Engine - 1275, 95bhp sports/tourer test result
DIY enthusiasts often believe that building an engine to give excellent all-round road performance is beyond them. Mainly from comparisons made between what they have been able to achieve and what specialists say should be achievable from any particular type of engine build. Generally scrambled further by the non-perfect match of parts and components used between aforementioned specialist and erstwhile DIY-er, and the ritual 'nose-tapping and knowing winks' display of those specialists. Something you can very nearly 'see' even when talking to such folk on the phone - or that inimitable 'ah, yes, well…' So some form of 'black art' is implied. Whilst there is most definitely a degree of 'feel' involved between the real specialist's results and those of just a good engineer - the bones of the deal is subject to no such thing and is certainly within the capability of the DIY enthusiast given the necessary information. And that has been the problem. Despite a true plethora of books written on the subjects of blueprinting and tuning of all manner of engines (i.e. 4, 6, 8, 12 cylinder and so on) not all of it is relevant to our wonderful, archaic A-series and not easily transposed by the DIY-er. What is needed is very specific information appertaining to our unique A-series engine.
To supplement this, it would be even better if this would encompass a very specific engine build as far as all components used and for a specific application. Daunting if you consider the myriad of cam/head/carb choices voiced by the multitudes of A-series meddlers (not at all meant in a derogatory way, as I include me in that description) used over the years. Of which there are roughly four 'camps' - the 'good old boys' from the Mini's inception, the 'young whipper-snappers' of more modern technology, the 'liberals' using a bit of both and lastly the 'T-BASE' brigade (those that have read and re-read David Vizard's 'bible' on A-series tuning so that they can quote chapter and verse, strangely enough encumbered 'Tuning BL's A-Series' - hence T-BASE).
Fortunately this whole tuning deal has gone round very nearly full circle and has tried just about every combination possible with whatever modern technology was suggesting was 'the way to go' at the time. And some very talented and clever folk have given more than their two-penny-worth into the bargain. What that has given us is a vast reduction in the prolific list of possible components to make an engine suitable to our needs. Particularly where modern road/street performance is concerned. The main criteria being an engine that idles smoothly, has exemplary emissions levels, pulls strongly from low rpm, will give rapid overtaking performance yet be fun all the way to the useable (sane/sensible?) redline when the situation presents itself.
It was to this end that I carried out the 1275 engine build detailed in the relevant articles, and to prove that having to go out to 73.5mm bore (1380) isn't an absolute necessity to have a blistering street performer.
So given a straight forward engine build with proper detailing and 'off the shelf' components list consisting Swiftune SW5 camshaft, Min Tec 'road rocket' type head (as supplied by Mini Spares/Mania), 10.4:1 compression ratio, standard crank, A+ rods, Mini Spares/Mania 'Mega' piston set +0.040", lightened duplex gear set, single 1.75" HIF SU, Mini Spares intake manifold, Maniflow medium bore LCB, RC40 exhaust system, K&N cone-type air filter, 1.5 roller-tip rockers and Aldon Yellow non-vac dizzy, along with the other necessary engine build components what kind of performance is easily attainable?
The first rolling road visit was a disaster as far as I was concerned. When running the engine in it felt terrifically strong. After 400 miles it went on the rollers. The result simply wasn't what I expected - a measly 78bhp at the crank. I had come to expect around 92-95bhp from engine dyno tests. The dizzy wasn't giving the figures it should and was making set-up difficult. So the testing was aborted. I started to think there was something else to blame. Once home I checked everything from the tyre contact patch to the carb mouth and everything in-between - tracking, camber, wheel bearing drag, brake drag, gearbox drag, cam timing, sorted the dizzy advance/ignition timing problems (not deemed to be causing the massive deficit in power), valve/cam timing, valve/lash clearances, valves sticking in guides, compression test, leak-down test, manifold air leaks, carb condition, fuel supply, everything. Absolutely nothing suggested anything was wrong anywhere. And that is very annoying since at least if a reason is found it solves the problem and takes away the doubts.
Then I started to suspect the exhaust system since manufacturing techniques had altered somewhat from the original RC40 systems. I decided to run a test on exhausts as part of the re-rolling road test to check on this (see 'Exhausts - Millennium and others tested'). But even this wasn't really conclusive in my mind. Then I remembered my notes when building the engine and went back to them - concerning the 'Mega' pistons. I had commented on how tight the engine felt when the short motor assembly was checked. Removing the pistons/rods and re-building/re-testing with the rings removed one type at a time until only the oil control rings were left I found the oil control rings were the cause of the increased tightness I was getting. I decided to re-run the rolling road test with the rings as is and just do the exhaust swap to see what gave there and deal with the rings if there was still a major power deficit.
Back on the rolling road with only the dizzy vac unit removed and re-timed as Aldon suggest and 1,000 miles on the clock, the first run was done with the mixture as it was last time. And bingo! - the missing power was there immediately! The mixture was leaning out slightly at the top end, so a needle change was made and a re-run done. The ignition wasn't changed any from where I set it - at 28 degrees max advance proving very efficient combustion. The conclusion was that the Mega oil control rings take a good few miles to settle themselves in (see 'Pistons - Mega ring performance').
The results were astounding:
Road speed Rpm BHP Torque
30 2,800 54.1 89.54
40 3,700 67.0 95.10
50 4,600 80.1 91.45
60 5,400 90.3 87.82
70 6,300 92.0 76.69
80 7,200 87.0 63.46
Emissions at idle were 3.5% CO, and only a mere 697 HC!! Where 1200 HC is a vehicle test pass!
I can't tell you how much fun this made the car to drive. It is blisteringly quick for general road use, has so much urge that over-taking is a cinch, and would definitely benefit from a final drive change to a 3.1. With the 3.44 currently fitted you get in to top gear and then just press the go-pedal no matter what road speed you're at! Incidentally the tests were all done in third gear to assimilate more closely road driving. It's not as hard on the car or rolling road either. These figures are almost identical to those gained from dyno sessions on this type of engine build - so the exhaust wasn't the problem at all.
These figures are real, no bullshit, achievable results from simply following the engine build articles and components usage. Sure, a 1380 will be even better - but not by that much. The dyno results suggest only a few more horsepower and barely a handful foot-pounds more torque. Going the +0.040" over-bore route you will still have at least two re-bores to go on that precious block!