Making back boxes

[paul r]

Hi,

Has anyone got experience in making back boxes. I'm starting to fabricate my own exhausts and I want to do as much as the work as possible to keep costs down.

I'm, thinking that I could make my own custom back boxes to keep costs down. Has anyone got experience of this?

What materials do I use to make the back box?
What goes inside the back box?
How do I alter the characteristics of the back box? ie amount of gas to flow, type of exhaust note?

Cheers,

Paul.

 

[malcolm]

Is it just for the one project or a mass production thing? For a one off see this thread for some suggestions that work out cheaper than making your own.

For materials, steel is generally the thing, either mild or stainless. Go for an oval or round cross section otherwise it will boom.

For the other questions silencer design is fairly involved. For the simplest absorbing type you would go for perf tube and e-glass stuffing. Push the solid tube into the silencer by at least 20mm, and leave the tail pipe loose and experiment with the noise. Length of tail pipe and the amount of solid sticking into the silencer will make a fair difference. Rule of thumb to avoid booming would be to keep the total length of the tailpipe at least 250mm and as narrow as possible - gas has cooled so narrow at the back doesn't restrict flow so much as narrow at the front.

 

[paul r]

Is it just for the one project or a mass production thing? For a one off see this thread for some suggestions that work out cheaper than making your own.

For materials, steel is generally the thing, either mild or stainless. Go for an oval or round cross section otherwise it will boom.

For the other questions silencer design is fairly involved. For the simplest absorbing type you would go for perf tube and e-glass stuffing. Push the solid tube into the silencer by at least 20mm, and leave the tail pipe loose and experiment with the noise. Length of tail pipe and the amount of solid sticking into the silencer will make a fair difference. Rule of thumb to avoid booming would be to keep the total length of the tailpipe at least 250mm and as narrow as possible - gas has cooled so narrow at the back doesn't restrict flow so much as narrow at the front.

Cheers for that. I would be making more than one. I'm slowly building upto complete exhaust fabrication. The exhausts are going to be performance. The sound I'm after is a deep throaty kind of burble (I knwo it depends on the engine too).

Would it be a case of cutting two round ends with holes for the perforated pipe, then wrapping some 1mm (or less) stainless sheet around the ends with some pipe stick out either end to attach the exhaust/tip to? and packing it with E glass?

I reckon it would cost about 30 quid for the materials?

Cheers,

Paul.

 

[Rick]

Cheers for that. I would be making more than one. I'm slowly building upto complete exhaust fabrication. The exhausts are going to be performance. The sound I'm after is a deep throaty kind of burble (I knwo it depends on the engine too).

Would it be a case of cutting two round ends with holes for the perforated pipe, then wrapping some 1mm (or less) stainless sheet around the ends with some pipe stick out either end to attach the exhaust/tip to? and packing it with E glass?

I reckon it would cost about 30 quid for the materials?

Cheers,

Paul.

Hello Paul,

I do this for a living.

I have thousands of end tanks etc already cut. If you do it the way you mention you'll probably have problems with the perf tube on high performance applications due to the way it expands at a different rate to the outter body.

I've got the perf tube/end plates and rolled tanks.

I'll send you a PM now.

 

[Dr pepper]

I worked at Bosal exhaust on the box line, but thats a mass production job.
The exhaust conatains 'guts', usually a couple of baffles with 3 tubes, one perforated, older ones used basalt as the sound deadener, buts thats banned now, later ones use e-glass.
Small production is totally diffo.
Lumenized steel plate, or stainless steel lasts the longest.
I had a mini with a rc40 exhaust, on reccomendation I layered the outside of the bos with a copper sheet, sounded very nice.

 

[paul r]

Just been looking on ebay and it looks like you can get stainless backboxes for around £35-£40..........I wonder if it's worth bothering to try and make my own?? hmm

Paul.