Fiat 126 with Supercharged Honda Blackbird power!
Project Undertaken 15th July 2010
Ivan's 126 will probably be the most insane project we've tackled to date! He wanted something very small and very powerful, but the 'generic' bike engined mini just doesn't do it for him. Ivan decided on an early (aircooled) Fiat 126 as an interesting alternative, and then sourced an ex-Radical, Rotrex Supercharged Honda Blackbird 1100cc Bike engine to go in it.... Dyno'd at 330 bhp!!
Our job is to combine the two. This will essentially involve constructing a spaceframe chassis, and fitting the Fiat 'shell over it, with bodywork mods to allow the wider track that will be neccessary.
Here is the car as we received it.
.....And stripped down! (photo shows suggested cornering technique!)
With the car stripped down it's out with the plasma cutter and grinder and out with the entire floopan. The shell will now only be 'cosmetic' rather than structural (the strength will be in the spaceframe within) so the usual care (bracing etc) need not apply at this stage - we will true the shell up with the panels during the final 'fit-to-chassis' stage.
The next step was to start designing the basics of the new chassis. This will be unequal length double-wishbone at the front, and trailing swing arms at the rear. CAD was used to design the mounting point dimensions within the space availabe. The constraints were the maximum track width we can sensibly run vs the width of the footwell (which sits between the front wishbone mounts) The wishbone lengths and relative mounting positions have been chosen to give optimum camber change during roll (given the space available). Caster will have some adjustment available via shims on the top wishbone bushes.
With the basic mounting dimensions finalised it's time to build the floor frame, and then bend up the tubes for the basic cage members. Below you can see the main hoop and one of the front legs as well as a sneaky peek at that Supercharged Honda engine!
Here we can see the cage taking shape. The fit is pefect, nice and snug to the 'a' pillars to minimise intursion into the rather small cockpit! The door bar 'cross' has been offset towards the rear to allow more space at the front for entry and exit.
With the basic 'cage' complete, attention turns to the front extension of the chassis - the area where the front wishbones attach.
Next work begins on the rear structure which will incorporate mounting points for the engine, transfer box and coil-overs. Here we see the engine hanging on it's upper mounts. The next step will be to construct a removable lower brace that will pick up on the lower engine mounts and transfer box.
Meanwhile, the rear arms have been designed. These will consist of a frontal 'tube' with threaded bosses at each end which will be mounted to the chassis via heavy-duty rose-joints. The arm will then be fabricated from laser-cut 4mm steel sections which will support a large tube & flange which will in turn support the rear hub assemblies.
In the first photo below you can see the arm being designed on CAD. The second picture shows the two front arm tubes as well as one of the rear tubes and matching flange. The third shot shows one of the four threaded bosses that will be inserted into, and welded to the front tubes to form the mounting points. The photos below then show the bosses being made.
Another major obstacle to clear was getting drive from the motorbike transmission to the transfer box. We've had a splined shaft machined in EN24T steel that fits the input to the transfer box, and a drive 'cup' (also in EN24T) made up that fits over the new 14 tooth sprocket on the bike engine. These will be pre-heated and then TIG welded together to form a one-piece drive shaft. The original sprocket cover has been modified to allow the shaft to pass through it.
With that hurdle overcome, it's time to mount the drive transfer box, and complete the rear of the chassis. The design we have come up with is effectively a 'bolt-on' rear subframe. 4 Bolts release this from the rest of the chassis, and one from the engine, allowing the whole subframe with transfer box attached to be dropped down and out of the car. The engine is then removed downwards through the space where the subframe was bolted.
The components we designed for the rear arms are back from the laser cutters. Here you can see all the parts laid out, and a rough demonstration of how they go together. One pair of side-pieces needs rolling to the correct curve and then it'll be ready for welding up. The inner reinforcers will make the arms very strong. the last photo shows one of the front, upper wishbone mounting brackets alongside a front coilover mount.
A jig was made to hold everything at the correct angles and the arms were then welded up.
Threaded bosses were then turned and mounted to the chassis - these hold the rose-joints that the rear arms pivot on. One joint is mounted vertically, the other horizontally, allowing ajustment of both camber and toe.
Mounts for the coil-overs were then made up and welded in place before fitting the hubs.
Meanwhile the front wishbone and coilover mounts have been fitted, followed by the wishbones themselves, and the hubs assembled and fitted. Temporary metal struts are being put in place of the coilovers for the moment purely so we can fit wheels and roll it around. Once the lengths are confirmed the shocks and springs will be ordered.
Here we've popped on a couple of wheels from an autograss car just to give the idea of what it will look like! There is still one final 'cross' to go in the chassis at the front, and a dash bar, but we'll need the shell back on to gauge the position of these. Next step is to get some suitable wheels fitted and cut the arches to allow the shell to go back over.
A set of Caterham wheels (thanks Grahame!) have been fitted to get the chassis rolling. Measurements were then taken to allow an initial rough enlargment of the arches so we can get the shell dropped back onto the chassis.
Then a bit more surgery to allow clearance at the front with lock applied, as well as an air intake area for the front mounted radiator. This will be joined later by the charge-cooler rad. A 'splitter' will be fabricated to duct air up through these radiators and out through a large bonnet scoop. The arches will also be fabricated in steel - the last photo shows a quick experiment at forming the large lip we intend to use with a smooth radius to the horizontal section.... This will all make sense later in proceedings!!
With the shell off again, some more trivial and uneccessary metal is removed!!
Next up is arch manufacturing! These are relatively straightforward with the right tools.... A piece of sheet steel is cut to size, before having a 30mm lip folded along the edge, with a gentle radius. A hand shrinker is then used along the lip to 'pull' the curve onto the arch. The sills were then folded up with a return lip at the bottom, and tacked in place.
Moving on to the front end, a 'splitter' is fabricated in steel, incorporating the same return edge as the sills and arches. An air intake is then cut out of the lower front panel and small lip sections made up and spot welded in place to give it a smooth radius. The area behind the front panel is then completed by panelling in the inside of the inner arches with a tapered section to duct air to the compact but very thick radiator. This will be joined by a second smaller rad for the charge-cooler circuit. Ducts will be cut in the bonnet to exhaust the warm air.
The Nearside front corner of the shell was quite rotten, and full of filler, so this was cut out and a corner sourced from another shell and let in.
Due to the wheels taking up the space the door hinges once occupied (when lock is applied) we had to come up with a solution for hinging the doors. We decided upon a 'suicide' door arrangment with the doors opening backwards. The front and rear of the doors were refabricated along with the 'A' and 'B' pillars to allow this, and the handle/latch/lock arrangment fron the driver's door swapped to the front of the passenger's door, and vice-vera. Shell fabrication is now pretty much complete - just the rear corners to make, a couple of small rot repairs around the rear window, and then it'll be making up the shell-to-chassis mounts.