• ray sherratt
    12 December 2013 at 20:18 #50560

    On the Lagonda circa 1960s I don`t know how mutch room is
    available front or rear of rad, but any modern electric fan
    needs ducting. The problem with fans placed in front spill a large amount of cooling air out to the side, usually returning
    through the fan. To the rear of the rad the fan sucks the air
    from the sides instead of through the rad. I would think the
    arrangement on the Lagonda is as the DB4/5/6. If you are
    retaining the engine driven fan, I would look at a ducted front
    fan, remember they pull a large amount of amps and therefore
    require large cable. Power it by rad switch placed in the top
    hose area, and a relay may be 2 in parallel. Startup amps
    can be between 25/30 depending on motor and fan.


    13 December 2013 at 10:28 #50561

    The setup I’ve gone with is a Revotec thermostat at the bottom outlet of the rad with a 16″ 80A electric fan which pushes through around 2100CFM , this sits in front of the rad. The Revotec thermostat is an adjustable inline type rather than the capillary type (which I think looks crude).

    The Rapide radiator is ducted on both sides, though on the engine side the cowl is designed to fit the mechanical fan. I have removed the mechanical fan as I don’t think it will add benefit when needed and may further restrict air flow. In slow traffic on a hot day the mechanical fan is spinning slowly when you really need it to be fast. I’ve only tried the new fan a few times but it seems to work well letting the engine run up to around 93 and then bringing it back down to around 88…ish.

    Also a mechanical fan reduces the HP by around 5%.

    I’ll let you know how I get on.

    13 December 2013 at 12:27 #50562

    I hope you’ve got enough electrical power to cope with that fan load as well as other stuff, e.g. at night in rain!

    13 December 2013 at 13:27 #50563

    I’ve put in a very large battery so as long as the dynamo output keeps up then I should be fine…

    ray sherratt
    13 December 2013 at 15:26 #50564

    I think you should be looking at fitting a modern large output
    alternator to keep up with demand. Battery size is relevent
    to starting demand, your dynamo only has an output
    29/31 amps if your lucky remember it is Lucas. This is the
    reasom they fitted a ballast resistor ignition systems, with
    the battery in the boot there is a large drop in volts at the
    coil on start up. Even the converted dynomo/alternator units have a hard time with demand.


    13 December 2013 at 15:47 #50565

    Yes, good points. I’ve fitted a 12V coil and by-passed the ballast resistor but the 6V system makes a lot of sense. Was it generally dropped because of alternators or for some other reason? I could easily fit a 6V coil, would it be worth it?

    I was planning to change the dynamo for an alternator but the Lucas ‘Special Equipment’ C45 is a lovely looking dynamo which suits the look of the engine bay (along with the Lucas RB310 voltage regulator). It is a reversible upgrade but personally I love those characteristic items in the engine bay which show quality engineering and technological advances of the day etc such as the Girling Servos, Dynamo, PHH44’s (carbs) and so on. It’s getting the balance of practicality and authenticity right which is part of the challenge.

    ray sherratt
    13 December 2013 at 20:23 #50566

    The ballast system was fitted to get round the problem of low
    voltage at cold cranking speeds. The coil is an 8 volt one which
    is suplied with 12 volts during cranking, if you look on the
    starter solenoid there is a connection usualy opposite the
    ignition switch cranking connection, this supplys 12 volts to the
    output/coil side of the ballast resistor in creasing the secondary
    output of the coil. If you are concerned about looks have a
    thought about the dynamo/alternators that are on the market.
    I dont know the amps output, but I think if you look at increasing the speed whith a smaller pulley it should keep the
    output up. The control box can stay and the wireing there will
    be instuctions with the unit. Your ground clearance should be
    6″ under the exhaust system.

    14 December 2013 at 14:27 #50567

    Modern Dynamo/Alternator. Just a warning to anyone intending to fit one. Check the output on these modern lookalikes. Usually they are at least 40 amp + and depending on how your car is wired you may damage your ammeter. I understand that for our type of cars you should get one that delivers no more than 30 amps. However I think that this type is no longer available. I bought one some years ago for a different car and now need another one . However I cannot find a 30 amp one anywhere so am uncertain what to do next. Anyone have any more information on this subject ??

    16 December 2013 at 16:56 #50570

    I think the C45 dynamo in the Rapide has a maximum output of 25A so probably not worth getting at 30A alternator instead (if one were available). I’ve not seen any retro alternators with an output of less than 40A and the ones I have seen are not the same size as the Rapide one – which is extra long. Could you fit a C45 (which is available in two sizes)? I’m assuming you don’t have a Rapide and therefore have a lower output dynamo…?

    ray sherratt
    18 December 2013 at 19:56 #50573

    According to the Rapide data I have tha dynamo should be a
    Lucas C 48 with an output of 29/31 amps. I know you like
    to keep things looking as factory manufactured under the
    bonnet. Have you thought of driving an alternator a small
    Japanese one, from the diff/prop flange. I`m shore a man
    of your capability can make a bracket to bolt to the diff
    cradle. Run the alternator in parallel with the dynamo.
    Demon-tweeks.co.uk have atlernators in stock at ?175+
    the dreaded. Or they do have converted Lucas C45 dyno/alt
    neg earth output 50/65Amp, for the sum of ?335+ VAT.


    19 December 2013 at 11:22 #50574

    Hi Ray, you’re right – it is a C48. – oops! An electric fan like the one I’ve fitted will put about 7 amps, but only when required. I think I’m going to stick with the dynamo and see how it goes… I would consider a conversion though!

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