I am in process of building a lq4, should be roughly 475 fwhp. It's in a 1998 z28 camaro. I am wondering what injector size to use? Put info into injector calculator and was unsure if it was correct. I'm not exactly sure of my fuel psi. I am thinking it's around 57-59psi? Calculator says #31 injectors @ 85% cycle. Sound about right to you?

 

36 or 42 lb/hr should do it. I picked 42 just for the sake of having a bit more head room... Mine idle fine.

 

I'd go with at least 36 lb injectors, but there's no need to go with more than 42 lb injectors.

 

30lbs injectors will feed 500rwhp.
85% is NOT a valid number to be using as a basis to change size it does help sell parts though.
Pcms don't report DC accurately.
When folks tell you they needed bigger injectors ask if the motor went lean, you will find they were fine with the PCM reporting stuff like 110% but wasn't lean.

 

The FAST 36lbs is what is in my car and I am very satisfied with them. I think if I remember right reading on the net here that with the LS Fuel Pressure being around 60lb, that they are like a 41lb Injector!

 

One of the reason a 85% duty cycle is often recommended to allow flow restrictions that can occur do to deposit build up in injectors, or in the fuel filter, and unless you're 110% sure your done with the quest for any more hp a little more flow is a good idea. Furthermore I doubt that all tuners leave the A/F ratio exactly the same under all conditions. IMO, any one that runs injectors rated at 30lb with 58-60psi to fuel a 500 rwhp engine is being rather foolish. Then there's still the possibility that the dyno you ran your vehicle on was very stingy, making the situation even less ideal. Btw, when I had 32 lb injectors with about 425 rwhp I was already at about 95% duty cycle. It's always better to error on the side of a little too much, than too injector, and there's really no down side, with little to no cost difference to be a little safer, and have the injectors work more efficiently, and room to grow.

 

Exactly. 85% on injectors wont make you go lean and even at 102% I still had an ok a/f on mine. However the problem many people recognize with this is that injectors "pulse" Ie squirt fuel into the port at the correct time to get a good clean burn. If you run over 85% the injector in essence never shuts off. It wont pulse, instead it just shoots a steady stream of fuel to try and keep up. This doesnt give as good of a burn and the flow pattern may become erratic.

The injector fuel flow isnt the problem over 85% its the way the injector is actually supplying the fuel. OP I run stock ls3 injectors on mine which are 42lbs. They can be had pretty cheap and then just need adapters. In the end you can have a whole setup for 200 bucks. They are easy to tune, and offer oem reliability

 

Thanks for adding that missing crutial piece of info, rebbird555. I wasn't completely sure about why the injectors get sloppy at the high duty cycles, so I want to hold off posting additionial info without first verifying it.

 

lol no problem. I had no problems running my stock injectors at 102% duty cycle a/f was fine. However the ls3's just offered peace of mind that the fuel pattern was doing what its supposed to. I now have like a 46% dc with the ls3's lol.

 

Again the displayed DC can not be trusted as accurate.

The guys running 30lbs at 500rwhp do so because the car leaves harder and they understand the 115% number the PCM outputs is bull.

 

Thanks guys! I really appreciate the info! I'm so lost when it comes to injectors! Bout to get this thing underway! Ls1 is bout to crap out and is due for a rebuild! And lq4 is going in! I'm a service tech for Robert Bosch and get discounts on Bosch parts so I'm looking and #42 Bosch injectors. Good choice?

 

42lbs will run and drive fine if tuned for but are wildly oversized, especially if 42lbs at 43.5psi. The 58psi LS pressure will make them bigger yet.

 

Yeah, there's big difference going from a 42lb @ 43.5psi and then giving it 58psi. You'll have 48lb injectors @ 58psi.. So Conv_z28_camaro when choosing injectors make sure you know at what psi the LB. HR. flow rating is given.

Btw, FIC has a few good injector calculators on their website.

 

It depends a lot on the injector itself with how it idles. For example, the new EV14s from Bosch idle much better than other big injectors. I have the 52s that are 60 @ 4 Bar. It idles fine. But it was rich as hell when I started tuning even with something like the stock VE table.

The Racetronix or FAST 36lbs would be fine though - I don't recall if the Racetronix is a Lucas type or Bosch type off hand.

But, I'd goto FIC and make sure you get a Bosch type injector as our heads were designed with that spray pattern optimization in mind.