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General 420a turbo. what ratio should my fmu be set and idle fuel pressure for 315cc injectors

Posted by langelg6, Apr 5, 2020

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  1. langelg6

    langelg6 Proven Member

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    ordered a t70 420a turbo kit on ebay that comes with everything I need to turbo (except downpipe).. on stock injectors which is 19lbs an hour I would need a 12:1 fmu on 8 psi of boost but if I ran 30lbs or 315cc injectors what would my fmu ratio need to be set at?

    also working on a jeep tb my buddy gave to me after both control arms rusted out on his. and looking to get my intake manifold ported matched. working to free up more air as possible without a 4-5 angle valve job
     
  2. BLACK'98DSM

    BLACK'98DSM Proven Member

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    So you're on stock internals?
     

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  3. langelg6

    langelg6 Proven Member

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    yes ive been looking around at the 2.4 edz block swap as there are plenty of crashed up stratuses in my area, with this stimulas check I see them going for $500 with for a block with 76k miles. srt 4 pistons and rods and srt arp head studs. Ive been reasearching the entire week and have come to the conclusion this would be my best option. alot of people in my family are good with custom fabrication so the labor aspect dosen't bother
     
  4. Canadian_CD9A

    Canadian_CD9A Proven Member

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    This is something that should be done with a wideband, but honestly, the FMU is a ticking time bomb. I would use that money to buy a real tuning solution with properly sized injectors.

    Also, valve jobs apply to cylinder heads, not intake manifold porting. There may be a bit of a gain to be had by hogging out the ports, but again, that's secondary to actually tuning the thing properly.

    Edit: wait. A T70? That's a massive turbo for running 8 psi. It will lag a LOT, but in boost, it will move a lot of air for that boost pressure, and your injectors are not at all equipped to handle it. For reference, back when I was young and stupid, I had a Hahn S16G kit on my 2.4L Neon, with a FMU and 36# injectors. The base idle pressure was far less than ideal (22 psi, which is almost fuel atomization issue territory), and spiked to 80-or-so psi at max boost, which the fuel pump hates. Your stock injectors will run out very quickly top end, but bigger injectors will cause driveability issues, especially since your ECU has no f***ing clue what's going on.

    With 30# injectors, you'll be in the exact same spot I was at for base fuel pressure - right around 22 psi, which is not great. I'm by no means condoning this, but you would need a 10:1 or more regulator to get a safe amount of fuel. Multiply 8 psi by that 10:1 ratio, and add 22 psi as base pressure - your fuel system is now over 100 psi and probably won't operate well. Fuel pumps operate very poorly at that pressure, if they even operate at all. A bigger pump will no doubt be necessary. AFRs will be all over the map since you have no control over them, and things will inevitably fail. Even though eBay turbo kits are pure garbage, do this properly.

    You bought this kit, didn't you? :ohdamn:
    https://www.ebay.com/itm/95-99-Mits...872129?hash=item1efdf77601:g:mRMAAOSwumJdKCrx
     
    Last edited: Apr 5, 2020
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  5. BLACK'98DSM

    BLACK'98DSM Proven Member

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    Oh, so you don't have a tuning solution?

    With boost and bigger injectors, prepare for a pig rich idle and a deathly lean WOT.
     

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  6. langelg6

    langelg6 Proven Member

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    I chose the turbo since I definitely wanna push the 420a platform further. my goals is to safely boost 15psi on built internals eithee through the edz or regular 420a block.

    as far as tuning goes I am a bit intimidated by the piggy back systems and megasquirt especially. Is an AEM FIC 6 1913 the right fic to use for my car. This is the tuning option ive been leaning towards, has anyone had good experience this route
     
  7. silvreclips

    silvreclips Proven Member

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    As @Canadian_CD9A said, you run larger injectors you lower base fuel pressure. I have played that game before, it did work ok for a budget fuel system. But it is far from the best solution. You also won't be using a FMU because that can only raise fuel pressure. You would need the SFMU which allows you to control base pressure and change out the rise ratio. It's been a while but back when I was running 315cc injectors I think my base pressure was about 22psi and my ride rate was 6 or 8:1. This was 10 years ago.

    But these parts aren't cheap and there are much better options now. The portfueler from Hahn was a great 8 injector solution that kept the stock ECU running the car and then you just added more fuel with boost through another set of injectors. I don't think they even sell these anymore.

    If your serious about making power, megasquirt or another aftermarket ECU is the only option. We haven't even talked about ignition timing, which you will have to change as you turn the boost up.
     

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  8. Canadian_CD9A

    Canadian_CD9A Proven Member

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    I would recommend that you return this turbo kit. Not only is it junk, but I would hop on Megasquirt while you have a running car; trying to troubleshoot problems while also dealing with new turbocharger-related issues is a nightmare. Seriously - Megasquirt and some modest injectors to get going, and then think about putting together a decent turbo setup once it's all running nicely.

    To get going, I would do this:
    -Megasquirt - preferably V2 3.0
    -Injectors - something around 450cc to start
    -Wideband o2

    You'll need to learn how to wire the car and what the function of everything is, but it's better that you learn those things now. If you don't know what each sensor does as you troubleshoot a highly modified, non-running turbo car, you'll give up. Alternatively, if you make a tuning mistake on a N/A engine, you can probably recover. If you screw up at 8 psi, your engine could be gone. Case in point: when I sold my Neon to my friend (who is no dummy), he decided to start fresh on the Megasquirt tune. He added a basemap but selected the incorrect MAP sensor that was installed in the MS (1.0 bar instead of 3.0 bar) and the engine went boom at 8 psi the next day. If you can't tell me specifically why the engine blew because of the incorrect MAP sensor setting, you're probably not ready to turbocharge.
     
    Last edited: Apr 6, 2020
  9. langelg6

    langelg6 Proven Member

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    I would much rather go
    Is $800 enough to convert to megasquirt? any links on where I can find a unit.


    and to answer the map question without looking it up I believe its that a higher preassure map sensor will understand boost and add fuel accordingly as to a 1 bar map sensor would go off the fritz once boost is introduced. Ive been leaning towards converting to E85 and remember seeing about a guy running 14psi reliably through stock internals, 440cc injectors and a 3 bar gm map sensor, he also did some thing to the intake temp sensor to retard timing while on stock ecu. I remember him saying that if you switch the gm map that you absolutely cannot run anything lower then 14psi of boost, he said it has to be 14 psi or higher or else the map will give an incorrect reading
     
  10. BLACK'98DSM

    BLACK'98DSM Proven Member

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    14 psi on stock 420a internals is less than a bad idea. You must've stopped reading there because I can recall more than 4 threads that say over and over not to exceed 7 psi on stock internals. Your saying you read that it could hold twice that? I've seen the pictures of burned up pistons and rings.
     

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  11. silvreclips

    silvreclips Proven Member

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    Diyautotune sells MS kits. You need to do a lot of research before just buying parts for this car. Buying a MS unit is not a plug and play kind of thing. It will have to be configured for your application, and you will have to wire it into your existing harness. Once all that happens the car will have to be tuned. That in itself can cost as much as the ECU.

    It's not the boost pressure that kills the stock motor. 14psi is not the same on a GT35r as a T25. It's the torque that will take out the pistons first.

    You need to be prepared if you really intend to go down this road. You aren't just talking about a 800 turbo kit. You are now talking another 600 for an ECU. Injectors, fuel pump, regulator. Now build the motor etc. Your gonna be in this 5k or more.
     

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  12. langelg6

    langelg6 Proven Member

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    thats what I believe too and still do but its on youtube. A guy claims to have ran his 420a completely stock, 14psi no missing link or piggy back but with the differences hes running E85 . I personally wouldnt risk it but it makes me wonder how good e85 is for a turbocharged engine
     
  13. Canadian_CD9A

    Canadian_CD9A Proven Member

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    It has to have an aftermarket management solution then, probably Megasquirt. Some Neon builders cracked the Neon ECU; I'm not sure if DSMs are the same, but the stock Neon ECU goes ballistic if it sees boost. It needs to have a WOT map that can handle that kind of airflow, which the stock ECU will not do. Fueling 14 psi on E85 takes a lot of injector, too. Nothing under 400cc would do it, and you wouldn't be able to run a stock ECU car on E85. The stoich ratio of E85 is different from regular gas - the ECU always aims for 14.7 in closed loop, which would not work with E85. You have a lot of reading to do, I think.
     

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