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Triumph experimented with 4 valve chambers designed by Cosworth in pushrod twins , unfortunately the castings were so porous they were not a success , although they did provide some benefit at 4500 Revs . Dusty
Harry Weslake not CosworthFull engines still available from Dave Nourish (Nourish on covers, not Weslake as orig )The conversion for unit Triumphs was paid for by Rickman (Rickman on rocker covers)Factory TSS (finned only rocker covers) was the one with porous heads but real problem was Margaret Thatcher, the co-op went into liquidation in August 83, bikes had hardly started production.Quite a few Weslake / Nourish engines about here + some unit Triumphs with the top end only, haven't seen a factory TSS for years
I believe a German company, owned by Mike Krauser, designed 4 valve heads for the old BMW airheads that utilized the cam in block and existing pushrod to do that. However, I don't have any info on what power gains were achieved.
Krauser heads were also available for Guzzi's the newer "hi cam" motors are a clean sheet design when given that, the question why would you engineer what essentially is a stop gap measure.
My thought was ..... Guzzi is a tiny mfg in the total scheme of motorcycle manufacturing. They sell (what?) 5000-7000 machines a year, of which possibly half are big blocks. Maybe a stop gap measure, if it was indeed a stop gap measure, would have been ok if the engineering $$ had been applied elsewhere to improve other aspects of Guzzi's operations .... distribution, sales, dealer support, and warranty.