Stages of tune
This whiole thing of stages of tuning has got out of hand. This is waht I did in Mini Mag back in october 2005 on the subject -
2005-10, Modification stages of tune.
An old saw often stamped out by many a journo is just how revolutionary the Mini was at its inception. And indeed it was – there is no disputing that. Cabin space was truly Tardis-like. The level of grip, often mistakenly quoted as handling, was awesome. Unfortunately the initial engine installation was a little on the wheezy side. Whilst I confess to admiring the little 850cc engine in the way it can be thrashed mercilessly for miles and miles without suffering premature malaise it most definitely doesnt set the world on fire in the power output stakes. Since the dawn of time, Mans competitiveness has ensured an all consuming desire amongst some to be quicker than the next bloke (or bloke-ess even) is applied to just about everything he gets involved with. The Mini was no exception. As soon as folk started driving those first 850s, they started developing ways to make them go faster; a strain picked up by the sports department at the time – Special Tuning at Abingdon. Realising the potential of the after sales market as being a healthy place to be they set about sorting out clearly defined tuning packages for the masses that could be easily applied, have all components required to do the job, and above all make decent improvements for the investment. They were a success. Fast forward some 45 years and tuning packages are still earnestly sought after by many a standard-engined Mini owner after a brief spell of initial bliss at how great a Mini is to drive. What has changed dramatically is the plethora of packages available to the point of mass confusion. A big prompt from Ed Helen got me thinking about this. Reflection via my notes on past subjects revealed Id not really done anything on this subject. A bit weird considering it makes up a huge chuck of what folk do to their Minis almost as a matter of course. So lets get that cleared up now then.
As mentioned earlier, Special Tuning Department (here shortened to ST to save a section of Amazonian rain forest) put a big effort into making performance improvements as painless as possible. An undertaking that no doubt helped boost sales of cars through the easily available and much respected upgrades. Folk complain now of the thin-on-the-ground rolling roads to get engine performance maximised. Back then they were all but non-existent except for the specialist few, so the kits had to be fit and run jobs. And the initial kits for the 850 made a pretty dramatic difference to how the car went, shaving a whopping 11.3 seconds off its 0-60 time – some 33%. This kit was dubbed the stage one kit and was hailed for addressing the asthmatic breathing problems that were strangling the motor. The kit contained a ported and polished standard cast iron inlet and exhaust manifold, new freer-breathing exhaust system, carb needle and modified cylinder head. The cylinder head retained standard valve sizes but was ported, chambers modified, and polished throughout. Curiously it retained the standard air cleaner and filter. Enter the 998cc engine, and it was given the same treatment, although the performance improvement wasnt quite so dramatic, cutting 20% off its 0-60 time. Still substantial though. The demand for even more performance saw the stage two kit developed, using a more modified head (bigger inlet valve and more modified port work) along with a pair of 1.25-inch SU carbs. Stage three followed soon after that that required a camshaft change and was considered race specification. The introduction of the Coopers and S derivatives threw a bit of a spanner in the works since technology was moving a-pace throwing new light on what was needed in the way of up-grades to maximise performance – and the whole stage whatever kits needed a re-vamp. The previous stage one and two kits became Pluspac A and Pluspac B and the stage... kits took on a different make up of parts which had expanded significantly, unfortunately throwing some confusion in to the mix over what is what. Today that confusion has worsened with the introduction of previously unheard of levels of tune – stages four, five, six and even seven being introduced to further befuddle Mini owners. Considered on their own it would seem logical that each step up the performance modification ladder should have its own title. And that would be fine if everybody was singing from the same song sheet. But theyre not and thats where the confusion comes in, although many of the higher stages of tune are really only applied to cylinder head modifications. The general public could easily take the rap for this because it is really only consumer pressure that gets vendors into doing all this stuff in the first place. So how to sift the chaff from the wheat or make direct comparisons? Oh – and adding the fact that we are now talking about both carburettered and injected engines sullies the water further. Thankfully most vendors would admit that there are certain basics stages of tune that can be compared since they offer similar modifications. What changes are the components within those kits. Sorting some basic guidelines will help make those comparisons easier. Check out the panels for a low-down on whats what.
In reality for road performance application there really only need be those same three stages of tune originated by ST all those years ago; a solution to the factory-fitted asthma-inducing induction and exhaust systems (stage one), a further performance boost without getting to busy with the engine in the shape of a stage one kit plus a decently modified cylinder head and may be high lift rockers (stage two) and lastly a mucky to the armpits kit (engine needs to be removed and partially stripped down) that is the stage two kit with a camshaft change (stage three).
PANEL 1
Stage One kit – carburetter-equipped engines.
Pic 1
Somewhat different to the ST-developed stage one kits, the modern kit should include a replacement air filter element to fit in the standard casing, an aluminium intake manifold, carb needle, carb to manifold gaskets, manifold to head gasket, exhaust manifold, free-flowing exhaust system, an exhaust fitting kit and decent fitting instructions. I believe Mini Spares Centre, London were the first since ST to make a big effort in developing this type of kit. They applied all that had been leant since concerning air flow and engine performance enhancement yet maintained that fit and run ethos through protracted testing and careful design of the inlet manifold. It was not long before others were producing similar kits. The well developed kits using quality parts should boost the power of your standard engine by some 20% and torque by around 10%. Cheap performance that.
Inlet manifold.
Having the inlet manifold joined to the exhaust manifold as per the original standard item is a bit of a disaster because the extremely high exhaust temperature is transferred directly in to the inlet – not at all good for performance. The intact charge needs to be as cool as it can be without actually freezing. Water-heated aluminium inlet manifolds were developed early on – partly because of this and partly because casting small volumes of components in aluminium is far cheaper than in iron. However, they didnt become particularly efficient until the early 70s when Howley Racing brought out their version. At around the same time Oselli Engineering Services also produced a similar product called the Torquemaster. These two manifolds changed the face of single SU inlet manifolds. Unfortunately both were conceived to maximise flow/performance which meant short-comings in fitment. The lack of up-sweep caused the carb jet to hit the bulkhead if the engine steady bushes were in anything less than perfect condition and precluded the fitment of the standard air cleaner. In fact it also precluded the fitment of most after-market replacement filters at the time until K&N got their act together on it. Not surprising really since the legendary John Chappel who owned Howley Racing also started Advanced Products and what has become the K&N empire in Europe. Others fell into the same trap by copying them, some applied some though to the job and got it right. Most kits these days come with a manifold that will take the standard air filter casing. This was considered essential for civility in use – replacement cone and pancake type filters producing a good deal more noise. Some manufacturers oopsed by copying the MG Metro inlet manifold. Performance-wise it was good, it was the 5/8-inch bore manifold heater pipe that was not. The Mini had 1/2-inch bore heater pipes at the time! So be aware of this one. For 1275 Coopers from 1990 on no inlet manifold is needed since it is already equipped with the MG Metro type item.
Air filter.
As mentioned above, retention of some civility comes high on many folks agenda. Open carb mouths or fitment of pancake/cone type filters produce prodigious noise when the engine is under load. A standard air cleaner with replacement element is much quieter and does not loose much, if anything, in performance.
Carb needle.
Essential item when changing away from the completely standard set-up. Improving the breathing capability of the engine means it will be able to inhale more air. This means more fuel will be needed to keep the mixture at the right strength. It does not mean you will use more fuel since the engine will make more power, requiring less throttle angle to make progress. Generally a better mpg will be seen. On the other hand – all that extra go does encourage more, shall we say progressive driving... If the kit doesnt come with a needle it is likely it hasnt been properly developed. As a guide line, efficient kits that retain the standard air cleaner casing will likely need an AAU needle and those with replacement cone/pancake filters an AAA needle for 998 engines. For early 1275s (i.e. Clubman GT) with single 1.5-inch SU an AAK with standard filter casing, an AAR or AAU with cone/pancake filter. For later 1275 engines with 1.75-inch single SU use a BDL with standard filter case or BBW, may be BDK with cone/pancake type. These are near-enough guesses. A rolling road tune should be sought, no matter what, to get the best results from the kit on your particular engine.
Exhaust manifold.
ST used the standard iron one, even with twin carbs. However, superior performance can be had from a quality tubular steel one. For 998s this has been distilled down to the excellent Maniflow Freeflow example and for 1275s a medium bore LCB. There is not a lot in it between the Freeflow and LCB on a 1275, and it has to be said that getting a good seal between manifold and system is a whole bunch easier on the Freeflow! For 1990-on 1275cc Coopers, no exhaust manifold change is necessary as the standard LCB type manifold is pretty good.
Exhaust system.
ST discovered early on what a difference a decent, low restriction system can make. In fact this makes more of a difference than the manifold does by quite a long way. Pictured here is the all-hallowed RC40 system developed way back in the 70s by a very clever exhaust systems designer at TI in Blackpool - often copied, never bettered. The kit should come with a free-flowing system with a bore diameter of no greater than 1-5/8-inches/41mm. Particularly for the small-bore (998 etc.) engines. A larger bore will cause performance loss on the small-bore engines and produce a serious resonance/droning on all motors at cruising speeds. Larger bores will make more noise at all times no matter what. Thats physics for you. Oh – unless its got a seriously restrictive silencer – which is defeating the object of the exercise. A good fitting kit is also essential for the heavier exhaust, and to keep the exhaust hung on rubber to avoid drumming on the body shell. For later catalyst equipped cars then a quality, free-flowing rear exhaust section is needed (same as that for the injection cars). Post January 1992 cars/engine numbers have to retain the cat – which is a shame as the cat used on these carburettered cars is grossly inefficient, consequently costing a pile of performance!
Panel 2
Pic 02
Stage Two kit - carburetter-equipped engines.
Wit h the induction and exhaust systems optimised with the stage one kit, the next restriction to air flow in and out of the engine is the cylinder head so the next logical step is a properly modified cylinder head. Great advances in head modification development has pretty much done away with needing a half dozen variations. For all but race use probably three specs will get the job done for 1275-based engines and really theres only one way to go for the small-bore units. For most road/road performance 1275s a head with 1.401-inch/35.7mm inlet valves and 1.16-inch/29.5mm exhaust valves and a good porting job (efficient, not BIG)will work well, even when going to stage three. A stage two kit here could also include 1.5-ratio rockers for the 1275-based engines. For the small-bore units the head needs to be pretty modified to make it worthwhile. So were looking for a healthy porting and chamber job and valve sizes in the 1.216-inch/30.9mm area for the inlets and 1.040-inch/26.4mm for the exhaust. Could include a 1.3-ratio rocker set, but dont be tempted to go 1.5-ratio rockers on the small-bore units. The kit should include all the gaskets required to fit the head and rockers if included.
Panel 3
pic 03
Stage Three kit - carburetter-equipped engines.
To get any decent power out of the A-series a better camshaft is needed. So with a motor already equipped with decent breathing capability choosing a suitable cam is the nest step. The kit would obviously comprise stage one and two kits plus a cam. There are all sorts of cams on the market with all sorts of performance envelopes. I would very strongly advise against anything too wild. It makes driving the car on the road a real pain unless flat out everywhere. If I were selling a kit Id offer two options here – one with a cam that gives a very smooth idle, pulls like a train from 1,000rpm, gives big torque and peak power around 6,000rpm and one with a cam that is OK low down, but really gets its butt into gear around 2,000/2,500rpm and takes off like a scalded cat for those wanting performance that can be used on track days and weekend race pursuits such as hill climbing. The kit should come with quality cam followers and cam lube as a minimum. Again, if they were my kits Id also include an adjustable cam drive kit so the cam timing can be set spot on – or maybe a set of offset cam keys – along with explicit instruction. Getting the cam timing set right is essential when fitting a sports cam otherwise a heap of performance can easily be lost. Note that the engine need to be removed and partially stripped foe a cam to be fitted, more so on the 1275-type engines.
Panel 4
Stage One kit – injection-equipped engines
pic 4
The advent of the factory injection-equipped Minis needed a re-think on the tuning kit front. Largely because an electronic brain (Engine Control Unit – ECU) had tight control over the fuelling and ignition systems and could not be re-mapped. Only the ignition could be altered slightly with a piggy-back unit that re-interpreted the info going in and out of the ECU. The fuelling could not be messed with. To do this meant an expensive alternative programmable ECU accompanied by its own sensors and pick-ups. Not at all value for money. So great care needed to be taken when developing a new kit to make sure the engine didnt run too lean – it would destroy pistons and possibly the engine. A consequence of this is fewer parts to replace initially.
Air cleaner.
As with the carburetter equipped engine similar rules apply here, although the standard injection filter casing is a little more restrictive than the carburetter version, but the row created by the cone replacement is as annoying!
Exhaust manifold.
Although the standard exhaust manifold and downpipes are not too bad, extra performance can be gained by changing the downpipes so the kit should include this. The assembly should have a knuckle joint in it to replace the standard flex joint (you REALLY dont want to break that cat!), a boss for the Lambda sensor and flange fort he cat to bolt up to.
Exhaust system.
The cat on the fuel injected cars is not at all restrictive so costs no performance but that rear exhaust section most certainly does. A quality rear section again with around 1-5/8-inch bore is whats needed. Big Boy drainpipe exhausts may not loose much performance by comparison, but boy to they get you down after driving for a while. Kit should also contain the necessary gaskets for the exhaust/cat, studs& nuts for the downpipes to manifold and new rubber hangers.
Stage Two kit – injection-equipped engines.
pic 5
This kit has also become known as the GSi kit, originally developed I believe by Swiftune Racing, Bethersden in conjunction with John Cooper Garages, Ferring to dramatically brighten up the performance of the injection-equipped cars that despite sporting 1275cc engines were strangled by the whole injection system. As mentioned in the injection kits intro, care had to be taken to ensure reliability where fuelling was concerned. Extensive dyno testing showed the system to be kind-of self regulating/limiting in the power out put stakes though since the ECU would only supply enough fuel to make at the most 85bhp no matter what you did. Generally a real 81-83bhp was achieved. And considering most folk would not be driving their cars with throttle buried in the floor for protracted periods, it was unlikely damage would occur. In any event, the most impressive change was how the cars drove generally rather than improved peak power. A whole lot more sprightly. Many tried to improve peak performance by fudging the fuelling by increasing the fuel pressure in the system – either by crushing the standard regulator (YUK!) or by fitting an up-rated regulator. The biggest draw back with this is that it over-fuels everywhere since it is not throttle position/load regulated. As a consequence mpg dived and engines ran very roughly low down. Many not passing emissions tests and trashing catalysts – a very expensive problem. You have been warned!
Similar to the stage one kit it does not generally include the exhaust downpipes to keep the cost down. If yours are tatty, then its a good idea to use the downpipes as in the stage one kit. The major inclusions here then are the cylinder head and rocker gear.
The cylinder head should be modified in line with what was said in the carburetter-equipped kit. Big ports mean low gas speed, and on an engine that is limited to 6,500rpm, big ports are most definitely not needed. Shape is all important. Plus retention of the locating ring recesses even in a small amount otherwise port miss-matching can be an issue. The rocker gear could be either roller-tipped or forged. The forged option should make the kit somewhat cheaper. Personally I find the forged rockers more than adequate.
As well as the necessary gaskets to complete the task, a set of colder running spark plugs are needed otherwise a misfire can develop on the standard fitment ones through getting them too hot, especially at the top end/peak power/rpm when the mixture is leaning off.
Stage Three kit – injection-equipped engines.
Just like the carbed version, with the induction and exhaust system sorted out, the cam is the next restriction. Unlike the carbed version, there is no choice – or should be no choice – in cam options as far as performance envelopes are concerned. Fitting a road-sports cam is just not going to work well bearing in mind the rev limit imposed by the ECU (6,500rpm) and the issue of a severely leaning out mixture at the top end. This will be exacerbated by the longer duration/greater valve over-lap of a road-sports cam since trapping efficiency will be worse. What is needed is a cam that has very little over-lap but a decent amount of lift and will work with 1.5 ratio rockers. Cam manufacturers have their own versions of cams for the injected road engines, and of course there is the ubiquitous Swiftune Racing SW5 profile. Personal experience pegs the SW5 as the cam to use.
It is absolutely essential that the cam chosen is the correct one for your injection engine as it has a sensor pick-up on it that will not let the engine run if it is not there! Consequently re-profiled cams can only be done on original injection cams. Quality followers and cam lube supplied, and again – as with the carbed kit – my kits would include some way of timing the cam in to its required position to ensure maximum performance is gleaned from the fitment since the engine has to be hauled out and partially stripped down to fit the kit.
Pic 06
The standard iron manifold is not conducive to improving performance beyond a certain limited level. Mainly because of the exhaust section being limited in area at the outlet where it meets the exhaust pipe. The other issue is the heat transferred to the intake because of the one-piece design.
Pic 07
Far better breathing capability is given by after-market ally inlet and tubular steel exhaust manifolds. In particular the exhaust, the large bore has the capacity to deal with greater exhaust gas volume.
Pic 08
A great deal of performance improvement comes from the exhaust system. Standard exhaust is serious small (the pea shooter as its affectionately known), RC40 on right is far more suitable and very non-restrictive.
Pic 09
Maniflow Freeflow on left is ace for 850/998/1100cc variants and will work well on 1275s too, but medium bore LCB gives an edge at the top end.
Sorry theres no pics - but Im sure youll get the drift fro mthe copy... KC
Posted: Feb 25, 2006 09:38 PM