Which fixed needles and springs should I use in my twin 1.5" SU's.
Engine has 60 thou oversized flat top pistons.

7 is a good start, CP4 if you need a bit more fuel at the top , 6 if you need less.

Twin HS4 Police SPO41 spec was Blue springs and CP4 needles

The SU numbering system is doing my head in.
Is the CP4 equal to AUD1118

Yes. CP4 is the needle number but the part number to order is AUD1118

By the time the Clubman GT SPO28 police spec came about the needle had changed to BG instead of CP4 as originally specified in SPO41, the blue springs being retained.

I was chatting recently to a BMC field service guy who drove around supporting country dealers and he always took with him a bag of BG needles. The typical feedback from the police drivers who had their Cooper S needles changed by him was that it noticeably transformed the car.

_________________
ex-NSW Police 1970 MK II Cooper S
VMCI #43

Here is a graph showing the BG compared to the others. Lots more fuel at the top end.



Here is a few examples that ST used on their Cooper Ss

The AEA648 cam had the BG and the AEG510 had the No7.

Amazing guys, thank you.

Excellent question and an identical one i was wondering about too. Thanks from me for all the answers too.