[Choda]

dads1le, thanks for the dyno and notes.

[Dads1le]

Choda. Welcome. My tuner was baffled by the results of changing injectors with the significant added torque at lower rpm and nothing up top. We’re guessing it’s a difference in the way the injectors atomize the fuel. More like a sprinkler head than a garden hose. Both same volume but spread out differently

[Vrodviddy]

Originally Posted by Dads1le

Attachment 1005833
First try at posting a pic Red line is current with lt4 injectors added. Blue line is after adding prays ported msd a year and 4 months ago. Orange line is prays ported stock Intake.
This is on a 17 1le with prays h/c stage 1 ported msd. Milled ported heads. Underdrive pulley. E85. 17/8 arh to borla s type

Are you running a bigger cam to?

[Vrodviddy]

Originally Posted by TJay74

I am gonna disagree, vast majority of the cars that are modded will need some sort of fuel system upgrades. Injector duty cycle and low side / high side fuel pressures will dictate this more than anything else.

Until the OP logs the injector duty cycle, low side FP and high side fuel pressure it will be a guess if he needs anything else. E85 will only make this problem worse due to the extra 30% fuel needs.

As said though to the OP, the fuel system will not in itself gain you any power, it will give you more headroom to be able to make more stable power and not take a chance of going lean and blowing the engine up.

You current and future power goals will dictate this more than anything else, without those no one can really comment. The 32% lobe on that cam only helps the high side of the pressure feeding the fuel pump under the intake (HPFP). It does nothing for the low side which is the pump in the tank (LPFP).

If money isnt an issue and you have time on your hands then I will say sure, go ahead and drop in the LT4 LPFP, HPFP and the LT4 non restricted fed pipe for the HPFP and the revised cross over fuel lines for the fuel rails. At least at that point you will know that you can support near 700rwhp with no worries.

Very well explained. Thank you. And It will definitely be the next thing i do. Just trying to get through Christmas first then will be upgrading everything i can with fuel. Going to have to anyways when i buy the supercharger next year.

[Vrodviddy]

Originally Posted by Dads1le

Choda. Welcome. My tuner was baffled by the results of changing injectors with the significant added torque at lower rpm and nothing up top. We’re guessing it’s a difference in the way the injectors atomize the fuel. More like a sprinkler head than a garden hose. Both same volume but spread out differently

What lt4 injectors are you using? Anything special for the spray pattern.

[Dads1le]

As far as I know all lt4 injectors are the same. I believe the spray pattern must be different from lt1 injectors to lt4 injectors. Both are being commanded the same air and fuel at lower rpm but lt4 injectors make more power. I do have pray performance stage 1 cam

[Umbriel]

I doubt you need any fuel upgrades with just a cam, your "lean" looking plugs are probably just from needing a better tune. I ran stock LT1 fuel system on my car using full E85 with a decent sized cam, headers, full exhaust, Rotofab and everything was fine. Car put down 492 rwhp on a stingy dyno and ran 11.2 in 2000 DA.

[Vrodviddy]

Originally Posted by Umbriel

I doubt you need any fuel upgrades with just a cam, your "lean" looking plugs are probably just from needing a better tune. I ran stock LT1 fuel system on my car using full E85 with a decent sized cam, headers, full exhaust, Rotofab and everything was fine. Car put down 492 rwhp on a stingy dyno and ran 11.2 in 2000 DA.

Awesome! That's exactly what I'm running. Good to know. I was starting to worry that I might be hitting a limit with what I have and e85. Thanks.

[Umbriel]

Originally Posted by Vrodviddy

Awesome! That's exactly what I'm running. Good to know. I was starting to worry that I might be hitting a limit with what I have and e85. Thanks.

You're welcome, I just wouldn't want you to buy something you don't need. My car runs completely fine with this set up.

Sent from my SM-G955U using Tapatalk

[KingLT1]

NA heads/cam cars have been 600whp and ran 9's on stock fuel system with E85. There is no need for LT4 injectors on a mild setup.

I would take those graphs from IMC with a grain of salt. Justin can tune LS but I wasn't impressed with his tuning on Gen 5 stuff.

[Vrodviddy]

All good to hear. I do plan on going forced induction eventually, but not for at least another year. So good to know ill be alright till then. Thanks for everyones input.

[DorkMissile]

IMO the bid difference between the LT1 and LT4 fuel system is the pressure. LT4 pump runs at 2900psi I think, LT1 stuff at 2100 (trying to work off memory).

I would deduct that the difference for the injectors as far as the fuel delivery goes is that they are optimized at the two different pressures.

[Vrodviddy]

Originally Posted by DorkMissile

IMO the bid difference between the LT1 and LT4 fuel system is the pressure. LT4 pump runs at 2900psi I think, LT1 stuff at 2100 (trying to work off memory).

I would deduct that the difference for the injectors as far as the fuel delivery goes is that they are optimized at the two different pressures.

That and the heads on lt4 i think ported and shorted.

[DorkMissile]

Originally Posted by Vrodviddy

That and the heads on lt4 i think ported and shorted.

They are actually completely different castings - different port sizes & combustion chambers

However - in regards to the LT1 vs LT4 injectors themselves, the holes / patterns are "different" to get the correct atomization at the correct pressure.

What does this mean? Yes, the LT4 injectors on paper "flow" more fuel, but it is because it has 38% more fuel pressure behind it on a stock LT4 vs a stock LT1. I think if you put a LT4 pump on LT1 injectors, they too would flow 38% more fuel, however you would have issues getting the fuel out of the injectors as the hole pattern / sizes on the LT1 injector were not optimized at 2900psi, they were optimized at 2100.