well yes i could run the stock supercharger without decompression.

it would be nicer off boost..

Less comp more boost, yes. But you will sacrifice power down low. Even though superchargers have boost from idle, it still takes time to get enough air speed for full boost.

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Carl
Previous Owner & Driver of 1 Morris "It's not a Cooper!!" 850

Because these are positive diplacement SC's ie they diplace about 1200cc of air each revolution and a 998 will take about 499cc of air per rev so you would get about 700cc of boost if we ran the SC at aratio of 1:1 crank speed (but it is actually less). Then if we get a 1275 and ran it at crank speed also engine will now take about 640cc of air so we have about 560cc worth of boost so you get less boost with the bigger engine.But the crank pulley can be made larger so on bigger engines the SC is driven quicker so more boost if you want, It can't be made any smaller though that is why small bores run more boost.
So yes a larger capacity engine can have higher compression because it can run less boost then also it can run higher boost if you want by increasaing pulley size. It just turns out that a 1275 with 8.8:1 comp and about 7-8psi works quite well.

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4efte powered Clubman
supercharged 998 race car

Thanks Ben. That's the answer I was looking for. My CR is 9.0:1 in a 1330. I didn't really want to have to use a decompression plate if I can get away without one.
So I think I'll try it as it is.

Not sure of my exact compression, but my car is a 1330cc and has a stock 12G940 head.

Seems to run alright, no pinging on 98 octane fuel (never tried it on anything less!) and runs around 7psi max boost at some silly rpm, so my guage says anyways. But I get around pretty quickly on about 3/4 throttle with around 4-5 psi max, so much bottom end.

<edit> I must add, I've got rather dished pistons. Not sure of brand. They don't have a curved dish but rather an angled 'step' and a large flat cut out. Look like some GR pistons I've seen on here but can't confirm.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

Hi Guys

I have this supercharger kit, but am still in the process of building it.

My question is what exhaust are you guys running for 1275?

Mine will be 1330 with about 8psi boost. Which exhausts fit and what would you recommend?

Regards
Smarty

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68 Mini
70 Moke

Also which fuel pump would be best.
I have the wiring for an electric fuel pump just do not have the pump yet.
Do I go for the SU electric pump or just a solid state one?
I am referring to the ones from minispares in SA

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68 Mini
70 Moke

your back - be still my beating heart

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did I tell you that I won a trophy?

As for exhaust, I just run a set of LCB and a 2inch straight through muffler.

I guess the best would be something like a maniflow LCB but they are expensive.

As above a 3psi solid state fuel pump would do it. I bought my Facet 3psi pump from Repco, but any car parts supplier should be able to get one.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

Jim the car in in the club shoot-out in the issues thats out in DEC.. it made 54bhp at the wheels on the day down 6 hp due to the timing being out,

We later found out that the dizzy was shot, the timing was jumping arround about 5 deg under the gun...

Now I'm running a megajolt kit thanks the Ben (92) the SC12 wizard. Ben made a great trigger wheel and sensor bracket that bolts onto the bottom pulley a great trick.

BHP backup to 60 I have tried some 1.5 roller rockers but they just seem to allow the engine to rev more... (My standard rockers were well worn.)


the update is a little late but it taken that long to publish... I gave Ausmini a shout...

how easily available are the supercharger kits?? are they still around??

ive stumbled accross a rarely used sc12 that would go perfect for my recently aquired 1275.

a quick question aswell.. 1275LS with the number 12H902.. Whats the compression ratio? ive been hunting all over the net, my leyland manual and keep getting different figures.

Thanks guys.

I still make the SC12 kits so you can still get them

Compression of that engine could be any thing from 8.8:1 upward hard to say without at least doing a compression test then still a guess.

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4efte powered Clubman
supercharged 998 race car

C/R of a 1275LS is 8.8:1.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

thats nice looking donk, if you ask me

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Bluey-1973 Clubby - 1330, high lift, big cam, 7 port madness in progress..

Gumby-1978 Minivan, British Racing Green - 1310, high lift, mild cam, enlarged porting and chamber shape with big valve head, supercharged build in ever slow progress!