Shorrock Supercharger

[Pistonpower]

HI everyone, i'm a new member here and am a recent mini convert (from Triumph) I have toyed with Shorrock superchargers in the past and have just seen one on ebay complete with all the parts for a mini. Has anyone fitted a Shorrock to a mini, and if so are there any major pitfalls that I should be aware of? Also what sort of price do they generally sell for complete?

Any advice much appreciated!

cheers

James

[mk1]

Hi James,

There are a few members on here who have Shorrock powered Minis, I ran one a few years ago & have restored / fitted them for a few people too.

Here's a couple of pics of my Traveller;





There are no real pitfalls with fitting a shorrock blower as long as you stick to sensible engineering procedures, make sure stuff is fitted correctly, firmly & you have as much clearance as you can get. The C75B works best on 850's but can be made to work on 1275's but will have to be over driven. If doinmg this bear in mind the blowers safe RPM limit of around 6,000. Oil feed can be an issue, but this needs to be dealt with on a suck it & see basis.

M

PS. Welcome to the forum.

PPS. Complete C75B kits for a mini usually go for around the £1000 - £1200 mark on ebay. Or at least they did when I was last looking.

PPPS. There is quite a bit of useful Shorrock info here - http://mk1-performance-conversions.co.u ... _intro.htm

[slowboy]

the inlet manifold is the hard bit to find, it doesn't appear to be in the kit for sale on e-bay, you can modify a cast one, but it aint easy !

[mk1]

The problem with using a cast manifold is that it makes the blower stand a little higher in the engine bay, my preference would be to get a steel one made by Maniflow, this would be a good £150 to ad to the price. M

[rich@minispares.com]

whenever I see anything about shorrocks chargers it just makes me think about the epic, motorway blocking, smoke screen emitted by marks woody (oh-er) when it had a bit of a sulk once!

[mk1]

Mini 40. . . . . Oh how we did laugh

M

[johnsimister]

I've been through the mill with the C75B on my slightly overbored 850, but it's now working very well after a rebuild by Derek Chinn who is a meticulous supercharger specialist. It has seized up twice, the first time causing/resulting from the breakage of the input shaft. The underlying cause of both disasters was probably a lack of oil. After the second one, Derek found that the feed was blocked and the main bearing at the far end from the input shaft was bone dry.

The fact that it was overspeeding probably hadn't helped - see Mark's observation above re safe rev limit. It was running at 1.25x engine speed, so 6000 engine meant 7500 'charger. The car went like a rocket, with stupendous boost at high revs, but now that I've had a new drive pulley made which lets the Shorrock run at engine speed I feel much happier. It's still quick - 70bhp estimated at the flywheel on the rolling road at CCK after some hand re-profiling of the SU needle - but stands a chance of holding together. It has just completed 1900 or so miles on the Minis to Ireland tour with no engine trouble.

My engine has bigger valves than standard and a Piper 265 cam, but I think it might be better with a milder cam. Exhaust is a Maniflow shortish centre branch and RC40. There's loads of top-end power but less low-end torque than expected from a supercharger. Acceleration at motorway speeds is excellent, and that's on a 3.44 diff. Drive is by a modern polyvee ribbed belt rather than the original pair of fanbelts, because it's more efficient and more reliable. It's tensioned by a Mazda MX5 cambelt tensioner.

Looking at the kit on eBay, as well as the inlet manifold you'll also need a suitable carburettor, an SU H4. There is no room for a decent air filter as orginally configured by Shorrock, but I got round this by getting rid of the orginal clutch master cylinder with its bulky reservoir and replacing it with a small Tilton racing unit and remote reservoir. That creates space for an ITG foam filter and the bores and rings now stand a chance of lasting.

Whereabouts are you? If near me in Berkhamsted, Herts, you're welcome to come and have a look and a ride.

John

[johnsimister]

Pics:

[hanlminiman]

John's car did smoke on start up on Minis to Ireland but once it cleared HE was gone and never seen again until the evening stop. A great car and well worth a test ride with a very good driver.

[slowboy]

the oiling is done by metering pins which are graded A-Z, these are ground and the tollerances are tiny, I had two sets done at british aerospace, kept one set and sold the other to pay for the two sets , our set up is not running yet, but without a good range of metering pins to try you will either smoke too much or too little, its a bit like su needle choice, agree mark, the maniflow option is the best one for an inlet

what we are using for a master cylinder to allow the use of a short bellmouth, I cant remember what its off , I seem to recall left hand drive innocent

[johnsimister]

Ha! Yes, it can be a bit cloudy on start up. It's best if I drive off straight away. Idling and low-revs manoeuvring cause oil to accummulate in the Shorrock and then it all gets blown through and combusted. The same thing sometimes happens when restarting after a long, fast run (such as a SW Ireland rally stage). Oddly, given the visual evidence, it doesn't seem to use an excessive amount of oil despite the Shorrock's total-loss lubrication system. The oil consumption actually improved on the Irish run and the engine is running better than ever.

Another quirk is that the idle speed has to be high - 1500rpm-plus - otherwise the engine just stops. CCK reckoned that the combination of small capacity, low compression (the flat-top pistons are about 1/8in below the tops of the bores at TDC), a fairly warm camshaft and the power needed to drive the supercharger stop the engine running below that speed because it simply doesn't produce enough effort down there. It runs on 95-octane unleaded with no sign of pinking, incidentally.

John

[mk1]

It took me ages to sort the oiling on that blower John, had to ream the oil way & make a new oversize pin. Glad to hear it is still acceptable. They will tick over perfectly normally with a standard cam.

M

[gr4h4m]

On my sc12 setup it's always needed 1200rpm to have a steady idle std or hot cam. I guess with a suck through setup they pull more fuel at all rpm locations, but then that's the point... I know with a carb that I could run a v8 for the price of the fuel.

Not sure now its injected as its yet to be setup....

[johnsimister]

Yes, economy is definitely not its strong point even though the colour of the spark plug deposits is always a nice light brown.

[johnsimister]

Another thought re the possibly excessive overlap of my car's camshaft. At idle and low speeds the CO reading is fine - around 1.5 to 2 per cent - but the unburnt HC is high. I thought that might be the oil passing through the supercharger, but it could well be because of the camshaft. With a supercharger and a longish-duration cam, I suspect the mixture is being blown into the cylinder and straight out the other side at low speeds, which would explain the poor mpg. Something with lots of lift but a short overlap would be better, but I can't face changing it just now given how sweetly the engine is running and how lively it is at high revs.

John

Edit: having said all that, at idle there's still a vacuum at the inlet manifold so the fuel/air mix can't be pushed out of the exhaust ports then - or no more than it would be in an unsupercharged engine, anyway, as the compression stroke begins. Maybe a 265-degree camshaft causes high HC whether induction is forced or not, although such a cam is hardly extreme.

[59fan]

I ran mine on a standard 850 and the idle was fine, also I got no smoke but the oil needle profile has to be pretty accurate for that and its better to push a bit more oil through the blower than a bit less for obvious reasons. Its going onto a 1040 with a mild cam now, so I'm hoping for a smooth idle again when it gets fitted to the car, which it should in the next 2 weeks. Just in time for winter.

Ian

[59fan]

Slowboy,

Did this master cylinder work for you?

Ian

the oiling is done by metering pins which are graded A-Z, these are ground and the tollerances are tiny, I had two sets done at british aerospace, kept one set and sold the other to pay for the two sets , our set up is not running yet, but without a good range of metering pins to try you will either smoke too much or too little, its a bit like su needle choice, agree mark, the maniflow option is the best one for an inlet

what we are using for a master cylinder to allow the use of a short bellmouth, I cant remember what its off , I seem to recall left hand drive innocent

[Dr S]

Does anyone else want to live in Slow boys garage?

[mk1]

To get decent oil flow to a shorrock blower requires the restrictor pin to be within .25 of a thou of the overall bore size. Any more & it will smoke like a train. Getting this right took me more time than installing the blower.

[Pete]

Period installation...