Short story: I think I need 30lb injectors for my 4.6L supercharged engine. Is there a preferred brand or configuration that I should be considering?

Long story: It's a long saga, and if I ever get it all figured out, I promise to share whatever I learn. At this point, I have a freshly rebuilt 4.6L with ported NPI heads and mild cams, with an Allen Supercharger kit on top. The 4R70 tranny was rebuilt also, with a slightly higher stall torque converter. None of the mods by themselves require a tune, but maybe together is a different story.

This truck just does NOT run right. Even with the idle adjusted up 200 RPMS, it tends to die when coming to a stop (especially after it's warmed up). It does NOT burn rubber from a dead stop, and seems to shift from 1 to 2 way too soon. It seems to be in a real hurry to get to the next gear as opposed to using the available power before shifting. By the way, it has 4.10LS gears and worn out 33" tires.

I've poured well over $10K into this thing. It should be shining MY helmet, amongst other things, yet seems to believe I still owe IT something.

So.... I'm considering upgrading the fuel injectors and getting a tune, perhaps from TP. I believe that 30lb injectors would be right in the ball park for my configuration, since I'm not trying to build a drag racer, but a daily driver and towing machine.

 

yes 30lb injectors are right for you im suprised the supercharger didnt come with direction or recomendations to upgrade the fuel system. hell i maxed my stockers out with bolt ons.

 

Bump!

The supercharger comes with an FMU, which negates the need for larger injectors. However, I plan on getting rid of it. Now my quest is to learn what and how.

What SPECIFIC injectors should I be looking for. Should I just go to a vendor, tell them what kind of vehicle I have, then ask for the right ones? It appears that they should be around 14.4 ohms, but I really don't know.

Why do almost all the supercharged engines go with 42lb injectors? Isn't this pretty serious overkill in most instances? As was pointed out to me previously, too large of injectors may cause driveability issues at idle and low RPMs. Did I misunderstand?

I still believe that 30 - 32 lb injectors appear to be the best bet for a supercharged 4.6L, unless it has other significant mods.

Any input is welcome.

 

You don't want a supercharged motor to run too lean, so +1 on the large injectors, upgrade the fuel pump, adjustable regulator, and a MAF calibrated to the injectors. Sounds like the engine is starving......I'm surprised the kit didn't come with all you need to make it run right.

 

Sorry, I need to clarify. The kit DOES come with everything needed. I think my issues are simply that I ported the heads and added cams on top of the standard rebuild. The computer just can't deal with ALL of it. At least that's what I'm hoping is the issue, since a good tune along with (the right) MAF and injectors would fix.

I know there are people out there so knowledgeable that they've forgotten more than I'll ever know. They have the answers at the tip of their tongue perhaps not realizing how ignorant and needy some of the rest of us are.

I've spoken with TP, and felt that I was being fed a sales pitch. Maybe I should try again.

 

try running a smaller gap on the plugs.. plug blow out is a big issue. also the tune makes the truck move.

 

Injectors are sized to support a given amount of air an engine can inhale/exhale. By changing the cams and porting the heads you have changed the configuration of the Supercharger package you purchased. You should talk with the supercharger manufacturer or even better, the programmer of the aftermarket FMU you purchased. There are three variables to work with on fuel injectors: Flow rate, pulse width, and fuel pressure. If you are running lean, do you have enough inital fuel pressure that the fuel injector is not on all of the time (pulse width; which is handled by the FMU). If you increase fuel pressure (need an adjustable regulator) and still cannot richen the mixture sufficiently then you will need larger injectors. Conversly larger injectors will make it harder to tune idle to off idle performance. How much HP do you expect to make from your combination of parts? Do you have access to a dyno and air fuel meter (an accurate one). Is your mass air sensor even large enough to handle the increased air required. Find someone who can asses your whole package and not just individual components. Read the FMU manual, maybe you need a different O2 sensor. Most sensors operate on voltage but maybe you need and MAP sensor thaat operates on frequency.

David