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DIY Exhaust Manifold: Reducer after Wastegate Mounting

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DIY Exhaust Manifold: Reducer after Wastegate Mounting

Old 09-16-2015, 05:42 AM
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Join Date: Nov 2013
Location: Redhill, UK (just South of London)
Posts: 5
Default DIY Exhaust Manifold: Reducer after Wastegate Mounting

Can anyone help me with their thoughts and experience of exhaust manifolds?

I'm designing and building an exhaust manifold for a Mazda 13B REW engine from an RX7 FD in an RX8 (relevant because rotary engines have hotter and faster exhausts than piston engines so I really need to use stainless; there are only 2 exhaust ports, both low down on the engine; and space limitations mean that I can't use off-the-shelf RX7 manifolds).

I've spent tens of hours of analysis on runner size and shape, turbo mounting and wastegate position (including from the turbo exhaust housing). I've mocked up several possibilities in plastic piping. But, after all that, I've come back to my first thought that is very much like the one below but with wastegate runners on the bottom.

So now to my issues. I want to use 1.5" [T304 Schedule 10 pipe] runners, the exhaust ports are just under 2" in diameter, I want as good wastegate operation as I can get and space restrictions limit me to taking the wastegate runners off the initial 90 deg bends. So I thought of using long radius 2" [Schedule 10 or 40] 90 deg bends at the bottom, putting the 38/44 mm wastegate runners directly in line with the ports on the outside of the bends and having a 2" to 1.5" reducer immediately after the bend with the expectation that turbulence at the wastegate runner joins will choke the flow less in the 2" runner and lead to a smooth entry into the 1.5" runners:

Any comments?
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