The 16 valve Peugeot engine is one of the most overlooked
powerplants available. Why it isn't used more in kit cars and the like I don't
know because it knocks most of the current crop of small bore, small valve,
asthmatic 4 pots into a cocked hat. Why is it so good? - simple - it's all a
matter of valve area. The ultimate restriction to the power potential of any
engine is not the bore, the stroke, the number of cylinders, the engine
capacity or the induction system - it's the total flow potential which
limits the amount of air the engine can process in a given time period and that
in turn is a function of valve area. Look at the valve size of some of the
other modern 4 cylinder 16 valve engines - Rover K series - 27.7mm, Ford Zetec
- 26mm in the 1600 and 32mm in the 1800 & 2 litre engines, VW Golf - 32mm,
Vauxhall 2.0 XE - 33mm, Peugeot M16 - 34.6mm.
What does all that valve area translate into? Well 160 bhp from
1.9 litres in standard road tune for starters and a whole lot more when you
start tuning it. That's 84 bhp per litre as standard without the benefit of
variable valve timing, which many other modern high output engines rely on. Not
only is the valve area huge for the capacity, the cylinder head and port design
is also superb. All this translates into an awful lot of airflow and that meant
Peugeot could get very good power without needing long duration cams which
would have hurt low rpm tractability. That was why they had no need to use
variable valve timing in the first place.
Any downsides to the engine? Well it's quite a tall engine and so
fitting is not always as straight forward as with shorter lumps. It was angled
over to get bonnet clearance in both 8 and 16 valve derivatives in the standard
vehicles. But being all alloy it is very light and this means that raising it
up a bit to get ground clearance doesn't hurt the centre of gravity of the
vehicle too much.
The bottom end is almost identical to the 8-valve engine so no
need to repeat the comments here. The liners are thicker - and in fact make
good high performance units in the 8v engine - the pistons are also different
of course with cutouts for the 4 valves per cylinder. Both items are expensive
from Peugeot but OE spec items can be obtained at a much better price through
the right aftermarket channels - email me if you need anything. The standard
bottom end seems to withstand 8,000 rpm in road use without problems - only if
you are building a race engine might you consider stronger rods and pistons.
Because of the alloy block, wet liner design there is no easy way to increase
capacity so most rebuilding is concerned with getting the unit back to good OE
condition. 0.5mm oversize pistons are available through competition channels
but the extra 23cc they give makes no difference worth having. One thing to
watch out for as with the 8 valve engine is that the oil pump on early engines
has no woodruff key drive and just relies on friction from the crank pulley
bolt. If this comes loose then the pump will stop rotating followed shortly by
the rest of the engine.
This is the heart of the 16v engine and it's quite superb. Good
big ports, well shaped, high quality guides which don't tend to wear much and
of course those huge valves. The best is to come though. Not only are the
valves huge but the valve seat inserts are even bigger. Peugeot seem to have
gone out of their way to make tuning this engine easy. The inserts at nearly
37mm are over 2mm bigger than the standard valves so you can fit 36.5mm valves
without any expensive machining to fit bigger inserts. That would normally cost
£20 or so per insert and add £160 to the cost of a big valve cylinder head. On
the Peugeot just remove the standard valves, recut the seats to suit, modify
the ports properly and drop those big inlets in. The exhaust valves are plenty
big enough at 29.6mm to not need changing. The extra 11% inlet valve area
translates almost directly into the same percentage power increase. Properly
porting a standard valve head is worth 10% extra power (15 to 20 bhp depending
on engine spec) and adding the big valves can double this to around 20% gain
(30 to 40 bhp).
The standard cams are fairly mild and a lot of power can be had by
changing them. There will of course be some loss of low rpm tractability and
the cam choice is down to the owner's driving style and the vehicle weight. In
a kit car you can get away with some loss of low rpm power and maybe use a bit
more cam than in a heavier saloon car. If you run throttle bodies and mapped
ignition/injection then you can use more cam and still retain tractability.
Even rally cams will be ok in a light road car with mapped ignition. Stick with
the hydraulic cams for road use - they can rev to 8,000 without problem and
that's as much as you need for general use. Figure on an additional 7% (that's
about 15 bhp) for fast road cams and up to 12% (say 25 bhp) for rally cams with
the right engine spec.
There are so many ways of tuning this engine and it all depends on
your budget. The ultimate way to go is throttle bodies, big valve head and cams
to suit your driving preferences. Not everyone will be able to afford the full
monty though. First off I'd suggest don't waste your money on aftermarket
exhaust systems - the standard item is very good - save the money and spend it
on cylinder head mods which will increase power throughout the range. As with
other engines the trick is to get as much cylinder head flow as you can and
then use as little cam as you need to avoid losing low rpm power. Retaining the
standard induction system and fitting a properly ported big valve head and fast
road cams will net you 200 bhp at about 7,300 rpm. Adding TBs and mappable
ignition/injection takes you to about 225 bhp at 8,000 rpm. A really well
ported big valve head has the flow potential for 300 bhp but you would need to
run the engine to 10,000 rpm to see that much power and of course without
extensive surgery the standard components won't rev that high. It does give an
idea though of the ultimate potential this engine has compared to other modern
engines which struggle to break the 200 bhp barrier.
For race use with the right valve springs and bottom end
components the power limit is just a function of your budget. 250 bhp at 8,700
rpm is easy, 270 bhp at 9,300 rpm is possible and that 300 bhp is there if you
can afford it. You'll need very special crank, rods and pistons to get there
though and pretty frequent rebuilds.
Ported standard valve head £550 plus the cost of new guides if
required. Guides tend to be long lasting on this engine, especially in
comparison with the 8 valve due to the higher quality bronze they are made from
and don't always need replacing.
Ported 36.5mm valve head £800 plus guides as above.