Our manifolds are plastic - already gasket matched. Turbotech racing has proven results, check the LNF and Focus ST forums. They're picking up 10whp & 15-20wtq. If you can TIG weld like this and have enough dough to throw designs out that don't make power, I'd buy one. But I gota see precedence & track record before I put down cash.
Designing a manifold isn't the hardest thing to do
Designing one that equalizes flow while in space constraints is
That's the hard part
Also depends on how you want resonances and intake pulses to benefit your where you want to in the rev range
Problem is mostly here is you're going from a plastic pice to metal
Also
Not everything has to be pretty shiny tig welds
Tig is great for looking awesome while doing a good weld
But it's not cheap or quick
I'd much rather take a continuous mig weld that won't look as pretty but will have less weak points than start and stop tig ( which is hard a lot of places will do it now or the same with mig because it looks better)
and then there's material choices That effect how you handle an fab a part
Etc
Stainless has more to do to it than mild steal
While aluminum is lighter you need special differences to weld it compared to ferrous metals
This is mainly the reason why if I'm going to already spring the money for a intake
Might as well pick up a set of itbs from a bike and fab it together and probably pick up 20whp in the process
Along with better throttle response and response to supporting mods
But i really doubt if ever we are going to get an aftermarket intake manifold
Especially with how gauging it went last time
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