What are the best fuel injectors to get when you need more fuel?

[SLOWBRAEATER]

I have about every bolt on including the supersix powerpack and i need to know what the best injectors to use are, and will i need to get my pcm programmed for them? If i got bigger injectors and the pcm programmed for them but didnt actually "need" them would that hurt performance?

[John_D.]

<blockquote>quote:</font><hr>Originally posted by SLOWBRAEATER:
...i need to know what the best injectors to use are, and will i need to get my pcm programmed for them? If i got bigger injectors and the pcm programmed for them but didnt actually "need" them would that hurt performance?<hr></blockquote>

I bumped mine up to 24 lb/hr Accels and did not need reprogramming. The pcm did have to learn to lean out the mix. It hasn't hurt part-throttle, and has allowed me to run more fuel (for nitrous) at wot.

If you go bigger than 24's, I would think you would need reprogramming. If the reprogramming is done correctly (the correct values in the fuel map table) for your injectors, it won't hurt performance. Figuring out the correct values is the hard part...

[SLOWBRAEATER]

Will 24 be big enough with the supersix powerpack and comp cam with a direct port shot?

[John_D.]

<blockquote>quote:</font><hr>Originally posted by SLOWBRAEATER:
Will 24 be big enough with the supersix powerpack and comp cam with a direct port shot?<hr></blockquote>

How much additional hp are you talking about?

I ran a 120 shot on these injectors, but I was also running a higher fuel pressure, so I got a flow rate more than 24.

With your direct port, are you planning wet or dry? (meaning additional fuel jets too, or just nitrous only) (since nitrous is often categorized as dry, wet, and direct, just making sure your direct does or does not include additional fuel delivery.) I would assume wet, but just double checking...

If you run extra fuel, then your na injectors won't have to support the nitrous shot. In that case the 24's only have to handle the powerpack and cam, and I would think they would cover that.

Some of the other powerpack/cam guys should speak up, as far as what injectors they're running, or if they are having any problems with pulse widths or maintaining proper a/f ratio at wot.

[ December 16, 2002: Message edited by: John_D. ]</p>

[pgriffith]

If you are running direct port I think you should be looking at the fuel pump and not injectors.

[SLOWBRAEATER]

I am getting a walbro 255 lph in tank just trying to find one that is a direct replacement

[SLOWBRAEATER]

Yes i will be running a direct port wet nx kit so do you think 24 lb accels will be suffiecient enough? since im getting my pcm programmed should i tell the guy i am running aftermarket injectors? thanks for the help

[Jerriko]

If you are getting the PCM reprogrammed anyways, why not just change the pulse width? You wouldn't have to change the injectors, save some money and get more gas! The pulse width is controlled by the PCM and determines the amount of time the injectors remain open. I understand aftermarket injectors look cool and add another item to your list of mods on your profile but they are not necessary. Putting aftermarket high flow injectors without the correct PCM mods since the PCM would just lean out the fuel mix always.
Jim

[SLOWBRAEATER]

I wasnt getting them because they look cool and add annother mod to my list, in case you couldnt tell i dont have a mod list, anyway, when the pcm is reprogrammed for the bigger injectors it wont lean out because it will be programmed to spray that much fuel

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Jerriko:
...why not just change the pulse width? ...the pulse width is controlled by the PCM and determines the amount of time the injectors remain open. ...but they are not necessary.<hr></blockquote>

The pulse width can only go up to a point. There is a point where you hit 100% duty cycle, and then an injector physically can't flow any more, no matter how long the pcm tells the injector to stay open.

For instance, lets say that at 5000 rpms it takes 25 milliseconds to to complete an intake cycle. The pcm can tell the injector to stay open for 30 milliseconds, and all that will happen is the injector will go static and be open all the time.

No matter how long the pcm tells an injector to stay open in milliseconds, it can't stay open longer than 100% of the cycle time for the rpms the engine is operating at, because then it's already on the next cycle.

The optimal duty cycle is supposed to be around 80-85% for best flow pattern and to keep from going static and locking up.

If the duty cycle starts going over that, then a bigger injector can flow the fuel needed, without having to be held open so long.

So if an engine has been modded to the point that it needs more fuel than 21-22 lbs/hr per cylinder, a bigger injector might be needed after all. Somewhere around 250hp is probably where you need to start thinking about injector sizes.