Need help fabricating exhaust manifolds

[Davey]

2" sounds a bit big for primaries and 3mm wall is a lot heavier than it needs to be. If you put a secondary tube across the ends of your four straight pipes you won't do your engine's gas flow wcharacteristics any favours. There is a good reason why tubular manifolds are made of smoothly swept bends. You can buy a variety of bends in SS tube for sensible money, all you need then is a TIG welder to glue them all together.

D.