Help with DIY Turbo Manifold - 304 vs 321, TIG vs MIG, Reliability, Operating Temperature and Boost levels
Turbo Mini Forums

Hi Guys,

I will soon be attempting to make a tubular turbo manifold and would really appreciate some opinions on what's a good idea and what is not, what people have done for themselves and with what results.

I have been researching materials quite a bit, and while a lot of DIY manifolds seem to be made from 304 S/S, there seems to be a lot of negative talk in terms of the operating temperatures they can handle. 321 on the other hand seems to be the preferred choice for high-end production manifolds.

I only have a Clarke 160TM MIG welder at the moment and wondered whether this was up to the job of fabricating a turbo manfiold? I don't want my welds to crack because I haven't used TIG combined with back purging.

If anyone would share their experiences of fabricating a turbo manifold that would be great

Cheers,

Mike

i tig weld stainless steel at work and yeah i would suggest purging it, stainless steel seems to distort like mad aswell whilst welding so make sure you have good tacks

You certainly do not need to TIG it.

TIG makes it look pretty ( if you can weld ), and with TIG it must be backpurged.

No such nonsense with MIG

Most manifolds are made from the cheaper stainless and will last years. Especially if there isnt much weight hanging off them, and you make some allowances for expansion/contraction.

Wrapping them with heat wrap will make it far more likely to crack too.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Thanks for the replies. Obviously opinions vary with this.....I would FAR rather MIG it if possible as I can do that myself rather than having to get it done especially.

I don't mind spending more on 321 if it is worth it. So 321 MIG welded should be fine?

Also forgot to put this originally, but hows does the boost level affect manifold reliability?

Does anyone have pictures of their DIY manifolds?

Boost level will affect reliability only from a point of view of EGT's and duration spent at boost and high EGT's
Although EGT's will also be effected by fuel, tuning, turbo choice etc

It will be very rare you find any manifold made from 321 on a cost basis alone. Most are 304 or 316, and if well made they give very good service.

I think I read somewhere that 321 expands and contracts more than other types, so from that point of view it may be a less ideal material even if it is actually stronger. Although it would depend on actual design and where any stress points would be.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Thanks , well I will be on boost for fairly long periods of time if racing so it does need to be capable of withstanding that.

Depends what manifolds we're talking I suppose, the high-end ones designed for racing tend to be made from 321 as it has better corrosion resistance at high temperatures....having said that, these are made by professionals, not homemade manifolds. I've read a lot about homemade 321 manifolds cracking. I really do not want mine to crack after all the time I put into it.

So 304/316, what thickness would it need to be?

Thickness will depend on weight hanging off it really.

If you take a long tubular Subaru manifold, generally they're only around 1.6-2mm wall thickness and as long as they are not wrapped, and not installed badly, then they give pretty good service ( ignoring cheap crap manifolds though )

The typical Sch10 type bends will be much thicker an stronger..
I wouldnt go any thinner than 1.6mm though, although doubtful stainless is readily available in thinner anyway

the most expensive manifolds will be inconel....but that'd be silly money

Is it a long/remote style setup you're going for ? Direct replacement for the typical metro turbo ? or other ?

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Ahhhhh I see, yes well it is a fairly weighty turbo unit. I was thinking this sch10, good prices for the bends but the straight only coming in a 3m length is slightly excessive http://www.allstainlessltd.co.uk/products....bfitt_elbow.gif

Yes Inconel is crazy money but then I suppose worth it if you have the money and facilities.

Yes it is a long remote setup, a "sidewinder" manifold I believe they call it. It isn't actually for an A-series, but a Honda lump (don't hate me haha). It will look something along these lines http://www.k20tuned.com/k24turbo/turbokit.jpg

You think SCH10 316 will be suitable then, even with the weighty turbo?

Cheers

Edited by Mowen123 on 10th Nov, 2013.

i was concerned about mine as well in the end i decided to just go cheep mild "wing it" and see if my design works i dont have to much fath in it time will tell if its good and cracks ill have a pro make me a good one ehh one of those things id do differently no i think about it properly..

Don't get too hung up about the material. The purest will say that you should not use thin wall 316 but then how many people have had problems with a Mirage manifold?

Ultimately the choice of material will be governed by what is available in the size that you need. There in lies another dilemma: what size do you need? Don't fall into the trap of thinking bigger is better. Like most things there is an optimum size and it's a lot smaller than you think.

As a guide, for optimum performance you should stick to the recommended LCB dimensions for your application.

I've made a couple now using the Sch10 1" stuff:

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

i should add that mine is 1.6mm wall mild steel inch and 1/4" into 2" for the pipe sizes
as paul says chose what is probaly right for you ie if it needs to rev hard then big and short may work vs low revs probaly wants longer thinner to help air speed
im no expert im just doing my best to put together things and see what the out come is for me this may work out??

what are you building this engine for?
engine size?
rpm?
there are calculations out there to help find the "correct" size and length all that stuff if you wanting to go that route but thease calcs are mostly for 4 port exhaust head not 3 so that may squew things a bit?

also dont wright off the simple log type mani it will still make good power.. just might not be as soon as something more creative

I did mine from the shcdule 10 stuff, didnt bother back purging and it has held up fine.

Cheers for the replies.

I'm fine on the diameter/design side of things, know exactly what I'm after. It was just the materials and processes I wasn't sure about.

I can get 304, 310, 316 & 321 in the diameter I need, so no limitations with regard to availability which is good :)

Tig.

Just be careful if you TIG and do not backpurge.

If you get crusty bits inside the pipe, or any intrusion where bits may come off at a later date. These pieces of debris can and will damage the turbocharger.

The Sch10 pipe might not see this as much as thinner wall tubing though. But bare it in mind.

With MIG, and presuming you dont get bits of wire stuck inside the tubes, this really isnt an issue, as you dont get the same level of crap building up inside the tubes.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

If you can get the bends with no gap between them, then back purging isn't really necessary, as the build up inside is minimal. And obviously the flanges won't require purging.

The biggest problem you'll find if you go down the thin wall route, is trying to get a good weld with mig where it's going from thick to thin material.

I've used 304 and 316 before with good results.

The main problem with stainless is warping, so if you're making one with multiple bends, you need to start at the head, and weld each pipe completely as you go. If you tack them, them fully weld them after, the last few bends will become misaligned.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

Thanks again for the helpful replies. I was thinking that about the stainless warping and the best way to go about tacking and welding it up. It's difficult because you want to tack it just to make sure it's 100% in the correct place, but then if it warps there isn't much point. I will work my way from the head in that case and carefully plan the route of the pipes....can't afford to mess it up if i'm fully welding each section as I go. Clearances are extremely tight so fingers crossed.

You can always tack all the pipes as you go, to get the shape right, then weld them one by one. But the last bit of the pipe to be joined may need to be fettled to fit.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

You can always tack all the pipes as you go, to get the shape right, then weld them one by one. But the last bit of the pipe to be joined may need to be fettled to fit.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

my approach was to cut n shape as i went making sure i didn't make gaps then tack all up test fit and then used an old head to weld it on worked well for me slight angle on the pipes at joins and away

I've seen people using insulation tape or gaffa tape to hold the sections together so they can weld it all at once.

surely the tape would melt?
i once seen an advert for some type of company that used a tight fitting spring to keep alignment on joints while welding?

All cracking ideas, not sure about gaffa tape though AP?


How hard was it to make the collector? I am dreading that bit the most, looks bloody hard to cut the pipes correctly, then welding it looks awkward too.

Edited by Mowen123 on 12th Nov, 2013.

The tape is just to hold it together while you get all the pipes/bends cut properly.