16v Conversion
When 8 Valves are not enough!
The
M16 - 16v
Conversion
I first saw this conversion done in 1984, two years before the Rover 820 and the M16 was
announced. A bit odd you may think, but this was a real odd ball car, which fitted the
description of 'development hack' perfectly. Take a 1983 'A' registration 1.6 Maestro HL
and cut of the front up to the A pillars. Then build a one off front end with a complete
development Rover 820 engine, drive train, suspension, brakes etc. The original Maestro
panels were then too short, so Montego front panels were used to provide a degree of
disguise. Remember that this was within weeks of the first announcements for the
Montego, so the resulting car was a trifle odd. I called it a Monstro, a mix of MONtego
and MaeSTRO.
The engine was fitted was an early development unit which later became the production
M16. In all main details it was the same basic spec, only differing in detail. One
thing was certain this was one fast mother Maestro, especially since the 2 litre 8-valve
engine was yet to be announced for the Maestro, although it had just surfaced with the
Montego. Interestingly there were a number of other standard bodied 'A' reg. 1.6 HL and
HLS Maestros running around complete with development 2 litre engines in various
different tunes, but all with injection. These were also quicker than the final
production package.
Although not allowed to drive these development cars I was given a demonstration of their
performance potential and it was the 16-valve engine that left a very deep impression.
The result being that I gave myself notice then that this would be a conversion that I
would undertake sometime, but in the meantime I would revert to my mildly tweaked MG 1600
- Doh!!
1986 saw the production M16 appear in the Rover 820, first with multi point injection
(Lucas) with 140bhp and followed by a single point injected version (MEMS) with 120bhp.
By 1989 there were sufficient cars in circulation for engines to becoming available on
the second-hand market at reasonable enough prices to suit my pocket. I sourced a nearly
new single point engine followed later by a complete multi point inlet manifold,
injectors fuel rail, throttle housing, with all the other bits that are attached to it.
This doesn't mimic the production multi point engine as it used different pistons, (with
the same 10 to 1 compression though) however the results were effectively the same.
Fitting was delayed due the Ambulance men's strike that involved considerable extra hours
to provide some sort of alternative cover. Afterwards I was able to plan the change and
since the car was my sole means of transport to work I could only afford to be off the
road for a weeks holiday.
The secret of a successful conversion is achieved during the planning stage where much
work was done and parts obtained. I had a complete engine built up with inlet and
exhaust manifolds, breathers, alternator and starter attached. One item that was not
going to be a fitting problem was power steering as the car didn't have it. As most
820's do have it, and most have the power steering at the front under the alternator this
presents a clearance problem with the Maestro/Montego front body member that runs under
where the radiator sits, if the car has power steering of course!
In my case all I had to do was obtain the correct alternator mountings for the very early
820 models that used a power steering pump that was driven from the rear of the inlet
camshaft via a separate and short toothed belt. This set up was dropped within 2 years
as many cam belt failures were attributed to the varying loads imposed via the power
steering pump. The alternator drive belt and the brackets are very useful for these
conversions though as they are off the shelf parts. I also believe that post 1986 Sherpa
vans with the 1700 and 2000 O2 series engines still use the same brackets and belts.
The only other thing was to remove the pipe extension, two way union, oil gauge sensor
and oil warning light sensor from the back of the engine. The 820 has an oil gauge as
well as a warning light and this is how both are sensed. Once removed the original type
of EFi oil light warning switch is fitted to the oil pump in the same way as in the
original engine.
The M16 engine is very similar to the 8 valve units it replaces since it uses the same
block. This means that it bolts to the original EFi gearbox, uses the same clutch, or a
Montego Turbo clutch which has a stronger cover (pressure plate), and can retain 3 of the
4 original engine mountings. There are sufficient other differences to make the
possibility of just a head swap totally impractical. (Different head stud spacing,
different pistons, rods and movement of various sensors for which several threads are not
available.
Returning to the engine mountings sees the 4th mount, the one on the right hand side of
the engine bay near the servo, needing to be changed due to the extra width of the 16
valve head and the run of the cam belt. The original mounting can be modified along with
the water pump casting so that it can be retained, but the work is involved and the
easiest alternative is to use the Rover 820 one. This is mounted to a cast iron boss,
which protrudes from the centre of the cam belt cover. Onto this bolts an alloy and
rubber mounting block which fits into a steel bracket on the cars body, much the same as
the original Maestro one. To use the Rover mount requires a fabricated steel bracket be
made that bolts to the offside chassis rail through existing mounting holes. Motobuild
were the main suppliers for this item.
With the engine mounting modification sorted the job becomes a pure bolt in operation,
unless you have power steering. If you do then for engine longevity I very strongly
recommend that the later lower front power steering pump be used. This requires that the
front lower member be cut into from the point where it meets the offside chassis rail
across towards the centre of the car for approx. 12". The depth of the cut (i.e. towards
the front of the car) is 2", and for the full depth of the panel. I then add additional
metal in a criss-cross pattern inside the open box to help recreate rigidity before fully
closing in the cut section.
Removal of the old engine is simple and this is best done with the gearbox attached.
With both units out of the car separate them and compare the flywheel starter ring.
There are two ring gears with different teeth, but otherwise the flywheels are the same.
In fact these different starter rings relate to all 2-litre engines with a change of
about 1987. If yours is different to the original then change the flywheels over, that
is if you are retaining your original starter and not using one from the Rover engine.
The various different 2 litre gearboxes, whether it be from a Maestro/Montego or a Rover
can all interchange, but there are quite wide variations in the internal ratios and
overall gearing with different final drive gears. The very nature of the M16 power
delivery and extra power achieved means that the gearing provided by the original MG
gearbox (coded K6AR or K6AO) is near perfect. If you are using a box from another source
then just check out the ratios and final drive.
Also check the clutch release as Rovers often used hydraulic clutch activation, and the
later cable clutches used a different cable end. If different then when the gearbox is
off the engine undo the 10mm bolt that holds the clutch release fork inside the clutch
housing and slide out the wrong release arm and fit the one from the original box. Now
the engine and gearboxes can be bolted together, noting that there is no spigot bushing
in the end of the crank for the gearbox input shaft to engage into.
The new engine will fit as an almost complete assembly as long as your hoist has the
capacity. It certainly eases fitting afterwards. A hint that I always consider useful
is those to ensure that when the engine is lowered into place keep the driveshafts in
place and do not let them get caught up. They can so easily be dragged into a position
where they can't be refitted into the gearbox without first removing them to get them out
of the wrong position they have got into.
The engine can now be bolted up exactly as standard for the three mounts and with the new
bracket and Rover mount, fitting of this fourth mounting is obvious. At this stage you
may note that the 820 sump is 10mm deeper than the Maestro EFi one, to cater for the fact
that the exhaust pipe runs under the sump so it has to be narrower in the well to allow
passage. The greater depth regains lost capacity, but on significantly lowered cars this
can be vulnerable. In such cases swap this sump for the one from any of the 220 or 420
models, which have a modified shaped sump of the same depth as the Maestro one but with
small wings for the capacity. The correct oil strainer and pick up pipe has top be used
with each of the different sumps.
The fiddle jobs now commence.
The water hoses use an 820 top hose which is cut down in length. It is also cut and
trimmed in the middle with a steel pipe inserted to connect the two halves together.
This is to remove a kink that forms when the original Maestro radiator top hose union and
the M16 thermostat housing are connected together. The hose from the water pump is 820
and this connects to an 820 main steel pipe. This is trimmed at the gearbox end to mate
to an 820 bottom hose which I turned round and trimmed the lengths. Other minor pipes
and hoses were used to match up the heater and throttle body water heating.
The wiring can be tackled in two stages to ease potential start and initial running
problems. The M16 and original injection systems run the same base hardware other than
the fuel ECU. The sensors etc are either the same or run the within the same parameters
so are retained. The thermostat housing and the knock sensor positions change sides of
the engine, so here knock sensor wiring has to be folded up and additional length fitted
to the water sensor. At the same time the alternator wires have to be lengthened, with
due regard to the position of the hot exhaust manifold. The plug on the M16 throttle
potentiometer will be different and has to be changed for the Maestro one. The M16
throttle pot operates in the opposite plane to the Maestro one so they can't be simply
swapped.
The final alteration concerns the wiring for the airflow meter. Once the engines fitted
it will be quite clear that the M16 inlet manifold is much longer than the old EFi's.
This means that the original position for the air cleaner, that also carries the airflow
meter, is wrong as it places the airflow meter too close to the throttle. I simply cut
the air filter-mounting bracket in half, welding in a 3" steel spacer to push the air
filter assembly towards the radiator. This provides the required minimum spacing between
the throttle and airflow meter, and also retained the insulated mounting of the airflow
meter. (The airflow meter has to be electrically isolated from the rest of the car) On
other conversions the original air filter has been mounted from the end of the battery
box which provides enough space for the original air hose that fitted between the airflow
meter and throttle on the EFi to be reused. Depending on the final position of the
airflow meter depends on how much extra length is needed for the wiring, if any.
Now if the simple route is being followed then the original ECU's can be retained, and
will work the engine acceptably (just!!). This simplifies fault diagnosis in the event
of problems later. Even so I would always fit the M16 ignition ECU since this is a
simple plug into the system and presents no problems to change. The Fuel ECU has a
different plug and three additional wires to be added to the system so is not quite so
simple a change. These wiring changes are shown in Annex 1 at the end of this feature.
The second stage of wiring modification is done once the engine has been proven to work,
when the change to the proper M16 fuel ECU is required to gain the full benefits of the
conversion. If this is done later then any non-start is far easier to locate.
The original throttle cable will be too short (just) and the best alternative is one from
a right hand drive Montego diesel. Some modification at the throttle end will be needed
and I always use a small screw on nipple to secure the end of the cable. These can be
found on MGB choke cables and push bike fittings.
We now move to the exhaust, which I find the most time consuming and troublesome. The
fact is that you have to run the exhaust through a very confined area between the rear
cross brace of the front subframe and the body. The exhaust is best at a bore of 2" and
has to go up and down for best clearance as well as taking engine movement in it's
stride. It can be done but takes time and a hell of a lot of patience. I have fitted
2.5" diameter pipes through here for turbo conversions so there is room for the 2"!
Please also note that the frequencies emitted from an M16 are different to the 8-valve
engine and in reality considerably noisier. A sports system with any degree of noise or
rasp with the original engine will be very noisy and even nauseating with the M16. The
recommendation for a twin box system is one where two like sized boxes are used, not the
usual standard and bomb set ups of most sports systems.
The best route may be to have a specialist make up a set of front pipes to negotiate this
area. You have the reassurance that once done these are likely to last for at least the
life of 5 systems. If you chose to do your own then I find that the best start is to use
the original 820 down pipes which when cut and shut do an excellent job. Retain the ball
socket in the system as this protects the exhaust against fatigue cracks, and shorten the
pipes so that you only have to run one pipe through the tight clearance area mentioned.
As a side note I did originally make up what was a very crude and rough down pipe that
worked well from the start. Later I spent much time and effort making up a very neat
smooth replacement with much longer secondary pipe lengths. This involved having twin
pipes through the tight area and the result was absolutely no power change at all!!
In fact I did a very large amount of exhaust testing since it was clear that the M16 (and
other Rover 16 valvers) are very sensitive to exhausts. I ended up with a twin box
(straight through) system with a 2" bore throughout to achieve 134bhp at the wheels with
a standard engine. Fit a system with more resemblance to the 820 one and you lose a
whole chunk of power. Go one stage further and fit one of the 2.25" sports systems for
the Turbo models and expect to be down by around 18bhp at the wheels at 6000 rpm. The
best is a simple and uninteresting 2" bore system with no fancy tailpipes or other
additions period!
The last points to connect are the fuel pipes and here it is a matter of remounting the
fuel filter as the new engine mounting occupies it's original home. The injection system
MUST be run with an injection filter, otherwise you will have major injector problems
sooner rather than later. As the original filter is rather large, adopted I'm sure to
help cater for the newness of injection to this market sector and the anticipated neglect
of change points, smaller ones are available. I use ones that are smaller than a coil
and being a similar diameter use a similar bracket. They are fitted to injected
Cavaliers and have a 24000-mile/2 year change cycle. The originals were 48000/4 year
changes, yet would often go double that with no problems. The only other point is that
you will have to extend the fuel lines to the different fuel rail of the M16 manifold, so
ensure that hose used is to the correct fuel injection specification.
Alternative Provisions...
If the car has power steering and this is to be retained then some extra plumbing is
required. I have mentioned the body modifications needed for clearance of the power
steering so here are the rest. The 820 uses a low mounting for the power steering pump,
and as such it is fed by a remote reservoir. This should be mounted on the front inner
wing near to the radiator expansion tank of the Maestro/Montego. Obtain as many of the
pipes and hoses from the donor Rover, because when bought new they are expensive. The
one pipe to take care with are the threaded pipes/hoses that go from the pump to the
rack. These carry up to 1500psi in pressure so have to be very high quality and secure.
Use of a mix of the Rover pipe from the pump mating to the Maestro/Montego one into the
rack is a proven reliable route. The return pipes are low pressure and can be held using
normal hose clips. For long term reliability retain the 'cooler' pipe that runs back and
forth across the underside of the front of the car. This can become rusted and porous
and if so replace it with small bore copper central heating pipe, widely available, much
cheaper than Rover spares and easy to form.
With the inclusion of power steering the relieved area of the front bodywork includes one
of the lower mounting holes for the radiator location pins. The general position of the
radiator also comes too close to the power steering pump. In this case create two new
lower location holes towards the front of the car, sufficient to clear the power steering
pump, yet is possible not too much that will lock the radiator cooling fan against the
reinforcing panel that runs below the headlamps. If, as I have found, there is not
enough room for both, then mark out the panel and cut a section out, reform it and weld
it back up to return some strength. This will provide a recess for the fan motor and
clearance for the radiator to power steering pump.
Note that only the bottom holes are moved, as if the top is moved, then the radiator may
foul on the bonnet safety hook, as well as making the modifications for fan motor
clearance much greater. (Option. The front mounted fans always seize up from constant
bombardment with water and rubbish. Replacement with one on the inside of the radiator
(Turbo or aftermarket for example) is a positive option.
The vacuum connection from inlet manifold to the servo will be much shorter careful
selection and positioning of the pipes from the EFi set up will enable the appropriate
bits to be Cut and used. The plastic pipe used moulds onto the unions used so the pipe
has to be scored and split from the unions. To remake these connections use a pan of
boiling water to heat the parts up, then with suitable protection push the hot and
pliable plastic pipe onto the union ends. Once cooled the join is as per the factory.
Note the correct way the one way valve fits and ensure that this is correctly fitted,
otherwise you have no servo!!
Conclusions...
The conversion from 8 to 16 valves is the ultimate head modification that could be done
and this is reflected in the gains that should be achieved. Of the very many conversions
I have done or been involved with the standard M16 in a Maestro or Montego should give a
minimum of 125bhp at the wheels, which is 30bhp up on the original engine. If the engine
is in tip-top order and the exhaust system is working well then this can easily rise to
135bhp at the wheels. A good Rover 820i gives around 115bhp so the exhaust advantages
are clear!!
Run the engine on normal unleaded, as this is what they are tuned for. Super unleaded
may provide some minor differences but not enough to justify the extra costs. With the
correct M16 ECU's not only will the power be at the levels shown, but also the fuel
consumption will improve in the order of 10%. Add this to the power gains, the vast
improvement in smoothness and the ability to use revs that were very strained with the
original engine and it is a wonder that this was never a factory option. The only down
side is a slight loss of low speed torque up to about 2500 rpm, a small price to pay in
my view.
A last point is that once you experience 16 valve Maestro or Montego power you will never
want to return to the original 8-valve engine.
Annex 1
Conversion of Maestro/Montego EFi wiring to 16 Valve 820i Rover
As promised here is the crossover list for conversion of your wiring from 11CU spec ECU
to 12 and 14CU series units. It is worth noting that several of the inputs and outputs
from the later ECU's do have alternative functions depending on the overall vehicle
specification. For example if the cars are fitted with either/or air conditioning and
auto transmission, then detail wiring differences will exist, when comparing them to
manual main stream versions. Also different model years that carry the same overall
specification have been known to have differences, such is the much greater capacity and
flexibility of the later ECU's. These differences should not affect the effectiveness of
your conversion by following the below cross-reference list.
The following information provides a route for fitting the M16 ECU's to the
Maestro/Montego which I used on my own car and which covered over 130,000 miles. Several
subsequent conversions have also been completed, following the same route with the same
degree of success. For future reference you should keep available the wiring diagrams
for both the Montego Efi and the Rover 820i, and by using this list you will be able to
see where the cross references have been made.
Start-up Information
The following reference to 11CU series of ECU's refers to the series type of unit fitted
as standard to all non catalyst pre 1989 model Maestro and Montego 2 litre injection
cars. The reference to 12CU and 14CU series ECU's refers to the series type of unit that
was fitted to multi point injection versions of the Rover 820, pre 1991. As a side note
the 14CU series was also fitted to later versions of the catalyst equipped 2 litre
Montego's, (still Lucas equipped systems) although the parameters in the memory are not
at all suitable for the M16.
General Information
Firstly the water temp and fuel temp sensors are on a common circuit with the 11CU
whereas the 12/14CU has them separated. The simplest way to separate these functions is
to add an extra wire from pin 24 of the 12/14CU to the fuel temp switch. You can run
without this switch, as it is just a simple temperature sensitive switch where the
contacts close when the fuel temp rises above about 90 degrees. Loss of this function
only affects hot restarts and would result in some few seconds of spluttering until
colder fuel passes through the fuel rain and injectors.
Secondly the 11CU obtains the engine speed signal via the negative side of the coil.
(Through a resistor found next to the main multi plug between engine harness and main
harness, between the washer bottle and inner wing) Whereas the 12/14 CU picks up the
signal from the crank sensor, via a bridge in the ignition ECU. The original feed wire to
the 11CU is pin 13, which should be disconnected. The 12/14CU uses pin 39 and you should
add an extra wire from this, to pin 11 of the AB17 (ignition ECU) which is currently
empty.
Lastly the 12/14CU has a specific direct earth lead from the ECU to the engine block,
which is to eliminate indirect resistance's. Simply run an earth lead from pin 4 of the
12/14CU to a suitable point on the engine. I found it convenient to use one of the unused
bosses on the gearbox end of the cylinder head.
11CU to 12/14CU Wiring Cross Reference List
11CU Pin No. 12/14CU Pin No.
1 13
2 29
3 26
4 12
5 14
6 6
7 11
8 38
9 3
10 7
11 24
12 25
13 not used, see text
14 28
15 1
16 16
17 27
18 19
19 15
20 17
21 35
22 20
23 2
24 (may not be connected) 34
25 40
The above wiring applies ONLY to the Lucas engine managed systems. MEMS is a Rover
(Motorola) system that uses some identical peripherals, but all control functions are
different. The conversion to MEMS is quite possible and has been done in an MG Maestro
using an early Rover 220 MEMS system, as well as a number of T16 Turbo converted cars.
Of significance is the fact that when MEMS is used on the M16 engine the economy bonus
over the Maestro EFi is not achieved.
Roger Parker
This is a conversion by Alan Law, it gives a whole new look to the engine bay!
Alan may have not followed the same route as described by Roger Parker!