A fellow racer that have been participating in the Swedish Street Week
and also some Drag N Drive events in the US with his Camaro needed to improve his car.
As we all know reduce of weight is the best way to increase performance,
rather than just to slam it with some extra hundreds of extra hp's worth of nitrous.
He had gotten a brand new aftermarket hood for me to make moulds from.
The first one was a bit damaged in transport so he showed up with a pair.
I used the good looking one to make moulds of the outside. The damaged one I could remove some
edges that I didn't want in the inside mould.
Step one was to prepare the fine one, polishing it as far as I could.
It had only a rough coat of transportation paint to prevent rust during transportation.
The idea of polishing it was rather to get a good release rather than to obtain a perfect finnish of the final part.
That polishing will be done in the mould later on.
Here I add flanges and put on the release agent.
I use a release agent called CR1. It shall be applied in 6 coats
with 10-15 minutes in between. Done in less than two hours and with none of the backsides PVA could give you.
The build up of this release agent is as close to zero there can be.
I make my moulds with regular gelcoat, regular polyester and fibre glass mat.
Have always done it that way and has always worked out well...
...until perhaps this time. More about that later on.
If paying attention to details you can see it looks like several moulds,
and that is exactly the thing. I had to make this mould twice.
The mould of the outside looked good and the original part didn't get a scratch. (neither of the times)
I put in bolts for the hood lock and the hinges and carefully pulled in the bolts to make the hood come out of its mould.
There got some air in some of the edges between the gelcoat and the fibre glass
that I had to fill with fibre glass putty. No big deal.
I do most of my carbon parts with wet layup and vacuum bagging technique.
The basics is that you paint the mould with epoxy and then put in the carbon cloth.
The pattern of the cloth is very fragile and the cloth pretty much tacks to the freshly painted mould instantly.
That makes it more or less a one try operation. If the cloth have to be lifted and repositioned to get a better looking pattern,
most of the times it ends up looking even worse than before so its better to stay with the first try or rip it all out of the mould
and start all over with a fresh cut pice of carbon.
Looking into details you can see there appears to be more than one different castings?
Yes I made more than one since the first one didn't come out as good as I wanted it to.
The inside of the outside skin looked perfect. (They usually do)
The inside.
At first I covered all holes with tape. The bigger holes were covered with aluminium plates.
All slips and joints were filled with filleting wax. Very similar to child's modelling clay
but in every way better and easier to work with. Release agent were applied between taping and claying.
The inside had so much shapes that I didn't need any extra strengthening's on its mould.
There was not much need of any filler. Some smaller issues, grinded off some edges and polished it.
The inside is such an advanced shape I didn't dare to first paint the mould and then try to get the carbon in nicely in one hit,
so I put the carbon in the mould dry, then opened and painted one half at a time.
Just adding epoxy on top of the dry cloth is a bad idea in general.
The normal and best way for the epoxy to wetten the fabric is to let it suck through the cloth
from the mould surface and upwards towards the vacuum bag. Not the other way around.
I must say I was surprisingly happy with the outcome.
A separator has to be made, making a channel between the air filter hole and the holes in the rear of the hood
which also works as a shield for hot air from the headers and radiator.
As a bonus it connects the inner and outer part of the hood making it stronger.
The separator was made free style and was laminated at the same time as I put in nut inserts for hinges and hood lock.
The nut inserts is nuts in A2 quality that I welded on steel plates, then the plate is drilled manually.
I put a small piece of carbon between the nut inserts and the part.
Screw them in place with these wax prepped bolts and add two layers of carbon on top of that and end with some peel ply.
When the epoxy is fully cured and I can rip off the peel ply, this is what it looks like.
It will be inside the hood in the end so no one will ever see it again.
After that I cut up all holes. One idea might have ben to keep the carbon in the holes.
The weight difference would not be big and since I was planning to cut them away from the beginning
I could cut the fabric as I made the casting. That reduced the risk of bridgening in other parts of the cast.
On top of that with the holes done it looks better. More like stock.
Here a big mistake was done. Or several actually.
I glued the inside to the outside skin, without loosing the skin from its mould at first.
I did so in order to make it absolutely remain its shape. The problem here is that when both parts are put together
they get so stiff it will be hard to de mould them. On top of that I used an adhesive called VM100 Black.
It is a bit too quick for such a big thing and when it cures it can get so hot leaving prints on the outside.
Post curing.
For a hood to withstand the engines and suns heat it is recommended to post cure it.
According to my supplier post curing should be carried out in 60 degrees C in 6 hours.
I build a curing oven with a small heater inside. I couldn't get it to more than 57 degrees so I went a got a bigger fan.
Now I got it easily to some 70 degrees C. Perfect I thought. Left it to cook for some 6 hours as I did other things.
As I the day after was about to de mould my master piece the part was stuck to the mould...
...and I really mean stuck. Took me a great deal of time and many hours of brutal forces to get it out of there,
resulting in the part cracking on several points and large areas of the mould followed stuck to the part. I later heard that 60 degrees C were probably a critical heat point for regular gelcoat,
so to play it safe, never exceed 60 degrees. Lets say, lesson learned.
This is why I had to make a new mould of the outside skin.
With the hood looking awful and needing of repair it was very light. Only 5,4kg.
If painted it will work for race applications but thats not really how it was ordered and definitely what I had in mind.
For my second attempt I added two strings of aramid honeycomb in the middle.
The first one felt a bit weak there. At first the aramid is glued to the part.
Then its covered with on layer of carbon, peel ply and vacuum.
Gets to be strong as a board.
This time I post cured it with only the 57 degrees fan for 6 hours, took the part out just to check it,
placed it back in its mould and then glued the inside into it. Now with a (for me) new glue called Permabond PT326.
This time it all came out as I had imagined the first one should have.
Some edge trimming. Thats all.
This one ended up allot better than the first one had ever done even if I had gotten it out of its mould unhurt.
The backside of this beauty is its weight. 5,9kg witch is 500g more that the damaged one.
The reason for the increased weight is not only due to the aramid and its cover with more carbon.
I also sealed the edge around and between the parts with glue this time.
On the first one I tried to poke in epoxy wetted carbon around the edge but I wasn't satisfied with how it came out,
so I tried the glue this time instead. Even if there was a weight addition to it I feel it was a better way.
Heavy or not, I can feel proud of what I had accomplished.
The pattern is not perfect at all places around the edges. Sometimes the pattern gets stretched,
there do exist some pinholes, there are places needed to be filled in with epoxy or clear coat...
...but I did this part my self in a suburb to Stockholm. No exotic super car-manufactorers was involved.
Its fun when you can see what you can accomplish.
