|
3 April 2001 |
The 1098 (1100) engine
has had a lot of bad press over the years - largely because of early experiences
when trying to tune the motor brought about problems with the then standard
components available - they simply were not up to taking any real punishment as
experienced in racing. This fallacy was handed down generation to generation
like some scary bedtime story. Those that have used the unit in more recent
years, employing more capable componentry know what a
demon motor this can be. Following is an initial look at what it will do with a
little modification - the results compared directly with it's
smaller brother the 998 for illustration of the potential.
Abridged History
When the Mini was first
conceived it utilised a de-stroked version of the then quite remarkable 948cc
A-series engine. The 948 was itself a development of the very first A-series
engine used initially to power the A30 in 1952 and the redoubtable Morris Minor
in 1953 - an 803cc job (2.28-in/57.91mm bore, 3.0-in/76.2mm stroke giving a
bore to stroke/stroke ratio of 1.316) designed in the philosophy at that time
of long-stroke, high torque engines needed to haul the tank-like structures,
called cars back then, around. Rpm for power wasn't in sight. In the good (?)
tradition of vehicle manufacturers, tooling costs featured prominently in
evolution of the species; so when a re-think on the rather wimpy and feeble 803
was conducted in 1957, they simply increased the bore size and beefed up the
bottom end components - a nod in the direction of the flowering idea that small
bores limit breathing capability and therefore valve sizes. Both
restricting rpm potential - and consequently POWER. Not that the 948 was
a fire-breathing monster with its new 2.477-in/62.92mm bore and slightly
improved bore/stroke ratio of 1.211, but it was a start and an appreciable
improvement power-wise.
More importantly, it was
more tuneable. The 803 would wilt at the thought of any decent modifications
for power, the 948 was a trooper! Willing to run easily to 6,500rpm (steady
now!) it attracted a host of tuners - some inexorably drawn into the
character-full A-series engine big time. The likes of
Alexander Engineering, Speedwell, Downton, and of course the irrepressible John
Cooper who was carving swathes through the field of Formula Junior
(yester-year's Formula 3000). We owe those folk a very great deal. Especially as it spawned the Mini Cooper legend, starting with the
997cc version.
Remembering the comment
re manufacturers and their production/tooling costs - the increase in engine
size didn't follow the short stroke/big bore angle being whole-heartedly investigated
by Ford at that time. No, they simply re-stroked the 948 to 3.2-in/81.28mm and
reduced the bore a tad to 2.457-in/62.43mm - giving a bore/stroke ratio almost
as bad as the 803 had at 1.302. Difficult to comprehend as it was clearly a
step backwards, but then this short-sightedness was the downfall of the whole
British motor industry. Didn't stop the car being embarrassingly quick though
as it was in a very compact, nimble little car - the increase in torque and
power doing it's job admirably.
Jumping forward a
little, The 997 gave way to the far better and more efficient 998 series. The
increase in bore and reduction in stroke to what the 948 was originally
(2.543-in/64.59mm, 3.0-in/76.2mm respectively) gave a healthier 1.179
bore/stroke ratio - the reason why it revs so freely without doing itself an
injury. Especially when a more efficient head with bigger
valves on it was used as in the case of the Cooper. The introduction of
the
Power Potential
I've ignored all the
different power figures for the multitude of variants thus far on purpose -
they're simply not relevant. The relevant figures are those directly comparable
for the mission of comparing the improvements made between the 998 and 1098.
The 998 in low compression guise (8.9:1) gave an OE recorded out-put at the
crankshaft of 38bhp @ 5250rpm, and 52lb ft torque at 2700rpm. By comparison the
1098 gave 45bhp @ 5250rpm and 56lb ft @ 2,700rpm. That's 26.5% more than
the 998 AND it had an even lower compression ratio of a measly 8.3:1! Not only
that, but the figures written down don't show the actual over-all torque curve
that makes the 1098 engine a much nicer road-orientated engine as it pulls well
from almost anywhere in the rev range. How? Surely it wasn't simply the stroke
increase and head up-grade? You're right - it wasn't. Much of this was down to
the camshaft. The increase in duration was a definite step forward. In fact the
camshaft proved so impressive that the profile was employed in the first
production Cooper Ss.
Through countless
rolling road sessions by the multitudes, we know we can expect a reasonable 20%
bhp and 12% torque gain simply by bolting on a quality stage one kit - so
that's an extra 9bhp and 6.7lb ft giving 54bhp and 62.7lb ft torque at the
crankshaft. Pretty much what the Cooper 998 variant was achieving bhp-wise, but
loads more torque. Definitely something to build on then.
The Test
What I was looking to
achieve was a usable, non-stressed, but substantial performance gain without a
wallet-shrinking budget. To wheel out that golden nugget of mine - 'tuning
should be a compromise of what's possible and what's necessary'. Applying this
will ensure the former stated goal and also be directly comparable to the 998
engine tuning covered in the relevant articles. Incomparable data and testing
is a complete waste of time as it means/proves little when the question 'but
how much better is it than what I have now?' is posed.
To ensure the test was
as comparable as possible, a similar set of rules was used as in tuning the 998
to avoid a car that is exciting for the first few miles, but a pain thereafter,
maintain some semblance of reasonable mpg, and not have the engine go 'pop' the
first time the pedal's firmly pressed to the metal.
For this test I had to re-build
an old engine. Simply because I didn't have a super-low mileage engine to work
with like when I did the 998 test. However, no 'trickery' was used to enhance
power out-put. This test had to be as comparable as possible to that which you
folk can easily achieve. The only concession here was to the pistons. The only
pistons now available in the
The gearbox used was a
straightforward, standard A-plus ratio-ed item with a 3.44 final drive, centre-oil
pick-up, and competition diff pin from Mini Spares Centre. Again, a nod in the
direction of spirited use the flywheel assembly is the old three-piece,
pre-Verto type. It did not influence the test in any way.
And to continue the
'totally comparable I decided to stick it in the front of my old nail - the one
I did the 998 test in - thus exactly duplicating the running conditions as far
as possible.
The Modifications
Minimal cost for maximum
gain is the name of the game. The parts I decided to alter slightly were the
camshaft and rockers. I've been itching to get some real data on how the
Swiftune Racing (01233 850843) SW5 cam performs in something other than a 1380.
Comparing the profile data using standard sintered rockers against the 997
Cooper cam with 1.3 ratio rockers gave fairly similar
results. I can't give exact data on what the special SW5 cam is - well I could
but then I'd have to kill you, and to be honest I simply don't have the time
for 165,000+ assassinations right now! Anyway, as the match was so close it was
a good chance to see what this cam did in a small-bore unit, and thought the
1100's characteristics would be able to deal with the slightly sportier
profile. This whole cams/rockers decision was based around the problems that
higher-ratio rockers can cause with various sportier cam profiles in certain
engine sizes/build specifications. The crucial point is at overlap; at best it
re-arranges where the engine performs or at worst it can kill an engine's
prospective whole power/torque out-put.
Unlike the 998, the 1100
is a little fussier on the ignition advance curve side of things so I contacted
those illustrious folk at Aldon Automotive (01384 572553) to brew me up
something a little different. I gave them some suggested criteria to work to,
as I had planned on doing the dizzy myself - but 'the best laid plans of mice
and men' and all that…Aldon's 'dizzy-master' built me
a dizzy along the suggested lines and a little of his own magic - and it works
perfectly! It isn't a great deal different to the Aldon 'Yellow' spec dizzy, so
one of these would function admirably. I'm also running one of the excellent
Aldon/Petronix Ignitor electronic ignitions. Having used these almost
incessantly since their inception they never cease to amaze me where
performance against cost is concerned. I've long since become blasé with how
easy they are to fit.
So the camshaft, rockers
and distributor were the only difference to that if the 998 test. Same spec
Mini Spares Centre-derived cylinder head, same compression ratio, same
induction and exhaust, same gearbox and final drive. Same car
even.
I swapped the motors
over, using the same carb, exhaust, etc. from the 998 test - even down to the
carb needle. A little contemplation revealed that it wouldn't be too far out.
In fact from previous 1100 experiences they seem to end up a slightly leaner
needle compared to a directly similar 998.
The Method
This time, instead of
doing the standard head and rockers thing to start off with, I'm doing the Full
Monty from the off. I already know what a standard 1098 is capable of. We have
relative and accurate data on what the various changes made on the 998. Passed
experience has proven the data collected when applying up-rated equipment to a
given power unit on GRV's rollers in stages is
accurate enough to make meaningful percentage-based comparisons. Plus it keeps
the costs down on this development work. What? You thought I was accruing all
this limitless expense out of the goodness of my heart and for your
delectation! You're mad.
The Facility
Once again I visited the
excellent GRV (01706 377410) rolling road at Littleborough, Lancs. This
maintained the comparative test idiom, and ensured the engine was set up
perfectly by the venerable Andrew Preston. For further information and
comparative data, I popped down to see my good buddies Peter Baldwin at
Wilshire's Garage in New Whimpole, Cambridgeshire
(01223 207217) and Michael Barratt of MBE in Lincoln
(01522 545189). Sticking it on their individual rollers after set-up at GRV
will give those of you obsessed with rolling road comparative figures something
to work on.
After having the 1100
engine set-up on GRV's rollers I then zoomed down to
M.B.E., and then down to Peter Baldwin's at Wilshire's Garage. I picked the
other two as they are well used by many a Mini owner, and are within reasonable
striking distance of my home in the wilds of
The result was M.B.E.'s gave exactly the same as GRV's
(54bhp at the wheels) and Peter Baldwin's gave 70bhp. I haven't said 'at the
wheels' here because Peter has had his machine set up by legendary
 Graph A |
Click to show an enlargement of this graph |
Graph B |
And this week's winning
numbers are…astounding.
KC1100 (graph 'A') -
Re-built 1098cc engine, standard apart from Swiftune Racing SW5 camshaft, stage
three cylinder head and stage one kit.
KC-MINI (graph 'B') - Standard
998 engine with 997 Cooper profile camshaft, same stage three cylinder head as
KC1100, 1.3 roller-tip rockers and stage one kit over-laid on KC1100 graph.
Taking graph 'A' on it's own, the results look quite impressive, considering
it's a 40+year-old design engine with some relatively minor modifications. Peak
power out-put is 54bhp at 5,741rpm at the wheels, pulling strongly from way
down at 1,500rpm with a slightly up-ward bulging curve all the way. Nice. But
just look at that torque! Torque is what accelerates the car - and this has
plenty of it in exactly the right place. When motoring generally the engine is
usually working in the 2,000-4,500rpm bracket. This little baby is producing
prodigious amounts of torque throughout the whole of this range - starting with
very nearly 50lb ft at 2,000rpm, peaking with 59lb ft between 3,500rpm and
4,100rpm, but hanging on with 50lb ft at 5,500rpm. Monster.
And there may have been a couple more horses, but Andrew didn't feel too
comfortable about running this near-standard motor up to 6,500rpm just for the
fun of it. After all, it's a long walk home from there to home!
Over-laying it onto the
previous 998 engine test results (graph 'B') the true picture really shines
through. The 998 was good - but the 1100 is stupendous. It makes an average of
7.5bhp (10bhp in most places) more than the 998 all the way up, and a huge
13+lb ft torque! As with the 998 - we both decided messing with the cam timing
wasn't worth the effort in view of the results. Ignition setting was 6.2
degrees at 1,000rpm, no vac advance, 15.4 degrees at
1,000rpm with vac advance connected. Nice one Aldon. All this and it's still on
a standard air cleaner case.
What this doesn't show
is how incredibly emissions-efficient this set-up is. At idle with 3.5% CO
showing, the hydrocarbons were a mere 380! Now that IS unusual in a tuned
'ancient' engine.
And just to prove how repeatable accurate this rolling road is - it even
reproduces the 'weirdism' that is the vertical line
at the start of the 998 torque test results. On the last test on the 998s - it
was KC-MINI1 that had the line.
Comparison
|
Standard 1100 |
34-36bhp
|
44lb ft torque |
|
Standard 1275GT |
45-47bhp |
|
|
998 'KC-MINI2' spec |
48bhp |
46lb ft torque |
|
1100 'KC-1100' spec |
54bhp |
59lb ft torque |
That's
a stonking 50% bhp increase and 35% torque
increase. That's the effect the SW5 cam has.
The
modified 998 went very well, but you had to work it to get the best from it. That
means revving it a little harder most of the time. The 3.44FD was just a shade
too high with the standard A+ gear set. But then again a 3.15 would have been
just a bit too much considering how it needed to be buzzed to keep it active.
The 1100, on the other hand, just pulled. From anywhere in
the rev-range. It swallowed gears faster than the 998.
Interestingly,
and another 'bonus' of a rolling road visit, is being able to check actual road
speeds against rpm. The 998 achieved a 'real' 70mph at 4,40rpm, where the 1100
managed the same speed at a lower 4,300rpm. You'd think they'd make the same
rpm to achieve the same speed considering the gearbox ratios were identical.
Just further illustration that the 1100 doesn't have to work so hard to achieve
the same speeds. The speedo was reading 74mph at this point. Not bad
considering I set out to match the FD with the speedo using available speedo
drive pinion and spindles. This gives 16.28mph per 1,000rpm. Even more
interesting is comparing this with the calculus I presented way back in the
September 1998 issue when discussing final drives and how to sort what speeds
you get with different wheel/tyre combinations with some accuracy. After all -
there are loads of proffered methods for this. My method described there works
out on paper to 16.46mph per 1,000rpm. Now that's impressively close!
Conclusion
Far
from being the 'non-revving, boring, slug motor' the 1100 has been drubbed
with, it's a very capable engine that gives exceptional results for little cash
input. It would quite easily pull a 3.1FD without loosing the performance
results here. In fact it would probably enhance it, allowing further distances
to be covered in all gears with a more relaxed cruising speed.
Further
- what I think it REALLY needs is a Mini Spares Centre 'Clubman' close-ratio
straight-cut gear kit and 3.1FD to see what it can do!
During
the rolling-road session, the needle choice proved to be very close, although a
little on the rich side - particularly on full load. After some discussion with
Andrew on this, we decided to leave the needle as was (AAA) and adjust the idle
mixture up a little to drop the CO at idle from the 5.4% it was reading to
3.5%; thus raising the jet and theoretically leaning the mixture out across the
whole range. The merest hint of adjustment brought about a massive change in CO
reading! Removing the dashpot, Andrew revealed the jet was all but flush with
the bridge. This affects the way the carb performs quite drastically -
generally caused by a worn jet. This would also go some way to explaining the
slight over-richness everywhere. A new jet would possibly get things into a
better position and improve the fuelling.
Despite
all this, the mpg is pretty good. Thrashing the thing mercilessly back from
GRV, it returned 35.2mpg. More sedate urban driving and general duty use has
raised this to a very respectable 43.6mpg! The 'motorway' run result is very
similar to that gleaned from the 998, the urban use is far better. Further testament perhaps to the slightly less 'busy' nature of the
1100. And this would improve again with a fresh jet.
The
SW5 cam is a blinder. Buy it and use it in anything road going - you won't be
disappointed. It gives - without doubt - the best performance increase
throughout the usable rpm range without causing emissions problems. In fact it
gives better emissions than most standard, un-tuned, carbed
engines I've come across! It has become my first choice road-cam over the 997
Cooper one I've used for so long.
This
all goes to prove what I've been banging on about for years - the A-Series is
not an rpm monster, so should be tuned accordingly. And an engine built to give
best power at 6,500-7,000rpm on the road is a waste and unnecessary. Good
torque over a wide rpm band means big fun on the road. You really ought to
drive this motor! And a final word from Andrew - 'Blimey! Fit, isn't it?'
NOTE: The engine components used
in this article apply to all in-line engines also (948/1098/etc.).
Useful
part numbers:
|
C-AHT88 |
Min Tec
stage 3 unleaded cylinder head, small bore |
|
ALDON Y |
Aldon Yellow
45D4 dizzy, road sports curve, preA+ |
|
ALDON Y+ |
Aldon Yellow
45D4 dizzy, road sports curve, A+ |
|
C-27H7766 |
Aldon Yellow 45D4 dizzy, road sports with vac pre A+ |
|
C-27H7767 |
Aldon Yellow 45D4 dizzy, road sports with vac A+ |
|
C-27H7768
|
Aldon Yellow 25D4 dizzy, road sports with vac pre A+ |
|
BAU1850 |
45D4 Cooper
S spec dizzy, non vac, pre A+ |
|
SW5 |
Swiftune
Racing sports/tourer camshaft -A+ drive only |
|
2A13 |
Standard cam
follower/lifter - 8 needed |
|
AEG584 |
Standard cam
follower/lifter with oil drain hole - 8 needed |
|
C-AEG580 |
Super-quality,
extra height followers/lifters - set of 8 |