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Thread: Two Level Boost

  1. #1
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    Two Level Boost

    I've posted this in several places, but still can't establish the problem...

    Don't know if anyone else has this happen...

    I appear to get two levels of boost when me foot is to the floor. I get a nice level amount of boost up to about 4500 rpm, then it suddenly leaps up to a more unpredictable level.

    I'm running an SBC iD-3, but it does it when just using the adjustable actuator.

    Refitting the carbon canister and plumbing its sensor back in (something not fitted on the ADM S15s) stabilized the boost somewhat. However, its still spiking.

    Checked for boost leaks, controller (turned off), and actuator (replaced) - still does it. Even when running on adjustable actuator only.

    Appears to hold boost fine up to 0.9-1 bar, after which it suddenly goes nuts on WOT.

    Its been suggested that the internal wastegate might be struggling and that an external might sort it. Can't understand why this would be a problem on the standard BB turbo...

    LATEST:
    For no explicable reason, my boost appears to have stabilised at around 1 bar over the last two days - without me doing anything.

    This is running a boost setting of 53/4 (can't remember) and 0 gain. I tried adding a gain of 7 to experiment this morning, and it immediately spiked the next time I overtook. Back to 0 and its fine again.

    This is bizzare because it was running exactly the same settings last week and was still spiking...

    Any idea how to make it more level (without changing turbo )? A gain of 7 on the SBD i-D3 is fairly standard.

  2. #2
    Brad Guest
    Do you use the auto-learn mode of the ID3 or the manual?
    I found auto was terrible and I would get spiking like you are describing, so I stick with manual now.

    Brad.

  3. #3
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    Its been on manual for a while now. Makes no odds though. Will do it when only running on the adjustable actuator...

  4. #4
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    Quote Originally Posted by Nicely
    Its been on manual for a while now. Makes no odds though. Will do it when only running on the adjustable actuator...
    is it a twin port actuator or a single port actuator?

    stupid question number 2 is whether the actuator is opening all the way ....

    I was doing a lot of searching on tt.net's tech section and a lot of similar issues all seem to be with bad settings of the gain... the only other thing that was similar to your issue was where someone had hooked up the hoses wrong and not removed all the plastic caps from the solenoid! I'm assuming that's not your problem.

    One suggestion was as follows:

    1. Start off with a low BOOST and GAIN setting.

    2. In a higher gear (3rd or 4th), run the car to see what boost level the BOOST number corresponds to by watching what steady/stable boost level is reached. Increment the BOOST with each run till you reach the boost level you want. Fine tune as necessary. If you notice boost spikes, then you have set the gain too high, you do not want spikes at this point since that makes it more difficult to see the steady/stable boost level.

    The reason why you should use the higher gears is because in the low gears, things can happen too fast to figure out what the steady/stable boost level is. Now that you have figured out the BOOST number that will give you the boost level you want, the next thing to do is to work out the gain:

    3. Make runs in lower gear (1st or 2nd), increment GAIN with each run till you see boost spikes. Then fine tune it till there is little or no boost spike. This is your optimum gain setting for that boost level.

    The reason why you should use the lower gear now is because boost builds much quicker in the lower gears, so there is a higher tendency to boost spike.

    (from here: http://splparts.com/doc/SBC-iD.htm) - this guy (Kuah) has some good experience with the SBC and may be able to help too. he probably doesn't remember me but I was one of the first people to buy his custom Z32 radiator many moons ago...

    I'll keep thinking too..
    Chris
    1999 S15 Spec S Auto (ever so slightly modified)
    1996 Skyline GTR (UK Holiday car); 2001 Lotus Esprit V8GT (moderate tuning); 2008 BMW 135i (looking for more power)

  5. #5
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    Thanks for the suggestions.

    However...

    The spiking occurs when the controller is off too. i.e. running solely off the actuator.

    The standard actuator has actually been changed to a HKS adjustable (single port). Its got a good preload (holds shut). How can I find out if it opens all the way?

    It appears to only spike when the boost goes over about 1 bar. I did get it to spike again this evening when applying WOT at around maximum peak in 5th. This is where is usually happens. When there's a sudden increase in throttle at around 4000-5000 in 5th or 6th.

  6. #6
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    I've wacked that link into Useful Threads.

    Tried this out this morning. Because my actuator is set to about 12psi (0.83 bar), the lower SET figures were all the same. It started increasing after SET 40. GAIN was set to 5 as recommended. Spiked when set to SET 45. Reduced to SET 42 then SET 43. It peaked at 14.7 psi (1.01 bar) on peak power in 6th (the worst gear for spiking). Couldn't test it on SET 44 as I was just coming into Basingstoke . I have a strong feeling that it will spike. From previous testing, spiking occurs when it gets to around 14.8-15psi (1.02-1.03 bar). When I say spike, I mean spike. As in anywhere from 18-21psi (1.24-1.44 bar) As soon as I hear the turbo start screaming, I let straight off (if it doesn't hit cut first). Usually less than a second.

    Spooling-up was quicker though on GAIN 5.

    Its mapped for 16psi (1.1 bar) with no det. It would be so nice to be able to run that...

    A guy on SXOC has been having similar problems with his S14 (although his is a higher tune with a bigger turbo). He's finally stopped the spiking by fitting and external wastegate AND running it as dual.

  7. #7
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    then, following on from that and the fact that the guy with the s14 only solved it with an external wastegate it suggests maybe the internal wastegate isn't letting enough exhaust bypass the turbine wheel... which would cause it to spike.

    my next stupid suggestion would be to reduce the opening pressure of the variable actuator to, say, 7psi or something lower anwyay. see if that makes a difference... maybe due to the way you preset it the actuator arm isn't moving far enough to open the wastegate all the way.

    just a thought
    Chris
    1999 S15 Spec S Auto (ever so slightly modified)
    1996 Skyline GTR (UK Holiday car); 2001 Lotus Esprit V8GT (moderate tuning); 2008 BMW 135i (looking for more power)

  8. #8
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    I'll give that a try.

  9. #9
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    Right. Actuator wound out and ready to try on the drive home.

    Interestingly, the Blitz manual for the SBC states a recommended GAIN of 20 for the SR20DET. I find this a bit odd as most of the other engines (including the VG30DETT and RB26DETT) are only 5.

  10. #10
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    Nicely - did you only go about changing your actuator as you thought this was the problem or was there another reason??

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