There’s another race meeting coming up so I needed to sort the Fury again. After Silverstone I was concerned that I might have deranged the suspension after narrowly missing a spinning Duncan by escaping over the huge kerb at Becketts. I noticed at the weekend that the F1 people were whinging about Monza having put some huge kerbs in. Serves them right, I reckon.
So, I tipped the Spectre chassis on its side-it’s still light enough to do that-and put the Fury in an accessible position and spent a merry 5 hours checking the suspension alignment, which all seemed to be fine. Hmm, that was a waste of time then.
In celebration I even washed the car, as above. What’s to bet that it pours with rain when we’re going to Snetterton and it gets all grimy before I even get on circuit?
Something else that happened at Silverstone was the the GPS receiver for the DL1 failed. This was rather surprising as it’s just a potted lump of electronics and as such you’d expect it to go on for ever, more or less. Luckly I had a spare one as I’d been concerned that something was wrong with the original one some years ago. So, I put the old one back in, this was in the assembly area before qualifying, and it worked fine. I’ll have to hope that this one works now.
I have been wondering what to do about data logging in the Spectre. Most likely I’ll just transfer the DL1, or buy a new one. However, the quality of Race Technology products seems to have gone down recently, especially after the problems that several people have had with the display products. But then, I’m not sure what I’d do instead.
All the same, I checked the GPS receivers again in the garage and, sure enough, I did have a dead one (or perhaps one with a a dead cable). I’ll stick with the original one for a while.
Back in the land of the Mysterons, I have finally sorted out where I want to put the rear ARB, which is sort of at the top rear corner of the chassis. With that sorted I’ve welded some tabs to the chassis to which I’ll bolt some mounting blocks when I’m actually assembling the car. The only problem is that I hope I’m not putting something where I want the exhaust to go. I’ve also got to weld some actuating tabs to the upper rear wishbones. In fact, I need to do that for the front lower wishbones too, as well as making up the actuating arms. That should be pretty easy though.
One of the things that’s been concerning me slightly about the Spectre is the width of the cockpit for the driver’s capacious bum. Although he does fit tolerably well it could be a just bit wider; it is actually a bit narrower than the Fury one.
There’s a pretty obvious resolution to this in that the centre “tunnel” of the Spectre isn’t really there for any obvious reason other than for routing the coolant pipes down it. As such it could easily be quite a lot narrower. So, after much humming and harring I decided to do something about it. So, I cut off the bottom of those two tubes that you can see in the photo and yanked them using one of my favourite tools, a pair of luggage straps, forcibly in the direction of the passenger side of the car.
With that done by about 40mm or so, I welded a new plate to the floor of the “tunnel” and welded a new harness mount plate in. Luckily, I’ve got a collection of these, as supplied with harnesses over the years.
With that done it all seems pretty strong (in fact very strong). It’s not spectacularly pretty but it should do the job.
I’ve been continuing looking at what the roll-cage should look like and I’ve finally come up with what I thing I want to do. This is pretty much what I did for the Fury although this time I will weld the main parts of the 
cage into the chassis. If only because when it’s welded it’ll distort anyway which is a bit of pain when it comes to bolting it in.
I’m intending to make the backstays removable by the approach of welding a threaded bush into each end of the tube and attaching a clevis that will connect to a tab welded onto both the chassis and the cage. The Blue Book permits such things and there’s certainly plenty of cars around that do this sort of thing. The Blue Book is pretty unhelpful though; it says the bolts attaching the removeable strut have to be of “adequate strength”. (I’m not making this up…) Given that elsewhere they say things like a bolted in cage needs attached with 3 M8, 8.8 bolts this is bizarre. However, I did some calculations which say that a single 12mm 12.9 bolt has sufficient shear strength to decelerate an entire 500kg car at over 10g. As such, that should be fine as there should be rather more than one bolt doing such work anyway.
With all that done, I’ve given the dimensions to Jeremy who has a company who can supply the tubes, and bend the front hoop which is the tricky bit. He reckons he can get the tubing fairly soon and in the meantime I can get on with things like the engine mountings.
Won’t the repositioned tunnel sides make panelling it a bit of a PITA? Admittedly, not perhaps as much of a PITA (literally) as leaving them in their original positions, but it looks as though the side panels will have to be fairly funkily shaped in order to meet up with the various tubes.
Does the swinging rear stays plan mean that you’ll have to undo 2 bolts every time you want to poke at the engine, or does when you say clevis does this mean you’ll be using clevis pins and a spring clip/R-clip? Having to wield spanners just to check the oil levels sounds like rather a faff…
I don’t think the panelling is changed at all, apart from a slightly larger flange on the rear of the side (of the “tunnel”) panel.
The plan is to cut slots in the rear deck so it’ll fit over the rear stays; it’ll probably have to slide in from the rear so that the slots are parallel with the car’s axis. In fact, I’ll probably make a virtue out of it and made an ally panel under the slot to support the front of the rear bodywork. The swinging legs will mean that the central tub can be taken off as a single piece as it ideally fits around the roll cage, like the Fury one does. The alternative is, of course, to just make the tub in two parts anyway and that is still an option which might actually be quite a good idea when I come to look at having to lengthen the bodywork anyway. Be nice to have the option though. I did wonder about using pins and a spring clip, but I’m not sure I’d trust it, and the relevant diagram in the BB has a proper bolt there. As you say, having to have a spannner to check the oil level would be a real PITA…
T
What about the attachment of the bottom edge of the transmission tunnel side panel though? If it’s a flat sheet you can’t rivet it to the outside of the bottom chassis rail, otherwise you’ll undo all the hard work to increase the width of the seating area. I suppose you could make a return and rivet it instead to the top of the bottom chassis rail.
Your plan with the slots in the rear deck was the same conclusion I reached on how to do it on my (entirely imaginary) Spectre. I hadn’t appreciated the bolt-on stays were to allow you to remove the centre tub. I think I’d be tempted to cut away the section of the centre tub which goes around the cage (the bit which the seatbelt bolts pass through) and make a flange with a Bighead fastener in it for the centre tub to attach to in order to hold them together.
| I suppose you could make a return and
| rivet it instead to the top of the bottom chassis rail.
Exactly. In fact the plan is to put the cr[ou]tch strap bush in that same plate. Admittedly the top of the side bit is 25mm above the top of the centre bit, but that’ll be all covered in foam anyway.
As to cutting the tub up, there’s something about that that I just don’t like. I may convince myself that I’m being daft though; I ordered the roll cage steel today so I’ll have to come to some conclusion soon. I think much of my problem is that I’m going to have to modify the tub anyway to stretch it backwards and I’m wary about ending up with a jigsaw of bits of GRP that don’t fit together even as well as one needs in a race car.
Look forward to seeing your front anti roll bar solution – it’s something I’ve been toying with for quite a while on the Mojo. Ideally the front springs could do with being a bit softer, but then my roll stiffness distribution would be very rear biased. A front ARB would help balance it out.
If the Mojo suspension is anything like the Riot/Spectre one then my calculations show that it really needs an ARB at the front. In particular, as you say, to keep the roll stiffness distribution sane. (Or, the “magic number” as it’s called in certain race circles. 🙂 )
My approach is going to be pretty much as I did for the Fury: a bar running in aluminium blocks bolted to the chassis, two actuating arms welded to the ends of the bar (previously I’ve just bent a solid bar but this time I shall have separate arms on the ends of a solid, or perhaps tubular if I can get the right material, bar), and actuating rods made up of aluminium shafts with 5/16″ rod ends the ends. The rod ends will connect to one of a series of holes drilled in the arms and a tab welded to the bottom wishbone. The issue is always to get the actuating shaft long enough so that the bar doesn’t bind up at the extremes of travel. It’s usually pretty easy to do for the front ARB as there isn’t a drive shaft in the way.
T
🙂 re the ‘magic number’!
Your plan sounds good. The front end of my Mojo is slightly different to yours (outboard shocks & sierra uprights, unlike later Mojos/Riots/Spectres) but I think the geometry in terms of roll centres etc is likely to be pretty similar.
Do you take ARB commissions? 😉
The term “magic number” comes from these people: http://www.optimumg.com. They say that experience is that the roll stiffness distribution (the MN) should be able 5% higher than the F/R weight distribution. Experience is that that isn’t far out as a start.
Oddly enough, building ARBs for people isn’t part of my life’s plan. Well, unless you paid me enough anyway and that’d make it the world’s most expensive ARB.
Come on though, it’s easy to make. I know you ought to use spring steel but cooking stuff seems to work fine!
Tim