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Thread: S52 turbo 8psi 12.1 afr with 21lb injectors

  1. #1
    Join Date
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    S52 turbo 8psi 12.1 afr with 21lb injectors

    Finally finish my turbo install. Iím running the 540i 3.5Ē maf in blow thru way. 21lb injectors. Trm chip for obd1 for s52. Precision entry level turbo. 60 trim.

    Here is my question. Running 8psi and at wot afr goes to 11.6 than 12.2. How is that possible? I did a quick pull. Once I saw the afr at the 12s. Went a little hard on it. Afr still 12.2-3. So, I floored it real quick and let go. Afr 11.6. After seeing those number Went for a full run. Afr 12.1 accross the rpm at wot.
    I know numbers are correct. Gauge and sensor brand new. I got 30lb injectors on the mail. As well as a emanage blue. I would definitely install them for better afr. But can someone with experience explain why with 21lb injectors Iím still able to get those afr numbers?

  2. #2
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    Ok, so this will definitely blow your motor up. Please consult a tuner.


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    1989 535i - sold
    1999 Tiag/Dove M3 - sold
    1998 Turbo Arctic/black - current
    2004 TiAg/Black - Current

    PTE6870 | 1.15 ar | Hp Cover, Custom Divided T4 bottom-mount, 3.5" SS exhaust, Fx725 twin ceramic, Dual Turbosmart Compgates, Turbosmart Raceport BOV, 3.5" Treadstone Intercooler, 3.5" Vibrant resonator and muffler, Arp 2k Headstuds | Main studs | 87mm Je pistons | Eagle rods | 9.2:1 static compression, Ces 87mm cutring, Custom solid rear subframe bushings, Akg 85d diff bushings, 4 clutch 3.15 diff, 14mm diff bolt conversion, Poly engine mounts, UUC trans W/ enforcers, Custom Ms41 id1700 E85 tune..... BUILD THREAD

  3. #3
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    Wut?

  4. #4
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    It is possible you don’t have a very good turbo system and are making only about 300 rwhp at 8 psi, and the 21 lb injectors can actually support about that much. I’d be worried about ignition timing related detonation if you are running a turbo on a stock tune.

  5. #5
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    You may be able to see those afrs because youíre not in boost. While out of boost the car isnít any different really.


    Sent from my iPhone using Tapatalk
    1989 535i - sold
    1999 Tiag/Dove M3 - sold
    1998 Turbo Arctic/black - current
    2004 TiAg/Black - Current

    PTE6870 | 1.15 ar | Hp Cover, Custom Divided T4 bottom-mount, 3.5" SS exhaust, Fx725 twin ceramic, Dual Turbosmart Compgates, Turbosmart Raceport BOV, 3.5" Treadstone Intercooler, 3.5" Vibrant resonator and muffler, Arp 2k Headstuds | Main studs | 87mm Je pistons | Eagle rods | 9.2:1 static compression, Ces 87mm cutring, Custom solid rear subframe bushings, Akg 85d diff bushings, 4 clutch 3.15 diff, 14mm diff bolt conversion, Poly engine mounts, UUC trans W/ enforcers, Custom Ms41 id1700 E85 tune..... BUILD THREAD

  6. #6
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    Iím in boost. Reading 7.65 to 8psi at wot.

  7. #7
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    We maxed out pink tops on the Dyno yesterday naturally aspirated. Thereís not much headroom. Probably refer to Philís post


    Sent from my iPhone using Tapatalk
    1989 535i - sold
    1999 Tiag/Dove M3 - sold
    1998 Turbo Arctic/black - current
    2004 TiAg/Black - Current

    PTE6870 | 1.15 ar | Hp Cover, Custom Divided T4 bottom-mount, 3.5" SS exhaust, Fx725 twin ceramic, Dual Turbosmart Compgates, Turbosmart Raceport BOV, 3.5" Treadstone Intercooler, 3.5" Vibrant resonator and muffler, Arp 2k Headstuds | Main studs | 87mm Je pistons | Eagle rods | 9.2:1 static compression, Ces 87mm cutring, Custom solid rear subframe bushings, Akg 85d diff bushings, 4 clutch 3.15 diff, 14mm diff bolt conversion, Poly engine mounts, UUC trans W/ enforcers, Custom Ms41 id1700 E85 tune..... BUILD THREAD

  8. #8
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    My set up.
    T3 precision turbo .63 ar turbine housing 76 trim. 60ar compressor. 2.5Ē charge pipe. 3Ē cold pipe. 12x33x3 intercooler. Bottom mount. 39mm precision wg.

  9. #9
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    Need a proper tune bro. Base map will put you around 10.5 to 10.9 afr and revisions you should be closer to 11.5 afr. Anything higher imo is pushing it.

    96 328is turbo
    98 Hellrot M3/4/5

  10. #10
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    Thanks for the advice. Upgrading injectors and getting it tune. I was just surprised that with the small injectors I was getting 11.6 afr.

  11. #11
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    I think you were heading for trouble. Hopefully you have not done any damage yet. I am not a tuner, though. You should pay more attention to Volosso,
    Last edited by pbonsalb; 05-09-2018 at 12:38 PM.

  12. #12
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    Iím taking all of you guys advices. Wonít be running the car with stock injectors/tune. That was just my test run. Was just confuse/surprised as how the 21lb injectors were able to keep the afr at 11.6 at wot. With 8psi of boost.

  13. #13
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    You are running a small turbo so it may be that you are not adding as much power as you think.

    Also, the S52 is very efficient, so the usual 0.50-0.60 BSFC that you rear about as the recommended number for boost is probably too high to use for these motors. I would guess more like 0.45 BSFC. Rough math is 6x21.5=129 lbs/hr and 129/0.45=287 crank hp. However, I recall reading of people making about 300 rwhp with these injectors.

  14. #14
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    That sounds about right. Thanks for the input.

  15. #15
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    You should probably consult your tuner first before purchasing those injectors. I could be wrong though.

  16. #16
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    The 30lb injectors?

  17. #17
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    30s are for low power assuming a safe duty cycle. You should look at 42s or 60s or whatever your tuner likes to work with. I am guessing that is you since you mentioned greddy emanage.

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