Stainless v Mild Steel Exhausts

[hendy]

I don't disagree at all that stainless will run hotter, in fact I know it will. I'm just saying that the % is difficult to be sure about without a raft of tests in various conditions.

In wet weather I'd bet my left gonad that the difference would be almost immeasurable.

Am I right in thinking that stainless exhausts are usually made of heavier gauge plate?

By the way, smoking has been shown to contribute to impotence.

[B-Race Tuning]

My mum always said I was impotent. I don't smoke since fortnight tomorrow. And my (currently, mahoosive, black) boys have been disconnected, but i agree, in wet weather my left gonads difference would be immeasurable too. (Sorry, could resist... bored again.)
When I set up a scoot, I have to allow for the rare times its not raining, so have to jet that in (temp rise that is).
Our exhausts are generally 50% thicker than the ss pipes. Haven't come across ss pipes being thicker per se over mild pipes. tend to vary from 0.7mm (some italian pipes) to Original Taffspeeds we made in 1.2. Ours 1.5mm. S

[HxPaul]

We set up my own TS1/225 scooter with exhaust a) mild steel, 1.5mm, and set out ten thermocouples along the length of the exhaust and run for an hour on the dyno under measured slight load. Repeat with exhaust b) Stainless steel 0.8/1mm. Both exhausts running the same AFR readings (at the start of set-up).
The temperature at various distances from exhaust flange differed by over 30% in places. Higher on the stainless exhaust. I have found similar but less difference on chrome exhausts. And at the end of an hour the AFR readings had changed enough to warrant going richer on the stainless pipe, but not the mild steel.
Bearing in mind what an expansion chamber should/does actually do and our own findings, I'll stick with mild steel. Additional to temps, stainless steel by its very chrome alloy make-up is more brittle, and especially after localised heat treatments (welding). This was in a controlled test on the dyno, whilst we were developing our exhausts to determine the material our own brand pipes were made of. Our decision was Cr1 Mild @ 1.5mm. Simon.

So it isn't "COMPLETE HOGWASH ",stainless steel exhausts actually do hold the heat more than mild steel.

[dapper]

After my two cracked U bends, I'd suggest that using a mild steel U bend would be the better solution as that's where the majority of the heat is. It's unseen under the scoot anyway, and if you like shiny stuff the rest of the exhaust could be SS for that bling thing, man

[hendy]

So it isn't "COMPLETE HOGWASH ",stainless steel exhausts actually do hold the heat more than mild steel.

No, it's not hogwash. Stainless conducts heat at about 30% the rate of mild (depending on what type of stainless and mild you're comparing, but they're all broadly similar) and radiates heat at about 10% of the rate of a black exhaust.

These are the 2 primary mechanisms for cooling, so yes, stainless gets hotter. Generally, thinner stiff cools better, and B-race tuning tells me that stainless is usually thinner, but the benefits for the thicknesses he quotes are so small in comparison to the 'problems' caused by the conductivity and emissivity that the thickness doesn't really matter.

Summary: matt black mild steel cools better; shiny stainless steel looks better.

No idea about weld strength as it's not really my bag.

[sydduckett]

Just to muddy the waters I had two Franspeed race pipes one mild steel the other SS. The mild steel one was welded up about 6 times and required re painting every 6 months, the SS one is crack free after 18 months and obviously doesn't need painting. In fact just had it re polished as I was having some other bits done and it now looks better than when I brought it....

I would suggest it's got more to do with the quality of the pipe build as opposed to the material. you won't see a mild steel exhaust on a super car or sports bike but then again the quality off the SS and manufacture will be spot on.

[gaz_powell]

taking on board everyones valid comments - I understand that ss is a more brittle medium by its make up and has different properties to ms but I believe through my own experience that mounting it correctly is a major factor.

as it is less forgiving you cannot afford to stress by simply forcing it to fit - especially with pipes that consist of 4 pieces + brackets etc.

todate ive always elongate , modified brackets etc to make them fit without any stress (only one I didn't do a vespa JL which failed - which I rectified second go for loads of trouble free miles)

ive personally got no problem using ss exhausts on mine and bikes I build for people.