Floor sheet metal above or below tubing?

In reply to Tom1200 :

Tom, what kind of spacing was between bolts? Did the floor bolt into the tubes or tabs on the tubes?

In reply to Dusterbd13-michael :

I've heard more than one horror story about leaky fuel lines causing fumes to fill the cockpit (not to mention the fire hazard) I'm sure someone learned this the hard way.

Are you looking for this floor to contribute to overall chassis stiffness?  On my old Formula Fords, testing (by others, not me) showed a properly bonded floor added some 20-30% torsional stiffness of the frame.  Good epoxy with rivets ~3" apart, primarily to hold everything together while the epoxy cures, is considered 'properly bonded' in this case.   I have no idea  how much impact it might have on a full sized car. 

For you with the cost constraints and the possibility of using a steel floor, welding would provide that benefit.  If in fact the floor is contributing to stiffness, bolts/rivets by themselves will tend to loosen and the holes get enlarged, and then the stiffness benefit largely is lost.  But the ability to easily remove the floor could outweigh such concerns.

In reply to pkingham (Forum Supporter) :

On our D-sports Racer we welded sheet with flared holes in the floor. After that we installed a bolt on pan. The reason being that we don't like the practice of drilling holes in the frame tubes.

In reply to DeadSkunk (Warren) :

We used tabs on the tubes. From memory there was a tab about every 6", could have been every 4"

stafford1500 said:

frenchyd said:

In reply to stafford1500 :

With the load in the fasteners when underneath. In addition to flush rivets I'd use a good adhesive like 3M's 

A person could turn the edges of the floor panels up at 90degrees and put the fasteners in shear instead of tension. That would also keep the bottom surface clean of bolt/rivet heads. Modern adhesives are very good, absolutely consider using them, but watch for cost since it is a challenge car.

Good point regarding cost.  I have family members who have retired from 3M which puts prices of their  stuff cheaper than hardware store.  With the addition of using exactly the right product for maximum strength ( and longevity ). Since you're challenge using this. Use regular dome head pop rivets with epoxy

Then once the event is over if you want you can drill out the pop rivets and using a propane torch break the bond  to remove.  Wire brush to remove epoxy , now using Cleco's to locate, counterbore for flush rivets. Then use the 3M adhesive and put in the flush rivets. 
  May sound like overkill but 60mph accident at the challenge and pop rivets and expoxy probably will hold up.   Wheel to wheel at a real race track? Extremely unlikely. 

Do both and fill the space with closed cell foam for heat and noise abatement.

Some more thoughts on this......

The entire floor area is about 51"x 47". The portion that would actually be flat, above or below the tubing, would only be about 60% of that. The transmission tunnel, especially when the transmission is next my hip, is quite large compared to the rest of the passenger compartment plan view. Because the exhaust pipes are about flush with the floor tubes the trans tunnel just gets wider to cover them.

I originally wondered about a flat floor for aero reasons, but a large chunk of the underside is going to be open. In theory I could almost run the floor under the trans, exhausts and drive shaft, but I already suspect it will be pretty darned hot in this puppy to begin with.

I should go get an overhead picture so you can see how much space the engine and trans are taking up..........

Edit:

If you notice the piece of blue tape , lower left, the floor panel width is 20" there and that's the widest part of the entire floor. The tunnel perimeter is going to follow the tubes on either side of the tunnel as the exhaust pipes, trans mount and drive shaft safety loop actually sit slightly above the upper surface of the floor tubes. It's going to be a bit like a Hummer in there, narrow foot well and wide tunnel. There's really not even a proper foot well on the passenger side. I'm leaning to just doing everything above the tubes to keep it simpler, and any of the tunnel is going to be above the tubes anyway. That's a sizable piece of the floor.

Adhesives and rivets would be in use if I were building a car for other purposes, but budget and limited equipment are pointing me at spot welding the steel closet doors ( a nice faux birch finish on them!) directly to all the various tubes and dropping tunnel sections on top, with more welding.

I did spend time today trying to figure out the best way to create pathways for gas and brake lines. Per Stampie's idea ,I threw a length of green tubing in the passenger side to visualize a conduit passing through the driver's compartment. If nothing else, this build is making me think a lot. Every time I think something is settled I realize there's a run on effect screwing with something else. It's a continually morphing puzzle. 

NOHOME said:

Do both and fill the space with closed cell foam for heat and noise abatement.

I do need to figure out some way to shield the tunnel from the driver's right leg, it's going to be hot.

In reply to pkingham (Forum Supporter) :

Anything that improves stiffness I'll take, but I'm trying to avoid adding anything that might be useless weight. None of the materials in the car are optimal thickness, everything is too thick, a result of budget rather than a material that's light enough to still do the job. This thing will be 10-15% heavier just because of wall thicknesses and larger diameter tubes. I looked at a couple of GT3 cars at Waterford earlier this year. They were something like 1750# with driver. I would be ecstatic if my car ends up at 2100 w/driver.

I did both sides with aluminum, rivets, and trick adhesives.  best of both worlds.

If i could only do one side it would be the bottom.

Of course I was not constrained by a $2,000 budget.

In reply to Purple Frog (Forum Supporter) :

That's impressive.....is that the chassis for the Beetle body?

Under.  Way easier to fabricate.  I have plywood where my ankles go on top of the tubes.  

In reply to nocones :

I agree, the floor sheeting on the underside would be easier, but I think that might make the transmission tunnel more work since there wouldn't be a flat surface to land on. I'll have to mate the sheetmetal to the curved tubes. I'll play around with more Rice Crispies boxes before I decide, I think.