Did a quick test fit of the su's today.. And the heat shroud seemed to male things extremely tight! Is it needed or if I just heat wrap the exhaust will it be sweet?
Also there is a a hose coming off the side of the block in-between the exhaust... What's it for? (obviously I lack in the mechanical side of things haha but I'll get there)
The pipe on the side of the block between 3 and 4 exhaust outlets should be connected into the Exhaust Gas Recirculation (EGR) valve screwed into the centre of the intake manifold balance pipe via a (flexible rubber/neoprene?) hose between them, so crankcase gasses are recycled into the inlet system.
I suggest you keep the original exhaust manifold initially. It will fit behind the heat shield, which is necessary for a road car, to avoid fuel vapourising on hot days in city traffic. Its not a big restrictor of gas flow either, unless you are using 5000RPM plus.
There is not a lot of power gain unless you fit "big bore" extractors, which feed out horizontally from the ports. Most smaller dia. extractors generally have tight bends from the manifold flange to fit around the factory inlet manifold, and in my opinion are little better than the cast factory manifold, they just sound louder.
You can get an improved factory manifold from an 80's Stanza, or L20 manifold from a 200B/Bluebird Series1 or 2, all are the same part. These anti pollution manifolds need to have the EGR pipe deleted and the fitting hole blanked off with a suitable bolt (or an old spark plug). This exhaust manifold is less restrictive than the older factory manifold, as it doesnt have the restriction cast into the top of #2/3 cylinders outlets that you will see in your original manifold. They are a lot quieter in the cabin than a tube extractor.
If you decide to go for an extractor system, get a "big bore" extractor. To fit this type, you will have to cut out the lower half of centre section of the SU heat shield, and grind off the bottom (only) of the interconnecting alloy tube section of your SU inlet manifold linking 1/2 and 3/4 inlets, to get clearance for the #2/#3 extractor pipes. Grinding off the bottom of the balance tube will break into the water gallery section, which runs underneath the vacuum balance section above it in the same casting, so you need to block off the water flow at the head and the pipe from the water pump, or fill the hole each side of the ground out area with silicon - not a recommended "permanent fix") . You will also have to find another way to fit the SU return springs, which are fitted to the lower section of the heat shield. (Not a difficult job to fabricate alternatives, fixed to the lower carb retaining bolts)
Hope these thoughts are helpful in giving you some development options.
Keep it going.
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