Midsummer mid-engined madness

car-garden-021Back home now with the Fury, I’ve been taking the time to check carefully the engine installation that we did in rather a rush in the Brands pit garages. Alarmingly, the propshaft bolts were, not loose, but not exactly tight which is a bit worrying. All the same, the car should be easily back together in time for Mallory which isn’t for a month yet.

In the meantime, I seem to have had a rush of blood to the head. I’ve been thinking for a while about building another car. The reasons for this are not entirely clear and to some extent, if I’m entirely honest, it’s because I feel like building another car. There are, though a couple of other issues about it all where there’s a more sensible rationale

  • car-garden-019A mid-engined car would be interesting. Obviously, all “proper” racing cars are mid-engined for various dynamic reasons. For RGB, the obvious advantage is really improved traction on corner exit; essentially because there’s more weight on the driven wheels.
  • The class B car has been a reasonable success. However, I don’t like the socking great lump in the bonnet. What’s more, although many people said it didn’t compromise visibility I find that it does. There’s a couple of corners, Graham Hill at Brands and the corner onto the start/finish straight at Anglesey where I find the bulge completely obscures the bit of track that I want to look at. That isn’t too big a deal, but it is annoying.
  • The weight limit for a mid-engined car is 30kg higher than that for front engined cars. If I could build a light mid-engined car, and fundamentally, at least, that ought to be possible. I might be able to get pretty close to the weight limit.

car-garden-034So, I’ve been looking around for a while for what to build, albeit in a rather desultory fashion. I’d decided that I wanted to stick with class B. The problem with class A is the increased complication of going dry-sumped, which I really can’t be bothered with. I was essentially left with thinking about the Spire. This is quite nice, although I don’t really like the styling, especially in wing-less RGB form where, frankly, it’s butt-ugly. What’s more, I’m not impressed by the lack of side-impact protection in the standard chassis; although that’s admittedly easy to fix. The biggest problem, though, is that I can’t fit my legs in it. This might be sorted in the latest version where they’re turning a bike engine installation around so that it uses a chain rather than a prop and a diff. That should mean that the engine compartment could be smaller meaning the driver could move back a bit. Mind you, that’s a big change to the chassis and bodywork which may not be feasible

And then I started reading about the Sylva Spectre. Sylva, which is really Jeremy Phillips, is the original source of many kit car designs, including the Fury. I have wondered in the past about building a Riot, which is a seven-style car with a bike engine in the rear. Sevenesque cars have never done too well in RGB though, the paddock hypothesis being that the aerodynamic value of a full-width body is quite high. The Riot chassis has always seemed a pretty sound design which was always attractive. Not exactly pretty though…

car-garden-045The new Spectre though, is very interesting. Essentially, it’s a Riot chassis, albeit with some additional triangulation and a little more width for the, errm, more capacious driver. On top of it is a body that, at least in my opinion, is absolutely drop-dead gorgeous. There’s some pictures of it scattered through this page for you to see.

I went up to Jeremy’s place a couple of weeks ago and spent a while looking at the car. I then went again last weekend and have decided to build one for racing next year! This is a bit of a leap into the unknown as there aren’t any Spectres at all in the world (the red one shown here is not yet a runner), and especially not any ones racing so it is a bit of a leap. In many ways I’m relying on Jeremy’s reputation. There as a rumour that the weight distribution was too rear-biased. However, on talking to Jeremy he says that a Riot comes in at 55/45 (rear/front) which is just about what you’d want for a race car.

It has to be said that the Spectre isn’t really a proper race car, whatever that means. However, I really like the fact that RGB, in particular, is a collection of different looking cars and this seems to fit that mould rather nicely. I might change my mind if I end up going slower than I do in the Fury, of course.

spectre-rolling-chassis-003The Spectre chassis looks like a pretty nice piece of work, you can see what’s really under there in the photo here. Note the side impact beam, and the rather nice ways it’s triangulated into the chassis vertically as well as horizontally with some little sacrificial members as well.

It’s clear that looking at the chassis although in many ways it’s clearly a descendant of the Fury there’s many things that are done rather better. For example, the front rocker arms don’t have the problematic roller bearings that the Fury ones have. What’s more, they’re sensibly spindly. Hopefully that’d mean in a crash the rockers would die but the chassis wouldn’t.

pedal_clearanceIn order to fit me in, I am going to have to be a bit careful about various things. On the Fury I extended the pedal box considerably from the standard version. It’s harder to extend the Spectre ‘box because it’s pretty close to the rear mounting of the lower wishbone as you can see in this photo. However, there is about 50mm or so and I think that’ll be OK. I am going to have to arrange to get the pedals as far away as possible though, as you can see the normal arrangement is for pendulum pedals. It really wouldn’t be possible to have floor-hinged ones as the master cylinders would be in the way of the front suspension.

In order to resolve these issues, I’ve arranged for Jeremy to deliver me an un-finished chassis with the pedal box area essentially left off. I can think sit in the chassis and work out where things go.

Interestingly, Jeremy is in the process of changing various bits of the design. In particular, he’s changing the uprights that he uses. The front of the rolling chassis above uses Escort MkII uprights are the front (pretty much like the Fury) and Fiesta front uprights at the rear. (The Fiesta is a FWD, remember, so it makes sense to use such things atΒ  the back.

However, Jeremy is moving away from these, mainly to guarantee supply and also because he’s concerned about the longevity of the rear uprights. He’s changing the fronts to use Triumph Herald uprights. That sounds like a retrograde step but they’re made in large quantities still, not least because Caterhams (following the original Lotus 7 design) use them at the front. At the rear, he’s using a custom fabricated steel upright. Perhaps not as light as it could be but hopefully more robust than the ones on the Fury which have bent over and over again for me.

my_riot_0486I’ve got a stack of things to learn about with this car. The driveshafts will be related to ones from, again, the Fiesta and I’ll need to learn about those. I’ll need to sort out a chain driven diff. Some people go about this in a simplistic manner but I think the easiest thing to do is to buy Quaife’s chain driven diff which is about Β£500. I will need to make a carrier for that though. Jeremy has an approach to this based on hanging a triangular frame off the back of the engine which carries the diff. The photo here is from another Riot build website and shows the Quaife diff in between Jeremy’s support frames. This should work OK and hangs the diff completely off the engine which has its attractions. However, there is some evidence that things work better when the diff carrier is also restrained to the chassis. What’s more, adjusting this carrier looks pretty tricky as it’s done which those four bolts that you can see at the bottom of the photo. This’d be fine for one-off installations but one of the huge attractions of a chain diff is that you can easily change the final drive ratio, especially if you make it easy to take off the diff sprocket by using a split sprocket.

Hence, I’m thinking that I could use something like a swinging arrangement with a turnbuckle to adjust the chain tension. Such arrangements are common on other cars and doesn’t seem too hard to engineer.

So, I’m getting all excited about this. I think I’ve got enough time to sort it all before next season. Mind you, I need to sort out the garage and sort out what to do with the Fury. Anyone want to buy a class C or class B RGB Fury?

13 thoughts on “Midsummer mid-engined madness”

  1. Tim

    A Swinging arrangement for the diff is much the best way. Dead easy to set chain tension, just got to make sure its all in line!

    Matt

    1. Yeah, the obvious fly in the ointment is making sure it’s all parallel to the engine and chassis. Actually, the neatest arrangment I’ve seen is done by mounting the diff in eccentric housings that you just rotate to get the desired tension. Machining it would be, to put it mildly, rather hard though, as would keeping it parallel…

      T

  2. Great plan.

    I always enjoy your builds.

    Regarding mounting the diff and fiesta driveshafts etc etc.
    I found an interesting book that includes a fair amount of detail on all this in hill-climb applications where rear engined bike engines are old-hat. Its not the greatest book, but it does have some nice pictures. How to Build Motorcycle-engined Racing Cars (Speedpro) Tony Pashley.

    I’m looking forward to you getting started!

    Matt

    1. I hope I can live up to your faith in me. Yeah, I’ve got the Pashley book. I reckon it’s pretty good with lots of good real world advice and, as you say, lots and lots of very useful photos. Sometimes, it’s a bit hard to figure out what he’s banging on about though. The idea about the eccentric mounting for the diff came from this book in fact.

      I’m looking forward to getting started too! πŸ™‚ I really, really, ought to tidy the garage up first though.

      Tim

  3. Weird, I’ve got the Pashley book too… πŸ˜‰ I suspected the eccentric diff mounting might have been inspired by that book. Looks like hard work compared to a pivot and turnbuckle, although with a decent rotary table I reckon it wouldn’t be too hard to machine – just use the rotary table to do the outside of the housing, move the X wheel a bit to one side and do the inside. Requires a decent mill and a sizeable rotary table, but I believe that The Collective has these available.

    Would it be worth asking for JP to provide you with the bits of steel that would otherwise be used to make the pedal box, so that you can fettle it to suit rather than making it from scratch?

    And if you want to IVA the Fury, the headlamp dongles of doom are here sitting unloved and unused…

  4. I like the look of the new car, sort of like the love child of a Lola T70 spyder, a Fury and an old Ginetta! Should make next season interesting anyway. What did SWMBO say? πŸ™‚

    1. Glad you like the car.

      As usual, she said something like: “why don’t you stop faffing about and just order the thing?”

      πŸ™‚

      Tim

  5. In the words of Monty Python “You lucky b*****d!”. So, do what she says, stop faffing!!

  6. Hi Tim, I too have been to see Jeremy and fell in love with looks of the Spectre. I run a Fury with a 2003 R1 which I have used for track days and have just started sprinting. Which engine will you be putting in the Spectre? I understand from Jeremy that an early R1 fits fine but some other bike engines are longer and need an extended wheelbase chassis (by 60mm). This of course means lengthening the bodywork by an equivalent amount. Too much hassle in my opinion!
    I shall try to follow your progress as I would love to undertake another build.
    David

  7. Tim,

    Great to see another build on it’s way…I look forward to the web updates…

    Alex

  8. Hi Tim,
    Good plan – like the look of the Spectre. The Fury has in that sense proved a good testing ground for you to learn about the art of race car maintenance. Now you can go out and do it as you intended from step 1. At least at any rate the bodywork should be lighter ;o)
    Anyway, was thinking about your chain tensioner issue and maybe the Global system might be an option. Simple, but effective I thought. The engine sits in a cradle that slides fore-and-aft on runners. This is then bolted on a friction basis and held in place with a large bolt at the back. Much like a kart system.
    I was forever changing sprockets with that thing (albeit fronts) and never had an issue.
    My 2p.
    Jon.

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