91-Z28-L98

I was planning on modding my engine after the summer when I finished school, but it seems some of my injectors are going bad so I want to get them upgraded now. How well would my stock L98 work with 30 lb/hr accel fuel injectors? If it wont work, then what flow rate should I go with? The 30 lb/hr injectors are the same price as 21 lb/hr ones, so if I'm gonna get new ones anyway I might as well go as high as I can.

cc89formula

you would think that would be a good plan, however with 30# injectors your going to be dumping too much gas into the cylinder which wont completly burn and your cars going to run like crap...

mako350Z28

On a stock L98 you could probably use 24# injectors but I think it requires a new chip.

I could be wrong but then turning your fuel pressure up to 50 psi does just about the same thing.

91-Z28-L98

So the computer wont see that its sending too much fuel and adjust?

Drkhrse89

I am probably going to do a horrible job explaining this, but when the injectors pulse they send a certain amount of fuel into the cylinders. And if you are just going to increase the injector size they will still pulse the same, but now you will be dumping more fuel into the cylinder. If you do not plan on changing the chip do not get those injectors. And unless you are planning on going high hp motor 30#ers are awfully large.

bubba353z

Unless you go with 21lb injectors, you will have to have a new chip burned. Drkhrse89 has got the right idea. I'm no expert, but I'll try to help.

This may be oversimplification of the process, but the computer calculates the fuel volume by the numbers that are hardcoded on the chip (injector constant). If you put 30's in without changing the "constant", the computer will still calculate the volume using the original 21's calculations. Basically it will dump in about 45% more fuel (than calculated) with each injector pulse.

In this case, the O2 will see that the engine is rich and try to pull fuel out. The problem is that it can't pull enough fuel, because the injector can't cycle fast enough (it can only pulse so fast). Without the right constant here, you will likely wash down the cylinder walls and ruin them. On the converse, if you use injectors that are smaller than the "constant" the engine will run lean.

You can affect the volume with fuel pressure, as well. Lower PSI = Lower volume at the same injector constant. The problem there is if you lower the pressure too much, the fuel won't atomize properly. Too high a pressure, and the pump may not be able to keep up.

Another word of caution - check the PSI at which the injector is rated (if you go aftermarket). I think Ford injectors are calculated at 38.5 psi, where GM / Accel are at 44 or 45 (3 bar?). It will make a slight difference (rich) in the flow if you run the Ford injector in a GM application (yes, they will work).

I have Accel 24's on my Z, with the appropriate chip modifications. I think they are good to 400-425 hp. If all you are going to change is the injector size, the chip mod is simple.

91-Z28-L98

Whats the approximate cost of a chip modification of this kind?

bubba353z

My first chip (Ed Wright) cost about $300, but I had a lot more mods done. I'm currently learning to burning my own, but I've got about the same into the parts for it.

If you only need a injector constant change, you probably can get someone to do it for you for the cost of a chip (under $10).

Check out Moates.net - he has everything you need to burn your own. Thirdgen.org has good DIY writeups - that's where I got started. If you are planning on future mods, it will be worth your time and money to learn to do it yourself.

Marc 85Z28

About as well as a 2.8L V6 with a 850CFM Holley on it!