[nortical]

G'day guys,

I know there are a few people into bikes on here so I was going to ask a few questions.

I am building a simple exhaust for a old Yamaha 250hp single cylinder bike. I thought 409 was the go for exhausts but there seems to be a fair few people using 300 series for exhausts.

I have a good scource for bends in 304 and don't want to root around finding a supplier of 409 if its perfectly fine to use 304. Weight not an issue.

Is 409 only used for reduced cost and better workability on production stuff?

[sedanman]

I don't know the answer to the question but I'll be the first to point out the typo. .............250 HORSEPOWER single!?

[nortical]

Haha, sorry. Got that wrong. Its a SR500. Got the 300 mixed up with 500 and hp mixed up with cc. I'm more of a boat guy so always thinking in HP. Think its more like 31.5hp.

Anyway from my research 304 seems the go.

The plan is to run the pipe between the tranny and seat and end up just before the rear tyre. Will involve a 180, and a few shallow bends. Still waiting on the plans with the muffler. Will post tome pics. Was planning on purging and not using filler, any imput on this affecting the strength.

[Kevin_Holbrook]

take a look at this place

http://www.jegs.com/p/JEGS-Performance- ... 2/10002/-1

304 sst will blue up , if you jet the carbs correctly it wont get too bad

[Arno]

Is 409 only used for reduced cost and better workability on production stuff?

Pretty much, yes.

409 is cheaper and provides improved corrosion resistance compared to plain mild steel, but it's still cheap, easy to work in mass-production and often (MIG) welded on production lines with plain carbon steel wire. (which is why on OEM exhausts often the welds rust out first and the pipes are still OK..). For manufacturers it has an attractive price/performance point between cost and lifespan.

304/316 is more common in aftermarket exhaust work as the profit margins are bigger, smaller/custom production amounts and the expectation of owners that the system will 'last' a long time.

Can be argued that 409 is actually better at sustaining the temperatures that exhausts can see as 304/316 alloys are not really made to be run at these temperatures, but in practice it work OK. The 304/316 won't stay shiny and it will scale over once it get hot enough like in manifolds though.

Bye, Arno.

[nortical]

Cheers guys, Looks like 304/416 is the go.

[nortical]

getting It tacked up, not much room to move but happy with the route so far. Last piece is a bit of scrap with dents in it taped on just to see where I am at.

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[Kevin_Holbrook]

looks good

Pre bent tubing ?

[ex framie]

Ah the old SR500, the base of many specials.
304 stainless is perfect for your application.
My Moto Guzzi LeMans has had a Staintune exhaust for the last 26 years, its made from 304.
It will take on a mild gold patina in all but the high temp areas, these will initially blue and eventually go grey/brown as it ages and gets exposed to rain, road grime etc on the front surface of the header.
All of this can be removed on a buffing wheel and suitable polish.
I would be doing a bit more research on where to run the exhaust and how many heat shields you'll need to fit, but its your project not mine.
Keep the updates comming.
Cheers

[nortical]

Thanks for the input guys.

Re the heat shields, I am just doing what I have seen done before and what the owner asked for.

Ex Framie: would like to hear your input on where heat shields might be needed. Thinking I am far enough away from the block/gearbox to not have issues, but we will keep an eye on the temp.

Here is the finished product before final polishing.

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