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Thread: 95 lt1 injector offset questions

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  1. #1
    Electronic Ignition! Mr.owl's Avatar
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    95 lt1 injector offset questions

    How important is the injector offset adder? Not the voltage offset but the injector offset adder
    smart enough to feel stupid

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    Fuel Injected! Terminal_Crazy's Avatar
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    Quote Originally Posted by Mr.owl View Post
    How important is the injector offset adder? Not the voltage offset but the injector offset adder
    Increasingly as your injector PW goes lower to where it starts affecting the fueling

    Really depends on how low your Injector PW Goes...
    If you've gor a big set of injectors, the PW is relatively shorter so the amount of misfueling starts to incxrease.
    Anything above 1.5mS - 2mS idling is probably tuneable around

    I have had injectors that didn't open reliablby below 1.5mS (actually rated at 2mS) which possibly caused issues.

    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

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    Fuel Injected!
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    Any fool can go in and set the flow rate and the motor will run fine above 20% throttle. But if you want idle and part-throttle drivability, and especially if you want it to start quickly and smoothly, you have to have the short pulse adders and voltage offsets correct, respectively.

    The way Ford labels and characterizes their injectors is really helpful - they actually have a number called MINPW which is the minimum pulsewidth the injectors will reliably fire. The last time I sized injectors for a friend's build, we were looking hard at injectors that had this data available. For this particular situation we actually discovered that a set of 80lb injectors had a lower MINPW than the 60lb injectors he was considering, even though the 60s would have met the fuel needs of the motor. Given that this was a heavy manual transmission car, I insisted that the injectors be able to reliably fuel down to 400rpm during clutch engagement, and so the 80s would have been the better choice despite their higher peak flow.

    Ford also includes two slope values (a high slope and a low slope) and a transition point. This transition point is where the pulsewidth gets so short that the magnetic field delays and the pintle rise/fall times become significant relative to the requested pulsewidth. Here's an example. https://performanceparts.ford.com/pa...-9593-lu34.pdf It's at this transition point where the GM short pulse adders start to grow. There are some posts out there how to convert the elegant Ford values to the verbose GM values, but the result is perfectly characterized injectors from the first crank.
    Personally I'm running 2011-2017 Ford Mustang GT injectors in my LT1 with fabulous drivability.

    It continues to blow my mind how places like Racetronix advertise GM injectors with NONE of these critical parameters available. Maybe they have it on their forums, but their rules state you have to buy something before they'll give you forum access. Huh?
    Last edited by sherlock9c1; 11-15-2018 at 06:48 AM.

  4. #4
    Fuel Injected!
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    I'll add too - when I swapped to Bosch D III injectors , just 32 lbs, I found that I had to just zero out the pulsewidth adder (not batt. voltage offset), because the Bosch injectors are the other way. I was told they flow more fuel at low PW, and with LT1 you can't take away only add, which is the wrong way. So it depends on which injectors you use as to what all you change in the tune. FIC was absolutely no help on this, even though I bought the injectors through them. They had the data somewhat tailored for the LS1 crowd.
    J. Moen
    91 Camaro - NASA American Iron Road Racer #91 "The Menace", carb'd 350, FloTek heads, "because racecar"
    91 Camaro RS - '93 LT1 /T56 swap, 224/224, 60lb Siemens, garage ported heads, VS racing 78/75 turbo, Intercooled

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    Electronic Ignition! Mr.owl's Avatar
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    I'm running fic blue demon 36lb injectors had same issue fic was no help. Issue I'd been having was cruise drivability bucking and the afr bouncing a lot. granted I have a pretty big cam. But idle and fire up have been no issue. I'm running sd because I was having issues with maf tuning with my 110 LSA but I've got it pretty close now in sd without changing my adder thanks to trimalyzer. Still think there's more room for improvement there though. But what you're saying is you zeroed yours out? Think I should go back to my base tune zero them out and start over?

  6. #6
    Fuel Injected!
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    Quote Originally Posted by Mr.owl View Post
    I'm running fic blue demon 36lb injectors had same issue fic was no help. Issue I'd been having was cruise drivability bucking and the afr bouncing a lot. granted I have a pretty big cam. But idle and fire up have been no issue. I'm running sd because I was having issues with maf tuning with my 110 LSA but I've got it pretty close now in sd without changing my adder thanks to trimalyzer. Still think there's more room for improvement there though. But what you're saying is you zeroed yours out? Think I should go back to my base tune zero them out and start over?
    Why not give it a shot, and if it doesn't work, go back to what you had.
    I don't have experience with this issue, but what came to mind was this thread on here where they delayed the injector start time until after the exhaust valve closed to avoid putting raw fuel into the exhaust. Have you tried that to see if it cleaned up the AFR instability when running in MAF mode?

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    Fuel Injected! spfautsch's Avatar
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    I ran across this thread a week or so back when I "forked" an EOIT thread to hopefully spark more focused and meaningful discussion on that particular subject.

    Anyway, the more I read the more I find in common. I'm also running a set of "recapped" / redrilled inectors from FIC. I asked them for data ahead of the purchase and was promised something would be shipped with the injectors but found no such information included in the shipment and received no further responses from them on the subject. These were sold as 42lb/hr bosch IIIs. Upon opening the package I found a set of 8 GM 12561462 / Bosch 0280155931 grey injectors that likely began life as 28 lb/hr LS1 injectors.

    Back to the present - several hours of reading later (most important reading found here) I come to a fuller realization that the original injector data is likely all but useless.

    So I'm wondering if anyone has any ideas / recommendations on who might be able to properly flow test injectors. Not an injector cleaning shop type test, but a real characterization test that demonstrates slope and offset at different pressures and voltages.

    Quote Originally Posted by sherlock9c1 View Post
    Any fool can go in and set the flow rate and the motor will run fine above 20% throttle. But if you want idle and part-throttle drivability, and especially if you want it to start quickly and smoothly, you have to have the short pulse adders and voltage offsets correct, respectively.
    I'm discovering that the slow and painful way. Though I've achieved relatively decent results using the SVO injector offset vs. voltage table, I think more accurate injector data couldn't hurt. After "a lot" of reading on the subject I've come to find that anyone that tests injectors and specs static flow rate should probably not be trusted to provide a truly matched set of injectors. And by matched I mean injectors that share the same flow characteristics at all pulsewidths, pressures and voltages. I believe this is why this particular company generally removes the Bosch part number from the body, and sometimes paints their "matched" injector sets (blue, hence the name "blue demon").

    Quote Originally Posted by sherlock9c1 View Post
    Personally I'm running 2011-2017 Ford Mustang GT injectors in my LT1 with fabulous drivability.
    Would you have a part # on those?

  8. #8
    Fuel Injected!
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    BR3E-EB-B556V is what I just pulled off the bodies of a set on eBay. I'm not near the car at the moment. Just make sure not to get the 18-19 ones as they're much smaller flow since Ford went to a combo direct AND port injection setup in 2018.

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    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by sherlock9c1 View Post
    BR3E-EB-B556V
    Thanks! Those look to be a drop-in except for the connectors. The only thing I dislike about using the Bosch injectors in place of the fat body Multecs on the LT intake is the need for something to stop them from "falling out" of the fuel rail. On my current injectors I cut stainless lock washers and fit them into the groove above the lower o-ring, but these look like the shoulders are large enough to act as stops.

    Edit: nevermind, I just found your other post on these here (datasheet also). I guess that'll give me an excuse to turn some spacers for them on the lathe.

  10. #10
    Fuel Injected!
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    Quote Originally Posted by spfautsch View Post
    from FIC. I asked them for data ahead of the purchase and was promised something would be shipped with the injectors but found no such information included in the shipment and received no further responses from them on the subject.
    Similar experience with FIC. They don’t seem to understand the importance of this data for proper tuning. I will never purchse from them again.

    There is a company near me called deatschwerks, they do all types of stuff with pumps, injectors etc.

    One of the services they offer is offset testing. I have used them before with positive results

  11. #11
    Fuel Injected! Terminal_Crazy's Avatar
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    I'll add a me too to this list

    I'm now on my 5th set.
    30# venom off ebay seemed ok at the time before I rebuilt the engine.
    Since the rebuild I've had a low speed surge I could never get rid off.
    Injectors have been swapped bank to bank & end to end with no changes.
    suspected injector data as tune had them zeroed out... makes sense if you don't know what they are.

    From FIC (Fuel Injection Connection)
    30lb Modified Bosch 3 Injectors ( Stainless later core )
    No data. still ran the same. excellent other than low speed idle.

    42lb @ 3 Bar Modified Bosch Blue Demon 3 Fuel Injectors
    No data again still ran the same. excellent other than low speed idle.
    Managed to get "some" data that didn't make much sense.

    Bought some "Black Ops" off the net. read reviews etc.
    Got "some data". Data on sheet doesn't match spec's quite the same & some variance on spray numbers etc.
    No real change to the way it ran.
    Given up with Black Ops injectors dropping out at low injector Pw..
    Min Listed PW is 1.4mS & I'm running idle around 1-1.2 other than that they are OK once rolling.

    Bit the bullet and went for "recommended" "quality" injectors from the _other_ FIC (Fuel Injector Clinic)
    445cc (50 lbs/hr at OE 58 PSI fuel pressure) FIC Fuel Injector Clinic Injector Set for LT1, LT4 engines (High-Z) (IS300-0445H)
    again got data ( off their website). Again didn't quite match the specs on the sheet. again some variance on the flow (They could write anything on the sheet though)
    Had to write a program to calc data required. Also flow rate is now a lot lower than it was with the Black Ops.
    OK My issue is still there but AFR is a little more stable than it was and is more readable on the guage. ( after trimming the AFR range etc)
    I've just raised the low pulse adder and it has richened up the idle quite a bit. ( I just slid the slope along a few points).
    Idle is in the 1.7mS time now rather than 1-1.2 with the black Ops so small pulses aren't dumping as much fuel.
    Injector EoIT is currently at &63.

    Car ran pretty well yesterday on a short run out.
    it was generally rich (as i'd raised the low pw adder)
    Sounds much smoother, not as lumpy.
    seemed to cruise much better when lifting and turning corners.

    We'll see once it's dialed in a little better.

    I don't think the numbers really matter if the injectors are within running spec. They can be tuned generally to run OK

    NON of the five sets (or the stock ones) actually flow anywhere near the "correct flow rate"
    That's just a starting point with the voltage figures they all supply.
    Get it running close with that then adjust VE tables A LOT.
    Then when VE hits 100+ ADJUST & REPEAT A LOT.
    When it's lean around the idle and below, try raising the low pw adders if they are around that figure.
    If they are rich at idle, lower something else and try adding in some slope to the low pw adders.


    That was just going to be a "me too" post.
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  12. #12
    Electronic Ignition! Mr.owl's Avatar
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    Also thank you to everyone for your replies. A lot of helpful information

  13. #13
    Electronic Ignition! Mr.owl's Avatar
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    Quote Originally Posted by sherlock9c1 View Post
    Why not give it a shot, and if it doesn't work, go back to what you had.
    I don't have experience with this issue, but what came to mind was this thread on here where they delayed the injector start time until after the exhaust valve closed to avoid putting raw fuel into the exhaust. Have you tried that to see if it cleaned up the AFR instability when running in MAF mode?
    I have not tried that no. Not sure how I'd go about that on a 95 lt1 but I've had pretty good success switching over to sd in terms of drivability, after much tuning obviously. I am running a wideband as well as my factory o2s and they're reading pretty close so I don't know that raw fuel tainting was so much the issue as much as what happens to readings from the maf with big cams. I also don't have as much experience in tuning maf as I do sd but It was a terrible tune, worst mail order I've ever seen. I might mess with it more in the spring or when weather permits but it's started snowing here already

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