Thanks to Paul and his continuing efforts well done!
the 4-2-1 made 10bhp over stock and 5 over the 4-1 , you may be puzzled why it out performed the 4-1 at high rpm also , but bear in mind the 4-1 is designed for the forced induction engine (cooper s) not the n/a cooper and one ,as I said previously the one /cooper do not like the larger diameter exhaust (cooper s size) either ,if you step down a small amount in exhaust diameter from the 21/2 cooper s size the power increases by 3-4 bhp and the peak torque point moves.
Now for something even stranger ..... the 4-2-1 out performs the 4-1 on the cooper S also!! even at the high rpms , I believe the cylinder head is such a poor design that even when the engine is supercharged it still requires an extractor manifold to aid the gas flow through the head and valves -despite the higher gas speeds of s/charging.
This is the reason that ported heads with cam and valves add so much power and torque -we have seen + 32 bhp on the S and + 16 on the cooper/one.
Paul keep the manifold and try it on your drag car,just match the exhaust flange holes to your head with a rotary file ,with a nice smooth radius,(The manifold you have is one of our older ones and the new batch are already done) and try on the strip -the clock never lies - I think you will gain a full 1/4 second
I really do wish someone would make a twin cam head for the Mini
