awesome fun to drive, horrible to own...
I had an SC12 on my car for a few years, initially I used an 1 3/4" and it was OK-ish, but not ideal because SU carbs don't have a throttle pump - you get a lean spike on sudden throttle opening - different springs/needles/oil etc. will go some way to fixing it but it's all compromises. I injected it after a little while and it was better but still not great, fuelling into the cold side before the blower means the fuel doesn't stay atomised and falls out of the air. Obviously can't intercool it so I was getting 100°C+ intake temperatures, I water injected it to help with that, but the water was only on while boosting so driving off boost had very hot intake air.
The first engine I had it on was a typical warm 1275 plus something, I had a thick copper head gasket made (maybe 2mm?) by a mob in Melbourne, I just rang them up and said I wanted one for a 1275 mini and the bloke said "yep, no worries" and it arrived in the post soon after. That engine didn't last long - a valve seat insert (aka "unleaded conversion") fell out - it jammed the valve open and destroyed a piston and one chamber. I built another motor with around 9.4:1 compression which was happier, but it was always painful, again, just too many compromises.
The clutch on an SC12 engages/disengages on the 4AGZE motor in conjunction with a bypass that opens to let air into the plenum without going through the blower. You don't have that luxury. When I injected it I made a smaller, fixed pulley, but initially I used the clutched pulley and I could turn it off - air being pulled in by the engine would make the blower turn - but didn't run very well... especially given the fuel has to go through the blower as well.
I spent a very long time trying to get it to be reliable, but the best thing I did was take the blower off - I now have the most reliable, easy to drive mini - I can leave it for months and months and it just starts right up and is happy, I basically only use it for competition and I haven't touched the motor in 7 or 8 years except for changing the oil... though I did have to top up the dashpot oil a few weeks ago... tsk tsk..
As with all modifications, it's the devils trifecta - performance, low cost, reliability - choose any two...
I'd do it again, but only on a 7 port head where I could intercool out of the blower and inject into each intake port. So my advice, save up and get a 7 port head with webers, then save up some more and inject it, then save up some more and a bit more and put the blower on, or a turbo, and run an intercooler.
edit: here's my build thread:
viewtopic.php?f=5&t=66558 the pictures are doing something odd, right click and open them in a new tab is fine so.. ?
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