|
5 March 2001 |
Terminology:
|
MSC/MM |
Mini
Spares Centre/Mini Mania |
|
ID |
Inside
Diameter |
|
OD |
Outside
Diameter |
|
BBU |
Big
Bore Unit (refers to all 1275cc-based units) |
|
SBU |
Small
Bore Unit (refers to all sub-1275cc units, here the 998) |
|
BHP |
Brake
Horse Power |
|
LCB |
Long
Centre Branch |
The
998cc engine is a very robust and tunable unit. It is also the most common
engine found in standard Minis. Despite the lure of the much-advertised 1380cc
alternatives, many simply want to get a little more from what they have at
reasonable outlay.
The
single biggest restriction on any standard Mini is the 'breathing apparatus' -
anything that is connected to the induction and exhaust systems. The standard
exhaust being the biggest culprit - it is desperately restrictive in the name
of noise suppression and cheapness of manufacture. Oddly enough it also
increases fuel consumption when tested over a better designed, free-flowing
unit, so this is the place to start - NOT I stress the intake which is where
many start in the belief that's the way to go. It is not. It is definitely the
EASIEST place to start, and possible the cheapest - but will nett less gain for your money. Your best budget-verses-gain
improvements should therefore be done in 'reverse' order - starting at the end
of the exhaust then working your way back to the air filter.
Exhaust
System.
The
key here is not to use something that is too big, as this will actually loose
power. Unfortunately it is a pitfall far too many fall into in the belief that
'biggest is best', and the recent crop of dirt-cheap, 2.0" systems. They
are made 2.0" for two reasons - Mini owners seem to be impressed by the
'2.0" exhaust' term, and the manufacturers believe they are making a more
efficient system as it slides over the tail-end of most commonly used LCBs. For further reasons 'why', see
'Exhausts - sizing and styles'.
It
is entirely possible to fit an efficient system on it's own to the standard
manifold as Mini Spares/Mania can supply an adaptor for just such an
application. This replaces the flared front down-pipe section from the cast
iron manifold down to under the car to mate up with the RC40. They used to do
just a short adaptor sleeve to fit the standard down-pipe but almost all folk
found the flared end of their standard one had broken off once they'd got around
to doing the job - so the adaptor was dropped as a pointless exercise.
1.625"
internal bore is as big as you need to go on an SBU to get the very last drop
of power out - even on a full-race engine. My recommendation here is the twin
Exhaust
Manifold.
Progressing
back along our route to power, the exhaust manifold is next. The standard iron one
isn't too bad for an entirely standard engine, but is less efficient than the
standard iron inlet manifold. The fact they are cast as one causes power losses
on it's own by creating a severe, power robbing 'hot spot' in the inlet tract.
Since separating them is only possible by destroying one or the other, loose
the exhaust manifold.
Generally
I use and highly recommend the Maniflow 'Cooper Freeflow ' exhaust manifold on SBUs. Originally developed by Maniflow owner Dave
Dorrington when he was at Downton Engineering for the 970 S, it definitely has
sufficient flow to cope with just about anything a 998 will could throw at it,
and is easier to fit/seal than an LCB. Its design also suits the SBUs torque/power curve better than the commonly used LCB.
And that's another common pitfall - fitting an LCB to the SBU. Some vendors
sell what has become commonly termed the 'standard bore' LCB to fit everything
- for exactly the same reasons they sell the 2.0" exhaust systems - it's
what the misinformed Mini owners ask for, and there is a very cheaply made
'budget' example available that costs less than a Cooper Freeflow. This
'standard bore' LCB is in fact a 'medium bore' LCB developed for the BBU so is
simply too big for the road-going SBU. In back to back tests I've done with
this budget LCB and the Cooper Freeflow, I've always found the Freeflow gives
better results. Not to mention the fact they last a hell of a lot longer
through quality manufacture too!
I
also use an LCB on SBU for the road, but this is the pukka
small-bore LCB developed by Maniflow specifically for the SBU. The primary and
secondary pipes are smaller, as is the tail-piece (fish-tail, 'Y'-piece). It
does produce slightly better torque/power curves than the Freeflow but is
marginally more expensive and less easy to seal off properly.
Inlet
Manifold.
Although
the standard iron inlet manifold is reasonably good, a well-designed and
proportioned one will better it. The iron one's main problem is it's internal
sizing - it's too big for the SBU. The MSC/MM aluminium
manifold out-performs the standard one by quite a margin in all areas, maximising airflow and gas-speed within the very
prohibitive space. The parameters for the manifold were to set to allow the use
on the standard air filter case should this be required, and this has been met.
It
also has the facility for water heating (not cooling as some folk believe).
This is essentially to provide trouble-free running where cooler climates are to
be experienced. Although having the intake temperature as low as is possible
without actually freezing the fuel out of the air gives maximum torque/power,
some manifold heating is required where climates are sufficiently cool enough
to cause frost or heavy, cold misting. Cold wet air causing the biggest
problems. Plumbing it into the system is a cinch - just take the hose off the
heater tap and connect it to the left side of the manifold, than get a short
piece of hose to re-connect the heater tap to the right side of the manifold
(for further detailed information, see 'Inlet manifolds - single SU'').
Air
Filters.
The
standard air filter casing is surprisingly effective and efficient. Utilising this with a replacement K&N air filter will
provide pretty much all the airflow the engine will need, even when fairly well
tuned. All that is needed to maximise the performance
is to remove the hot-air 'snorkle', and drill a
half-dozen three-quarter-inch diameter holes around the front underside of the
casing. Ensuring these holes are OUTSIDE the cleaner element of course! The
bonus of retaining the standard casing is the civilized noise level it provides
in comparison to the cone/pancake type K&N…
It
may look prettier - but that cone/pancake makes a mighty row. It's OK at idle,
and tolerable when cruising at low speed, but any load or high- speed motoring
creates an ear-bleeding din. Not only that, sorting the fuelling can be very
arduous, AND recent testing has proven that this et-up actually LOOSES power
over the aforementioned by around 5%! Now that's definitely not good.
The
Wholistic Answer.
The
ingredients described above when added together comprise the 'stage one kit'. Although
the above can be done one piece at a time if the budget is VERY tight, the
complete stage one kit with all necessary gaskets and new carb needle required
to provide correct fuelling only costs a comparatively small sum. The main
benefit of doing it all in one go is actually reducing costs. Doing the job a
piece at a time will involve re-tuning at each stage with the associated costs
(carb needle, gaskets, etc.). Not to mention the aggravation of having to cut
the manifolds apart - a very tiresome job! And you get the full power increase
in one hit!
I
developed the stage one kit for MSC many years ago to deal with just such
tuning exercises. I used my every day 998 Mini. I took it to Peter Baldwin's
rolling road, optimised the performance of the standard
unit then took some power readings. Off the rollers and up in the air, the Mini
had the aforementioned components fitted then went back on the rollers. Again
performance was maximised, the new power readings
recorded. The needle type was kept as a standard, available as stock
replacement so it was repeatable indefinitely. Filing one was no good as it's
impossible to file two the same, let alone multitudes! The new ignition setting
was duly noted also. The kit was then tried on several other 998 Mini with
different engine specs/ages, and all results recorded and compared. The stage
one kit gave essentially identical improvements on each engine.
Power
Gains.
Using
figures when discussing power gains is pointless. The improvements entirely
depend on each individual engine's output prior to tuning. These vary
considerably because of various factors - such as engine mileage, how well it's
been maintained, low or high compression, pre-A+ or A+, and so on. We therefore
use percentages, as these are more realistic and comparable.
I
haven't tried testing each item as a replacement and seeing what power
increases each made - the exercise would simply be too expensive. In fact it
would cost something like three times the cost of a stage one kit! And the
claims made by certain component manufacturers are unfounded. For instance -
K&N would have you believe fitting a cone/pancake filter would unleash
6bhp. That would represent a gain of 14% all on it's own! Considering the WHOLE
stage one kit gives 20% extra, and the exhaust is the most restricting
component in the whole induction/exhaust system - the claim is impossible. It's
more likely that replacing the exhaust would nett a
12% gain, the rest down to the induction.
My
recommendation then is to go for the stage one kit first hit. If the budget is
tight, borrow the money or save up - it won't break the bank and you'll get the
best improvement in one shot with a great deal less hassle. The MSC/MM stage
one kit contains all the right ingredients - K&N replacement air filter,
high-performance water-heated inlet manifold, Maniflow Cooper Freeflow exhaust
manifold, RC40 twin-box exhaust system, complete exhaust hanger kit,
replacement carb needle, all gaskets and fitting instructions. It takes about
2.5 hours to fit taking things easy.
By
way of a warning - some vendors advertise greater than 20% power gains. I'd
like to see the proof of this as I've never seen more than 22% on one engine
only where the exhaust was in particularly bad shape! I find it really hard to
believe that a consistent 25% is possible. Only maybe on a one-off.
Useful
part numbers:
|
C-STN17 |
Complete stage one kit |
|
RC40 |
RC40 twin-box exhaust system |
|
RC40-051 |
Stainless steel rear box |
|
RC40-060 |
Stainless steel centre box and down-pipe
for above |
|
C-STR809 |
RC40 rear box only |
|
AN180V |
Exhaust pipe required when fitting
single rear box |
|
RC40FK |
Complete RC40 fitting kit |
|
C-STR816 |
Cooper Freeflow exhaust manifold |
|
C-STR817 |
Small-bore LCB exhaust manifold |
|
LDP1 |
Front repair/conversion down-pipe for
RC40 to standard exhaust manifold |
|
C-AHT770 |
Aluminium inlet
manifold, 1.5" single SU carb |
|
E2601 |
K&N replacement air filter element |
|
56-9320 |
K&N cone filter |
|
AJM601 |
Exhaust manifold gasket |
|
AEC2083 |
Carb to manifold and throttle abutment
plate gasket (3 required) |
|
CUD1018 |
AAU needle for stage one kit with
replacement element air filter - non-modified casing |
|
CUD1011 |
AAM needle for stage one kit with replacement
element air filter - modified casing (with holes drilled in) |
For
full Millenium range of exhaust options, see stock
listing.