97formulakid

Ok, I finally tracked down my hard starting problem to my injectors. So I need to replace them. What size should I go with??? I think the LT1's came stock with 22lb/hr right?? So would 24's be ok??

I will be running a 150 shot and maybe be putting in a cam within the next year.

DrewHMS97SS

Go back and read your original post.

Injuneer

Stock for 94-97 LT1's is 24#/HR. Unless you're making upwards of 400flywheelHP, you'll be fine replacing them with similar size.

If you're running a wet kit, you don't need larger injectors. If its a dry kit, what you have to do with the injectors depends on how the kit makes the injectors add the extra fuel.... e.g. boosting fuel pressure.

97formulakid

Would it hurt to run 30lb??? I can get those a little cheaper and I would be able to go further on them then the 24lb (as far as modding goes)

OBE1 95Z28

You'll need to have your computer reprogrammed to use 30# injectors.

LameRandomName

Sure, with a new program to run them. Easy.

You should give careful consideration to what your future plans are NOW, because ideally it would be better to only replace your injectors ONCE.

For reference, I am running 42lb injectors on a bolt-on motor with stock cam. I don't NEED them (YET); I only mention it to illustrate that you can go much bigger than you might think you can, so as to leave headroom for other modifications.

You should NOT however buy injectors based on best price.

You should buy injectors based on NEED, both present and future.

97formulakid

well here is my plan. I am going to have nitrous on it by the end of the summer. and then by next summer I will try and have a cam in it. Sometime within the next 5 years I would like to have a LE3 383 spraying 200-250. But, that is sooo long in the future that I wouldn't mind buying new injectors then. I just don't want something that is going to be overkill and way too much injector.

LameRandomName

Nitrous? Dry or wet?
It makes a difference in injector selection.

If you plan to run a wet nitrous kit and you don't mind buying new injectors when you get your LE3 setup, then get something in the mid-30's, which is enough headroom to account for a variety of bolt-ons.

If you're going dry, then you should probably get 42lb injectors. At least, that's what I did.


BTW, although there is at least one guy here spraying over 200lbs dry, you ain't in his league. Spraying 100lbs dry is one thing. Spraying two or three times that much calls for a level of experience, knowledge and skill that only comes with years of experience and many broken parts.

At least, that's been my observation.

97formulakid

No, I am going wet. I have had very good luck with wet shots and so I am going to go with that. So would 30-36lbs be okay without them being overkill???

LameRandomName

Assuming about a 12.5 - 13.0 AFR, 80% volumetric efficiency, and max torque at around 6000rpm, 30lb would get the job done at about an 80% duty cycle.

If it were ME, I would use a 36 for daily driving or a 42 for a car that was going to see regular bracket racing on the weekend. However, that's because I have certain personal prejudices in terms of duty cycle that may or may not be valid.


My suggestion to you is to use a 36, unless Rich, Fred or one of the other top level gurus says something different. If they do, you would be wise to follow their advice instead of mine.

97formulakid

See I think I may just go with 36lbs injectors. Will that effect gas mileage or anything of the sort???

Injuneer

If the correct injector flow rate is programmed into the PCM, gas mileage will not be affected. You will just end up with a lower duty cycle (shorter pulse widths for any given engine load) and that's "good". The only possible downside of a very large injector is whether the stock PCM can turn the injector down to the very short pulse widths required for idle. I haven't seen people complaining about idle problems with 36's.

LameRandomName

FWIW, my stock PCM idles the car beautifully with 42lb injectors.

I have seen only one difference.

When the stock injectors were in the engine the car would crank for one second before starting.

With the bigger ones, it'll sometimes crank for 3-4 seconds; generally only when cold.

Injuneer

What are your pulsewidths at idle with the 42's? What is your idle RPM? What is your MAF GPS?

LameRandomName

Let me get back to you on that Fred. I want to make sure I have the correct info. The only thing I know off the top of my head is the idle, which is 700.

I know some folks like to go lower on idle speed, but I worry about oil pressure.

=================

OK, sorry that took a couple of days.
I wanted to check with Bryan, since HE does my tuning, not me. Naturally, he was out of town for a couple of days...
Anyhow, according to Bryan; my Pulsewidth is 2ms and MAF GPS is 7.