Increasing Fuel Pressure on Spider Injectors

[chris2323]

Does anyone have any experience increasing fuel pressure on the spider injectors? Its my understanding that there is a torx adjustment screw on the fuel pressure regulator. Some people have said they were able to increase pressure up to 70psi.
Currently seeing over 100% injector duty cycle at WOT. Im hoping a pressure increase could help get me by for a while.
I have a 383 with a big cam, aftermarket heads, 411pcm, and hptuners. Unfortunately I am still running the stock L31 intake and mpfi injectors.

 

[618 Syndicate]

Over 100% duty cycle? At 100% the injectors are constantly open, they can't exceed that. Raising fuel pressure will deliver more fuel until you reach the mechanical limit of the injectors, but running even close to 100% duty cycle is asking for trouble. You might be ok, but injector failure will likely result in a severe lean condition, and that puts windows in shìt.
You need bigger injectors, there's no safe way around it.

 

[PlayingWithTBI]

Currently seeing over 100% injector duty cycle at WOT. Im hoping a pressure increase could help get me by for a while.

Yes, it can help. With a WBO2 you can see your AFR, you may be running too rich but, you s/b able to reach commanded AFR @85% or less DC at WOT.

 

[618 Syndicate]

Yes, it can help. With a WBO2 you can see your AFR, you may be running too rich but, you s/b able to reach commanded AFR @85% or less DC at WOT.

If it's running rich at 100% d/c wouldn't raising fuel pressure just make it worse?

 

[PlayingWithTBI]

If it's running rich at 100% d/c wouldn't raising fuel pressure just make it worse?

Yes, you're right, I was saying it may not be running too rich, need to check that, and a NBO2 won't give you the feedback to tell. It s/b able to achieve commanded AFR without running 100% DC. OP may have plugged injectors or low pressure.

 

[L31MaxExpress]

I have increased fuel tables and seen the air/fuel richen even at an indicated 100-115% with the stock spider. The math is often not accurate for duty cycle. Even if the injector is open 100% of the time its not going to hurt the injector. I ran an upgrade MPFI spider at 75 psi for a while and it did not hurt anything. I have a Racetronix Hotwire setup so my pump has good voltage to it. When I put the stock intake back on the 383 in my van I ran it with the stock spider for close to 2 months. I had to program the WOT shifts at ~5,200 rpm because that is where it started to run out of fuel. My 383 makes 470ish HP at 5,200 and peaks about 500 hp @ 5,600. If the wideband is not showing the air/fuel mixture leaning out, nothing to worry about. I have a 48 lb/hr spider and recently put a higher volume E85 pump in it.

 

[618 Syndicate]

Even if the injector is open 100% of the time its not going to hurt the injector.

This is patently false. Running an injector above 85% duty cycle can cause the injector to fail, if it fails closed it will cause a severe lean condition. The higher the % of duty cycle, the higher the likelihood of failure.

 

[L31MaxExpress]

This is patently false. Running an injector above 85% duty cycle can cause the injector to fail, if it fails closed it will cause a severe lean condition. The higher the % of duty cycle, the higher the likelihood of failure.

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.

 

[Erik the Awful]

Is there a difference in definitions, such as between "absolute" duty cycle and "intended" duty cycle? That would explain how a duty cycle could be 115%, and how a 100% duty cycle is acceptable. I've always heard that injectors should max out around 80% duty cycle, and that a good tuner could take that to 90%.

 

[stutaeng]

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.

Edit: looks like 19 lb/hr for spiders and 21-23 lb/hr for MPFI spider?