Injection cars - SPi-TPi tuning, basic information
I've been getting a lot - well even more than normal - of questions concerning tuning the injection engined-cars of late as more and more folk are looking to tune their modern Minis. Many are frustrated by the lack of product availability to achieve what they want, some are experiencing problems with the standard ECU and others are plain hacked-off at the lacked of useful information on how to go about tuning the injected cars. In particular whether removing the Cat is a good idea, and whether there are any problems as far as the standard ECU (electronic control unit, or 'brain') is concerned when changing chunks of the standard engine - like rocker gear, cylinder head, etc. and just what can you do in the way of tuning and it's effects. It would seem other sources approached for the information are either playing their cards close to their chests, making loud sucking-air-through-teeth noises and 'hmm, well...' black-magicky sort of inferences, or simply/patently just don't know. So let's tidy that lot up for a start.
The standard injection Cat is very efficient - both from a 'cleaning up emissions' point of view and from a 'non-restrictive' one. Tests carried out by both myself and A.N.Other prominent A-series tuner have found the Cat to cost only a couple of horses right at the top end of the rpm band on modified engines developing more than 104-ish bhp (where the standard ECU has been replaced with a programmable one along with sensors, wiring harnesses, etc.). Junking the Cat is therefore pointless unless absolute maximum power is sought, and the aggro of re-fitting the Cat each MOT-time won't be an issue.
The standard ECU has a very broad operating range. I am currently doing a development program in cahoots with a learned friend and colleague to cover the whole schmooze of SPi/TPi tuning from simple add-on bits to serious add-on bits and power increases. As far as we have gone, the standard ECU copes with up to the 'GSi'-level tuning (Modified head, high lift rockers, replacement air filter element, rear exhaust section, etc.) offered by a number of the specialists.
Incidentally - this development program was instigated by the lack of available information on such stuff, and a worrying lack of information known by some who are marketing these kits. Brought to the fore by the aforementioned enquirers being worried about being flogged a heap of bits with little more than - 'nah, it'll be alright mate'…It has taken nearly a year (excluding all the time I have previously put into the injection tuning possibilities right from the start) so far to uncover all the why's and where fore's, do's and don'ts, what's possible and what isn't and source a suitable programmable ECU that doesn't cost a fortune that will integrate with the standard sensors and Rover harness (to include alarms, etc.). The standard ECU is of the very powerful and sophisticated 'MEMS' type - not the simple-by-comparison systems used on most Fords and Vauxhall's. Consequently most electronics engineering companies that develop chips and such for tuning electronic engine management systems have been defeated by the Mini's complex system. And that's one of the reasons for folks' frustrations - there's a plethora of stuff available for Ford/Vauxhall tuning but very, very little for the good old Mini!
My colleague and I have sourced the 'Holy Grail' - but the manufacturers are being very dogged about releasing the ECU before they are more than happy and confident with it - they want it to be totally reliable and fit as many MEMS-controlled engines as possible. Consequently ironing out any bugs that surface when used on any of the systems has taken time. Neither they nor us have the sort of budget and facilities the major manufacturers have to carry out such projects so patience is required. Unless someone out there wants to invest a very, very large sum on money in the project?
Anyway. The standard set-up copes, but it is getting border-line on mixture strength with the afore-mentioned 'GSi' kit fitted. The engine survives at this level because of the carefully controlled ignition timing. Addition of what would be described in the motorcycle world as an 'ignition advancer' (items like the 'Icon' boxes) really doesn't appear to do a whole lot - except perhaps push that borderline a little closer to the edge of the envelope. Also, the practice by some of crushing the fuel rail pressure regulator to increase fuel pressure in the rail in an effort to richen the mixture isn't warranted at this level. A number of piston-melting situations have also high-lighted that if you are going to advance the ignition timing by moving the reluctor ring - you need some accurate data on engine performance before you do so, and be vary careful how far you advance it.
We have tried all the combinations of parts, adding one component at a time to see where the major improvements were made. In conclusion it we decided that really the whole Gsi package is needed to give any definitive benefit. Adding just the rear exhaust section helped more than the air filter replacement. It sounded better and gave a very small on-the-road performance increase. Adding the rockers achieved a very small further increase not really detectable on the road. One of these ignition advancers was tried in conjunction with each component fitment after the test on each addition was done. At times it seemed to make the engine run smoother at idle, other times not. It certainly didn't make any discernible difference to on road performance or power output. The final addition of the modified head seemed to pull all the oddments together as there was a reasonably significant over-all performance improvement.
Power output claims don't vary a whole lot - and for good reason. The limiting factor, as stressed previously, is the ECU. Beyond the aforementioned GSi type kits, further modifications net no further power output. Well, may be the odd one or two, but not significant gains. From all the combined efforts of myself and Swiftune Racing the most we've seen is 85bhp. And that is despite going further with mods to intake manifold, throttle body and air cleaner, adjustable fuel pressure regulators, complete replacement exhaust systems, current specific camshafts and higher ratio rockers (over the 1.5s). The best average is 82-83bhp. The worst was 78.4. Standard the injection engines give a quoted 63. And this - oddly enough - is pretty consistently accurate. A couple of companies claim considerably higher outputs. I have tested a couple of cars fitted with the 'Full Monty' 90bhp kits - and found them lacking. One gave just a tad over 81bhp, the other 83bhp. Both owners were somewhat disappointed considering the comparatively large extra cost involved, and the poor mpg.
The main power increase is at the top end; only a small increase in power is gained from low, through mid range and up to the top end. There is also a marked difference in power actually achieved with some kits as opposed to that advertised. Generally though, most do make the car a much better drive.
Instead of brutalizing the standard fuel regulator to increase fueling you can fit an up-rated pressure regulator that increases the fuel pressure in the fuel rail, which richens the mixture. Trouble is it richens the mixture through the whole engine performance band - and that means a very marked increase in fuel consumption. Down to around 22-24mpg - bit rude for a Mini! Our testing has concluded that, although there is a definite increase in power, it isn't sufficient to justify installation and running costs! Plus you must remember over-fuelling will destroy the Cat pretty quick…
Next stop is what does a cam change do, and how far can you go with it. In particular - what happens to emissions and mixture since most performance cams use an increase in overlap in the quest for more power, which will murder emissions and cause rough-running nightmares. Folk have spoken to me that have fitted cams like Kent 276 and 286 types and claim the car runs fine. I have experienced only one such engine - and that ran far from 'fine'. It had the lumpy-running attitude of an engine that promises to give a blitz of power once it comes 'on cam'. It even had that slight 'kick' when the engine components eventually got themselves to a point where the engine would run OK. Bu the bald truth was soon uncovered on the rolling road. It was 15% DOWN on power and the emissions were all over the place! Either a very special cam needs developing, or a fully programmable ECU is needed…
There is currently only one ECU on the market that has been specially developed that will run off the standard Mini sensors and basic harness. It still requires a jumper lead between ECU and standard ECU wiring plug to work since there are several versions of ECU and loom on the injection Minis to further complicate the issue. The snag is the cost - it's £750 + VAT, plus a further cost for the jumper lead. And you still need to buy the software to program the thing! For those that are desperate and have hoops of money burning a hole in their pocket - we can supply them if necessary. BUT - my advice is to be patient. The ECU we are after is currently being reliability tested on a standard MPi here in the UK right now. And we're looking at a customer purchase cost of around £350…
Useful part numbers:
C-STN20 Performance kit for SPi Mini containing; modified cylinder
head with race quality valves and guides, RC40 rear exhaust
box and Cat link pipe, 1.5-1 ratio
roller-tip rockers, K&N replacement element air filter, set
NGK BPR7ES spark plugs, head gasket, thermostat gasket
Injection manifold gasket and rocker cover gasket.
C-STN20BUDGET As C-STN20 except head fitted with modified road-
spec valves and guides and non-roller-tip 1.5-1 ratio
C-STN21 TPi performance kit - as C-STN20 but uses TPi head casting
C-STN21BUDGET As per C-STN20BUDGET but uses TPi head casting
C-STN22 Stage one kit for SPi and TPi Mini containing: RC40 rear
Exhaust box with Cat link pipe, downpipe from manifold on
TBI and pipe, new downpipe studs, new downpipe nuts, new
Downpipe to manifold gasket, new Cat gasket, new rubber
Exhaust hangers, K&N replacement air filter element and