I'm thinking of making my transmission tunnel without tubing as suggested by Cymtrics. I would think that a rounded top would be torsionally stiffer than a rectangular cross section. Or does the square bottom negate the benifits of the round top

If I decide to make it round would it hurt to make it with facets. I don't have access to slip rolls so I was going to gradually fold it around. Something like 18 10 degree folds.

Thanks

It would look better IMHO!

for the same width and height the round top has slightly less stiffness. This is because by taking off the corners the cross sectional area of the tunnel is slightly reduced.

I would think that from a practical point of view this wouldn't be a significant difference and in any case is easily made good by slightly increasing the tunnel height at the top, say by up to an inch.

One factor that might be much more important is the build. Rectangles are easy to cut and fold to shape. With a curved tunnel you will need to work out how to cut the tunnel sheet material to give a "slash cut" round profile that will weld up to the seat back panel and then bend it to the right profile.

I made mine into a rectangular v! it creates added strength!

Hey Cymtriks

I'm glad you responded. You seem to have put the most thought into this chassis.
I've made a 1/4 scale wood model of the chassis. When you grab each end and twist. The cockpit is definitely the weak spot. So I'm hoping that a good tunnel will help. My question is what keeps the rectangular tunnel from distorting into a diamond wheen you twist it. I'm pretty sure that the lotus elan and europa use a "bulkhead" in the backbone to keep it square. The book tunnel is to small for these bulkheads and still have room for the prop shaft.
As far as building it. I'm pretty confident that I could do a good job of it.

I'm just a dimwit who reads and thinks to much.

Thanks

Ah, another dimwit. I sense a kindred spirit!

It's interesting that (according to Evo) when C******m tested the new CSR with the rollcage loosened, it did not meet their torsional rigidity requirements. They then had to do some quick mods to make their numbers. In addition to adding some tubes and increasing others, they added a bulkhead (with holes for drive shaft, lines, etc.) at the front of their (spaceframe) tunnel. I intend to try this with a cymtiks tunnel, if I can figure out how to route and connect everything.

If your tunnel is unfoldable, I could model it in SolidWorks and send you a flattened drawing of it, if need be.

Regards,
Pete

I have a standard transmission tunnel but I have created a round top for it. I don't have rolls either but used a CO2 welding bottle to form the panels around prior to fitting them.

I have routed all my fuel/brake pipes and all the electrics through here.

The panel shape gets a bit tricky at the front (by the gearstick) and the rear (where it joins the rear bulkhead) but nothing that can't be overcome.

Ignore the cat for now

[img][/img]

The rear end of the tunnel is braced by the vertical tubes on the seat back frame, tubes f and e. The bottom of the tunnel is braced by tube B1 or, if a gap is made in B1 to clear the diff, by a tube slightly forwards of B1. The top is braced by tube O3.

If a round top is used then a panel with an arch shaped cut out can be put between tubes e and f, under tube O3, to fill the gaps where the tunnel corners have been rounded off.