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Mini Cooper

Published: 11th Jan 2017 - 0 Comments - Be the first, contribute now!

Mini Cooper
Mini Cooper
Mini Cooper
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Something old, something new, something borrowed and something blue – we show how best to hot up the evergreen Mini

One of the world’s most modified and tuned cars, you’d think that there’s was nothing new and so little more to add to how to mod a Mini. Well, you’re wrong because almost 60 years since its introduction, there’s no shortage of modern ideas to tune one of the world’s most favourite hot cars!

Thousands of books and magazines have gone in-depth to reveal the secrets of Mini tuning over the decades and we could fill the magazine entirely on the subject! So, in this Road & Track special we look at what’s been done before as well as future trends to keep this small wonder well, – simply wonderful!

Before you start

Minis can rust just as badly as they ever did and it’s an awkward car to repair on a DIY basis. Usual rust areas include the rear subframe (which last on average seven years if untreated), sills and floor panels. New subframes are cheap to buy if not fit, with a new Heritage rear subframe costing £325. However, the good news is that panels are readily available to practically build one from scratch with only some panels for early models being harder to source. For instance, you can buy a complete (MkV only) Heritage bodyshell for £4650, or £4800 for the Clubman.

Many Mini experts reckon that the Rover models are not as well built as early types. Post MkIV new shells not made by BMH although other than front subframe mounts moved 3/8in forward, it’s much the same. If hunting for used panels, while they look the same, subtle differences lurk on the wings and front end, for example, according to year so are not direct fits.

Engines are robust. Metro A+ engines are an improvement over earlier ones but still suffer from usual wear including worn valve guides leading to smoking. If Mpi engine cuts out at idle it is normally MAP wire breaking due to engine rocking (worn stabiliser bar) or failed Stepper motor which slightly raises engine speed.

The former can be by-passed or fit a new loom. Other problems relate to sensor failing causing high emissions.

If it’s done a significant mileage then think about overhauling it at the same time as major tuning will finish it off – ditto the transmission as Mini ’boxes can give trouble and injection models in particular have a reputation for weak second gears which some say is due in part to the gear casings being made thinner! Jumping out of gear (an old Mini trait) can also be due to simply excessive engine movement caused by a worn engine stabiliser bar. Mini Sport sells transmission overhaul kits for under £200. You can fit tougher competition driveshafts costing a similar amount (Mini Sport).

Hotting one up

A whole tuning industry was built around the Mini and is as vibrant as ever. Old tuning trickery starts from a few quid with a richer needle and spring for the SU carb and sports exhaust before fitting a Cooper (or 1100) cylinder head. However, even with a basic Stage One kit for around £182 (from Mini Sport who celebrates 50 years of Mini magic during 2017), generally consisting of a modified inlet manifold, exhaust manifold, exhaust, air filter plus where needed, a new carburettor needle it won’t release a mine of power – a healthy 20 per cent admittedly – because today’s Mini experts look for around 85bhp for today’s roads – which is a lot to wring out of a 1-litre engine.

Which is why – unless you want to stick with period mods, perhaps to abide with historic competition regulations – it’s recommended that you start with a 1275cc engine which has been fitted to all Minis for the best part of 30 years; that’s around 60bhp for starters. Some fit 72bhp and 95bhp MG Metro engines but it’s tricky, especially the Turbo one and you’ll have to modify the cooling system.

If you need an engine rebuild then you take the easy way out by purchasing a ready-made tuned engine. The 1275 block can be stretched to 1380cc or more than 1400cc, if desired but this needs care.

Typically, a 1293/1380cc engine from Minispeed starts from under £800 for a budget build-it-yourself kit to approaching £1100 for a ‘fast road’1380cc kit. At the other end of the scale Minispeed sells, a 1293/1330cc fully-rebuilt unit, complete with a Stage 4 cylinder head, reground nitrocarburised crankshaft etc, costs £2797. But when you consider Mini Sport sells recon standard engines from £1665, tuned ones look good value. This, according to leading magazine MiniWorld, is partly due to the exorbitant prices A+ engines now sell for – £600 over the phone, it adds!

Mini Sport sells Stage 3 head and exhaust for later Mpi engine yielding 90bhp for £1319. CAT replacement pipes from Minispeed cost £25, a free-flow exhaust a smidgen over £60, DTM tail £115 and you can ditch the simple fuel injection for good old fashioned carbs. A Swiftune camshaft and replacing standard ECU with a mappable type or ‘tricking’ existing type to suit gives almost Metro Turbo power claims The Real Mini Company.

If you do your own thing then first concentrate on the head and camshaft – there’s plenty to choose from and modern machining techniques can improve the tried and tested tuning gear. The ultimate in A-Series cylinder heads has to be modern eight port cylinder heads which can cost a hefty £2000 alone!

Latest news for road use is Mini Spares’ five-port alloy cylinder head. Based upon the original Cooper S 12G1805 version of the 12G940 casting, it comes already gas-flowed and being alloy is said to offer significant cooling improvements – but prices start at £1000 for base head and £1043 fully built. A similar head is produced by Webcon.

Camshafts follow the tried and tested BMC tuning ‘648’ and ‘731’ profiles albeit improved upon from the likes of Piper and Kent Cams but it’s generally accepted that the Swiftune ‘5’ offers the best mix of power and usability.

If you don’t want to strip the engine down you can alter the valve timing ‘up top’ by fitting ‘roller rockers’ which essentially is a trick tappet set which acts like a sportier camshaft. Convenient and cheap, at some £180, which is less than what a sports camshaft retails for. They can be had in various ‘ratios’ depending on how much power you wish for, although some tuners reckon it’s a half-hearted measure which also places undue strain on the valve train.

SU carbs still work well on this evergreen engine, so much so that for road use there’s not much to gain by going the Weber route and a good 1380cc tuned engine can use a large 1.75in carb effectively – unthinkable behaviour not so many years ago!

Exhausts are still based upon the LCB (long centre branch) manifold and sports system – post ’90 cars already employ Cooper S piping – and apart from looking and sounding the part is an inexpensive £200 mod. On all models fit an electronic ignition or, best of all, an Aldon distributor, and invest in a uprated radiator plus oil cooler if necessary as the latter also usefully increases the sump’s capacity.

Racing engines can yield 150bhp+ which is massive for a Mini but to achieve this you’re looking at tougher crankshafts (£1639 from Minispares.com) along with uprated con rod racing-spec pistons and so on. Specific regulation racing engines are available from the major Mini tuners.

Ever heard of a 16-valve A-Series engine? Well, it’s possible care of a BMW motorcycle cylinder head that can be made to fit after fairly minor re-engineering; kits are available. Elsewhere in this issue you can read how to mod and mend BMW Minis. Well, the supercharger fitted to that Cooper S can be also fitted to the A-Series – again, kits and advice are all out there.

Earlier on we touched on period tuning gear but let’s not forget that you also buy pukka John Cooper kits. Not cheap, starting at over £1800 but the Cooper Car Co kits aren’t just tuning parts but a ‘Cooperised’ conversion complete with alloy rocker cover, decals, authentic paperwork and a special plaque for good measure.

At the other extreme, you can say sod originality and fit other engines such as Honda units and – of course – the vastly underrated K Series unit that was fitted to late Metros and Rover 100s.

According to MiniWorld, there’s a shed load of new tuning ideas and equipment coming, meaning that nearly 60 years on, the Mini isn’t dead yet!

Handling the power

In contrast, Mini chassis mods, whilst not remaining static, have evolved less. Uprated dampers is still the first step. From Mini Sport, its Sports Suspension Kit with Spax adjustable shock absorbers currently costs £228, for instance. Next – on ‘dry’ models is lowering cones. Try the Moulton Smootha Ride kit, which http://www.minisport.com markets as a package with its Adjusta Ride system at £275, for a complete front and rear kit, depending how you want your Mini to ride and handle; preferably ‘neutral’ with a trace of oversteer say experts. Fitting a rear antiroll bar in isolation to cure the famous Mini understeer makes the car very twitchy.

Further detailed mods include adjustable suspension tie-bars and negative camber kits (front and rear) and Mini geometry settings are pretty important. Front negative camber kits cut down understeer; Sports Ride kit (from £254) comes with them. Classic Hi Lo kits still available too at £92 (Mini Spares). Minispeed sells a simple ride height kit for less than £50 so there’s something for all pockets.

Some Mini experts say Rover Cooper Minis can run with incorrect chassis geometry due to subframe misalignment plus can foul the body unless official shims are added (part no 2A4292).

If the standard rack and pinion steering is not nimble enough you can fit a ‘quick rack’ but the tiller will be notably heavier.

Brakes used to be notoriously ineffective on Minis – even Coopers – but since the adoption of generous disc brakes, a Mini pulls up well in standard trim and there’s no shortage of upgrade options. Some owners fit the four-pot vented disc set-up from the Metro Turbo, which can be grafted on to the standard calliper-type Mini hub; www. minispares.com sells a Metro Turbo vented disc front brake kit for £297. If you’re on a budget simply using uprated pads works well for general motoring, however.

Here’s a Mini laugh. Many owners of later Minis running on meatier 12 and 13inch wheels as standard, actually prefer the look and handling of earlier 10inch models and convert their cars accordingly!

A typical conversion kit from Mini Sport costs £200 but some models will also need to run on smaller brakes to suit! Conversion kit cost over £200 but this may mean that you need alter the brakes as the original 8.4inch type now won’t fit. Trick is to use 7.5inch Cooper S discs with uprated four or six pot callipers costing around £350.

If you stick with 12inch wheels then try EBC brake kit for £70. The ultimate are alloy brake callipers costing some £350; at the rear use alloy finned brake drums.

If you stay with the standard wheels there’s more than ample choice of tyres and rims including period go faster Revolution and Mamba types; £60-£75 according to type. In contrast, Mini Sport produces exact replica Cooper S steel rims at £56 a corner but they may need rear spacers to fit. As standard, all Rover Coopers came on cast Minilite wheels and 145/70 SR12 tyres covered by screw-on wheel spats.

Tyres (165/60SR 12) may also require rear wheel spacers while some believe 13inch ones never get up to temperature but that’s on the track we assume!

Transmissions: 1275 Rovers used the same internal ratios but fuel injected ones used a lower final drive ratio of 3.2:1 against 3.1:1 which gives slightly better acceleration although the latter is best for cruising. If you wish, earlier transmissions can be fitted with more frantic gearing or you can fit a close ratio gear set; Mini Sport sells a complete new ’box with diff for under £1300. However, being straight cut gears they are more aimed at competition and too noisy for road use. Mini Sport LSDs from £193. Experts such as http://www.guess-works. com can supply units with modifications such as straight cut gear sets and drop gears. Prices start at £550 for a standard gearbox, up to £1315 for a modified box. Minispares sells new close ratio kit for under £200. And we could go on…



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