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Thread: Injector location: in head or ITB?

  1. #1
    Join Date
    Jan 2006
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    Seattle-ish
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    Default Injector location: in head or ITB?

    I'm curious if anyone with ITBs has experimented with injector placement? V1 of my Duratec utilized stock internals and cams. At the time, the recommendation was to leave the injectors in the stock factory location in the head. Apparently the fuel spraying on the back of the hot valves promotes lower emissions and better idle/low speed drivability.

    V3 of the engine has far more aggressive cams with an 8000+ rpm redline. I'm wondering if moving the injectors out to the ports in the ITBs is a better compromise with the current internals? From what I've read, at higher rpm, the extra distance gives the air and fuel more time to atomize, creating a better mixture that burns better, and hence, develops more power. As seen in the photo below, the difference between the two location is about 4 inches.

    Name:  tb injector port.jpg
Views: 75
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    The benefits of each location make sense to me, but it's the quantity of difference I'd like to better understand. If it's another 4-5hp at the top end with marginal difference to the low end, then I might give it a try, but if it's 1-2 hp and idle becomes noticeably less happy in traffic, then there's no point. The change will require removing the plugs in the ITBs (I have a feeling that will be a PITA), buying new plugs for the head, a new fuel rail, and doing a little replumbing, so not a quick, simple update.

    Thanks,
    John
    '95 Westfield SEiW w/2.0L Duratec
    '68 Lotus Elan FHC
    '91 Miata w/Flyin Miata suspension & brakes
    '95 Porsche 993 C2
    '86 Porsche 944 turbo (neglected project car)
    Throttle Steer

  2. #2
    Join Date
    May 2010
    Location
    Laurel MD
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    Default

    I could not find much information but I did find this video, a more extrema movement but little gain. The guy has some interesting videos on velocity stack length changes.

    https://www.youtube.com/watch?v=u_E14RKskbM&t=262s

  3. #3
    Join Date
    Jan 2006
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    Default

    Thanks for the link, it's a shame he was comparing TB mounts to shower mounts rather than in head, but that one portion of the video showing the fuel spraying down the intake from the shower mount really highlighted the potential improvement at low rpm if the injector is in the head and hitting the hot valve. Jenvey claims that mounting in the TB below the butterfly is the best compromise for a modified engine. If this was a simple switch, I'd just try it.

    Slightly off topic, but if you are like me and interested in velocity stack length and design, definitely check out this guy's other videos. Very interesting stuff.

    Thanks,
    John
    '95 Westfield SEiW w/2.0L Duratec
    '68 Lotus Elan FHC
    '91 Miata w/Flyin Miata suspension & brakes
    '95 Porsche 993 C2
    '86 Porsche 944 turbo (neglected project car)
    Throttle Steer

  4. #4
    Join Date
    May 2010
    Location
    Laurel MD
    Posts
    203

    Default

    The guy has some very interesting posts, this one about AFR is great.

    https://www.youtube.com/watch?v=yjvPmG123nI

  5. #5
    Join Date
    Jan 2018
    Location
    Northern Virginia
    Posts
    23

    Default

    Some very sophisticated race engines run two injectors per cylinder to gain a little top end advantage from having a injector mounted high in the manifold. If you look at some of the drag race dyno comparisons between the long runner carburetor manifolds (tunnel ram) and fuel injection with the injectors mounted low and the back of the valve. Typically the carburetors make more power but the fuel injection has a better power curve. They do not show how well the carburetors control the fuel curve, but I would speculate the fuel injections advantage is in the fuel curve.

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