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It's interesting to me, too, as Mark made a very safe map for my Harrop. I did consider replacing the fuel pump with a higher performance one, but awaiting further advice.

This is all very interesting, especially to me as I have the smaller pulley waiting to be fitted. I just have to be brave! Matt said that his map (specific for my car) would happily adjust to the smaller pulley, but that I was using up the safety margin built in and should not take it on track or "dump the clutch" too often in a short space of time. Thanks to Martin for accommodating all this specific chat on his thread.

Lots of forums/tuners say different things about the FA20 rods. But I know lots of guys in the US are running 10psi+ on stock rods and aren’t having rods bending. And people are running 330bhp on the stock fuel pump so I don’t think it can be maxed out at 300bhp. Just my opinion but I suspect most bending rods are caused by poor fuel/low octane/bad mapping/misfiring/knock rather than boost torque/power levels. Going back to the Cosworth charger specifically I honestly don’t think it matters which pulley you use. Correct me if i’m wrong but the larger pulley is 0.5bar (7.25psi) and the smaller pulley is 0.6bar which is 8.7psi. So less than 1.5 extra psi. I think even with the smaller pulley and 8.7 psi boost we’re still well on the side of caution. I think as long as the engine is well maintained, in good health and running 99ron it should be fine as long as temperatures are constantly monitored and you dont go dumping the clutch doing 1/4 mile drag racing as that really is asking for a rod to bend.