Hi all

I would just like to mention that I have changed the pulley on my sc12 from 120mm to 103mm with the following results:(may help someone contemplating the same)

120mm = 7.5 PSI under 4,000 rpm (around town), 10 PSI at 6,000 rpm (high load highway)
103mm = 13 PSI Under 4,000 rpm (around town), 15 PSI at 6,000 rpm (high load highway)
(Crank Pulley is 100mm)

It loves the extra boost. No audible detonation problems at all on 98 unleaded. (drove it in 40deg heat the other day and no issues). I have put quite a few km's on it now since the upgrade and all is holding together well.

I have also changed to a 50mm thick china alloy rad which has made a huge difference in cooling. Would get up to 105deg c when pushing it hard before, now never over 85deg

Thanks Ben for your advice at the Coffs Harbour BMC Car Show re higher boost on the sc12.
(mine was the silver deluxe with the home made manifold similar to your design)
Gave me a bit more surety that the blower could handle it and the inspiration to go ahead with the plan.
Hopefully everything holds together long term. If not I have a few spare sc12s there anyway .

cheers
Rick

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1310 SC 1969 Morris Deluxe - 15psi boost
1293 1968 Morris Deluxe Miglia - 45 Weber
HSV Maloo Z Series - Comp Cam - 300rwkw

Sounds good, are you really pulling 6000rpm on the highway? or was that a "speed run/test"

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Respect mine and I'll respect yours.

Yeah that was 6k on the highway. Not sure of what the speed was but it was well past the 90mph speedo limit. In reality, it probably reaches 15psi closer to 5200 rpm though. 3.44 diff ratio.

For the record, I don't condone such behaviour and it was a one off (or maybe a two off?) but it was in the interest of testing the detonation threshold.

For a 4 cylinder it pulls hard from 60 mph as the blower is at full boost.

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1310 SC 1969 Morris Deluxe - 15psi boost
1293 1968 Morris Deluxe Miglia - 45 Weber
HSV Maloo Z Series - Comp Cam - 300rwkw