Lynx to remake Sierra Crossover Manifolds?
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    Fellow Frogger! R10S FAN's Avatar
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    Default Lynx to remake Sierra Crossover Manifolds?

    Something i found recently on the interweb. It would appear that Lynx have been bought out and will be making some of their older inlet manifolds including the Single Side Draught Weber for the Sierra engine.

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    1000+ Posts bowie's Avatar
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    Well this is perhaps good news.

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    Quote Originally Posted by bowie View Post
    Well this is perhaps good news.
    It is good news. I've got an old lynx and it helps the poor little r12 breathe.
    Now it makes noises like a race car. Still slow but sounds the goods.

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    1000+ Posts bowie's Avatar
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    Sounds good! That's worth decent imaginary hp anyway.

    I didn't realise you have a lynx in that beast of yours, I should have looked closer.

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    THe lynx and side draft webber and extractors are a more recent addition.
    Dual side draft webbers look fantastic but probably overkill for a 1297cc R12

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    1000+ Posts bowie's Avatar
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    I don't know.. after reading about really big Webber's on race cars, and something to do with vacumm... I should really read more about how carbs work...

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    bob
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    G'day,

    Quote Originally Posted by IThompson View Post
    .......Dual side draft webbers look fantastic but probably overkill for a 1297cc R12
    oh, I dunno, my misspent youth was with standard/triumph motors, a pair of 1" SUs and tuned exhaust system on a standard 10 worked, less than a litre. But I cheated, the manifolds way back then were over the counter factory parts for modded triumph spitfires, stage 3 I think....

    Quote Originally Posted by bowie View Post
    I don't know.. after reading about really big Webber's on race cars, and something to do with vacumm... I should really read more about how carbs work...
    nah, just bolt 'em up and see what happens. The one above was wearing a Furd v8 carby on a bodgelled up manifold before the SUs. Big valves and lots of overlap also help....

    cheers,
    Bob

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    1000+ Posts bowie's Avatar
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    thats right, with enough cam and revs, big carbs seem small

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    Quote Originally Posted by IThompson View Post
    THe lynx and side draft webber and extractors are a more recent addition.
    Dual side draft webbers look fantastic but probably overkill for a 1297cc R12
    Not so sure about that. Gordini is 1255cc with two 40 side draughts. The G is cross flow however with a decent calculated breathing system the non-cross flow will make hp over a good range. I had a 1108 flying with two 40mm Webers on my 4CV. Top secret there will be high velocity so don't even think of going big exhaust pipe like the gutters we see on some of the youngsters' Jappers.

    Just my

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    On sporting Renaults the factory always put on big carburettors. 2 x2 barrel X 40mm on 8G, 2 barrel x 40mm IDF on rally R1063's for 904cc. 2 barrel down draft Solex on 750cc R1063, 2 X 2 barrel X 45mm on 17TS/G for 1565cc and 1605cc. Put two 40mm DCOE's on the R12 with right jets etc it'll be fine.

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    1000+ Posts renault8&10's Avatar
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    I disagree Bowie
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    1000+ Posts bowie's Avatar
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    I'm not sure we disagree. I think Ian was the one being conservative.

    But I must confess, after some reading, I'm still a little confused. There seems to be magical folklore about matching carb sizes to engine displacement. Why can't one just fit a 58mm carb (say the biggest) and restrict it down with appropriate jets? Well why isn't that better then just using a 40mm?

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    Multiple carbies are so overrated.......
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    1000+ Posts bowie's Avatar
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    Is that turbo sucking the air/fuel from the carb directly.. like.. it's passing into and via the hot turbocharger.

    Mad

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    COL
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    Quote Originally Posted by bowie View Post
    But I must confess, after some reading, I'm still a little confused. There seems to be magical folklore about matching carb sizes to engine displacement. Why can't one just fit a 58mm carb (say the biggest) and restrict it down with appropriate jets? Well why isn't that better then just using a 40mm?
    http://www.classicrallyclub.com.au/d..._DVAndrews.pdf
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    1000+ Posts bowie's Avatar
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    Ah right! so;

    -Venturi controls the atomise of fuel, (well increases the vacumm on the main jet, which draws in all in)
    -To big and there wont be enough vacuum to suck on the main jet, thus you are waiting later in the rev range for the effect on the main jet.
    -Kinda useless if you are driving around town, but great if you are going to spend all day in the top end of the rev range..
    -Ah but with a Venturi to small it itself becomes a restriction.
    -The difference in 40,45,58 really is just to do with the Venturi sizes the bodies make!

    That is the light bulp moment I had been waiting on.

    Bloody thank you Col!

    Works: 2003 YV Commodore (That is Cecil to you)
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    1000+ Posts bowie's Avatar
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    I suppose the question is then with a manifold that accepts a single carb, well is that carb providing more fuel then a twin carb setup to compensate for air / fuel ratio across all the cylinders, or it simply a matter of less of everything generally / thus less power.

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    bob
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    G'day,

    it's really pushing the memory cells, but if I recall, the arguments for and and against big pipes, in and out, went on forever and everyone was right....

    It's all a matter of what works for you. What worked for me on a tiny standard 10 engine was a tuned exhaust, 4-2-1, with pipe sizes that kept up the exhaust velocity - the whole system only went as far as the b pillar and was a tad raspy....

    Inlet was big, as above, and really short.

    Valves were whatever could get in the space, pistons were tiny skirt Mini Cooper with the bores ending up 3/16" apart and the pistons popping up into the gasket space - 11:1+ CR. Cam was a standard spitfire stage 3 [?] with lots of overlap and fast lift, balanced and polished combustion spaces. Head all ported and polished.

    It got a Cortina tacho, as was usual for the times, which I think went to 7k, no trouble...

    Funnily enough, believe it or not it idled ! Nothing happened until you got to about 2000 revs.....

    cheers,
    Bob

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    1000+ Posts REN TIN TIN's Avatar
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    Unless you have forced induction by a turbo or supercharger, the maximum amount of air you'll get into an R12 1289cc cylinder is about 322cc. (1289cc divided by 4).
    The ideal Stoichiometric ratio is 14.7:1 so you need to provide 21.9cc of fuel for the most efficient burn. This is under ideal conditions with perfect valve timing and no restrictions in the inlet plumbing. Putting more fuel into the mix is just going to get blown out the exhaust as unburnt fuel. Less fuel and you'll run lean.

    Or have I got this wrong?
    More fuel won't do much unless you get more air as well.
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    RTT,

    You are correct in theory with static calculations. The same as we calculate compression ratio in static format. ie air being sucked in is x amount of cc and compressed to y amount of cc. That will work with a solid like water, but air can be stretched or compressed and is never what you see when doing calcs.

    So, with the intake stroke the air is stretched because of the suction effect and then compressed. but the air won't be 1000cc in a 4000cc 4 cyl engine. (round figures). It would have been 1000 cc if it was water that is sucked in.

    That is why tricks with the camshaft is being made to keep the valve open longer (valve duration). So long duration that when the piston is moving back up after the intake stroke, the intake valve has not closed yet. So with a slow running engine it becomes in-effective and sluggish because the fresh air/fuel mixture is being pushed back into the carbs. But at say 3500rpm the velocity of the air coming in through the intake ports becomes so fast that it overcomes the push back effect of the piston going up and more air/fuel can be taken in before the intake valve closes. That is when the "cam comes in" and suddenly it becomes a very effective engine.

    Now you can get more air and fuel in because it is the air that sucks the fuel in so it will automatically increase in almost the correct ratio but then you have to work the outlet system to get rid of the additional burnt gases. And so it continuous.

    I hope I understood your statement/question correctly.

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    Default Hmmmm remembering rembering ???

    Hi
    All good discussion. My . There are some good books( what are they ??) on the subject for those who want to know more. The internet is full of sh*t on a lot of this and who knows who wrote what you are seeing !! Most stuff applies to V8s or Jap crap.

    From my memory a single dual sidedraft Weber on a Lynx manifold, extractors and some other mods is a great easy drive and tune daily driver. The Reno motors were bullet proof and responded to a bit of a tweek and produced the goods for a fun sporty drive.

    The answer is, always to mod as appropriate for the driving required. Keep the cam reasonable, keep the venturies not too big, and the manifold and extractors a sensible design that is technically correct. Then rejet the carb properly so it runs well as it should. This is the failure of many I fear, as if it runs then they just drive it. I spent many a mile driving with an old thermal exhaust analyser up the pipe rejetting modified cars. Rennos mainly. The owners were always so gratefull and came back singing the praises and the economy had returned as well
    Good luck Jaahn

    PS RTT. The only job for a carby is to supply the correct fuel for the air going in. Not dump in more or dribble it in but meter it correctly and mix it for every type of running. The fuel must match the air going in and the air fuel ratio varies depending on the loading and other factors.
    The ratio is based on mass of fuel and air, not volume. "21.9cc of fuel" every stroke would empty the tank quickly
    Last edited by jaahn; 4th September 2017 at 09:58 AM.

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    1000+ Posts bowie's Avatar
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    I love the conversions above, but just as a community announcement, in case one wasn't ware.

    https://www.dellorto.co.uk/shop/car-...ngle-dhladcoe/

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    Quote Originally Posted by bowie View Post
    I love the conversions above, but just as a community announcement, in case one wasn't ware.

    https://www.dellorto.co.uk/shop/car-...ngle-dhladcoe/
    Hi bowie
    Of course that manifold is not a crossover design. Just saying !! In case people think it is the same design. IMHO there are some "wrinkles" in a good design and also the port design. So depends on what you want, and how much work you want, and the end result you want, a Lynx crossover on an 8 port head would be superior. Torque and flexability springs to mind
    Jaahn
    PS dual twin throats on individual runners always sounds just great on the go

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    1000+ Posts bowie's Avatar
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    So a cross over design.. a common collector close to the cylinder entry with 2 inlets, as apposed to a channel dedicated to each port?

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    Hi bowie
    The theory behind the 'crossover' manifolds is this for a 4 cyl. Two cylinders 1 & 4 are piped to one throat and two cylinders 2 & 3 are piped to the other throat of the dual throat side draft carby. This is achieved by the design of the cast in runners 'crossing over' the other runner where necessary.
    The idea is to get the firing order of the cylinders evenly spaced over the two throats so they all get equal suction on the carby and even filling between the cylinders and equal mixture too. Make it run smoother and better. As the runners are also usually a bit longer that helps the torque also. Not perfectly all equal runners but pretty good really and they worked well.

    The fly in the ointment is the port arrangements on those motors as they went back to siamised ports again. So the perfect arrangement is again compromised but still works OK. The best is the 8 port heads of the 956 R8 and 10S motors. I think I remember You could put in a partition if you wished to improve it and seperate the ports.
    Jaahn

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