Exhaust manifold design

[Mazdabater]

So I was sitting there having some beers in the shed the other day and my bloody turbo/manifold setup was staring at me. Half an hour later I have decided that it it too poorly designed and ugly to be on my car.

Back before all my problems started I brought a turbo kit off a "good shop" here in aus, turned out to be full of ebay parts, the manifold cracked and they made me a steam pipe one but copied the ebay design so as not to change the exhaust and the runners vary at least 3" in length, not to mention it's running a chinese wastegate so it's not worthy of going on the FC.

It's probably going to cost more then buying one, but I'm going to make my own one as I think my welds are decent enough now. Planning on making it out of SS321 as it should be alot less prone to cracking under the weight/heat of the turbo.

I have also discovered this site http://www.spdexhaust.com/ and am in love with their collectors

Problem one: Wastegate placement

I know there are mixed opinions on this, I was planning on getting the above site to make me a T4 flanged collector and then tapping the wastegate line in at the flange, are there any downsides to running it off here?

Problem two: Wastegate size.

I'm aiming for 500rwhp. Just brought one of rice's WI kits, have enough fuel and a bridgeport so I'm pretty damn sure I'll hit the mark it's just a matter of how much boost it's going to need. I'm looking at upgrading the turbo, as it's also chinese. A few people have told me to run with it as I might be shocked at how well they perform but it just doesn't sit right with me. I really wanna try the Borg Warner EFR-9180 and now my missus has a decent job, I should be able to buy it in a month or so! This said I'm looking at a Tial 44mm gate going cheap on ausrotary, is this going to be big enough for that size turbo?

Problem three: Runner length

Is there an optimum length for your runners. I know they have to be the same length and in as smooth a flow as possible, but are there advantages to having a shorter or longer manifold?

Problem four: Exhaust flange

Where can I get a stainless 13B flange (preferably 321 but probably doesn't matter for the flange) I could get one made locally but if there is somewhere in the states that does them, will most likely be cheaper.



That's about all the issues I can think of at the moment. Any advice is appreciated.