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  1. #1
    skigolfnut's Avatar
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    Injector questions for the 48s and 50s need input?

    It is Official now that in the Limited Class in Closed course racing we can now use aftermarket injectors.(yea)

    My current set up is ET-137 charger, Rotax racing Ecu with 8600 rev limiter, RRFPR,valve train upgrade, AFR Gauge, Walbro, 08 mid-pipe exhaust, EXIC and the usual free mods,

    I have been running lean at WOT(8500 rpm) with my current 42s Bosch injectors, and I have the RRFPR dialed up pretty high,

    Some members are saying that I need the Bosch 48s that they work perfect with the ET-137 set up and some are saying Bosh 50s work well?

    Then some say the Riva or Accell 50s work just like the Bosch 48s? because they flow a little less?

    6 in one hand and half a dozen in the other, money is tight,

    open for more suggestions,


  2. #2
    Eric Ocman's Avatar
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    Re: Injector questions for the 48s and 50s need input?

    Bosch 48s are what you need.

  3. #3
    RipNSki's Avatar
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    I did a lot of investigation and asked the fellas on here that would know best... I heard Bosch 48's would be the way to go for me...(see sig.) So I got 48's and will install them this year...

    Good luck!

    I do plan to get a XX charger or bigger wheel also...

    Rip

  4. #4
    skigolfnut's Avatar
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    I forgot to mention that I wanted to go with a higher rev limiter of 8900? would that change things?

  5. #5
    boost junkie skidoochris's Avatar
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    a 48lb injector @ 43.5 psi ( the psi most injectors at tested at) run at 58 psi is now a 55.4 lb injector
    and a 48 lb injector is maxed out with your ET and rpm
    a 60lb injector @ 58psi flows 70 lbs
    I run a 110lb injector

  6. #6
    skigolfnut's Avatar
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    so if I take a 50 lb injector and run it less than 43 psi then it wiil be less than 50??

  7. #7
    JT jpt7779's Avatar
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    Quote Originally Posted by skigolfnut View Post
    I forgot to mention that I wanted to go with a higher rev limiter of 8900? would that change things?


    With your original post and criteria, OEM 48's would work perfect. BUT, if you are going to raise up to 8900 they will NOT be enough. I noticed with my stock 48's, V-TECH tune, that around 8600-8700 my AFR's would start creeping up to mid 12's. I raised the base RRFPR pressure to compensate. In the cool months I started to see 8840 rpm and AFR's mid 12's to low 13's. I didn't feel safe with this, so I had my 48's resized to 55#, 580cc flow rate. AFR's are back down in 11's now at 8800 or so. Once it warms up a little I will do more testing and probably have V-TECH tune modified accordingly.

    Here is the link: http://fuelinjectorconnection.com/index.html

    Cost is only $30 per injector for re-sizing and flow matching.

    Just another option!

  8. #8
    Eric Ocman's Avatar
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    Quote Originally Posted by jpt7779 View Post
    Quote Originally Posted by skigolfnut View Post
    I forgot to mention that I wanted to go with a higher rev limiter of 8900? would that change things?


    With your original post and criteria, OEM 48's would work perfect. BUT, if you are going to raise up to 8900 they will NOT be enough. I noticed with my stock 48's, V-TECH tune, that around 8600-8700 my AFR's would start creeping up to mid 12's. I raised the base RRFPR pressure to compensate. In the cool months I started to see 8840 rpm and AFR's mid 12's to low 13's. I didn't feel safe with this, so I had my 48's resized to 55#, 580cc flow rate. AFR's are back down in 11's now at 8800 or so. Once it warms up a little I will do more testing and probably have V-TECH tune modified accordingly.

    Here is the link: http://fuelinjectorconnection.com/index.html

    Cost is only $30 per injector for re-sizing and flow matching.

    Just another option!

    I jumped up to 55lbs when I added the 9.5K ECU but my base pressure is still relatively low (42 lbs) making me think the bosch 48's probably would have worked but I could be wrong. Im running between 8800 to 9100 depending on Temperature.

  9. #9
    You guys are flirting with real trouble on several fronts.

    First, when injectors are rated, they are measured when the pressure at the fuel rail is 43.5 PSI higher than the pressure at the spray tip. If you have 43.5 PSI in the rail and 43.5 PSI in the intake runner, The flow thru the injector WILL BE ZERO. This is a big deal and is everything to why RRFPR's were invented.

    When you start upping the RPM on a centrifugal blower, the the boost goes up fast. This rising boost messed with the injector flow big time.

    The flow requirements of an injector goes up with the formula

    FuelFlowRequired=RPM X MAP in the intake. So if stock the bike was running 8000 RPM at 160 KPA in the intake the result is.

    8000 x 160 = 1280000

    now if you increase the RPM to 9000 and up the boost to 250 KPA

    9000 x 250 = 2250000

    2250000 / 1280000 = 1.75 or 75% more fuel thru the injectors. That is a huge increase in fueling.

    Next is an injector is only consistent in fuel metering when energized about 88% of the time or less. This is known as the duty cycle. These bike are running real close to this number stock and it is running lean at that. It is possible to go to 100% duty cycle but the injectors get really hot and tend to fail. The fuel metering is totally flaky between 88 and 100% DC.

    Doing any of this stuff without knowing your DC, fuel pressure differential and your AFR is really dangerous. I like using a Dynojet CMD, Motec, Megasquirt, Innovate, Haltech or any other reliable data logger.

    Have fun tuning

    Andy

  10. #10
    imp0ster's Avatar
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    Actually I've ran Green Giants to 92% duty cycle consistently on LS and 3800 engines for years with no issues of running static. Bosch injectors run separate from the bunch in quality, pulse width and atomization. I have a few different threads on here about this and comparisons to other injectors also including flow variances when buying sets and how BS most "flow matching" is. With any boost referenced FPR, assuming the diaphragm can keep up with the extra pressure brought on by boost, all you're worried about is the base setting. As long as it's is a quality FPR and your IFR table is ramped right then the FPR will rise on 1:1 consistently keeping your relative(base) FPR the same since for every 1 psi forced into the chamber the injector has to counteract that force via the FPR pushing back an extra 1psi keeping the set pressure the same

    dolla dolla bill yall

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