Fuel pressure and tuning?

[96ss1664]

In the process of adding a few more mods, so I asked my tuner how my fuel pressure looked during the dyno pull. He responded with this:

"Fuel system wise you were good before. I purposely ran the fuel system at a lower pressure to bring up the duty cycle on the injectors for better atomization under boost. With the fuel system commanding 350kpa (~50psi) it stayed fairly stable across the entire RPM range and injectors were running 80-81% duty cycle. With that said we have plenty of headroom on the injectors because I can raise the fuel pressure back up to the standard 4bar (58psi) it'll drop the duty cycle back to 68-69% duty cycle."

I became very curious about this because I thought the fuel pressure should be above 65+ psi during WOT. I then asked him about the variable fuel pressure and this is what I got.

"The 50psi is being ran all the time on yours right now. It does have a variable fuel pressure system but is regulated at 58psi meaning 58psi is the most you can go up to without modifying the physical pressure relief within the tank. Bumping fuel pressure to 58psi will greatly increase the headroom you have on your injectors however something like E85 would really need to be boost referenced or increased further than 58psi to maintain injector duty cycle."

So is he confused on the ZL1 vs SS fuel system or am I looking at this wrong. The car on a wideband O2 and the spark plugs has never showed a lean condition but I feel devastation is going to happen if I don't get this changed.

Any Advice?

[ZO6 Bryan]

There are some half truths in there. But he apparently isn't terribly familiar with the ZL1 CTS-V and ZR1 fueling systems.
You should be at 65 psi at WOT
Same for the CTS-V
And 85 psi in the ZR1

And higher pressure yields better atomization. Not lower. And you have to make up the difference in the manifold pressure. If you are at say 15 psi boost, then your 50 psi just became 35 psi. He's wrong about a few things.

[96ss1664]

Do you know what the fuel pressure relief for the ZL1 is and does the SS cars have the 58 PSI relief?

[ZO6 Bryan]

Not sure on the SS. But the ZL1 is about 68 psi

[hawk02]

Originally Posted by ZO6 Bryan

There are some half truths in there. But he apparently isn't terribly familiar with the ZL1 CTS-V and ZR1 fueling systems.
You should be at 65 psi at WOT
Same for the CTS-V
And 85 psi in the ZR1

And higher pressure yields better atomization. Not lower. And you have to make up the difference in the manifold pressure. If you are at say 15 psi boost, then your 50 psi just became 35 psi. He's wrong about a few things.

Z06 Bryan brings up a very good point. It's been my experience that a fair number of tuners don't know or understand the intricacies of the ZL1/CTS-V. Many see it as just an SS with a supercharger slapped on it.

Several years ago when I went through my own tuning adventure, I had one tuner who didn't understand why the fuel pressure was going up at WOT and not down. Another one reduced the fuel pressure and made it a constant value across the board because he thought the injectors I had in at the time were too large for my level of mods and reducing the pressure would compensate for that!

At least you seem to know enough to question what your tuner is telling you. Unfortunately, a lot of us don't have that knowledge and accept what is said as the truth. That can sometimes lead to an expensive learning lesson.

[Russell James]

I'd call one of the vendors you've got parts from. I see you have some LPE parts... they do tons of tuning work on these engines. I'd call one of their tech persons and ask that general question of what fp and inj pulse should be at WOT.

[ZO6 Bryan]

Originally Posted by Russell James

I'd call one of the vendors you've got parts from. I see you have some LPE parts... they do tons of tuning work on these engines. I'd call one of their tech persons and ask that general question of what fp and inj pulse should be at WOT.

Yeah, good luck with that.

[Russell James]

Never hurts to ask. Or buy some parts from JRE, and give Ted a call. He'll give you the straight poop on ZL1 tuning.

Probably several approaches to get to the same thing. One thing to consider too is if Cat protection mode is turned on or off. That will really affect how WOT should be tuned.

[vicnkathy]

This is the case of a tuner with a little knowledge thinking he knows more then he does. It's extremely dangerous putting the car in the hands of a self proclaimed expert. Stick to the guys that tuned hundreds of these cars. Get a mail order tune if need be, data log and fine tune it from there. Don't leave this to chance!

[96ss1664]

Thanks for the input guys!! Does anyone know if other tuners lower the fuel pressure?

I'm also having a hard time on how I'm going to approach my tuner with this, he is a very good LS tuner and has some record holding cars that he has tuned.

[fif_gen_powa]

Originally Posted by 96ss1664

Thanks for the input guys!! Does anyone know if other tuners lower the fuel pressure?

I'm also having a hard time on how I'm going to approach my tuner with this, he is a very good LS tuner and has some record holding cars that he has tuned.

I don't see the big deal personally. If the car makes power and has a good safe reliable tune I don't think it matters what the fp is. You can't be on the fence with your tuner either you trust him or not. If you don't like his approach than find someone else imo