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How do I know when larger fuel injectors are needed?

This is a discussion on How do I know when larger fuel injectors are needed? within the General Help forums, part of the LSx Technical Help Section category; I was wondering how one knows when it is time to install larger injectors? My engine dynos at 404 RWHp ...

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    Member Sam-SS's Avatar
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    How do I know when larger fuel injectors are needed?

    I was wondering how one knows when it is time to install larger injectors? My engine dynos at 404 RWHp and has most all of the free mods, CNC heads, Crane Cam and SS long tube headers w/3" "Y", intermediate pipe and muffler.
    My tuners have had problems in getting good drivability
    and when they get it worked out after a while it seems to fall back to occasional jumping, bucking, idle serge etc.

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    Visualize°Design°Create SSwt00SS's Avatar
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    your stock injectors are fine. im running a H/C/I/E car and putting down 444rwhp and im still on the stock injectors...

    whatever the issues that your tuner is having is a result of his tuning, not your injectors. your tuner would be able to tell you if your injectors are either maxed out or close to being maxed out...

    also, what size heads and what are your cam specs...?

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    I was just told that you need to change the injectors after 400 horse.

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    Quote Originally Posted by stephen02ws6 View Post
    I was just told that you need to change the injectors after 400 horse.
    sorry, i dont buy into that. my stock injectors are still performing and supporting nearly 520 flywheel hp and they are not maxed out. there is a difference between being TOLD and having it 'recommened' to swap out injectors...

    however this winter i plan to install the TSP 231/237 cam i have and install an UD pulley as well. it will be at that point, that I will install new injectors from 28lb/hr to only 36lb/hr...

    without knowing the specs of the cam the guy is running, the LSA, if he has an A4 or M6, gears, etc..., there are too many factors that could be the reason that his tuner is having issues w/drivability fine tuning, etc...

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    Quote Originally Posted by SSwt00SS View Post
    sorry, i dont buy into that. my stock injectors are still performing and supporting nearly 520 flywheel hp and they are not maxed out. there is a difference between being TOLD and having it 'recommened' to swap out injectors...

    however this winter i plan to install the TSP 231/237 cam i have and install an UD pulley as well. it will be at that point, that I will install new injectors from 28lb/hr to only 36lb/hr...

    ...
    Sean @ LG said the 99's have 26lb injectors, I upgraded mine to Ford 30lb injectors (36lbs in reality) It helps on warm starts and always gets enough fuel to that bad boy, do it.

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    ah, i thought 98's only had the 26lb/hr injectors...

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    You need to check the duty cycle of the injectors. If you are at 80%, then you should upgrade.

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    Quote Originally Posted by SSwt00SS View Post
    ah, i thought 98's only had the 26lb/hr injectors...
    That's what I thought, Sean said differently...

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    Quote Originally Posted by SSwt00SS View Post
    sorry, i dont buy into that. my stock injectors are still performing and supporting nearly 520 flywheel hp and they are not maxed out. there is a difference between being TOLD and having it 'recommened' to swap out injectors...

    however this winter i plan to install the TSP 231/237 cam i have and install an UD pulley as well. it will be at that point, that I will install new injectors from 28lb/hr to only 36lb/hr...

    without knowing the specs of the cam the guy is running, the LSA, if he has an A4 or M6, gears, etc..., there are too many factors that could be the reason that his tuner is having issues w/drivability fine tuning, etc...
    Sorry that I started this thread and have not kept up with it. I had a problem that I had to take care of.

    To answer your questions, the cam is a Crane 228/238
    @ .50 w/1.8 rockers giving .600 lift at the valve. Heads are LS6 heads CNC ported by Texas-speed, LS6 Intake,
    80mm throttle body, Granateli MAS. The car is M6 w/3.73 gears. Long tube SS headers, 3" Y pipe,
    3" intermediate pipe and 3" muffler by Brassani.
    Injectors and ignition are stock. Car has 74k miles on it.
    Dyno at 404 RWHp. I dono what LSA is that you mentioned.

    Since I started the thread, I have installed an 80mm
    throttle body and this seems to have helped the drivability. The biggest problem that I now have is
    it dropping from my normal idle of 950rpm down to
    say 600 rpm occasionally and then it returns to normal.
    Also, when taking off from a city traffic light in slow
    traffic, I have to be careful as sometimes it will bog,
    dropping the RPM, at off idle when letting the clutch out.

    Ok, that is the long and the short of it.

    ...>>Sam

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    Simple. Your tuner should be logging the duty cycle of your injectors. If the exceed 80% then you need more injector. Period. I dont give a rats butt what RWHP you are putting down.

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    Quote Originally Posted by SSwt00SS View Post
    ah, i thought 98's only had the 26lb/hr injectors...
    98's have the biggest injectors 28.8lbs/hr

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    For that size cam, you are way under powered, especially if you have heads and an M6 car. Your tuner does not know what he is doing. With cheap (in cost but not in quality) heads $1300 and a cam .644/.598 and full bolt on's I am getting about 470rwhp. Now I do have the fast 90/90 set up but you should hit about 440 to the wheels easy.

    Change tuners. Trust me thats where it's at. I have 37# injectors but the stock ones would do you fine.

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    Quote Originally Posted by Zoilus View Post
    For that size cam, you are way under powered, especially if you have heads and an M6 car. Your tuner does not know what he is doing. With cheap (in cost but not in quality) heads $1300 and a cam .644/.598 and full bolt on's I am getting about 470rwhp. Now I do have the fast 90/90 set up but you should hit about 440 to the wheels easy.

    Change tuners. Trust me thats where it's at. I have 37# injectors but the stock ones would do you fine.
    Problem is that I am on my third tuner, all well respected in this area. I agree with your assessment but no one
    has been able to figure out why it does not make more
    power than it does. It is easy to say that the tuner does not know what he is doing but with three different respected tuners doing their best and making no progress, one has to say what else could be the problem.

    ...>>Sam

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    Quote Originally Posted by Sam-SS View Post
    Problem is that I am on my third tuner, all well respected in this area. I agree with your assessment but no one
    has been able to figure out why it does not make more
    power than it does. It is easy to say that the tuner does not know what he is doing but with three different respected tuners doing their best and making no progress, one has to say what else could be the problem.

    ...>>Sam
    how long are these tuners taking to tune the car? More or less? In terms of hours I mean

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    Quote Originally Posted by Zoilus View Post
    how long are these tuners taking to tune the car? More or less? In terms of hours I mean
    16 to 20 hours each for the first two. Maybe 8 hours for the last one. Four sessions with 12 total pulls on the dyno. I have spent 6 or more hours behind the wheel with one of the tuners in the passenger seat with a laptop working on the driveability issues. The last tuner has made the best progress in drivability but there has been no change in the
    RWHP with any of them.

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    Quote Originally Posted by Sam-SS View Post
    16 to 20 hours each for the first two. Maybe 8 hours for the last one. Four sessions with 12 total pulls on the dyno. I have spent 6 or more hours behind the wheel with one of the tuners in the passenger seat with a laptop working on the driveability issues. The last tuner has made the best progress in drivability but there has been no change in the
    RWHP with any of them.

    who installed your stuff? Do you absolutely trust the people. You sure what you bought went in the car?? Maybe they put a small choppy cam and cheap heads and kept the good stuff for them. Just a thought only.

    That is a lot of time. My guy did it in about 4-5 and car runs like a champ on the street as a daily and vicious at high rpms. Don't know what else to tell you.

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    Ok, I finally got some figures on the FI duty cycle. It is running up to 90%.

    So from what i have read here, it seems as if I should change injectors from
    the stock '99 LS1 units.

    I keep hearing of the Ford injectors being a good choice. Could someone shed a bit more light on this. How big should I go? What part number so I
    can search for them? How big should I go?

    As a reminder, this is a '99 LS1 in my SS with heads, cam and headers.
    404 RWHp.

    Thanks much,

    ...>>Sam

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    ^ Personally I know and have heard around the world of LS forums, a lot of people using Racetronix brand. I have em, my friend with an 00 750hp Maro has used them for over a year, Pat G. and many others. No issues.

    You can find them almost anywhere for about $290 shipped or less brand new. Me and Pat use 37lbs. Definately enough for your app. However if you are going to use a power adder in the near future, then you may want to go with something larger. Maybe 42-50. But bigger is not always better, just depends on what you have now. Some 37's would be just fine.

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    Senior Member mrr23's Avatar
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    98, 01-02 has 28# injectors
    99-00 has 26# injectors

    sam, at 90% i wouldn't bother. 80% is a nice safety margin to keep them cool. if you want to get injectors, go with SVO 30# injectors. that will be more than enough.

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    Member Sam-SS's Avatar
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    Quote Originally Posted by mrr23 View Post
    98, 01-02 has 28# injectors
    99-00 has 26# injectors

    sam, at 90% i wouldn't bother. 80% is a nice safety margin to keep them cool. if you want to get injectors, go with SVO 30# injectors. that will be more than enough.
    Hi Robert,

    I am having a problem with one cylinder bank going lean between 1200 rpm and 1800 rpm. Everything has been checked that can be thought of but the problem persists. I have checked O2 sensors, exhaust leaks, intake leaks, and anything else that I can think of. It is going lean by about 300mv. This is driving me nuts. The thought is that the only possibility left is the injectors.

    This is the last of my problems. Other than that, I can report that all of the other problems are now gone (for good I hope). I am checking the gas mileage now to see if it has come back up to a reasonable level. I would
    hope for around 14 to 15mpg around town.

    ...>>Sam

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