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  1. #1

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    injector's who really knows there stuff

    Now heres the questions stock 38's are used in the 185 that uses a 44psi reg so aprox 3 bar of presure. The way they all seem to spec injectors is at 3 bar so the question is, if they are spec'd at 3 bar they are a true 38lb injector in a 185 hp seadoo. but kick up the presure to the 215 reg making 58psi that turns these things into 43.80lbs so the guys putting in ford or other brands of injectors i question this due to the fact that if you put in a 50 that is bench tested to 50lbs at 3 bar then kick up the the presure due to the fact your using a stock reg that makes 58psi turns these things into 57.74lbs and 42's are 48.8lbs at this presure im wondering what psi the stock injectors are really spec for i'm guessing 3 bar making the stock injectors 43.8's at the 58psi reg in an rxp or rxt here is where i got some info http://www.gtsparkplugs.com/InjectorSizeCalc.html


  2. #2
    Autism Speaks. Its Time To Listen gOt BoOsT's Avatar
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    injectors can only flow so much fuel regardless of pressure before they go static. fuel injector clinic can flow test injectors at various pressures with exact results.

  3. #3

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    thats where im lost that site i posted and others say that flow changes with presure thats where it all gets foggy

  4. #4
    Moderator beerdart's Avatar
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    Yes flow does change with pressure. But remember on a boosted motor its differential pressure across the injector. So 58 psi from the pump and 10 lb boost = 48psi at max boost that is why most use a 1:1 rising regulator so the system maintains 58 psi across the injector under all boost conditions.
    Quote Originally Posted by trent_girardrxp View Post
    thats where im lost that site i posted and others say that flow changes with presure thats where it all gets foggy

  5. #5
    imp0ster's Avatar
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    that's with a good FPR and what I'm concerned with is how the ECM compensates for the IFR table if you have no way to modify it yourself. The Ford racing injectors to not have the same pule width as stock and most people just throw in the 42s with an x charger and are done with it. In my normal world I modify the offsets, IFR tune to as close my preferred ARR as I can then MAF tune until my trims are where I want them to be and my AFR is .5 richer than the vehicles perfect tune.

    Boost referenced FPR add 1psi per pound of boost to compensate for that boost pressure trying to force the fuel back into the injector. It works the same for vacuum just in the other direction. The FPRs goal is to keep rail pressure the same no matter what happens. Once again this is assuming these come with a BRFPR from the factory, like they should.

    I am assuming the stock FPR is boost referenced and the IFR table within the ECM is either flat-lined across the board or is a single static number since there is no table ramping due to the FPR keeping rail pressure static.

    Now I know I can't just hook up my laptop to the ski and tune away so I'm really wondering if the ECM auto learns parameters. I have a spare Aeromotive compact EFI FPR that I want to put on but I'm trying to find out a lot more about this ECM before I destroy something. Sorry if this is a thread jack but I'm trying to learn fast so I can make it go fast.

  6. #6
    Moderator beerdart's Avatar
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    The stock FPR is not boost referenced. The ECU only monitors MAP and Knock. Pulse width has nothing to do with the injectors its controlled by the ECU.

  7. #7
    imp0ster's Avatar
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    Quote Originally Posted by beerdart View Post
    The stock FPR is not boost referenced. The ECU only monitors MAP and Knock. Pulse width has nothing to do with the injectors its controlled by the ECU.
    I know PW is controlled by the computer. My worry was how does the ECM compensate for different injectors unless it has a learning curve like modern cars do for trims(which seems highly unlikely in a ski). I would usually modify offset vs PW vs manifold pressure but I cannot tune this pcm with my current setup. I might try to get tinytuner or tunercat to work with it after I figure out the cable situation but as of this point I am terrified that the tune will be off if I tinker too much. Even a air intake should be tuned in because it is going to throw the factory trims off. I know most people will think I'm crazy and going overboard but when you trash a number of your own expensive engines you start tuning everything in. Look at my link for the normal injector modifiers I deal with for the GM 3.8(this is missing tables normally associated with LSx and more popular engines). The picture is for the Ford Racing injectors everyone here uses.

    I honestly thought about installing a thermocouple for each cyl to monitor EGTs so I know my injectors and plugs are all the same. I can go into detail about the scarey side effects of an off injector if someone would like.

    At least this market is using the green giants but I personally prefer the siemens dekas. They do great on cold starts and are easy to tune with.

    Click image for larger version. 

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  8. #8
    Moderator beerdart's Avatar
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    The stock ECU has no clue what injector is installed.

  9. #9
    imp0ster's Avatar
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    Quote Originally Posted by beerdart View Post
    The stock ECU has no clue what injector is installed.
    lol really? So from the factory it sends a static flow rate through the rail and the ECM fires the injectors at a preset rate? Any idea what stock rail pressure is? A better question is what's the ideal AFR on this engine, around 11.7 or 12 since it's all AL?

    BTW I appreciate the knowledge.

  10. #10
    Moderator beerdart's Avatar
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    Fuel pressure on the 215 is 53 psi. The only way to add fuel is with bigger injectors, adding fuel pressure or A piggyback unit. The problem is finding and injector that is big enough for WOT AFR around 11.5 and small enough where your idle is not pig rich. I use the duel regulator set-up and for me it works great but im just a rec rider. My fuel pressure is 20psi idle 50psi mid and 70 psi wot running 42# injectors and aprox 12lb boost.

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