MD wrote:If you know where you want the torque, top or bottom and know what application the car is being put to ie street ,rally or racing then why is it so hard to front up to a mechanical workshop specialising in hand fabrication of exhaust systems and use the magic words..."just make the fkkrs"
You don't live in Bagdad do you? If you are going to seriously modify Alfas , you will learn that many things don't just come off the shelf. That's what makes them the challenge..
Making a good turbo exhaust manifolds, especially for the angle flanged Alfa heads, is a lot more work than most people realise. And making 1 that is long term durable gets expensive when you start paying some bloke with a nice and expensive TIG welder who should be pumping sheilding gas both inside and outside of the manifold when welding. Add the 'fun' to do machining costs after welding the flanges (figuring out how to clamp the manifold to a milling machine table is the 'fun' part), and epense's get high.
Think 20-40 hours work making a 1 off manifold. Using Ozzy dollars and a conservative $50 an hour "just make......." isn't in everybodies budget.
But if you can make a jig to suit your custom set up. If you can get the head flange propperly made with the angle cut ports. If you can make a decent collector and can make the individual pipes with weld prep chanfers (chamfers should be 2/3 of the pipe wall thickness) wherever 2 pieces join and can either tack them your self or even tape them together for later welding, then you can do a lot of the time consuming work that is within the skills of most hands on petrol heads.
BTW, only use 'steam pipe'. It's actually only a thicker wall (about 3mm) pipe than normal water pipe (it's also not galv. plated
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) and the bends (at least here in Oz) get reffered to as 'butt weld fittings/bends'.
Stainless just doesn't have a good reputation for long term durabillity and will cost 2-4 times as much in materials.
Don't waste your time building a 'log' manifold. They are the easiet to make, but they are the crappest flowing pieces of junk that will limit your engine badly and will cause even more heat retention due to their poor flowing abillity. People that say they are fine, either have no idea or are just lazey. I know they are crap, I have 1 on 1 of my cars. Yes, I've been lazey
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.
Don't use MIG welding to weld your manifold. It's quick and easy, but MIG welding lacks weld penetration and is a rather 'stressed' weld. To see what I mean, put 2 pieces of metal together and add a small tack to join them. Then watch and see how far the 2 pieces move when the weld cools.
In heavy industry, it is only TIG and Arc welding tht are used in pressure vessle welding. MIG has it's place but it's not here.
I have welded manifolds together with my Henrob 2000 Oxy/Accetylene torch. The excellent thing about this is that it is a very ductile weld (the complete opposit of the MIG weld) and, when done right, gets full penetration. It also is also a very clean, oxide free weld. The only bad thing is the amount of heat that you get subjected to when welding.
But I whole heartedly agree with MD about the challenging part.
Owning a Nissan Silvia, probably 1 of the most supported cars in the after market performance industy, is/was boring compared to the Alfa.