sequential twin chove VS single
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  1. #1
    1000+ Posts jo proffi's Avatar
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    Default sequential twin chove VS single

    I'm at the 'thinking about' stage of a new after market ECU for my car.
    The option is there for using a twin choke sequential throttle which comes with the rig.(may be off a camira??)

    I have noticed that the single choke I am running now seems to have tune issues at fractional openings, like when driving down hill, and am thinking the twin choke would give more data points through the tps at small throttle openings than the same airflow through a single choke, which I'm thinking would improve the chances of the ecu getting the tune right.

    Does this sound correct??

    Also, what are the general advantages and disadvantages of controlling the airflow with the twin sequential butterflies (comparing to a single choke)???


    Jo

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  2. #2
    1000+ Posts bluey504's Avatar
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    Jo IMHO the sequential system can work very well it just depends on if it has two seperate plenum tracks. Much like twin choke carbies on a rotary Mazda, the primaries are mounted outboard and have a longer intake path, to optimise torque and low speed running. The same holds true for Ford I6 motor's in EF Foulcan's.
    Pure performance motor's usually have single butterflies for each inlet and Mazda even went to the extent of variable length trumpets to get the best result. Forget which year but it was an outright Le Mans winner with a four rotor Peripheral Port engine based on the 13B. Pushing out around 700 Bhp, but with good delivery and reasonable fuel economy and less stuff to go wrong, turbo's/intercoolers etc. All in a nice neat package.
    Hope this helps but some photo's would help the discussion.
    and

  3. #3
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by bluey504 View Post
    Jo IMHO the sequential system can work very well it just depends on if it has two seperate plenum tracks.
    I dont think i understand what plenum tracks are, bluey.
    Jo

  4. #4
    1000+ Posts alan moore's Avatar
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    Of course the R25 ran a twin throat butterfly system that looked remakably like a downdraft Weber upside down, and would fit on your Fuego easily. The R25 injection relied mostly on the vacuum sensor to work out how much fuel to inject, where I guess you will have a bigger cam than std and will upset this.

    A Megasqirt would be cheap and quite capable and would just need a throttle pot instead of the std switch type arrangement, although it wouldn't read the original type R25 crank pulses to the best of my knowledge.
    '56 Renault 4CV (16TS Power)
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    '82 Renault Fuego GTX
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  5. #5
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by alan moore View Post
    ...... although it wouldn't read the original type R25 crank pulses to the best of my knowledge.
    And 4kg of flywheel gets turned into steelwool.

    Jo

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    bob
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    Default try this way

    G'day Jo,

    JyDog had a much sexier solution.....

    cheers,
    Bob
    Attached Thumbnails Attached Thumbnails sequential twin chove VS single-fuego-project-023-2-.jpg   sequential twin chove VS single-fuego-project-024-2-.jpg   sequential twin chove VS single-fuego-project-025-2-.jpg   sequential twin chove VS single-fuego-project-026.jpg  

  7. #7
    1000+ Posts jo proffi's Avatar
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    Its nice and sexy, but I'd rather run a 5litre V8 and get some real power rather than blow my hard earned cash out the exhaust pipe as unburned fuel.

    I want it all, power, drivability and economy.
    Jo

  8. #8
    bob
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    G'day Jo,

    Quote Originally Posted by jo proffi View Post
    .......I want it all, power, drivability and economy.
    Jo
    Interestingly enough I found all that applied with better breathing & multi carb setups - in days gone by. Repeated those same exercises now I don't reckon there would be any difference in the approach, maybe apart from multi point injection, separated inlets & black box management provided you knew exactly how it all worked and had the instrumentation to prove it.

    Downside to this day and age is that the carby setup, whilst really nice - you can't really beat that DCOE noise, would likely be multi times dearer that the EFI.

    cheers,
    Bob

  9. #9
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    Quote Originally Posted by jo proffi View Post
    I'm at the 'thinking about' stage of a new after market ECU for my car.
    The option is there for using a twin choke sequential throttle which comes with the rig.(may be off a camira??)
    I have noticed that the single choke I am running now seems to have tune issues at fractional openings, like when driving down hill, and am thinking the twin choke would give more data points through the tps at small throttle openings than the same airflow through a single choke, which I'm thinking would improve the chances of the ecu getting the tune right.
    Does this sound correct??
    Also, what are the general advantages and disadvantages of controlling the airflow with the twin sequential butterflies (comparing to a single choke)???
    Jo
    Hi,
    Depends on what type of EFI system is fitted I think. Is it a Map sensor type or an Air Flow type. (I guess it is not individual throttles)
    The twin progressive throttles 'only' give better driver control for smoother low power use I think. Particularly Map sensor types. The computer does not use feed back from the throttle position for much, only acceleration enrichment except for close to closed and fully open.

    It sounds like there is a low throttle point which needs altering. I have used a "piggy back" unit from Jaycar which enables +- 100% through the range, to trim the mixture of a modified car with a fiddled standard EFI MAP system. Works well. This car had problems at the low throttle end after we set up the full power end.
    An Air Flow system seems to cope better to minor changes without problems.
    Jaahn

  10. #10
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by jaahn View Post
    Hi,
    Depends on what type of EFI system is fitted I think. Is it a Map sensor type or an Air Flow type. (I guess it is not individual throttles)
    The twin progressive throttles 'only' give better driver control for smoother low power use I think. Particularly Map sensor types. The computer does not use feed back from the throttle position for much, only acceleration enrichment except for close to closed and fully open.

    It sounds like there is a low throttle point which needs altering. I have used a "piggy back" unit from Jaycar which enables +- 100% through the range, to trim the mixture of a modified car with a fiddled standard EFI MAP system. Works well. This car had problems at the low throttle end after we set up the full power end.
    An Air Flow system seems to cope better to minor changes without problems.
    Jaahn
    Thank you for your reply, jaahn.

    The factory ECU is going, and I now have a fully programable ECU, which can chose map or TPS, but as you say uses the map as main and the tps as enrichment and similar adjustments.
    This is my first venture into programming the ecu so i have sooooo much to learn, but look forward to tuning all the little things.
    Roughly half my driving is done down hill off throttle in top or 4th gear, and pedantic as this may seem I'm especially interested in the tune at zero to 5% throttle openings and will be spending a great deal of my efforts in this zone.
    If I can make the smoothest, most fuel efficient tune, and it works out smoother than regiies tune, i'll be stoked.
    Jo

  11. #11
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    Quote Originally Posted by bob View Post
    G'day Jo,

    JyDog had a much sexier solution.....

    cheers,
    Bob
    Sexy? Yes. Legal? Um no...

    Then again, technically even Jo's EFI setup isn't legal, even though his car would probably have better economy and more accurate fuel metering than any factory carb Fuego.

    You can have a cars emissions system re-certified after changes but it is rather costly if memory serves.

  12. #12
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    A twin throttle plate is simply used to make the car easier and smoother to drive down low.

    The EFI system doesn't really care what TB is fitted and it makes no difference, except to how the driver perceives it (ie - twitchy power delivery)

    The EFI system just measures the airflow/vacuum and then uses that (and all the parameters it receives from the other sensors) to look up the correct value in the stored tables and then add the correct fuel based on that table.

    By having a twin throttle plate you can achieve good driveability and still retain good flow at WOT.

    I personally think the twin throttle plate setups were used back in the transition days between carby and EFI so cars felt 'normal'.

    With a carby, if you wanted substantial power, you generally had to floor it to open the secondaries.

    With a large TB on a mdoern EFI system it's almost the opposite. You can open the throttle 1/4 of the way and still get good performance, floor it and the increase in performance isn't proprotional to the mashing of the right foot.

    I think twin plates were used to retain a similar feel to what was previously the norm.

    A progressively actuated single throttle plate does the job almost as well and with greater simplicity but if you are really chasing accuracy and efficiency in the lower rev/throttle opening range, the twin will technically be better.

  13. #13
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    Default Off idle !

    Quote Originally Posted by jo proffi View Post
    Thank you for your reply, jaahn.

    The factory ECU is going, and I now have a fully programable ECU, which can chose map or TPS, but as you say uses the map as main and the tps as enrichment and similar adjustments.
    This is my first venture into programming the ecu so i have sooooo much to learn, but look forward to tuning all the little things.
    Roughly half my driving is done down hill off throttle in top or 4th gear, and pedantic as this may seem I'm especially interested in the tune at zero to 5% throttle openings and will be spending a great deal of my efforts in this zone.
    If I can make the smoothest, most fuel efficient tune, and it works out smoother than regiies tune, i'll be stoked.
    Jo
    Hi,
    The ecu has a 'special' set of rules that it applies when the TPS tells it is near idle. This is able to be programed of course. If the transition to the main program is a large step then it will be noticable as a problem. I guess you should look at the mixture and the timing around this point to see what is happening and make it blend smoothly from one to the other. Probably the sort of detail that often does not get done properly by the dyno boys. A friend has smoothed out a couple of 'lumpy' cars by doing this, even though they had been dyno tuned by 'experts'.
    My experience with tuning carbys back in the 'Good Old Days' was that time spent on progression jet selection demonstrated that you could get excellent economy and drivability from a big set of carbys on a modified car. Less problems with plugs etc too. Same principle.
    Jaahn

  14. #14
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by jaahn View Post
    Hi,
    The ecu has a 'special' set of rules that it applies when the TPS tells it is near idle. This is able to be programed of course. If the transition to the main program is a large step then it will be noticable as a problem. I guess you should look at the mixture and the timing around this point to see what is happening and make it blend smoothly from one to the other. Probably the sort of detail that often does not get done properly by the dyno boys. A friend has smoothed out a couple of 'lumpy' cars by doing this, even though they had been dyno tuned by 'experts'.
    My experience with tuning carbys back in the 'Good Old Days' was that time spent on progression jet selection demonstrated that you could get excellent economy and drivability from a big set of carbys on a modified car. Less problems with plugs etc too. Same principle.
    Jaahn
    That is an encouraging post jaahn.
    Also thank you mistareno for your post.

    I now feel like I am more informed to make a decision on which TB to use.
    I have been reading the manual for the new ECU about 5 times per day and dredging over all the posts on Af and am starting to form a clearer picture of the parameters of low load tuning.

    I'm leaning towards the OE single choke TB, for a number of reasons, not least of which is in reference to post 11.

    Some people have given me a fair bit of grief about cracking into the ecu to tune the motor, whilst others have been full of info and support.
    I have anticipated that a dyno tune will be a high power tune, but all the little transient settings at minimal throttle openings would be left a little short of the mark.

    And besides, my budget will only stretch to a power tune.
    Everything else is up to me to tune, and I look forward to it.
    I always maintain if you can tune a primary school band, you can tune a motor.
    Time will tell.


    Jo

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