Carbon Fibre Bonnet

Whilst researching 'carbon' stuff, I found that Ultimate Carbon (along with a number of other carbon Caterham bits), also manufactured an S3 louvered bonnet (Ultimate Carbon are the guys who made the bespoke parts for me/you!)...  It was advertised as pretty much ready to fit, but just needs the catch plates fitting... I asked Bryn about the weight saving, but he wasn't entirely sure, so thinking that 'its carbon - it MUST be lighter!' I took the punt and gave him the go-ahead.

At first he was reluctant as they had to get the mould out of storage or something (I can't quite remember) but after a bit of pestering he sorted out what they needed to and said he'd make it for me :-)

Here's my first sight of the bonnet - a picture of the item that Bryn sent to me prior to collection.

My first sight of the carbon fibre bonnet

It then dawned on me that I've a massive great hole in the side of my bonnet for the air filter / trackday airbox.... Bryn said it'd be fine to make a paper template up and he'd cut the hole out... 

Bonnet cut-out template

Trusting that my template was fine - he cut the hole out and cleaned up the rough edges.

Hole cut in my Carbon Bonnet for air filter / carbon track day airbox

A few days later, we met at an M1 service station car park, I handed over some money - he handed over a lot of carbon; which didn't look dodgy at all :-) but joking aside, it was pretty much central for both of us, and meant I could get my hands on the parts sooner rather than later.

I got home, checked out all of the bespoke bits (which are awesome by the way) and put the bonnet on the car to ensure it fit - and yes it fitted perfectly, thank god. 

Unpainted Carbon Bonnet on car - looks odd so needs some paint!

The car looked odd with a carbon bonnet - and the intention was never to leave it in the carbon finish, so I didn't get them to lacquer it...

Prepping and Painting
The next bit was for Dave at Daytona Coachworx to do!  Dave wanted me to be exact with the paint that I wanted (obviously) which can be a little tricky with Caterhams (so I'm led to believe).  Luckily I moaned about the quality of the factory paint job, and when the car was waiting for the fuel pump to arrive it was repainted by XK Engineering.

I rang and spoke to Gary at XK Engineering who had to look into the records, but rang me back a little later on and said the car had:-

• Porsche Riviera Blue 39e colour
• Glasurit Basecoat (which is water based)
• and a DuPont solvent based clear coat (VR-1120)

With the paint details in hand, Dave ordered up the paint and got cracking with the bonnet prep.

The bonnet was given an initial flatting.

Carbon Fibre Bonnet after initial sanding

The inside of the bonnet was then masked - love their attention to detail!

Inside of bonnet masked

With the nature of carbon fibre, there is a tendency for there to be many pin-holes and small grooves (which would show up when painted), so the bonnet was primed, flatted, and primed some more.  In the picture below you can see one of the grooves on the left edge of the louvre.

Small grooves in the bonnet to the left of the louvre

In the end, Dave put three medium coats of high build on the bonnet, and flatted with P320.  He then flatted it almost back to the carbon so as to take up as many imperfections with the primer, and not leave loads of excess on there (weight!) He then put another three medium coats over that. Again he flatted as much as he could, so as to leave the minimum amount of material on the panel before painting.  Dave said this took a long time to do due to the complexity of all the louvres.

Carbon bonnet primed, flatted, primed and flatted again to achieve a perfect base.

The primer was left to dry, and then it was time to apply the colour...

Porsche Riviera Blue 39e Glasurit Water Base Coat Drying

With the base coat sufficiently dried, the clear coat was then mixed with a bit of flexible additive (to reduce the chance of cracking) and was sprayed on and also left to dry.  The flexible additive slows the drying process, so it took a little longer to dry than expected.

Once fully dry the bonnet was polished and ready for collection...

Carbon Bonnet Flatted and Polished - Job Done

The finish on the bonnet is ace, it feels very light indeed and the colour match is spot on too!

Drilling the Rivet Holes and Fitting Catch Plates

The old rule of measure twice and cut once certainly applies when you're drilling into an expensive bonnet!  No going back now! I started off by drilling a small pilot hole with a 2mm metal drill, then opening it up for the rivets with a 4mm drill.

The catch plates were fitted with two rivets (which was a little awkward to get access to, due to the shape of the end of the rivet gun), and a small metal plate on the inside of the bonnet to support the rivet and give strength to the catch hook.

Drilling holes into my new bonnet for catch plate hooks to be fitted - measure twice and drill once!

Applying The Decals

I know the stripes on my car are pretty bright, but I like that... I've had a number of people comment on them and also contact me to find out what they are... So to avoid further questions :-), they are MACal 9807-07 Pro Super Luminous Orange and I bought them from http://signsuk.co.uk/ as they were the guys who supplied decals and stone chip protection film for Caterham Midlands.

MACal 9807-07 Pro Super Luminous Orange Caterham Triple Stripe laid out ready for application

A couple of weeks ago I got SignsUK to send me some more decals in prep for the new bonnet... Applying the centre stripe was more fiddly than I thought it would be.  The process is to wipe down the area with methylated spirits and a clean microfiber cloth to remove any residue, dust particles and to get a good clean base for decent adhesion.  Then spray the area with a little water to allow for movement if you lay the decal down incorrectly.  Peel back the underneath to reveal the adhesive, and carefully lay the adhesive in place, pushing out any bubbles that may appear and then remove the paper top layer (carefully!)

The only problem with the Super Luminous Orange is that it has a tendency to fade in direct sunlight (over the course of a couple of years), but I couldn't really notice too much difference once the decal was fitted.

I also had a few variants of the blog's domain put together a couple of years ago, and cut (again in the MACal material) to match.  I decided to go for a change this time round, and went with the more 'square' version, which I think looks good too.

New carbon bonnet domain decal applied

A lesson to be learnt - do not apply decals outside in the wind... Quite frankly I thought this would be easy but the centre stripe was a right pain in the a$$... Not only that I had a fair hangover which didn't help with such a fiddly job! 

Onto the Weigh In
My favourite bit - seeing how much lightness has been added!  You can immediately tell the difference by picking the two up, so I thought that a decent saving was to be had.

I popped the aluminium bonnet onto the scales and they weighed in at 2.956kg.

Caterham Aluminium Bonnet (with cut-out) weighs 2.956kg

Then (and in a like for like state), the carbon bonnet was on the scales, I held my breath hoping for a significant weight saving... The carbon bonnet weighed in at 2.13kg which is 826g lighter - nearly two pounds saved and is around 28% lighter than the aluminium original, so I'm happy with that. 

Carbon Fibre Bonnet (painted with cut-out) weighs 2.130kg

The final reveal

And for the final 'reveal' the carbon fibre bonnet! Which aside from the weight saving, you really wouldn't be able to tell was carbon fibre! 

Painted Carbon Bonnet with decals applied, all fitted to my Caterham and looking very good!

A big thanks to Bryn at Ultimate Carbon for giving into my continual pestering and agreeing to make the bonnet, and also 'my mate Dave' at Daytona Coachworx for doing another fab job at prepping, painting and finishing off the bonnet.

The total cost of the bonnet including painting, catches, and decals came it at just shy of £800 - which works out to £1 per gramme saved!  I'm sure there's cheaper ways of removing weight!