Stuart, no apologies necessary; all very good information, thank you. So, continuing the thread drift...... 
Phil wrote that karts deliberately have flexible chassis but I don't think any car with suspension benefits from chassis flex. It is my thinking that for a suspension to be set up and to operate predictably, it must be mounted to a firm platform that holds everything in position.
I remember that Arthur Mallock used a crude but effective way of checking torsional deflection of a chassis which involved a bar and a weight. I thought I might check a standard chassis and then experiment with boxing and further stiffening to see what benefits can be obtained. One obvious way to reduce twist is to build a spaceframe for the body but this will add weight and my aim is to build as light as possible. I very much like the way Ian has tackled the rear firewall which must add stiffness but still allows access. I would like the transmission tunnel to be removable so I doubt that will contribute much to stiffness. There's nothing in the way of bracing to prevent chassis lozenge so perhaps a stressed floor might help. JO 66 has an under tray so this might be a possibility. I'm not sure this is practical but I would like to make the underpinning body hoops in aluminium rather than steel tube to produce a light car. Extruded T or L section would work providing that once annealed I can shrink and stretch it to the desired shape.
John
Phil wrote that karts deliberately have flexible chassis but I don't think any car with suspension benefits from chassis flex. It is my thinking that for a suspension to be set up and to operate predictably, it must be mounted to a firm platform that holds everything in position.
I remember that Arthur Mallock used a crude but effective way of checking torsional deflection of a chassis which involved a bar and a weight. I thought I might check a standard chassis and then experiment with boxing and further stiffening to see what benefits can be obtained. One obvious way to reduce twist is to build a spaceframe for the body but this will add weight and my aim is to build as light as possible. I very much like the way Ian has tackled the rear firewall which must add stiffness but still allows access. I would like the transmission tunnel to be removable so I doubt that will contribute much to stiffness. There's nothing in the way of bracing to prevent chassis lozenge so perhaps a stressed floor might help. JO 66 has an under tray so this might be a possibility. I'm not sure this is practical but I would like to make the underpinning body hoops in aluminium rather than steel tube to produce a light car. Extruded T or L section would work providing that once annealed I can shrink and stretch it to the desired shape.
John