[Mahdi ZL1]

Sorry for lack of knowledge on the LT4 platform in advance.

Ultimately my mod list consists of:

Ported Blower, Ported Snout, 103MM TB, 2.30 Griptec Pulley, 2” Kooks LT headers, AWE track edition catback, SMG lowside aux pump, SMG flex fuel kit, rotofab intake, and 160° thermostat

Having my car tuned and i’m just confused at this point. Seems like based on all the other builds I have seen online, I followed what seemed like an ideal build for me turned money pit.

Current issue, my tuner explained that i’m maxing out my stock high side pump on e40. He was having other issues with pressure dropping off on 93 but got it dialed in on 93 at 570ish WHP with around 680 trq. Now this is down on power from previous tuner but with an increase from 550rwtrq to 680. Horsepower before was around 600rwhp now 570rwhp. Not sure exactly what was the reason for it being down on power because i’m not tuning it. But then, we filled e40 and we managed to squeeze 594rwhp/714rwtrq. Tuner stated the car is maxing out it’s stock high side fuel pump which he has never witnessed at the horsepower number. I want to say something is wrong, because my made those horsepower numbers on just the previous 93 tune.

Our next diagnosis is to fix the exhaust leak before the wideband o2 sensor because we believe it may be reading inaccurately causing us to tune the car richer than it should be. We hope that this fixes the issue and we see its rich because of this in accuracy. Besides this we don’t know what or where the issue is because this is a car that should be seeing closer to 700rwhp range.

[Mahdi ZL1]

I should also mention my car was only seeing about 12.3lbs of boost on the dyno.

[ShockingZ]

edited

[Schlok]

Your local MI options are Katech and Livernois...see what either of them say...

[IneedAZ]

Did they mention what your injector Pulse Width was? A Stage2 cam will wake the HP up and help high side

[Katech_Zach]

Not unusual at all.

The factory HPFP runs out of pressure on 93 octane, with just a 2.3 upper pulley OR a factory upper, 15% lower. When you add an aux pump and bump up the base fuel pressure, you will get a slightly higher cap, but not much.

E85 requires 30% more volume of fuel by nature, because it is oxygenated fuel. So instead of being at 100% maxed out, you are now 30% over the limit, and will face huge problems like you currently are.

By doing a mix, you are still maxed out. The only way to give yourself flex fuel capabilities, is to underspin the blower and pull power out of the car.

General Ethanol Fuel Limits to follow for OEM Redline (Based off of a baseline dyno number of ~520-540rwhp on 93 octane-ish)
~600rwhp Full E85: Bone Stock ZL1, With an Aux Pump, Flex Fuel Sensor
~630rwhp E25-E30 Mix: Modified ZL1, 15% Overdrive~ + Exhaust, Aux Pump, Flex Fuel Sensor
~700rwhp Full E85: Head/Cam/Ported Blower, XDI30% Injectors, Aux Pump, Flex Fuel Sensor
~730rwhp E25-E30 Mix: Head/Cam/Ported Blower, XDI30% Injectors, Aux Pump, Flex Fuel Sensor

You can screw with this a bit if you add supplemental Methanol or Port Injection, at that point your power limits have much higher limits.

You're down on power because you aren't out of fuel until you get into the higher RPM's. Horsepower is a function of torque over RPM, the less RPM you spin, the less HP you make. So you are making much more torque, because you have the appropriate fuel at the given RPM points down low. When fuel demands get high with higher RPM's, you're out and the entire system doesn't mesh, resulting in no power.

Hope this helps.

[KingLT1]

Stock LT4 fuel system should keep up with your Mods on E50 @ .84-.85 Lambda with a low side upgrade. I have cars doing that with just a JMS on stock tank pump. If you run richer you run out of fuel system a lot sooner. If you run leaner, you can go further. I personally wouldn't run leaner than .85

The exhaust leak sounds plausible. It would cause the wideband to show lean and then you would be adding fuel to compensate for a false lean condition which will run the fuel system out of headroom sooner that it should for the mods and power level.

[SOCAL.M6.ZLE]

Originally Posted by Mahdi ZL1

Sorry for lack of knowledge on the LT4 platform in advance.

Ultimately my mod list consists of:

Ported Blower, Ported Snout, 103MM TB, 2.30 Griptec Pulley, 2” Kooks LT headers, AWE track edition catback, SMG lowside aux pump, SMG flex fuel kit, rotofab intake, and 160° thermostat

Having my car tuned and i’m just confused at this point. Seems like based on all the other builds I have seen online, I followed what seemed like an ideal build for me turned money pit.

Current issue, my tuner explained that i’m maxing out my stock high side pump on e40. He was having other issues with pressure dropping off on 93 but got it dialed in on 93 at 570ish WHP with around 680 trq. Now this is down on power from previous tuner but with an increase from 550rwtrq to 680. Horsepower before was around 600rwhp now 570rwhp. Not sure exactly what was the reason for it being down on power because i’m not tuning it. But then, we filled e40 and we managed to squeeze 594rwhp/714rwtrq. Tuner stated the car is maxing out it’s stock high side fuel pump which he has never witnessed at the horsepower number. I want to say something is wrong, because my made those horsepower numbers on just the previous 93 tune.

Our next diagnosis is to fix the exhaust leak before the wideband o2 sensor because we believe it may be reading inaccurately causing us to tune the car richer than it should be. We hope that this fixes the issue and we see its rich because of this in accuracy. Besides this we don’t know what or where the issue is because this is a car that should be seeing closer to 700rwhp range.

Curious... did you get this sorted out?

[Megahurtz]

E40 on those mods is real close to the limit depending on AFR. I was able to run E50 with the same mods but that was on edge and the high side was dropping. E40 would have kept it in the safe range for weather changes. Perhaps your tuner is being safe or has it tuned rich. You can target .84 lambda for that setup.

[Evansa22]

Fix the exhaust leak first and check it. I was running out of lowside fuel on 91 when I should have easily been fine with my mods. Leak right in front of the wideband was causing it to read leaner than actual like others have said. Lambda was way richer then we were seeing. Fixed the leak, and lambda was way rich at WOT. Adjusted the tune, wouldn't you know lowside pressure was fine. Did some unnecessary upgrades to the fuel line like LPE check valve just to figure out it had nothing to do with the stock fuel line.

[JSH]

My OEM high-side makes 1000+ on race fuel. Most high HP guys running Eth. run LPE's BBFP.

[laynlo15]

Time for TooHighPsi Port Injection and call it a day. I'm still running the stock Lt1 fuel system with just a JMS boost a pump with a little Maggie 2300, plenty of fuel with the Replex controller and PI. Running on E65 with 11 psi of boost making 707 at the wheels and 669 torque. Best bang for the buck, no tearing the top half of the motor off for a cam, you can add the PI when you do the ported blower and then you'll be stellar. No changing the stock Lt4 fuel system, just great power with plenty of fuel for the power you want to make.