ABS if you can get it

 

I would not use wood anywhere near the exhaust system

 

I can get anything I want locally, however went I went in and spoke to the materials expert we talked about some things and came to the conclusion that PVC would be the best for the front bar for example.

Also is ABS just going to melt and sag under the exhaust?

Dann

 

Yes it is! Haha. Ask me how I know...

I'm currently remaking my flat bottom out of aluminum.

-Ryan

 

How thick is the AL you are using? Are you using straight AL sheeting, or a corrugated product like Alumalite? That could get expensive fast.

 

Volcanic I checked out your fab thread on CR.net. Nice DIY fab work!

 

This is what Im wondering.

Alumalite has a plastic core.

I think thin ply with a reflective material on it and a fully wrapped exhaust would do the job just fine.

The below pic is a cross section of the MX5 tub. You can see the trans tunnel in the middle, the pinch welds are the vertical lines at the outside and inside them is the frame rails.



The pink represents aluminium angle, the blue is 1/4" ply sheet, and the red are fasteners.

Looks ok?

Anyone think exhaust heat wrap and reflective tape cannot save the timber?

Dann

 

Hmm i thought i was subbed here.

 

A couple things -

First off, don't wrap your exhaust. The header is one thing, but under the car can easily get soaked with oils if you develop a leak since it is downstream of the engine/trans, and then instant fire. This has happened to people before. Whatever you make the undertray out of needs to be able to handle the heat without needing to add exhaust wrap.

As for my particular design, I'm not using alumalite. I have alumalite in the garage, but after my first version which was made from ABS, I have seen how much heat is under there, and I feel that the core of the alumalite will quickly be compromised by the heat just like the ABS was. I am making version 2 from .030" aluminum, which by itself is quite flimsy, but it's being reinforced with a gridwork of small aluminum angle, and I've worked out a permanent and lightweight way to bond the angle to the sheet.

-Ryan

 

Bonding the angle with urethane?

Im pretty sure ply with alluminium glued to it along the exhaust path will work fine.

Only one way to find out.

Also Lightbulb moment.

Ill fasten everything to the car with rivnuts (also known as nutserts).

Dann

 

Forget the nutcerts, dezues fasteners.

 

For an undertray I would rather use rivnuts than Dzus fasteners. If everything under the car is built well, then the undertray will not have to come off often, maybe once a year, and rivnuts/bolts will be a lot stronger.

 

I haven't used rivnuts, but Dzus fasteners suck

 

From a fabrication standpoint, the rivnuts would be a much easier install to boot. You could just drill holes in the frame rails to mount the rivnuts, whereas with dzus fasteners you'd be forced to install dzus plates anywhere you want to install, since you can't access the backside of anything to locate the springs.

 

I've seen this said numerous times but I've had 0 problems with them on 2 different cars now. What kind of problems did you have?

 

I would make the blue line (floor) a lot wider than just to the pinch welds. The air will be sucked in from the sides. At least go a couple of inches past either side.

 

I used them to attach bodywork on road racing motorcycles. The damn things would always come undone. We had to cover them with duct tape to hold them in place.

 

My rear diffuser is aluminum and going with aluminum underbody after birch splitter. Currently not turbo, but I imagine if it actually got hot enough to melt it then you can just line the top side of the tunnel to insulate. My 2 cents.

 

Weld-nuts are better than Riv-nuts. Riv-nuts are great until they come loose, then you can't get your bolt out because the riv-nut is just spinning in its hole, so you have to cut the bolt head off. Weld-nuts won't do this to you.
-Ryan

 

Wood is also a bad material for under the car due to oil soak/fire danger. This is why any wood or ply splitter should get a layer of fiberglass laid over the top so it can't absorb oils.