RS Z28

Hello All,

I have been busy away adding parts over the past few months adding parts and I am about two weeks from starting waking the car from a extended nap. While preparing to put the headers back on the car I removed the rags from each cylinder and noticed fuel from the injectors leaked into the cylinders from sitting. Car also smelled rich when it was running which this could of been a prior problem, 146,000 miles on the original injectors. 7 out of the 8 leak.

While I believe this to be an existing concern that I have had for a while I am now going to be replacing the injectors. In addition to this I will be getting my computer tuned for the recent gear change, converter and now injectors.

Here is where my two questions come in;

First I see many people recommending injectors ranging from 24lb to 42lb, 42lb seems way excessive with my listed mod's. What would be a suggested injector for the mods that are do to my car? I searched and nobody has a standard rule, X parts require this lb injector.

Secondly, today Keith from PCM for Less recommended 42lb injectors to cover all future modifications, like my plan heads and matched cam with a 150 shot. Does this seem like a decent recommendation? Can the dwell and duty cycle could be reduced in the tune to work in my car ? Wouldn't that affect the spray pattern of the injector?

I am not a tuning expert or a injector expert but would like to learn from peoples past experiences and their knowledge, hope someone can school me and provide some advice.

Moderators...this fell in to tuning and fuel categories, if it needs to be moved please feel free to move it.

Injuneer

Rule of thumb (at least mine): Multiply flywheel HP by 0.07 to get minimum injector size for your setup. This is for normally aspirated engines. Does not apply to power adders - forced induction or nitrous.

You have to estimate HP at the flywheel. Basically, you have a cam, CAI and long tubes. The emissions deletes have nothing to do with WOT power. The 58mm TB is oversize for the setup. 180-deg is a stock t'stat for the LT1.

Let's say you are under 400 HP at the flywheel.

400 X 0.07 = 28 LB/HR

Heads and cam might take you to 500 HP

500 X 0.07 = 35 LB/HR

With 42's you could make 600 HP. That's a rare LT1 on straight motor.

The 150-shot of nitrous only affects the injectors if it's a dry system. Most people (myself excluded) run wet nitrous. The fuel does not go through the injectors. Flows through a nozzle, where it's atomized by the nitrous stream.

The injector is strictly on/off, not pulse width modulated. Turn it on, it spray, turn it off it doesn't spray. For all practical purposes the spray pattern doesn't change. If you try to exceed 85/90% duty cycle, it can screw up the spray, or cause the injector to go static. But my formula keeps the DC below 85%. It also assumes a brake specific fuel consumption of 0.476 #/HR/HP. Good combustion chamber geometry and a decent tune should be below that.

Next problem is turning the injector down to the short pulse widths required to idle below 1,000 RPM. The LT1 PCM injector drivers don't seem to have a problem with this when running 42 LB/HR injectors. But do you expect to go over 500 HP normally aspirated? Running 36's, you would have the option of increasing the fuel pressure to effectively increase the injector flow capacity.

RS Z28

Injuneer, thank you for your response. It is tough to estimate the horsepower that the motor makes but since its just a estimate I would like to believe the car makes low 300 horsepower based on reviewing other cars with similar modifications to mine. So based on future plans to go with heads and a matched intake with spray, I decided to go with 30lb injectors all flow matched and also have it tuned accordingly for the time being.

With the 30lb injectors it allows me to have a little headroom to have the car retuned once I take the car to the next step.

The 58mm throttle body was on the car when I got it so it will stay until all the other concerns are fixed.

Thanks again for the advice,

Richard

IowaSS

30's was a good decision.
And you have a LOT of room for future power upgrades with them.
If they're the SVO 30's, those have supported up to 500 rwhp.
I've been running them at extended high power (roadracing) for two years making 430 rwhp.

RS Z28

The injectors are the Bosch 30lb EV6 Red SVO new style from the Fuel Injection Connection. Those guys know there stuff! Hope the wakes from dead, I have had my hands in so much of the car.

Thanks for the good heads up on the choice of injectors. I see you have AI heads, have you been happy with them?

IowaSS

Very happy with the performance. Not so happy that 2 of the exhaust ports were ported so thin to the water jackets that they began leaking water into the cylinders after very little use.