Firebird's original head, stock valves and ported to 34mm PWKs.

This is interesting because I tested side by side with a stock head using the same valve, 40.5mm. I assume the stock head is 109cfm minus carb. With carb then 106.5cfm. The ported head is 155cfm through the 34mm carb and same valve. Or some where near it. 45.5% approximately more air. And importantly much faster. And in the Wallace hp calculator for hp based on flow about 45.5% more powerful. Std 106.5 works out at around 50hp. On their mildest spec Street/strip. High comp, 11 or 12-1 should put it in race motor mode and hp estimation. It would be interesting to see. 750cc brings rpm down.

The 42mm valves are about plus 50% through the 34mm carb.

This shows ports at stock valve size, stock 40.5mm valve, 42mm and 44.5mm.

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