C7 inj duty cycle max 49% ?

The car is a C7 cam heads E-Force supercharger 2in Kook Headers
Car was running great with E85 and 3.5 inch pulley 6-7 psi
After a 2.75 inch pulley swap 11.5 psi cant seem to get desired A/F
even with alky meth injection... What i noticed is that Injector duty cycle only goes to 49% max
is there a table which will let me open it more? Maf/Pe wont cut it, added a good bunch and still wont go over 49%
it seems it doesn't affect it as i change the values.
cam has the highest fuel lobe too. Any help will be greatly appreciated

Have you modified the injector timing (SOI)? DI IDC isn't the same as PI, you have a much smaller window in which to get the fuel in...

I've noticed that much past 35% and there just isn't enough time to properly mix and atomize the fuel for combustion.
What fuel pressure are you running? How does it compare to commanded?
I'll also ask about SOI timing. Lots to adjust there with FI.

Post the file... a friend had a similar problem i will ask what he did to fix it.
Not sure if the injectors were maxing out or the fuel pump, I will ask and let you know.

The duty cycle isn't true duty cycle. That duty cycle calculator is simply calculating the duty cycle based on a convensional 720 crank rotation port injection engine. There is a much narrower window on a DI engine to determine true duty cycle. If you are showing 49% on the standard duty PID built into the scanner then you are well past maxed on fuel system or injector. Like stated log rail pressure commanded and actual to see if fuel flow is there. If it is you can try increasing the pressure slightly to gain some head room. You can also adjust SOI (Start Of Injection) to fire the injector sooner which will give it a few more crank degrees to inject fuel.

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Originally Posted by LSxpwrdZ

The duty cycle isn't true duty cycle. That duty cycle calculator is simply calculating the duty cycle based on a convensional 720 crank rotation port injection engine. There is a much narrower window on a DI engine to determine true duty cycle. If you are showing 49% on the standard duty PID built into the scanner then you are well past maxed on fuel system or injector. Like stated log rail pressure commanded and actual to see if fuel flow is there. If it is you can try increasing the pressure slightly to gain some head room. You can also adjust SOI (Start Of Injection) to fire the injector sooner which will give it a few more crank degrees to inject fuel.

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Why not just start injection at EVC in all conditions? You don't blow any fuel out the exhaust and there is more time to complete injection. What is the point of delaying injection? Injection is delayed at low RPM/high load and also at high RPM/low load. Idle, normal throttle application, and high RPM/high load all inject sooner.

What's the philosophy on this?

Thank you all for your response we will put it up on the dyno today and i will save the logs and post... We haven't adjust SOI yet so its something we will try
also we have E85 we will bring it back to 93 pump gas that should give us back some more room since we have Meth kit installed... Car was making around 650 WHP with 7 pounds on e85 no meth...

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Originally Posted by Higgs Boson

Why not just start injection at EVC in all conditions? You don't blow any fuel out the exhaust and there is more time to complete injection. What is the point of delaying injection? Injection is delayed at low RPM/high load and also at high RPM/low load. Idle, normal throttle application, and high RPM/high load all inject sooner.

What's the philosophy on this?

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There is more to it now than just valve events. The factory tune is setup to use the least amount of fuel and burn the most efficient that it can in that setup. The location of the piston in the bore has alot to do with when the fuel is injected as well. On a setup needing more pulsewidth there is no reason why you couldn't start the injection process under moderate load and high rpm a bit sooner. The target here is to find that magic point where the start/end of injection on a particular setup allows enough pulsewidth to supply fuel and makes the most power from complete burn.

Went ahead and switched back to 93 pump gas with methanol injection... adjusted SOI table Psi 11.5 with e force supercharger left it at 11.4 a/f put down 703 whp
the injector duty cycle was around 34-36 if i remember correctly, at the end everything went fine.. Thank you all for your help!

What injectors in this combo? Stock?

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Originally Posted by GPGTP

What injectors in this combo? Stock?

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only ones available that i know of....the am is working it....

Ed M

Do z06 injectors fit?

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Originally Posted by GPGTP

Do z06 injectors fit?

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good question......will the fuel system be capable??
Ed M

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Originally Posted by mowton

good question......will the fuel system be capable??
Ed M

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I like your first response better... If the injectors fit and swapping the cam with a bigger fuel pump lobe big power should be available.

I would expect the z06 injectors to be worth an extra 100 hp.

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Originally Posted by GPGTP

I like your first response better... If the injectors fit and swapping the cam with a bigger fuel pump lobe big power should be available.

I would expect the z06 injectors to be worth an extra 100 hp.

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found this...

Fuel system

The LT4’s direct injection system is similar to the LT1’s, but it features a new, higher-pressure engine-driven pump capable of delivering fuel at an astounding 2,900 psi. The LT1 pump is capable of “only” 2,175 psi. The LT4 also features a unique, higher-capacity fuel-rail assembly designed to accommodate the supercharger manifold. It’s fitted with injectors rated at 1.5 liters per minute, while the LT1 uses 1.2-lpm squirters.

Ed M

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Originally Posted by mowton

found this...

Fuel system

The LT4’s direct injection system is similar to the LT1’s, but it features a new, higher-pressure engine-driven pump capable of delivering fuel at an astounding 2,900 psi. The LT1 pump is capable of “only” 2,175 psi. The LT4 also features a unique, higher-capacity fuel-rail assembly designed to accommodate the supercharger manifold. It’s fitted with injectors rated at 1.5 liters per minute, while the LT1 uses 1.2-lpm squirters.

Ed M

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http://media.chevrolet.com/media/us/...owerhouse.html

yes fuel pressure was increased as well as injector flow rate.

If you look at a stock LT1 tune vs LT4 you will find that the LT1 has 121.1 lb per hour injectors and pump pressure only commands 2175 psi. The LT4 has 140.7 lb per hour and 2901 psi.

I can see getting the most power out of these engines is going to be a balance of injector timing when reaching the limit of flow rate.


You can also see that the injectors were rated at 10 Mpa. Also, after the 15 Mpa max multiplier, the LT1 injectors flow 149.4 lbs per hour compared to the LT4's which are 203.4 lbs per hour after the 20 Mpa multiplier.

I'm interested to see what kind of pressure people are able to run with the cam upgrades. 20 Mpa bumps the LT1's up to 175 lbs per hour which is a 17 percent gain.

While on the subject I would like to know if the LT1 injectors fit the truck engines since they are even smaller rated at 96.5 lbs per hour. The LT1 injectors would be a 25% gain in fuel flow at stock pressure

heres a question, how much of an advantage is there to up the pressure to get the same amount of fuel spray in less time?

I was actually reading an SAE paper last night that was discussing early vs late injection and pressure vs its outputs on power.

I was actually reading an SAE paper last night that was discussing early vs late injection and pressure vs its outputs on power.

In all cases increased pressure and early injection made the most power.
The injection window was from 6 degrees BTDC to 5.5 ATDC.

I also want to add that if you were going to just increase pressure, I believe it would be wise to make the SOI earlier as well??? The LT4 does this, increased pressure/earlier SOI