Trust rust to spoil things

[papa_lazaroo]

Well as the designer who Issued the design notes to release them into the system I can tell you they were stainless, However, Many people seem to think of a Stainless exhaust as something that will be still standing after we are all dead and gone, but not so.
The Basic Construction (rover 200,400 spec)was 2 lavers of Galvanised Steel 1.6mm thick with end plates roll crimped on the ends and various dots of weld added for extra strength. (weld then ate the galvanising and began the corrosion process) I Then was recruited to switch to Stainless steel. But the finance department at Rover wouldn't fund 2 layers of Stainless, so we went with 1 layer, and thickened it up to 1.9mm. This meant there was a gap, where previous material thickness had been, so the fitment in the Jigs was nasty.
Any way, the corrosive deposits that sit in your exhaust (exhausts rust because of the acids plus condensation concentrated daily attacking them. If you do 30,000 a year your exhaust will last 3 times longer than if you do 3000) and eat away at the (Now thinner walled Exhausts) sides and so you still get corrosion, but not rust corrosion.
Rover Paid the manufacturer - Unipart Eberspacher, in Coventry, less than £20 for each complete car system, this is why although stainless it is not a thick gauge, and not a high grade. A system from Janspeed or similar will cost 3 times as much to make, but will also be something like 304 grade (harder stainless but easier to polish). Hence aftermarket ones all look shiny.Rover only ever used 304 on tailpipe trims.

Hope this makes sense.

Rob

[Southern Storm]

Explains alot thanks Rob

[interceptor]

Ok, thanks for the explanation. The janspeed exhaust which i have now is indeed stainless 304 grade with a thickness of 1.5 mm (measered myself) so it will get coroded at the end but hoppefully will last longer than the lesser grade stainless which was used on the oe. exhaust. I always thought a magnet will stick on normal steel and not on stainless, so when i did that the magnet kept sticking on the oe. exhaust but it doesn't stick on the janspeed one, hence why i thought the oe. one wasn't a grade of stainless.

[papa_lazaroo]

Alesser reason for the lower grade as well as the material costs (and you are quite right by the way, the lower the grade of Stainless the higher compliance to magnetic polar attraction) there is the cost and associated wear factor on the manufacturing tooling. Even if 304 were the same cost per tonne as 441 and vice versa, the car companies would opt for 441, as the bending and forming mandrels on a production nolume part, would wear out quickly agains 304.

Immagine you are Mr BMW, A) you like women with hairy airmpits, and B) you make 100,000 3 series exhausts per year, so tou tell the supplier that for your hard earned 10 million Euro. you expect 5 years tooling life. he designs the tool for 500,000 units, and then you say I want 304 instead of 441, he's gonna hit you for more tooling monez after 18 months.

Janspeed etc, make a far higher mark up, but onlz probably make 5,000 parts per year, so their tooling is far less sophisticated.

I tell you, the car trade is a huge con. It's like, If you say, you don't want, erm, aftermarket brakes or stereo or wipers, you'd prefer OE stuff, you aren't neccesarily getting the best Quality, you are just getting a more massed produced part.

I'll shut up now. Any one for beer