what thickness is best for ex manifold?

[dnb]

ok guys lets hear what you think.

ive been wondering about this lately.what do you think the best thickness of pipe is for an exhaust manifold?

some people use very thin material where as others go for steam pipe.

[Roy]

Id say stick with tube over pipe. For the following reasons:

- weight, tubular manifold will be lighter

- welding, its easier to get a top quality internal weld bead when welding tube rather then pipe which would normally take several runs after the inital root run. Tube you can use square weld end preps meaning you dont need filler wire so its a complete fusion weld. Pipe typically require v-butt weld preps meaning you have to use filler wire and unless purged perfectly its easy to get a concave weld bead on the internals

- Strength, if you use the right tube and it if fabricated properly, ie things like full penetration welds, and the manifold is gusseted properly to support the weight of the turbo and gate/exhaust then all the manifold is doing is flowing air, nothing structural so will limit cracking. Things like the exhaust support that bolts to the gearbox and cat also helps the manifold from applied loads when very hot and vulnerable...something my mechanic doesnt seem to care about as mine wasnt put back on the car:(

- With tube you can actually get the tube mandrel bent to minimise some weldign / fabrication though it is expensive, rather then with heavy wall pipe where you have to use off the shelp long and short radius 90 / 45 deg bends.

Anyway there my thoughts:)

[dnb]

thanks roy.

anyone else?

also.where can i get some 38mm pipe mandrel bent?

please excuse my use of the word "pipe".anyone who wants to elaborate on the difference between tube and pipe please feel free to do so

[Roy]

Basically tube is measured in OD and then you havew certain wall thicknesses. So for instance 38.1OD x 1.6wt...

Pipe is measured in nominal bore and then comes in various scedules of pipe, sch10, sch 40, sch80 std weight etc. Bigger the number the thicker it is. The thinnest pipe sch10 is still considerably thicker then the most common 1.6mm thick tube.

As far as using tube i would only consider using stainless for an exhaust manifold...if you are using the thicker pipe then mild steel would be ok. But in tuibe as a minimum i personally would be using 304L or 316L. The "L" is important because it has a more controlled (and reduced) carbpon content making it better to weld and more suitable for high temps.

In sydney i know places like Walker Engineering do mandrel bending but the price will scare you. Your best bet is to ring your local steel merchants. I take ig "gong" is Wollongong, if so try places like Prochem, Austeel (usually cheapest) Atlas Steel, Carrington Products.

Essentially it sounds like you are after either

38.1OD x 1.6wt A554 AWA 304L tube (or 316L if you can pay a bit more)

OR a slightly better grade of stainless again is:

38.1OD x 1.6wt A269 AWA 304L tube (or again 316L if you can have the coin)

Dont let them price the seamless tube, it again will scare you. The A556 and A269 are often the same steel but tested differently so be accepted by different industries. Too much information????

[dnb]

not at all champ!!!!! i love information:)

and yes gong =wollongong(the town of steel)

i know the seamless pipe is dear as i have a rollcage being made of it atm.

i appreciate your help roy:)

[ylwgtr2]

the last manifold i made was with pipe from reece plumbing.....i found it welded up quite good.....this manifold has glown to an almost transparant state and hasnt cracked yet!

[dnb]

what thickness was the pipe mate?