I think I found a great idea to run properly with bigger injectors on the LSJ ...

[jmc007]

One problem when installing some bigger injectors : they are difficult to tune when the engine is not fully loaded (mid RPM's) but are ok at WOT where the engine needs the extra fuel.

Since the LSJ fuel pressure (PSI) is constant at 60-62 PSI under every conditions, it throws waaaaaaaaaaay too much fuel at midrange RPM's with the bigger injectors so it's difficult to tune them (with a Mini AFC or a MAF translator) to achieve a flat air fuel ratio curve.

Here it is : Along with some just nicely calculated bigger injectors than stock (maybe 42's, 48's or 50 lb/hr ones, depending on your mods), how about controlling the fuel pressure (less than 60 PSI at low load, then more pressure at midrange and then the max pressure for WOT) ?

It could be done with this :

SUPER FUEL MANAGEMENT UNIT (SFMU) (a kind of ADJUSTABLE fuel pressure regulator)

http://www.vortechsuperchargers.com/.../fmu_sfmu.html (the second model; the "Super" one).

(Don't get me wrong; I know it will not add extra fuel with the stock injectors neither rising the stock 60-62 PSI fuel pressure at the fuel rail. And it's not a pump booster too, since the stock fuel pump is flowing enough).

I continue ... The formula for injector duty cycle include the differential pressure passing through the injectors. So the problem with running a small supercharger pulley is that the differential pressure (passing through the injectors) at WOT is too small ...

Here is an example :

Let's say I run a 2.6 pulley and boost 20 PSI in the manifold, so the differential pressure passing through the injectors is :

62 PSI (stock fuel rail pressure) minus 20 PSI (manifold pressure) = 42 PSI only ! If I calculate my injectors needs for (as a pure example) 350 BHP (engine power), it woukd need some 47 lb/hr injectors (rated at 43,5 PSI).

Now I could install the SFMU unit, install some 48 lb/hr (or 50's one), then (as a pure example) tune the pressure down to 30 PSI for idle, 35 PSI for 3000 RPM, 40 PSI for 4000 RPM, and 62 PSI for 5500+ RPMs (those numbers are some quick non-calculated examples).

What do you guys think ?

[Sinister redlines]

All of that sounds good and all but at the end of the month (hopefully no setbacks again) the stagged upgrades will do all of this without the headaches. JMHO good to keep the options open though.

[clownhair]

I think youll need a fuel return line to use that FPR.

[dL_RL]

Originally Posted by clownhair

I think youll need a fuel return line to use that FPR.

correct you are sir..

[goofyguy]

THe best way would be the larger injectors, piggy back computer, and a map sensor to get rid of the hot wire setup used.

[playboy]

running a return line wouldn't be that hard i'm sure someone could fab up a fuel rail with a spot for a return line right? i mean if this is worth the trouble...

[goofyguy]

Originally Posted by playboy

running a return line wouldn't be that hard i'm sure someone could fab up a fuel rail with a spot for a return line right? i mean if this is worth the trouble...

yes but now you need a new fuel pump, fuel pressure regulator, return fuel rail, way to get the fuel into the tank, then your FMU to change the Fuel pressure. Too many added parts.

[playboy]

oh okay i guess i just thought adding a simple line would be enough not thinking that it would all still have to be under pressure as well they just need to trash this pcm and make an totally contollable aftermarket one that would solve all of our problems up until we start blowing motors but that's the easy part to fix hell i love building motors

[DarricksZ28]

Really I've heard that FMUs are just bandaids and aren't really reliable. And better way would be just to get rid of the returnless constant pressure setup and go with a return style system using a rising rate fuel pressure regulator. That way your pressure would be set at idle and as boost increases so will your fuel pressure in reference to boost.

What sort of af ratios are you getting through the midrange? I haven't seen a graph or put Frankie's car on a wideband yet? I know sometimes more fuel is needed through the midrange due to engine load, and a flat fuel curve isn't the best curve.

[goofyguy]

If your going to use GMs factory tune then add more fuel the best way is form of piggy back. This way you can still utilize the millions of dollars already put into making the PCM work then you can use the piggy back to add/pull fuel out of the equation. I would remove the MAF install a map sensor and drop in some monster injectors. If you use a good setup you can work timing as well.

If anyone is interested in a setup like this let me know. I might be able to setup tuner kits.