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If you bore a B18 block and use standard B20 pistons you should probably try to get a B20 head as the combustion chambers are sized appropriately and they have larger valves. And an injected head would have even bigger intake valves and work slightly better. A B18 head on top of a B20 sized bottom end might work, but it won't work well.

*Most* often this hefty overbore (by general automotive standards) works out OK on a Volvo block, occasionally it will uncover some voids in the block and you'll have to pitch it. (If you start out with a B20 - you can do the same trick and use B21 pistons and a big overbore to get up to 2.1/2.2 liters)

If you have a single downpipe exhaust manifold you should definately scrounge up a dual downpipe manifold, and have (or buy) a 2 inch exhaust built back from the downpipe. (2 inch should be fine for a B20 in more or less stock trim, 2.25 for moderate mods, 2.5 for lots).

Once you have 2 liters under the hood, you might need new needles in the carbs (assuming you still have the twin SU's).
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