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  1. #1
    Ultimo Miembro Fantástico Gigantesco ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD's Avatar
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    Default Personal musings on 3SGTE fuel requirements

    Well I've been having a hell of a time getting my car started since installing my 540cc/min injectors, I've been playing around with some ideas and thoughts about my fuel set up.

    I've started to consider returning back to the stock injectors. Even though 540's are *theoretically* sized "better" for my set up, hear me out.

    Now we all know I don't want to run at 100% duty cycle, and don't be fooled, the stock ECU does go there. I have an injector duty cycle monitor, and I was hitting 100% at 3000rpm if you can believe it. Maybe I should take a video of that and post it on the mr2 board with ATTN: RickyB!!! in the title. Nah he still wouldn't believe me.

    Okay, at roughly 275 whp the stock injectors @ stock fuel pressure start to lean out. This is the max horsepower you can support with stock injectors at stock pressure, at 100% DC.

    For proof of this, here are some dyno's of people running roughly that amount on the stock injectors:

    http://www.turboforum.net/dyno/image...ikner/dyno.jpg
    http://www.turboforum.net/dyno/image...in/dynorun.jpg

    Okay, so lets say thats the way it is.

    Now I personally don't have any sort of WHP target, I just know what I'd like to run. I would like to run ~16-17psi, on my car. That will keep me more than happy. The thing is, I would like to reduce my duty cycle to something closer to 85-90% if possible, to leave some room for that "what if" category.

    Based on everything I have seen, and my own dyno, I believe that at 17psi I will be *somewhere in the range of 270-290awhp. Thats on the ragged edge for the stock injectors at stock pressure.

    So the original plan was to use 540cc/min injectors, since they are 'better' suited to this kind of power. However, my problems getting the car running have gotten me thinking. (I'm not assuming that my injectors are why I can't keep the car running, in fact I know it is somehow related to the AFM, however I started thinking none the less)

    What about using the stock injectors? I'm going to have to reduce the load by the same amount regardless of which injectors I use (to bring the DC to a level I am happy with). So what would I need to do in order to deal with this?

    Increase fuel pressure. But what is a "safe" fuel pressure? I began to inquire on various boards, searching google, and the best I can come up with is some heresay that the fuel injectors do not like to see any more than 70psi base pressure. Well that seems like a lot considering the stock pressure is 42.

    Still not knowing what a "safe" pressure is, I remembered ATS will upgrade your FPR to operate at 50psi. I have never heard of anything saying that they have had *any* sort of problem, so I'm going to assume that is safe as long as one has a proper fuel pump to support it. I have a Walbro 255L/h.

    Where does 50psi take me in terms of horsepower?

    @ 50psi 440's = 480cc/min

    sqrt(50/42) = 1.09 * 275 (old max hp at 100% DC) = 300whp @ 100%

    That leaves me a little room to play with DC, maybe get it down a tad. So lets say that I end up needing 55psi, as a worst case scenario. The question I have is, is this *too* high? Can this extra 5psi on the injectors cause problems? I'm not sure. It is surely far below the 70psi I have found at other sources. Is 55+17psi too much for the rail? I plan to use a wolfkatz rail, which *should* be a little better to hold the pressure, and should better take care of variances in fuel pressure as it is cranked up. Can the fuel pump handle it? Well the 255L/h seems to be one of the best upgrades I can get, with marginal comparison with the Supra TT pump. I would be able to monitor this at least on my electronic fuel pressure gauge.

    So where does this leave me.

    On one hand, I'd have to run very high fuel pressures to use hte 440's. On the other, I'd have to run very low fuel pressures on the 540's to get it to idle nice. There are probably issues on either front.

    I'm not entirely sure what I'm going to do yet. Still gathering thoughts. Maybe I'll see how it goes with trying to get my car to run, we'll see.

    Maybe I've taken a step back and decided that simpler is better. Stock injectors almost always will be more *driveable* than bigger ones, on the stock ECU at least.

    I'm NOT willing to buy a standalone, it is not something I'm interested in looking at @ this time. I'd like to maximize do with what I've got for now. So I don't know.

    I'm sure you loved reading my ramblings



    Chris
    1988 ST165 2.2L @ 370awhp
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  2. #2
    CelicaTech Supporter Trance4c is a splendid one to behold Trance4c is a splendid one to behold Trance4c is a splendid one to behold Trance4c is a splendid one to behold Trance4c is a splendid one to behold Trance4c is a splendid one to behold Trance4c is a splendid one to behold Trance4c is a splendid one to behold
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    The extra 5psi of pressure will have no negative side effects to your injectors. I for one have been running on a Supra TT fuel pump for nearly a year now at around 55-57psi. On only reasons you will have injector issues is duty cycle or mechincal failure. The increase pressure will only work in your favor as you have calculated.

  3. #3
    Ultimo Miembro Fantástico Gigantesco MrWOT has much to be proud of MrWOT has much to be proud of MrWOT has much to be proud of MrWOT has much to be proud of MrWOT has much to be proud of MrWOT has much to be proud of MrWOT has much to be proud of MrWOT has much to be proud of MrWOT has much to be proud of MrWOT has much to be proud of
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    I wouldn't exceed 60psi base on stock injectors, mostly for personal preference, but anything up to that is perfectly fine. Just make sure to check a flow chart to make sure the pump you get will still flow sufficient volume at that pressure. If you want to be sure, set your base pressure to 55 and use a 1:1 rising rate regulator. With the 440's that should give you plenty to work with. The stock 440's will probably handle about ~80psi before they are forced open, but this is just an estimate. The base 55psi is much preferable to a lower base with the 540's, esp for cold starts because the better your pressure (to a point) the better spray pattern and atomization, which is real important for cold starts. If the 440's dont like the pressure, you can always switch back to the 540's, so it's a win-win anyway.

    And btw, some BMW's run over 95psi at the rail chew on that.
    I really like the way aaawelder put it: "do not include yourself in this circuit"

  4. #4
    Ultimo Miembro Fantástico Gigantesco ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD's Avatar
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    Quote Originally Posted by Trance4c
    The extra 5psi of pressure will have no negative side effects to your injectors. I for one have been running on a Supra TT fuel pump for nearly a year now at around 55-57psi. On only reasons you will have injector issues is duty cycle or mechincal failure. The increase pressure will only work in your favor as you have calculated.
    One vote for 440's.

    You have an adjustable FPR? How come you set the FP so high?

    Quote Originally Posted by MrWOT
    I wouldn't exceed 60psi base on stock injectors, mostly for personal preference, but anything up to that is perfectly fine.
    Cool.

    Quote Originally Posted by MrWOT
    Just make sure to check a flow chart to make sure the pump you get will still flow sufficient volume at that pressure.
    Fuel pump test:



    Walbro in tank pump will still flow 216L/h at 75psi pressure.

    So lets say 440cc/min injectors @ 100% @ 75psi (55base + 20 boost) (absolute WORST case).

    So 440's = sqrt(55/42)*440 = 503.5cc/min

    503.5cc/min = .5035 L/min x 60 min/h = 30.2 L/h x 4 injectors = 120.8 L/h

    If I need 21L/h to flow out of the FPR as assumed in the Wolfkatz tests,

    120.8 + 21 = 141.8 L/h total required : well within the scope of the Walbro pump.

    I'm not sure if you should integrate boost into the equation here (wolfkatz didn't)... if you do, the results are:

    sqrt(75/42)*440 = 588cc/min = .588L/min x 60 min/h = 35 L/h x 4 injectors = 141 L/h

    141 + 21 = 162 L/h absolute max requirement if using boost pressure to determine injector flow


    So yes the pump is very much able to handle this, with a wide margin of error available.

    Quote Originally Posted by MrWOT
    If you want to be sure, set your base pressure to 55 and use a 1:1 rising rate regulator. With the 440's that should give you plenty to work with. The stock 440's will probably handle about ~80psi before they are forced open, but this is just an estimate. The base 55psi is much preferable to a lower base with the 540's, esp for cold starts because the better your pressure (to a point) the better spray pattern and atomization, which is real important for cold starts. If the 440's dont like the pressure, you can always switch back to the 540's, so it's a win-win anyway.
    So thats two votes for 440's so far? I'm being convinced slowly... Well I definitely don't want to suffer from poor atomization in the winter, where I occasionally see temps as low as -45C, although I rarely start the car when that cold! And yes my FPR is 1:1. I would never see anything like 80psi...I'm thinking the most I'd need is 55psi.

    Quote Originally Posted by MrWOT
    And btw, some BMW's run over 95psi at the rail chew on that.
    Wow!

    Good info guys!
    1988 ST165 2.2L @ 370awhp
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  5. #5
    Ultimo Miembro Fantástico Gigantesco ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD has much to be proud of ChrisD's Avatar
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    This is an interesting dyno. It is an ATS car, with the CT27. 290whp on the stock injectors. This is using an ATS FPR, 19psi.

    Also, to add. This is with 69psi of rail pressure. (50psi base + 19psi boost)

    I haven't heard of any problems whatsoever by doing this. I've seen some other dyno's of them running 22psi as well (72psi rail pressure).

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