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 has basically the same block and bore and stroke as the 8V engine. 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. The crank has double counterweights for sustained high rpm use but is very heavy as a consequence. 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. 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 36.5mm valves represent an 11% increase in valve area and power potential plus they allow a somewhat better throat and three angle valve seat to be machined which increases the power potential still further. Properly done a BV head is worth up to 30 to 40 bhp depending on the state of tune of the engine. The pistons need larger cutouts of course if larger valves are being used. Theoretically the 36.5mm valves will just clear the standard cutouts but it's sensible to enlarge them to get back to a safe clearance. This can be done by hand with a dremel tool if you are careful. Mark a pencil line round the cutouts and just open them up by 1mm to compensate for the 1mm extra on the radius of the big valve.
Update 05/09/2003 - I get a lot of emails asking "if I buy your big valves do I just have to get the seats recut and that's it?" Well no. To get the full gains out of a big valve head is complex. The guides need to be removed and the port shapes changed. Then the guides go back in and the seats are cut. That isn't easy either as the cutter will hit the spark plug boss and also possibly the exhaust seat inserts when the inlet seats are being cut. The cutter needs to be adjusted just right and not everyone has the right type of equipment. Then the inlet throats are bored out to match the enlarged valve size and blended into the port again by hand. The seats also have to be blended into the chamber and the chamber unshrouded to the head gasket line in specific places to let the valves breathe properly. Seat widths and angles, throat diameter, chamber shape and port shape will determine if you get 30bhp extra or next to nothing. I wouldn't trust most so called cylinder head experts to open a can of beans for me so who you use and what they achieve is in your own, and their, hands. I can't tell you what some other unknown engine tuner will achieve for you or how to modify a head if you buy my valves. A) it's too complex and B) I wouldn't give away for free what I've learned over the years by spending countless hours on the flowbench doing tests.
The Peugeot recommended tightening sequence puts an absurb amount of stretch into the head bolts which weakens both them and the threads in the block.. It's not uncommon for the block threads to strip or the bolts to break when either fitting a head or trying to remove the existing bolts. When fitting a head it's essential to do the following. Make sure the threads in the block are clean and free from corrosion and debris. The best way to do this is run a tap through them with some oil on it as a lubricant. As the bolts are 11mm thread size very few people are going to have a tap. A serviceable alternative can be made by grinding flutes into the threads of an old head bolt on the edge of a grinding wheel. New bolts must be well greased with moly grease both on the threads and under the bolt head. Finally rather than use the Peugeot stretch method I tighten these bolts to 75 ft lbs in three stages - 25, 50 and 75 ft lbs which loads them sufficiently to clamp the gasket properly but doesn't stretch them. Once the head is fitted it isn't a bad idea to fill the bottom of each external block thread hole with grease or silicone to stop water getting in there and corroding the new bolts. That will hopefully ensure that at rebuild time the bolts will come out easily without breaking or stripping the threads in the block.
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.
The flywheel takes a larger clutch than the 8v one and is a popular fitment for highly tuned 205s. At 6.5kg it's pretty light already compared to many other vehicles. Peugeot used a high quality iron and fairly thin sections to keep the weight down. It can be lightened further to about 5.8kg by removing the timing gear teeth and the material inside them outboard of where the clutch plate sits. If you need to retain the teeth to drive the ECU then nothing can be done but it's a sensible mod if carbs are being used.
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 36.5mm valve head £850 plus guides as above.
36.5mm inlet valves - £140 per set of 8. UK postage £4. Overseas postage POA but around £8 to £12 to most places.
I can't answer emails from people who want to know why their car won't start on rainy Tuesday mornings or why their engine blows smoke out of the exhaust every time they start it up. Despite the polite request on the contacts page I still get lots of "please help" emails from people who don't want to buy anything but think I'll be a good source of free technical advice. Newsflash - there's only me here and I don't sit at the pc all day waiting for emails to answer. I have engines to build. I used to at least try and find time to send a brief "sorry but I can't help" reply to these but nowadays they just get deleted so please don't waste your time typing. The place to ask is on the car newsgroups and when I have time I try to answer as many of these as I can.
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Last modified 09 April 2006.