I have moved the thread here as the direction has turned onto your actual cylinder you've made so its more of a project now.


The tank does look to have a nice weight saving.  The proof in the pudding will be leak tight fittings and the pressure testing.

Definitely ensure it is tested professionally so that if it fails there is adequate shielding around the test rig to avoid splinters flying out.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Yes  -- very nice weight saving there ..

I have a few points though:

1:
I would have used the Kevlar mix cloth on the outside of the tank!!   The purpose of the kevlar IMHO is to prevent cracking of the CF, and stop it from forming sharp shards in case of failure.
It also protects the tank from impact damage from the outside ..

2:
The shape of the tank with sharp corners is not the best way to take advantage of the strength of the CF/Kevlar composite .. If you want the outside to look like the original, but save weight, I would have made the inside "plug" with radiused (Domed) ends .. Then added some foam core to "fill out" the outside radius, to make the more "perfectly cylindrical" outside on the tank ..

Judging from the thickness of the Alu tank, you would still have at least the same internal volume, even with a radiused end.    The sharp "Corners" you have are an obvious weak point, where there will be an outward localised bending force on the corner when the tank is pressurized ..

One more thing .. How do you plan to "close" the tank? -- For the fittings to stay attached at 10+ Bar, they will need to be mounted with a flange from the inside .. !!

Anyway .. Good luck with the project ...

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

Thanks Dravis for your good comments.

There is also kevlar on the outside layer, but i decided to finish it with one last layer of CF for the esthetic. (CF airbox and tube in the vincinity)

It does not need to be protected from anything as it is covered by the rear clam directly 1mm above it.
My choice to keep the design as close as possible to the original was guided by the only 10mm left clearance I have in length and 1 mm in high and the need to stick as close as possible to the identical volume. The tank is designed to allow 7 gear change and that occurs in one single second so it can't be smaller.
The tank is closed as you see it. I decided to mount the connections as they are on the original, no flange but just 7 steps screwed in with Teflon tape.

I always tend to follow my feelings. A challenge indeed.

Threads in carbon don't work very well, it may be worth submerging it under water to pressure test it

I VERY much doubt that those threads in the CF can hold 10 Bar .. I would certainly glue them in with a good bonding agent at the very least ..

You probably should have bonded in some thread inserts (alu or Stainless) when you did the lay-up --

In any case, the risk of knocking or vibration loosening whatever you screw into those threads will be very high .. NOT a very reliable solution IMHO --

Pressure -testing under water is a brilliant idea --- why didn't I think of that when we did the rockets --

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

So the part is now finished. I will test it on the road as soon as the weather allow me, and if approved, I will bring it to the track to address the reliability. Some feedback now...

- I decided as a test to glue 3 inserts on one side but not on the other where I just added Teflon tape. No issues on both side.
- The core cylinder is far too strong
- You need to be 2 or 3 people to tow correctly as it was a nightmare alone. Very hard to keep the tension, wet it, and deal with everything going not that well...
- The weack point is the design of the side. I will probably build another one using the rocket technics as my tank could be then 20% lighter
- Need to be tested at the track to address the stress issues, vibrations and heat.
- Final weight saving is 682gr where the optimum should be around 800gr.

Does anyone else feel this chap has just built a bomb for his car! ?

Chris, as said, this is too strong so it won't. I actually fear to get some leaks as this will be shaked like hell in a 100+ °c environment at the sides of the tank.
I am now starting a second version with inside hermetic plastic tank that I expect to be stronger, lighter and more reliable (semi sphere ends).

You've actually just highlighted the two main concerns I have with this which may lead to premature failure.