fabricating a turbo exhaust manifold
Discussion
Hi, i am building a 1998cc 8 valve turbo engine from a peugeot 406 at the moment, to go into my 205. The exhuast manifold is a terrible deisgn and was produced so it would limit the power output of the engine as standard.
I want to build a custom manifold, but am unsure of what material to produce it from, i was thinking mild steel but i think this may warp and fail. Stainless steel? any other thoughts?
cheers lee
I want to build a custom manifold, but am unsure of what material to produce it from, i was thinking mild steel but i think this may warp and fail. Stainless steel? any other thoughts?
cheers lee
To make power, a turbo manifold doesnt need to flow that well in reality.
Unless you are seeking huge amounts of power, it is surprising how a crap looking manifold works.
Stainless expands more, so would tend to crack easier, unless you fabricate in some way to allow for expansion. Although it will look nicer.
Mild steel works fine. Ive used plumbers black iron pipe and bends before. Although it too has a tendency to warp.
Make sure the manifold is strong enough to support the turbo. If not, bracket it.
A lot boils down to design, but as far as reliability is concerned, a cast manifold wins every time.
Unless you are seeking in excess of say 150bhp/litre, I'd stick with cast every time..
Peugeot did make a 2.0 8v turbo 406. I assume this is the base you are using ?
Unless you are seeking huge amounts of power, it is surprising how a crap looking manifold works.
Stainless expands more, so would tend to crack easier, unless you fabricate in some way to allow for expansion. Although it will look nicer.
Mild steel works fine. Ive used plumbers black iron pipe and bends before. Although it too has a tendency to warp.
Make sure the manifold is strong enough to support the turbo. If not, bracket it.
A lot boils down to design, but as far as reliability is concerned, a cast manifold wins every time.
Unless you are seeking in excess of say 150bhp/litre, I'd stick with cast every time..
Peugeot did make a 2.0 8v turbo 406. I assume this is the base you are using ?
Whatever material you decide on (applies more so to stainless if youre going to fabricate one) make sure you put a cut of approx 1/8 of an inch between each port outlet on the manifold flange.
The holes should be accurately drilled for the centre two ONLY to give a good location and the rest of them should be progressively larger. For example if the centre holes are 6mm dia, the next pair out from the centre need to be 7-8mm dia, the pair after that 9-10 mm, and this applies especially so to stainless due to its high co-efficient of expansion.
If you dont use oversize holes (and suitable washers to clamp it with) when you get it under load and the manifold expands itll shear off the studs in the head.
You have to have a clearance for the studs. The further away the larger the hole, cos the larger the expansion effect will be from the centre.
BTW the nuts securing the manifold dont have to be absolutely super tightened; You want the manifold to be able to expand/contract and this will happen if the bolts are nipped up just tight enough to give a gas tight seal.
The slots cut into the manifold face between ports will accomodate the expansion of the flange. No cuts equals a big fat warp condition before very long.
Hope this helps.
The holes should be accurately drilled for the centre two ONLY to give a good location and the rest of them should be progressively larger. For example if the centre holes are 6mm dia, the next pair out from the centre need to be 7-8mm dia, the pair after that 9-10 mm, and this applies especially so to stainless due to its high co-efficient of expansion.
If you dont use oversize holes (and suitable washers to clamp it with) when you get it under load and the manifold expands itll shear off the studs in the head.
You have to have a clearance for the studs. The further away the larger the hole, cos the larger the expansion effect will be from the centre.
BTW the nuts securing the manifold dont have to be absolutely super tightened; You want the manifold to be able to expand/contract and this will happen if the bolts are nipped up just tight enough to give a gas tight seal.
The slots cut into the manifold face between ports will accomodate the expansion of the flange. No cuts equals a big fat warp condition before very long.
Hope this helps.
the standard manifold is really bad, the only way i can be described is as a cast block with 4 holes drilled into the flange and one hole for the turbo. There are no port seperations, so the gases colide into each other.
Il try and post a picture, so you can see how bad it actually is.
I was going to support the turbo with a bracket anyway, as the manifold is going to be quite long (similar design to the renault 5 turbo)
just wondering what material would be best for the runners, I have already ordered a flange for the head and the turbo, just need to find a suitable material for the runners. Any idea what would be the best material?
cheers lee
Il try and post a picture, so you can see how bad it actually is.
I was going to support the turbo with a bracket anyway, as the manifold is going to be quite long (similar design to the renault 5 turbo)
just wondering what material would be best for the runners, I have already ordered a flange for the head and the turbo, just need to find a suitable material for the runners. Any idea what would be the best material?
cheers lee
Plain mild steel works fine. I have made a few, and never had any concerns about rust. The heat takes care of that. Usually plumbers/gas pipe whatever you want to call it, about 4-5mm wall thickness.
If you are getting flanges, I wouldnt use anything less than 13mm thick. With DIY made stuff, they have a tendency to warp.
If you are making a tubular design, I wouldnt cut the flange as mentioned. there would be enough give in the tubes to allow for any expansion. I would prefer the strength of a complete 1 piece flange.
If its a short log style, then I would cut it, to allow it to expand.
If you are getting flanges, I wouldnt use anything less than 13mm thick. With DIY made stuff, they have a tendency to warp.
If you are making a tubular design, I wouldnt cut the flange as mentioned. there would be enough give in the tubes to allow for any expansion. I would prefer the strength of a complete 1 piece flange.
If its a short log style, then I would cut it, to allow it to expand.
stevieturbo said:
Plain mild steel works fine. I have made a few, and never had any concerns about rust. The heat takes care of that. Usually plumbers/gas pipe whatever you want to call it, about 4-5mm wall thickness.
If you are getting flanges, I wouldnt use anything less than 13mm thick. With DIY made stuff, they have a tendency to warp.
If you are making a tubular design, I wouldnt cut the flange as mentioned. there would be enough give in the tubes to allow for any expansion. I would prefer the strength of a complete 1 piece flange.
If its a short log style, then I would cut it, to allow it to expand.
Tend to agree with the mild steel being ok, i suppose its just down to personal choice in the end.
Also agree with the milds steel flange being ok regarding expansion.
The stainless one will very definitely need a cut between each port tho, especially if its any kind of length.
En58A is an austenitic heat resisting nickel chrome steel that resists rust acid and heat.
C .16%
Si .2%
Mn 2.0%
Ni 7% - 10%
Cr 17% - 20%
The letter code signifies all sorts of additional constituents. Don't be surprised if it's tuff stuff! It's probably good for superheated steam.
Edited to add;
58J looks like what you want - it's weldable, free cutting and has better thermal resistance (to corrosion) properties.
>> Edited by dilbert on Wednesday 29th June 20:49
>> Edited by dilbert on Wednesday 29th June 20:59
C .16%
Si .2%
Mn 2.0%
Ni 7% - 10%
Cr 17% - 20%
The letter code signifies all sorts of additional constituents. Don't be surprised if it's tuff stuff! It's probably good for superheated steam.
Edited to add;
58J looks like what you want - it's weldable, free cutting and has better thermal resistance (to corrosion) properties.
>> Edited by dilbert on Wednesday 29th June 20:49
>> Edited by dilbert on Wednesday 29th June 20:59
Ive made a pair for my v8 out of 16 gauge mild steel, done around 500 miles so far with no problems at-all.
Details here:
www.mez.co.uk/turbo3.html
weld-el's (thick plumbers pipe) is another popular choice also, but take the time to do a decent job like this one:
www.sdsefi.com/techheader.htm
Ive got some links for weld-el suppliers in the uk.
eliot.
Details here:
www.mez.co.uk/turbo3.html
weld-el's (thick plumbers pipe) is another popular choice also, but take the time to do a decent job like this one:
www.sdsefi.com/techheader.htm
Ive got some links for weld-el suppliers in the uk.
eliot.
eliot said:
Ive made a pair for my v8 out of 16 gauge mild steel, done around 500 miles so far with no problems at-all.
Details here:
www.mez.co.uk/turbo3.html
weld-el's (thick plumbers pipe) is another popular choice also, but take the time to do a decent job like this one:
www.sdsefi.com/techheader.htm
Ive got some links for weld-el suppliers in the uk.
eliot.
I reckon he's got the right idea. En58 work hardens and is not heat treatable! If you do go that route, make sure that you get plenty of spinach, in a Popeye stylee.
I like the gas pipe approach. I'd not have thought of that, but it's simple and effective.
I'd use the thickest mild steel pipe I could bend up right. Make up a jig to bolt it to and then fire the whole lot to stress relieve it. Stainless manifolds are a nightmare unless you like chasing cracks with your welder!
I'm not sure what guage it is but old TVR chassis are made out of "exhaust pipe" and it's not the sort of crap you get from Kwik Fit, THAT thickness. 3/32?
I'm not sure what guage it is but old TVR chassis are made out of "exhaust pipe" and it's not the sort of crap you get from Kwik Fit, THAT thickness. 3/32?
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