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Peter Cobbold

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Peter Cobbold last won the day on November 23 2018

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  • Location
    North Wales
  • Cars Owned:
    Wade-blown TR6
    TR7 fhc - not blown, yet....
    Science. Microscopy
    Creative conservation
    Birding, Iceland, UFO science.

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  1. I wonder if it is ethanol. BP Ultimate and maybe others are adding agents to remove deposits from fuel systems in a bid to gain mpg. Tesflon lined hoses and nitrile seals should be OK in 10% ethanol http://www.efunda.com/designstandards/oring/oring_chemical.cfm?SM=none&SC=Ethanol#mat However, ethanol can slowly oxidise in air in the MU to acetaldehyde that might well during winter layup split the diaphragm between the MU and castle. Ive no idea if fuel stabilser additves prevent etoh oxidation Peter
  2. When a spring allows the wishbone to compress the bumpstop in a bend all the cornering forces transfer to that tyre which will give way very rapidly indeed. Too fast to catch. So cutting a spring to lower ride height is not advisable. Shorter springs should also be uprated to match.
  3. Ahead of its time ! Somewhere there must be a scavenge blower. Peter
  4. Rubber hoses, rubber bushes.......... If we had a rubber trumpet we could form a rubber band
  5. John, Have a good trip. Fuel consumption at altitude will rise, and not only because of the gradients ( slide 34) . Best carry spare fuel ? Peter
  6. Thank you Tony. I had to ponder the fundamentals of SU/Strombergs when feeding the supercharger with one HS8. I gave a talk at an IWE , here: https://supertrarged.wordpress.com/2017/07/10/how-does-an-su-carburettor-work/ The explanation of "mixture spread" is not as far as I know available elsehwere. Mixture spread is how that < or >30deg butterfly opening gives a different mixture at the same station on the needle. Peter
  7. The depression above the jet will stay constant as it is set by the mass of the piston and spring force divided by the are: those wont change with altitude. So we need to know if the lower atmos pressure will affect lift and hence needle position. At 8000 feet (= 2400 m ) atm press is 75 % of sea level, and air density likewise. So if the piston/needle stays fixed the mixture will richen by about 25%. However, the atm pressure below the piston has fallen by 25% too, so the force too lift the piston against that constant depression is less. So at 8000 feet the piston will assume a lower position, the needle delivers less fuel and that 25% richening wont happen. It might evn go leamer dependong upon the needle profile. However there is a possibilty of richening due to a greater throttle opening. No free lunches, at altitude you will need more throttle!! If at cruise at sea level the throttle is open less than 30 deg and open more than 30 at altitiude the mixture will richen, but still to nearly the same mixture as that >30 deg opening at sea level. Overall a sllight leaning or richening might happen but not affecting driving. In short the SU Stromberg is a brilliant design because there is no venturi. Webers at altitude cant sense the air density change as their venturi operates on air 'particle velocity': they will go rich, badly. Peter
  8. With only 5 litres in the tank the fuel will heat up, depending upon how the car is driven. If it is poddling along using little fuel almost all the pump's output ( roughly 80% at 40mph cruise) is returned to the tank by the PRV. So heat is added to the tank by the pump. unless you drive flat out, when the prv barely opens and all the pumps output is burned. Its a good idea in hot weather to refill the tank when its half-full. The heat transfer is the same but the temperature rise and gassing will be much less. Peter
  9. If the dashpot oil is too thick it can slow the descent of the SU piston upon sudden butterfly closing and gives an over-rich mixture briefly
  10. Tony, You flushed me out of hiding. Profundities with a pessimist's view of reality, are alive and kicking elsewhere, eg anticipating the threats to classic motoring: http://sideways-technologies.co.uk/forums/index.php?/topic/8495-rehearsing-our-arguments/ Peter
  11. For the first ten years all the TR did was get me to work and back, reasonably reliably. Happiness was a quick swap of a drive shaft UJ, or piston. Curiously the PI was faultless. Running well was almost taken for granted. Which is why I never sold it.
  12. A cam with really wild overlap will do that if the engine is run at road rpm. Unburned mixture enters the exhaust during the overlap period. At race rpm the overlap is too brief to allow that.
  13. If the flame was steady and not the flash of a backfire I'd check the timing, could be too retarded. If timing is OK running very lean can cause sustained exhaust flame.
  14. Hmmm. I'm struggling too. Why did it sink? Peter
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