on. Now if you already have the 42's give them a shot, but I wouldn't buy them new for your application.

Chris

 

As Chris said, BSFC will tell you. A BSFC of .500 (lbs fuel/hp/hr) would be high, but fairly safe. .500 x 700 hp = 350 lbs/hr / 6.15 lb/gal(gasoline)= about 57 gal/hr. or about 15 L/hr. Obviously you'd want pump capacity to be somewhat more than that minimum.

At 350 lb/hr(700 hp), that's 43.75 lb/hr per cylinder.

 

You mean 215 L/hr?

and 43.75 lb/hr is at 100% duty cycle, which we all know isn't ideal.

 

OOPS! I gotta multiply, not divide! Getting older here, and still think in English units. And you were nice enough to think it was just a typo.

Thanks for the correction!

Yep, 100% duty cycle isn't good. FASTBOY mentioned 42 pounders; that's why I mentioned the 43.75. Maybe he'll detune to the 600 hp level.

 

Well 700 fwhp is what Performance Trends engine pro simulation says, how accurate, who knows. But I do want to be safe, Brady had a custom fuel setup on his TT, but his horsepower was way over what mine will be. Another friend here in town has a custom setup, he is at about 600/630 (guessing) fwhp, works very well for him, he has 42LB injectors and they are at only about 60% duty cycle at WOT if I remember correctly(Clyde).

David

 

EA Pro gives BSFC and fuel flow (lbs/hr) in its output. Looking at PRO with a 700 hp NA stroker with a .41 BSFC. At 700 fwhp it was about 36 lbs/hr per cylinder and at 630 hp and a little better BSFC, it was about 31 lbs/hr. (74% of 42).

PRO, like any simulation program, obeys the GIGO rule.
(Garbage In = Garbage Out)

You need REALLY good flow numbers for head and manifold to get close to reality. 700 NA ain't easy or cheap. What style and size engine are you looking at?