Quote:
Originally Posted by pjbgravely
Back in the old days I saw some cars with a butterfly valve in the collector of the exhaust manifold. It had a thermal spring so it would open when it was warmed up. This was on V engines and on one side only. It may have had been a way to warm up the engine sooner. This was before ERGs.
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...that spring-loaded/thermally-operated 'butterfly' ("rattle") value was used to close-down one side of a dual-exhaust system so as to force the exhaust from one bank of the engine across (thru a cross-over passage under/within the intake manifold) to the other side to speed-up engine warmup and enhance cold-weather driveability.