As said, my numbers from the 140 parts books. Amazons and pre F.I. 140's with B20 heads I'm sure don't have the pads. 7 different heads listed which would have different specs of valves along with other fittings for both types of F.I.
As Rob said smaller ports keep the gas flow up, larger valves would slow it down and those heads may have had no extra port work. Some say keep the inlets small and make the exhausts bigger as the exhaust ports are so bad. No mention of raising the exhaust port floor but that takes us out of simple and cheap.
He said that they keep their engines simple. Fair enough, that also keeps the costs down too. £1k for a stage 2 (?) head for little practical gain. Rallying at less than works level and a little less power won't keep your engine from performing well. Lots of tuning things not mentioned. Decking the block to match the lowest piston for instance and that is basic blue printing and not "tuning". This maximises squish to get the maximum amount of fuel into the combustion chamber. Relieving around the inlet valve on the b18 if you fit a larger valve is effective on B20 too but it lowers the CR.
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