In 2002 we built a pair of MB1350sc engines for a friend in Italy he's got them in a 47 Apache the engines have been worked on a couple of times over that side of the pond the last time they worked on them I sent them new valves springs and so on when they put the engines back on the dyno they found they had lost 170 hp and 190ft lbs with the same components. The performance had also dropped so Dino the owner sent me the cylinder heads to redo for him the seat shape had been changed to the point were I could not reshape to original so we replaced all the seats in both heads replaced the guides and re sized and shape the seats to an even newer shape we've been working with on the Big chief stuff they reinstalled the heads and found 185hp and 215 ft lbs from were they originally were. Dino is happy and the performance is back up like before. Cylinder heads are important in any application and should always be inspected when worked on to ensure you don't loose any of it's original shapes or characteristics.

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Many people out there focusing on their "ports", and they neglect the seat/chamber/throat area, where in most bbc heads, the real restrictions are. Especially in the low lift world. Example, a well setup 2.19 intake valve can easily outflow a 2.300 with a poor valve job/throat diameter. This post also proves that a flow is critical, even when theres a blower on top of the engine.

On a set of heads like that the valve job can be 30-40 cfm. Naturally aspirated that can be 70-100hp.