L31 injection system upgrade?

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Numbah1

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Hi guys, i have been doing research for a bit now and i seen that the stock csfi / poppet injection system is only good for ~320hp before the injectors are a problem. I read on hptuner that even the upgrade mfi spider was good for 340hp w/ 80% duty cycle.

Is there a way to get into upper 300s with without re wiring or a pcm swap? Like the holley 9901-107? Ive also seen mixed reviews of the marine intake. I feel like there has to be something i haven't seen yet...
 

1998_K1500_Sub

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My understanding is that the MPFI upgrade was available with larger injectors from third parties.

@Supercharged111 has, I believe, commented on this very topic, I hope he’ll add to this.

Regardless, search using relevant keywords and @Supercharged111 as the member name, you’ll likely turn up something.
 
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L31MaxExpress

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Hi guys, i have been doing research for a bit now and i seen that the stock csfi / poppet injection system is only good for ~320hp before the injectors are a problem. I read on hptuner that even the upgrade mfi spider was good for 340hp w/ 80% duty cycle.

Is there a way to get into upper 300s with without re wiring or a pcm swap? Like the holley 9901-107? Ive also seen mixed reviews of the marine intake. I feel like there has to be something i haven't seen yet...
I got to more like 450 at the crank before injectors became a problem. The L31 injectors have no problem running 70-75 psi and 100% duty cycle.
 

L31MaxExpress

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How were you able to achieve 70-75 psi? Im currently hitting 100% duty cycle at the stock pressure.
Adjusted the regulator. With the plenum open and the engine off, I hooked up a pressure gauge, hooked a test lead to the fuel pump prime terminal and gave it 12v from the battery, took a Torx bit and adjusted the pressure until the gauge read 75 psi. Then calculated and adjusted the flow rate in the PCM tune.
 

L31MaxExpress

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Do you have a wideband on it? At 12.6:1 air/fuel ratio I was able to spin my 383 to 5,200 rpm and make ~460-470 hp with 75 psi on the stock spider. It moved over 6,200 lbs of van from 0-60 in under 7 seconds with a 4L85E, 3.73s and 31.6" tall tires.
 

chris2323

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That’s awesome thanks! Is it a torx bit with the hole in the middle? Or just a normal one? Yes i have a wideband. Im running 13:1 at WOT and seeing 105% duty cycle. Have a 383 with big cam and aftermarket heads k1500
 

L31MaxExpress

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That’s awesome thanks! Is it a torx bit with the hole in the middle? Or just a normal one? Yes i have a wideband. Im running 13:1 at WOT and seeing 105% duty cycle. Have a 383 with big cam and aftermarket heads k1500
Torx bit was in the center of my regulator on the spider. Both the OEM GM spider and my circa 2006 GM MPFI upgrade spider had the torx screw. I will say some are sealed and non adjustable though.
 
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