Bulkhead replacement

[erictharg]

Having realised that Spa this year is a 90 minute race I think I need a decent seat. The factory seat has me hanging onto the steering wheel and bracing myself against the tunnel in most corners. Favourite has to be one of the new moulded bead seats, both for comfort and safety (Real & HANS kits). But what I realise is that it will be sitting against the GRP bulkhead behind the driver, and that does not sit hard up against the chassis tubes and so flexes by 15 to 20mm when pushed. Hardly the best location for a seat that might have to absorb lots of "G"'s in an accident. Never mind just trying to get the seat belts done up tight. So, looks as if I've got to remove (cut out) the factory GRP bulkhead and replace with an aluminium one that is rivetted to the chassis tubes. For the flat portion behind the driver and over the tranmission tunnel that's simple enough. But replicating the curvey GRP as it sweeps out to the sides is a little trickier. Cue lots of cardboard patterns and ally beating...

[Westfield 129]

Just like it was done at Williams and Pritchard.

You can hammer a bunch of panels into compound curves, using the 'glass panel as a guide, or you can do it in flat pieces, riveted together.

You can also reinforce the seat area as necessary.

Fact is, the floor is not that strong to support the bucket seat, and the flat seat just uses a the 'glass panel as a seat back anyway. Feel free to reinforce the existing panel and pour your bead seat, or make up a seat bottom form, and use Tempur Foam to finish the padding.

[adamwilkinson]

I believe our seat is the same as they use in Mallocks, nice snug fit. Our seat back is also made from ally, didnt realise they are now fibreglass.

I hear what you are saying about having to brace yourself, my first ever go in the 11 was at Snett in 2001 after my uncle decided on the day he didnt want to drive it (i was there racing another car too so had all my kit). Que me driving pretty much one handed the whole race whilst bracing myself in the corners, still i got pole, won the class and got fastest lap (back in the days when there were lots of class entries)!

I am actually getting pretty excited about Spa, going for the 3min lap time this year - 4 seconds to shave off which i think can be done over a 7km lap.

[sgrant]

Charles, I'm really interested in where you go with this one. With my back gently falling to pieces, I'm thinking about replacing the seat in the eleven with one that offers some support. I've poured seats before, but only the "two-pack expanding foam into a bag" variety and they don't really offer proper support in my view (unless I did it wrong of course).

stephen

[erictharg]

Adam - I'll be very impressed if you get below the 3:00! Also gives me a real target. Cuddley broke 3:00 first time out last year and I though that was pretty good, but didn't dream of getting an Eleven there. From memory I did a best of 3:12 last year.
Stephen - I did a lot of thinking on a seat. Could have spent the thick end of £300 on a Tillet (and that's just the GRP version) and still not have it fit, so whilst £200 is a lot for a bag of poly beads and some epoxy if the blurb is anything to go by it should provide the best fit and protection. I did think about conventional two part foam but it seems too hit and miss and not as durable as the bead seat. Besides, once I've got the kit I can see what it's made of and then copy it for future reference, hopefully at lower cost. Bean bag poly beads plus a couple of litres of epoxy and one tough plastic bag feels more like £50. For road use I think you could safely mould it against the GRP bulkhead, but being the perfectionist you are you'll likely end up going the ally bulkhead route!
Jan - Agree about shaping the ally. Just might not be as pretty as Williams & Pritchard! I'm also tempted to get rid of the dropped floors as they can't do much for the underfloor aerodynamics, but too much work for Spa.

[Westfield 129]

I am making a new seat for my early car, with the flat floor.
Starting with a sheet of stainless, I am contouring a bottom, onto which, I will lay three layer temperfoam.

I am using hard foam to make a seat back, as my car is set up for a guy about 6'4". This will be covered with a two layer temperfoam sheet.

As far as bracing, I can form the seat back any way I want, and add padding as necessary, then send the whole thing to the trim shop for upholstering.

It is pretty easy to reinforce the back section to support the hard foam back.

The chassis is pretty narrow, and it is not likely that you will need much padding to keep you centered during cornering.

The bead seats work fine, but to get the support, you have to mold the seat so that it has that support. This means building up the inside of the car so that when you finally plop yourself in the seat, it squishes out in the right directions, with sufficient thickness to support itself when you are done. Then, cut and finish to taste, and cover.