Bruce ( Shrinker )

Fuel and Air Systems

  1. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    this is one aspect of what happens in the cylinder in regards to ignition timing being linked to CO production/flame kernal.
    Spark timing for power is generally the same at 8,000rpm as it is for 3,000rpm.This is because the flame speed increases at the same rate as the rpm.There is no real evidence as to why this occurs but most will say it is a engine phenomena.Bruce thought that there was a link between piston movement and the styles of fuels.Engines of the past employed totally different piston velocities to now because of the differences in fuel.
    He went on to say that it is possible that people stumble upon piston speeds and velocity profiles that produce best power in racing,when actually what they are doing is optimizing the burn speed to the piston speed.
    so if you do this successfully you dont need complex timing lines.
    Some engines need advancing as the rpm increases as it depends on the CO residual of the cylinder.
    I see a lot of engines with lots of CO residual and that needs a complex timing line,thats why im always spending time with timing just about more than the fueling when i tune.Ignition strength and advancing is terrible in most jobs i go to.
    What is wrong is that CO slows the reaction in the unpredictable ways and it slows the reaction differently from one reaction to the next.
    I make sure that when the plug engages more fuel molecules,the gassing of the fuel is improved first.
     
  2. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    yes when you get it pretty right you can hear the air going down the airbleeds quite loud.
     
  3. Hysteric

    Hysteric Well-Known Member

    Messages:
    858
    Likes Received:
    348
    Joined:
    Dec 31, 2005
    Local Time:
    4:55 PM
    Is this in reference to Isothermal and Adiabatic Compression?
     
  4. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    it certainly is linked to it thats for sure.camshaft profile is very important.
    just remember this.
    we all have to deal with engines that make quite a bit of CO.we tune with holleys etc..
    We dont have the luxury of very good droplet control so CO is there and a big part of it is good because its a colder burn.its a safer burn.
    just the other day i had to tune a blown motor on a 42 degree day getting it ready for power skids that will happen in hot weather,without vacuum advance,and make sure the car doesn't overheat,fully heat soaked .So thats what i did,tuned all day in the heat making sure its ok.CO burn is your friend.
    Just as well i tuned it for him as it was very lean over 50% load.haha..
     
  5. Hysteric

    Hysteric Well-Known Member

    Messages:
    858
    Likes Received:
    348
    Joined:
    Dec 31, 2005
    Local Time:
    4:55 PM
    Does camshaft profile relate to the valve curtain area's effect on the vaporization rate and droplet size considering piston speed influences the vacuum generated in that area?
     
  6. Bewy

    Bewy Well-Known Member

    Messages:
    1,505
    Likes Received:
    962
    Joined:
    Jan 1, 2021
    Location:
    Australia
    Local Time:
    9:55 AM
    Greg,
    Always great to see the TQs get a good wrap. The most underrated 4 bbl carb of all time. I first started using them in the late 70s. I have two 850 Comp Series & a mate has an 850 & a 1000. When I put a Ford TQ on my 440 Dodge & went for a drive, the engine almost stopped when the secondaries came in. I went home & increased the sec MJ & AB to the same size as a Mopar TQ I had, & presto, problem fixed. Any idea why the Ford TQs used such small sec jets, some the sec jets were smaller than the pri! The only downside is that the Idle Down channel is a pain to enlarge.

    The spray bar nozzle concept in post 21 has been around for a while. CB Performance in the US was offering it over 20 yrs ago for 40 & 44 mm Weber & Dellorto carbs. May have been others before them.
     
  7. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    The camshaft profile greatly effects the vaporization of the fuel,especially in low load driving.There is potentially a large amount of vacuum generated as the intake valve lifts off the seat area and its this area where a lot of vaporization takes place.You can kill this area real quick when you change cam profile,speed of lift etc..
    You can tan a plug on wide LSA cams real easy even at idle if you get the fueling correct.narrow lobe cams need a lot of comp and good fuel.
    Fuel is such a key component to it all,the quality that is.
    The inlet valve closing point in relation to piston speed will determine the first stage of compression,whether it is slow or fast.The energy that is added to the fuel molecules in the first stage is very critical.
     
  8. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    i dont know
     
  9. Hysteric

    Hysteric Well-Known Member

    Messages:
    858
    Likes Received:
    348
    Joined:
    Dec 31, 2005
    Local Time:
    4:55 PM
    Hey mate. That's not where the magic happens in Bruce's carb. You would have to study the patent and understand the difference between Laminar and Turbulent flow designs to really get an insight to what he was doing with his design.
     
  10. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    Yes that is correct.
    With the smart carby there was no air correction system for the mains fuel,so the mains fuel is initiated at lower cfm flow.it was pretty cool.
     
  11. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    i agree.
     
  12. Hysteric

    Hysteric Well-Known Member

    Messages:
    858
    Likes Received:
    348
    Joined:
    Dec 31, 2005
    Local Time:
    4:55 PM
    If I'm correct in how I read that then different valve curtain areas would need a different lobe designs to create the vacuum necessary to maintain vacuum profile to suit the fuel being used in relation to piston speed and cylinder fill time.

    I take it that low loads means Isothermal Compression and high loads are Adiabatic so how would you have to balance out those demands with intake closing and rpm ranges.

    I remember Bruce saying this about it:

    The time spent in isothermal compression is critical to the vaporization level of the chamber. When you close the intake valve earlier you increase the time of isothermal compression, thus the engine gains low down power, however the trade off is as you rev it faster the valve closing goes straight into adiabatic and the vaporization suffers and the engine looses power. What ever the temperature of the air in the chamber at the point where it crosses to adiabatic will be the temperature until it drops back out of adiabatic somewhere as the piston slows in the top half of the stroke.
    So now can anyone see why I say what I keep saying?

    Hint, if you decrease droplet size you will increase vaporization at all points especially in the zones where its inhibited by the type of compression
    That’s what carby sizing does too. The whole intake system is a vital part of the vaporization.
     
  13. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    vaporization and timing.
     
  14. Bret Tschacher

    Bret Tschacher Well-Known Member

    Messages:
    98
    Likes Received:
    58
    Joined:
    Oct 29, 2020
    Location:
    Custer,S.D.
    Local Time:
    3:55 PM
    We should share emails so we can share our experiences with carby's. I spent many years of my own life drilling, soldering, and drilling jets again inside carbs, installing different sizes of copper or brass wires soldering those in jets and replacing jets and metering rods, adjusting rod positions chanhing power valves and power piston springs, experimenting with Holleys, Carters, Rochesters, Webers, even brasing old cast iron carbs from tractors to repair rust. I had an exceptional learning curve with old Thermoquads, Quadrajects, AFB's, AVS's, Holleys among others, just to see if we learned the same stuff or whatever. Now I'm deep into a MegaSquirt SFI, COP with 2 stage injection AND 2 stage nitrous, dual channel knock sense, 8 channel EGT, CANbus, dual wide band O2, SD card datalogging. The second stage injection will use P&H injector drivers on 2 batch fire channels. The first stage nitrous hopefully will be dry and the second stage will be standard wet behind the 102mm TB.
     
  15. Hysteric

    Hysteric Well-Known Member

    Messages:
    858
    Likes Received:
    348
    Joined:
    Dec 31, 2005
    Local Time:
    4:55 PM
    Here's another interesting paper:

    Why Gasoline 90% Distillation Temperature Affects Emissions with Port Fuel Injection and Premixed Charge

    Why Gasoline 90% Distillation Temperature Affects Emissions with Port Fuel Injection and Premixed Charge on JSTOR

    "However, with PFI( Port Fuel Injection)the fuel is exposed to the air for a short time before it is inducted into the cylinder. This could result in incomplete fuel vaporization, particularly with T90 fuels. On the other hand, with a carburetor and as with TBI the fuel has a long exposure to the air before entering the cylinder. therefore it is conceivable that the mixture is better vaporized and premixed prior to combustion with carbureted and TBI fuel delivery. More complete vaporization could result in better combustion and lower unburnt HC emissions"

    There's obviously a lot going on in the intake manifold and port than most people would think. If the fuel required more "energy input" to improve the mixture quality the intake tract could be a good place for that to happen.
     
  16. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    Hi Bret,
    You sound interesting.
    i have one question for you.
    What is the greatest thing to date that you have learnt in tuning cars?
     
  17. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    The unleaded fuel that we have to deal with today is difficult to understand when tuning with large cam street engines.I did one today,350 chev with world product cast heads and big cam with not enough compression and not enough spark energy.So it likes to run more on the light vapors.required specific timing curve.Had to be a bit richer to get it nice but thats what it takes sometimes.
    IMG_9540.jpeg

    IMG_9547.jpeg
     
  18. carby tuning techniques

    carby tuning techniques Active Member

    Messages:
    39
    Likes Received:
    21
    Joined:
    Jan 5, 2022
    Location:
    perth western australia
    Local Time:
    6:55 AM
    i agree with what they say.
    Time is so crucial for air saturation,as it is for compression.When you reduce both you have a mess to deal with.
     
    • Like Like x 1
    • TT5.9mag

      TT5.9mag Two atmospheres are better than one

      Messages:
      2,121
      Likes Received:
      2122
      Joined:
      May 5, 2016
      Location:
      So cal
      Local Time:
      2:55 PM

      Will you share some timing specs associated with the plug in your picture please.
       
    • Hysteric

      Hysteric Well-Known Member

      Messages:
      858
      Likes Received:
      348
      Joined:
      Dec 31, 2005
      Local Time:
      4:55 PM
      Hey Greg can you share what the cam specs are?
       
    • carby tuning techniques

      carby tuning techniques Active Member

      Messages:
      39
      Likes Received:
      21
      Joined:
      Jan 5, 2022
      Location:
      perth western australia
      Local Time:
      6:55 AM
      Mechanical:
      17°@idle
      25°@2200
      32°@3300
      33°@4000
      34°@5000

      Vacuum:
      3°@8"
      7°@11"
      15°@15"

      total 49°@cruise with vacuum timing starting as soon as you move the throttle.This requires tuning as to get blades exactly in the correct spot for the vacuum pickup point with where the vac hole is located in base plate in this particular carby..i find a lot of them to be very different and the clone and quick fuels etc all different again.

      This is his summer setup,winter will be different .This is in a heavy station wagon with 3.08 rear ratio.

      98 unleaded pump fuel
      Fully heat soaked - no pinging,run-on etc...
       
      • Thanks! Thanks! x 1
      • carby tuning techniques

        carby tuning techniques Active Member

        Messages:
        39
        Likes Received:
        21
        Joined:
        Jan 5, 2022
        Location:
        perth western australia
        Local Time:
        6:55 AM
        he doesn't know.its a narrow lobe cam.
        When i looked at the car it wouldnt idle or drive correctly,no power very rough.
         
      • Hysteric

        Hysteric Well-Known Member

        Messages:
        858
        Likes Received:
        348
        Joined:
        Dec 31, 2005
        Local Time:
        4:55 PM
        But its got that sick idle sound. Yeah its sick alright......
         
      • Bewy

        Bewy Well-Known Member

        Messages:
        1,505
        Likes Received:
        962
        Joined:
        Jan 1, 2021
        Location:
        Australia
        Local Time:
        9:55 AM
        Greg,
        Post 67. With that big cam, it is going to need a LOT more than 17* for best/smoothest idle, more like double would be closer.
        One way of doing this is to use an an adj vac adv unit connected to manifold vacuum.

        This is a most misunderstood subject.

        People often tune the carb idle before dialling in the timing at idle, when it should be the other way round.

        From D. Vizard:
        "The optimum idle advance is typically about 35-40* for a short cammed street engine & [ though not commonly realized ] as much as 50* for a street/strip engine."

        And [ scroll down to post #6 ]:
        www.hotrodders.com/forum/vacuum-advance-hooked-up-directly-manifold-bad-47495.html
         
      • Hysteric

        Hysteric Well-Known Member

        Messages:
        858
        Likes Received:
        348
        Joined:
        Dec 31, 2005
        Local Time:
        4:55 PM
        Here's what Bruce said to me when I asked him about this particular issue:

        "I assume your talking idle timing as being 20 to 25 for best idle running on your engine. Lean mixture requires more timing advance. Lean burns slow. The other thing that slows burns is exhaust gas contamination of the fresh charge. So think about what 108 lsa does compared to say 114.
        The relationship of vaporization to timing is thus. With equal fuel for comparing purposes of 2 engines, one with poorly vaporized mixture the other with very good vaporization, the engine with poor vaporization will require energy that is released from the combustion to bring it to an equal state of vaporization compared to the very good engine. You can think of its in as simple terms as that and you wont be wrong in any conversation. Any energy removed from the combustion to achieve further combustion is wasted and non productive at the crank."

        And

        If you enrich the mixture at idle it will require less timing and the volume of gas expelled from the chamber will be greater (because there is more fuel in the cylinder ). The greater volume exhausting resists reversion backwards up the exhaust port therefor it actually runs with a cleaner chamber. Funny stuff isn't it.
        BUT what you have to do is enrich it correctly with the right processes in the carburetor, sometimes it's not just a matter of winding out the idle screw or changing the IFR. Every engine has a design to it and Chrysler's are a bit different to the other US products, they are not chevs or fords, they are better. They have better combustion and its not necessary to follow the rules of the hotrod industry, as the industry is very Chev orientated.

        Lots to think about in those 2 paragraphs.
         
        • Agree Agree x 2
        1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
          By continuing to use this site, you are consenting to our use of cookies.