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JohnD

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Posts posted by JohnD

  1. Colin is very clear and correct, except for...

    Rings spin in their grooves, at about 1000th of the rev rate, and they don't do so at exactly the same speed, so after a few minutes of running they are in random relative positions.    No point in careful positioning of ring gaps on installation.

    John

  2. If that's how Pete is using his Spit - on a track day understandable! -  then remove the Valve!  It's there to prevent excess aspiration from the crankcase when the throttle is closed, and the vacuum in the inlet is maxed.   At WOT, it will be minimal.

    Yes, I use the fuel pump port as an extra vent.  That and the rocker vent go to a catch tank on the bulkhead.

    John

  3. Absolutely, Croft is a great circuit!  It's the same distance from me as Oulton Park, but North East,  instead of South West

    But even at Oulton, where the CSCC goes every year, attendance is always down and people moan about 'how far it is!'

    As if Snetterton (for example) isn't seven hours from me!  (It's too far - I don't go these days!)

    John

  4. Having two valve springs is  not really a matter of  damping one by the other.    It's about resonance, not damping.

    Two springs may be mounted in series, one after the other, when the combined spring stiffness (k) is found by adding together their 'reciprocals' thus:-

    1/k1 + 1/k2 = 1/k3.   To use a random example, two springs of stiffness 135 and 125: 1/135 + 1/125 = 1/64   So k3=64.  So two springs like that are weaker than each other

    But in parallel, like two springs around a valve, to find the combined stiffness, you just add them together!    135 +125= 260   a much stiffer combination spring!   But that's not the end of the story - what's important is the 'resonant frequency'.

    A spring will resonate, vibrate more and more like a swing being pushed in time as it goes back and forth, when energised at a certain frequency.  That frequency may be calculated  by:-

    Resonant frequency, F = (1/2π)√(k/m)

    where 'k' is the stiffness and 'm' the mass that is resonating.   

    So the resonant frequency varies by the square root of the stiffness divided by the mass.  Valves that are too small in mass will break up, but we can change the frequency (see above).

    This becomes important at high revs when the valves are bounced at a frequency that approaches resonance. Valve bounce ruins valve sealing, which loses power.    Simply by adding another spring, we can raise the frequency at which valve bounce will occur way above the rev range of the engine!

    Simples!

    But you knew that, didn't you, Colin!

    John


     

     

  5. If I may add some Triumph race meets?   The CSCC Swinging '60s series will take place as shown:

     

    image.thumb.png.63358fc9187eeecc819a2310b702fcdb.png

    There are usually four to six Triumphs entered.     This series  runs two races at most meetings, for Group 1 and Group 2 (-/+ 2L) cars, with about half in eah race, unless they are amalgamated.

    There isn't a Triumph area, but all the Sw'60s cars should be in the same part of the paddock, where visiting Triumpheros will be most welcome.  I'm entered for Donington on March 23.

    For anyone who must stay at home, all the meetings will be 'live streamed' onto YouTube, just announced in  addition to those marked above. "Classic Sports Car Club" channel.

    John

     

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  6. My first race Vitesse had front and rear roll hoops connected by bars secured by straps around the hoops.    When I took it to a hill climb and the paddock was a grassy field, the 'shoogle' meant that I could SEE the movement between the two hoops!  Later models had/have welded joints!

    • Haha 1
  7. On 2/5/2024 at 7:50 PM, Escadrille Ecosse said:

    Today I...

    Had a visit to the podiatrist on Great Western Road in town as after an absence of 15 years or so my plantar fasciitis has returned with a vengeance in my left foot. Turns out I have flat feet. I'll call them fallen arches because pretty sure they were fine when I was younger.

    Weather grim so I took the Subway out to St Georges Cross from West Street. Third oldest undergound railway opened in 1896 after Budapest Metro (also 1896) and of course the London Metropolitan in 1863.

    20240205_150127.thumb.jpg.5297d415077ca27ca332a467dc882f1e.jpg

    Sympathy re feet!  I had that about five years ago, really disabling!   Insoles helped but I'm sure you will have been advised about them.

    For someone brought up on the London Underground (as it were) the Glasgow Tube was remarkably low in height. I couldn't stand for any length of time.   

  8. And here's where it's coming from:

     

    image.thumb.png.24e4735cb6bbce94e39c91eb907e5102.png

    Sundhnúkar - Live from Iceland - Webcams around Iceland

    That line of fire fountains is three kilometres long.   It's on the other side of a low ridge from a different camera, and you can see the lava flooding over towards the road on the left of the picture.   On the live view the flow of lava is clear and fast.

     

    And!  Now, drone footage of how the lava flow has covered the main  road and threatens the Blue Lagoon!

    Confirmed - hot water pipes that heat Grindavik town's homes has been destroyed.  This could make nit only that town uninhabitable at their latitude, bu also Keflavik to the north.

    • Thanks 1
    • Sad 1
  9. This is a screen grab from Google Earth.     The camera is on thorbjorn (Iron village) hill to the right (south) while the eruption is from the old scar  along the top edge of the view.  The main road along the middle is to Grindavik to the south (right).  The lava appears to have come around the hill between the road and the fissure, Mount Sylingafell, over the road and towards the Lagoon.

    image.thumb.png.4276584036eed2a97b0e2171d0359e4d.png

  10. The eruption on Iceland that has threatened the existence of the fishing port of Grinadvik has started again.    This is the live view from a fixed camera on  a hill, just south of the Blue Lagoon and power plant, north of Grindavik and looking at the main road to the town .  In the last 15 minutes the lava flow has moved from the centre of view to almost the left (south?) side, following and blocking the main road to Grindavik.

    AND!   In the last few minutes  (11:30 GMT) vehicles and diggers have appeared on the southern margin, apparently digging a 'berm' to hold back the lava!

    Now the view has changed, moved I think to the left.  Many more vehicles have arrived and the edge of the flow is now in the centre, but still moving, so fast that the turbulence at the tip is well seen , even in this low definition view:

    Camera moving again, showing how near the flow is the the Blue Lagoon complex.  More information in the news tape under the picture.

     

    GRRRRRRRRRRRRRRRRRRRR!!!!   The board won't let me post the link to the YouTube camera link.  It says, "The value entered includes a character that is not allowed such as an Emoji."    Can't see anything like that in the URL.  

    Here's another livecam, same site: https://livefromiceland.is/webcams/fagradalsfjall

  11. John,

     May I suggest a NACA duct?     Other forms of intake look plebeian or just gross, but the sculpted lines of a NACA are just beautiful, and grace the greatest cars ever made.  This Ferrari seems to have an excess of them!

    Show me NACA ducts | VW Vortex - Volkswagen Forum

    There are many websites that describe the design of a NACA duct, eg https://cozyserenity.weebly.com/uploads/2/1/8/0/21804934/__naca_duct_design.pdf  which is for aircraft, but none the worse for that!

    But what goes in must come out.   Extra air under the bonnet will escape under the car, and at speed may add to lift.   An intake should  be matched to an extractor duct.   The type chosen  by many classic car owners and self builders is the louvre, which as a single slot is efficient.  But that slot mucks up the airflow for the one behind it, reducing it's efficiency by about a third, and then  the one behind that, a third of a third.  A bank of louvres is only as effective as the size of the first slot, and a third!

    NACAs do not work in  reverse.   Instead a wide duct, with a floor that slopes up to join  the rear edge at no more than 15 degrees will work.  Better is one with a small lip on the front edge, like a Gurney Flap .  This causes a vortex behind in the throat of the duct, energising the air there, so that it moves into the outside airstream and is replaced by air from within.   The shallow slope of the rear wall prevents the duct 'choking'.

    These show extractors like that on m y SofS:

    image.thumb.png.3af397781999558c56da9d4fbfb4a372.png

    Good luck!

    John

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