In order to have a solid mount for making the bonnet, I started the slam panel. It needs to be strong, so a simple piece of tin would not be enough. This panel needed to be part of something bigger, how big I didn’t know, so I started by cutting the outline shape and rolling in a simple pattern.
Even without a clear vision of what I was making, this grille shell was going to be a massive challenge. – my biggest yet
As it stood, it would not be anywhere near strong enough. I did not want something that weighed a couple tons, so I was going to make the whole grille surround and slam panel into one combined panel. I used 18awg steel and to stop everything from ‘oil canning’, I used the bead roller. The under-side of this panel will need a lot of support.
The internal framework has a secondary function. I want all the air passing through the grille to either go through the radiator or into the twin air filters. There will be an under-tray that will continue to guide the air through the oil cooler and over the engine.
I’d previously done some measurements and sums that said cooling on this car was marginal. I therefore needed to ensure all the incoming air could not simply pass around the radiator. Whilst stationary, I want air to get sucked through the twin fans, then over the engine and not just straight back out the front. I want air to exit either through the louvres by the exhaust or out the vents in the side of the bonnet.
The slightly rusty ‘U’ section the slam panel sits on is just for mocking-up purposes. This shape will eventually be formed by the bonnet sides and the grille shell.
The bonnet edge will not be straight. It will come down similar to a 1937 Chevy.
Currently I have a P38 serpentine Rover V8, with a single air filter. I’m swapping this for a Thor V8 with cross over plenum and twin MGF throttle bodies. With this set-up, I’ll have two cone shaped 70mm air filters. This is not a performance upgrade, this is purely down to having a symmetrical looking engine bay.
With these pointing forward behind the grill, at speed, air will be force fed into the induction system.
As always I’m just making this up as I go, so I started by cutting out the hole for the radiator fan and mocking up the air filters. I wanted the filters to provide a solid mount for the slam panel. So I started with some cylinders to direct air into the filters.
There were quite a few pieces of steel going into this panel. I had an approximate idea of what I wanted but in reality this was a fluid design that evolved with every piece. I’ll work out one side, then mirror it when I’m happy.
I’ve developed a technique, that I call ‘Gaffa tape modelling’. I’ll cut a hole; like around the fan; then bridge said gap with hundreds of strips of tap. I then take a knife and cut a piece out I can use as a template. As you’d expect, they don’t quite lay flat but often it’s surprising how little shrinking and stretching a distinctly contoured panel needs to become 3D.
This tape is one side of the fan surround. I simply flipped it to make it’s mirror. With it’s steel counterpart, just 6 pulls of the stretcher and a bend around a fence post gave me the shape I wanted. Maybe for my next fabrication challenge I’ll go for a bigger jigsaw with fewer pieces.
Around the hole for the radiator fan, I’ll put some rubber edging. Hopefully that should stop any annoying squeaks and help prevent any wear. When I tested the air-flow through a radiator, I was gob smacked by the improvement an air-tight fan shroud made. Ensuring all air passed through the radiator dropped the cooling time from 121 to 38seconds. If the incoming air could simply pass around the fan, that effort gone into the shroud is wasted.
Plus, it gives the nose that Thrust 2 rocket car look.
I had to drop the air filters by nearly 2″, which puts them pretty close to the radiator. The gap between the air filters is where the expansion tank will sit, so I’ll need to cut another cut-out to clear that.
When I want to recess an odd shape into another shape, the hole I need to cut isn’t obvious. I therefore shine a laser pointer through one object to see what outline it leaves on the other.