Increasing Fuel Pressure on Spider Injectors

[PlayingWithTBI]

Is there a difference in definitions, such as between "absolute" duty cycle and "intended" duty cycle?

It's all a calculation with RPM, BPC, Pulse Width, # of injectors, etc. I don't know the actual formula though. All I know is, to get your DC closer to 85% at WOT, you adjust injector size and/or pressure to change BPC in the ECM/PCM so it can calculate proper DC.

I've always heard that injectors should max out around 80% duty cycle

Normally 85% is used and .45 BSFC (Brake Specific Fuel Constant). Here's an example, I just threw some numbers in, with 3 BAR boost.

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[L31MaxExpress]

What is flowrate of the spider injectors? Seems better to increase to aftermarket injectors they make, no? I believe there's a company that makes them...I thought I saw that here somewhere?

They made a lot of different flowrate injectors for the 4.8/5.3/6.0. Only the earliest ones (99-00) are the same IIRC. Around 22-24 lb/hr. Later ones have higher, and different flow and pressure ratings. Some of high performance car engines got as high 50 lb/hr. so it's pretty easy to swap those injectors on those smaller engines for doing big power.

The L59 5.3, for example, has more flowrate (33 lb/hr) because it's designed for flex-fuel. I think some guys use those as a "budget" way to get more fuel delivery for high performance use.

I don't know about increasing fuel pressure. Injectors are rated at a certain pressure. Isn't there a risk of blowing them off by almost doubling the fuel pressure? Or causing pump failure? Is the pump even capable of producing 70 psi?

Once I plugged the feed line of the fuel pressure line on my truck, and saw maximum line pressure (was trying to see if I had fuel pump problem), but don't remember what it was.

All Gen3 truck engines (01-07) including the LQ9 on Gasoline used the same part number injectors and they are like 23ish lb/hr. The 99-2000 used an even smaller injector, about 21 lb/hr from memory.

The stock spider ran at 66 psi, the MFI upgrade runs at 62 psi. 75 PSI is not much of an increase. The older Wester's 28 lb/hr spider was a factory GM MPFI spider with the fuel pressure bumped to 100 psi.

AUS makes spider replacements in 36, 48 and 62 lb/hr for both V6 and V8 applications. They are $$$$. If he can get the fuel he needs from a slight pressure increase and verify the WOT air/fuel ratio I don't see the point of changing injectors.

 

[stutaeng]

All Gen3 truck engines (01-07) including the LQ9 on Gasoline used the same part number injectors and they are like 23ish lb/hr. The 99-2000 used an even smaller injector, about 21 lb/hr from memory.

Not really, they made a lot of different ones: https://www.psiconversion.com/tech/ls_guide/fuel_injector.html

The L59 I mentioned is a good example. Gen III 5.3 truck engine with 33 lb/hr injector flowrate.

 

[L31MaxExpress]

Not really, they made a lot of different ones: https://www.psiconversion.com/tech/ls_guide/fuel_injector.html

The L59 I mentioned is a good example. Gen III 5.3 truck engine with 33 lb/hr injector flowrate.

Actually your post just proved my point.

Since I said on GASOLINE not FLEX. LR4, LM7, L33, LQ4 and LQ9 are all gasoline powered RPO codes for Gen3 and they all use the same injectors 01+.

 

[chris2323]

I have a wideband, tune the vehicle myself, and there are no issues with running rich or lean. Im just looking to increase fuel pressure so i dont have to run at max duty cycle during wot. Dont want an injector to get stuck. Engine probably makes 450hp. Looks like i will be removing my upper intake and turning the torx screw up to 75psi. Then i will adjust injector data accordingly and go from there.
Only trying to do this as a temporary solution until i buy a new intake and fuel system.

 

[618 Syndicate]

What I said is absolutely correct. GM and almost every manufacturer does it themselves. For emissions and fuel economy reasons they use just enough injector to get the job done at WOT. Datalog a STOCK Gen3 6.0L engine or a an earlier model 03-08 Hemi Ram sometime. The Gasoline 4.8/5.3 and 6.0L all use the same injectors. The 6.0L runs 95-110% duty cycle in stock form. The Dodge 5.7L Hemi also does the same thing. Injectors do not just fail running high duty cycles. As long as they are capable of hitting the target air/fuel ratio at WOT and high rpm it won't hurt a thing. My old 383 with Vortec heads, modified TPI and a custom cam hit 95-102% duty cycle using 96 LT4 injectors and was never a problem either.

If the injector were to fail closed, there would not be any fuel in that cylinder to combust so no damage could be done. GM kills injectors for torque management, traction control and rev-limiting without damage.

You're wrong and that's that. It's a generally accepted practice that running injectors at anything over 85% duty cycle is unwise. Your statement about failure is based on the assumption that the injector fails closed before it releases any fuel. Which it might. Or might not.
I get that you think you're a great tuner, and that you've found ways to succeed contrary to the laws of physics, but in stating that running injectors at 100% duty cycle "won't hurt anything" you're wrong. It absolutely can, and probably will. If you want to take the risk, cool. But suggesting that doing it doesn't contain risk is irresponsible.

 

[618 Syndicate]

I have a wideband, tune the vehicle myself, and there are no issues with running rich or lean. Im just looking to increase fuel pressure so i dont have to run at max duty cycle during wot. Dont want an injector to get stuck. Engine probably makes 450hp. Looks like i will be removing my upper intake and turning the torx screw up to 75psi. Then i will adjust injector data accordingly and go from there.
Only trying to do this as a temporary solution until i buy a new intake and fuel system.

The only issue with monitoring the wideband is that only tells you what's happened after it happens. I use an AEM Failsafe wideband to kill the boost controller and revert back to gate pressure (3lbs) if it sees a lean condition. It can react to it faster than I can.
I get that you're using raised fuel pressure as a temporary fix, and understand that we gotta do what we gotta do, I'd just hate to see you have to redo an engine because of something preventable.

 

[chris2323]

I dont see how a slight pressure increase would really hurt anything on my NA engine. !!As long as the pcm tune is adjusted correctly!! My stock flow rate spider injectors are no where near capable of running with forced induction. If i had boost, i might be a little more worried about it. The best solution would be to run the spider from Aus Injection, or a whole different intake/fuel system. They are both expensive, but I still plan on the upgrade in the future. Thanks everyone for their input!

 

[618 Syndicate]

I dont see how a slight pressure increase would really hurt anything on my NA engine. !!As long as the pcm tune is adjusted correctly!! My stock flow rate spider injectors are no where near capable of running with forced induction. If i had boost, i might be a little more worried about it. The best solution would be to run the spider from Aus Injection, or a whole different intake/fuel system. They are both expensive, but I still plan on the upgrade in the future. Thanks everyone for their input!

The pressure increase in itself isn't an issue, it was more that you had run out of injector, indicated by the high duty cycle.
As long as you're comfortable with it, send it!