Water cooled exhaust material

[cameronbezett]

Sure it has been covered before but have had not much luck finding. I am setting up a new engine for my boat and need to fab up a set of manifolds, honda j30 v6. Stainless vs aluminium, what is the better option and why? What wall thickness for the runners and the water jacket in chosen material? And probably the more disputed part logs vs risers?

[Jeff B]

Material is up to personal preference, whatever you feel comfortable working with or have access to material and tooling etc..
Thickness, Ali I would go minimum 3mm for the inner, outer doesn't matter, 2, 2.5 or 3mm.
I always make the jacket thinner, all it does is keep water in and if you have corrosion problems it will hopefully eat through the outer jacket first.
I find stainless easier, 1.5mm inner and 1.2mm outer.
You can get closer tolerances, smaller welds and welds in much more tricky spots.
Risers or logs? Up to you?
Risers make the whole engine wider
Logs are easy.
That's only my opinion

[cameronbezett]

Cheers for that, looks like stainless logs it is. Bit more experience with stainless and have plenty of exhaust tube kicking around. Trying to keep the engine nice and compact