|Pushrod 4 Cylinder Engine
(XC, XM, XN)
|to go to a page with photographs of some very modified pushrod engines|
The pushrod 4 cylinder engines fitted to the 504 and 505 started off as the XC 1618cc three main bearing engine with a single 32mm Carburetor, fitted to the first 404s. The carburetor fed into a large plenum chamber cast into the head which fed the inlet ports. A 1468cc version was available in some base model 404s.
- In 1962 a version of this engine was available with Kugelfischer Fuel Injection. This engine had four convention inlet ports as did every subsequent fuel injected version.
-In 1965 the engine block casting was changed to incorporate 5 main bearings and the valve sizes were increased. This engine was called the XC5.
-In 1966 the compression was raised to 8.35:1 and a dual tract exhaust manifold, and 34mm Carburetor were added. This engine was called the XC6.
-In Argentina an 87hp 1657cc (85mm bore) version with a dual throat Solex 34mm Carburetor, was produced, called the XC6A. Later an 1838cc (85mm bore, 81mm stroke) engine called the XMA was produced in Argentina. A unique feature of the XMA was a head with 4 separate inlet ports and a 4 branch inlet manifold.
-In 1968 the 504 was released with a longer stroke 1796cc version of this engine called the XM. A fuel injected version called the KF6 (after the injection system) was also available. The Argentinian built 504 used the 1657cc XC6A and C3B gearbox until the mid-1970s (as well as 404 front suspension, rear suspension, brakes, hubs, etc).
-In 1970 a bigger bore 1971cc version of this engine became available and the engine block casting was changed to an open top design with cylinder liners that had metal seals rather than the previous rubber ones. A dual throat carburetor was fitted as standard for the first time feeding through 3 ports leading into the common plenum chamber. Carburetored versions were called the XN1. Fuel injected versions were called the XN2. The XM engined 504 was discontinued at this time. Around this time a low compression version of the 1618cc engine, called the XC7, became available in the 404 in some countries.
-In 1974, a low compression version of the 1796cc engine, called the XM7, became available in a new cheaper version of the 504 sedan called the 504L, which had a live rear axle and rear drum brakes. The cylinder head of the XN1 was also redesigned, eliminating the common plenum chamber and replacing it with a kind of square siamesed port design. The 3 port common plenum chamber head was still available until the end of the decade in North America and Australia (until 1978) with 2 single throat Solex carburetors to satisfy strict exhaust emissions standards. This engine was called the XNA in Australia, as was the square siamesed port engine, when it was introduced into Australia in 1979.
-In 1975 a 504 TI, with a 170hp modified XN2 engine, driven by Ove Anderson, won the East African Safari Rally.
-In 1976 8.8:1 pistons became available in Europe in the XN1 and XN2 (these became available in Australia in 1979 with the introduction of the square siamesed port head).
-In Argentina, a high performance (110hp) version of the square port XN1 was available for a short period in the late 1970s in the 504TN. It had a special camshaft with longer duration, a dual throat 36mm Solex EIES carburetor and a special exhaust manifold fabricated from steel tubing. In the early 1980s this engine was re-released with 116hp, in the 504 GRTN with a 5 speed gearbox.
-In 1980 a Bosch K-Jetronic injected version of the 1971cc engine, called the XN6, was introduced for the North American market, to satisfy Californian exhaust emissions standards. This engine became available in Australia in 1986, with the introduction of unleaded fuel.
-In the early-mid 1980s, the carburetored version of the 1971cc engine received a similar four port cylinder head to that fitted to the XN6, with a similar (but longer) four branch inlet manifold to that fitted to the 1.8 litre Argentinian 504. This engine was called the XN1A. A new version of the 1796cc engine, with the square siamesed port head, called the XM7A, became available around this time.
-Double row timing chain (strong and long lasting)
-Double valve springs (help to dampen out spring surge at high revs)
-Easy to work on
-Good exhaust manifold design, particularly the large bore version fitted to some 505s and 504 coupes/cabrios (very similar to manifold homologated by Ford for their Escort RS2000 MkII)
-1796cc and 1971cc engines have a conrod length to stroke ratio of about 1.63 which results in some power loss due to excessive piston to cylinder wall friction. Ideally it should be more than 1.7. The 1618cc has an ideal ratio of 1.8
-Exhaust ports have a tight short side radius
-XN2 engines have inlet ports which are larger than optimum for carburetors (should be around 36mm diameter)
(Note: 1mm = 0.040")
Typical 504 XN1 camshaft specifications
Cam lobe lift approx 0.245"
Typical 504 XN2 (TI) camshaft specifications
Duration 260 degrees (200 degrees at 0.050" lift)
Cam lobe lift 0.263"
Wade profile no. 112 specifications
(Good flexible cam for road cars with plenum chamber or single carburetor induction systems and less than 9.5:1 compression)
Inlet timing 22/63.5
Inlet duration 265.5 degrees (207.5 degrees at 0.050" lift)
Inlet cam lobe lift 0.285"
Exhaust timing 63/23.5
Exhaust duration 266.5 degrees (208 degrees at 0.050" lift)
Exhaust cam lobe lift 0.285"
Lift at TDC at no.1 inlet cam follower 0.039"
Pistons should be flycut to provide clearance for the valves if more than 0.5mm is shaved off the head face.
Wade profile no. 240 specifications
(For engines with a separate 40-42mm throttle for each inlet valve, 30-34mm venturis/chokes, and 10:1 compression or more. Tuned length 4 into 2 into 1 exhaust headers are also a good idea.)
Inlet timing 32/70.5
Inlet duration 282.5 degrees (219.5 degrees at 0.050" lift)
Inlet cam lobe lift 0.283"
Exhaust timing 71/29
Exhaust duration 280 degrees (219.5 degrees at 0.050" lift)
Exhaust cam lobe lift 0.283"
Lift at TDC at no.1 inlet cam follower 0.054"
Pistons should be flycut to provide clearance for the valves.
Wade profile no. 140 specifications
(Useable rpm range of 3000 to 7000rpm. Suitable only for engines with a separate throttle for each inlet valve, atleast 11:1 compression, larger than standard valves and tuned equal length 4 into 1 exhaust headers flowing into a large bore low restriction noisy exhaust system. Titanium pushrods are also a good idea.)
Competition use only! (not for road cars)
Inlet timing 40.5/70.5
Inlet duration 291 degrees (237.5 degrees at 0.050" lift)
Inlet cam lobe lift 0.296"
Exhaust timing 74.5/41
Exhaust duration 295.5 degrees (238 degrees at 0.050" lift)
Exhaust cam lobe lift 0.297"
Lift at TDC at no.1 inlet cam follower 0.093"
Pistons MUST be flycut to provide clearance for the valves.
Contact details for Wade Camshafts:
Wade Camshafts Pty. Ltd.
113 Dryburgh St
PH: 03 9328 4001
FAX: 03 9329 8318
Compression Ratios and Pistons
Peugeot make a number of different pistons with different dome heights on the crown to give different compression ratios. These ratios are 8.8:1 (approx 2.5mm high dome), 8.35:1 (approx 1.5mm high dome), 8.1:1 (approx 0.5mm high dome), 7.6:1(?). The 140hp 504 factry rally cars used a piston with a 3.5mm dome which gave 9.5:1 compression. The standard head is approximately 92.5mm thick (+/- 0.15mm) and the face is not supposed to be machined more than about 0.5mm, however more can be machined off the head provided that the pushrods are shortened by a similar amount and piston to valve clearance is taken into account. Each millimetre that is machined off the head, raises the compression ratio by approximately 0.8 of a ratio point. It is possible to achieve 10:1 compression, if 8.8:1 pistons are used and about 1.5mm is shaved off the head face. To achieve much more than 10:1 compression, either special pistons must be found or made, or the combustion chambers can be partially filled with weld to reduce their volume. If the combustion chambers are partially filled, it is a good idea to focus on creating squish/quench areas on the opposite side of the combustion chambers from the spark plugs. This will improve combustion efficiency. Care must be taken to make sure that the dome of the piston and the filled area of the combustion chamber don't interfer with each other. Also, any material added must not cause obstruction to air entering through the inlet valves, otherwise any power gained by the increase in compression ratio will likely be negated by a reduction in induction efficiency. By far the strongest pistons I have seen for these engines are the pistons made by AE. These are far more sturdy than the other pistons, although many of the other types are generally strong enough for normal use providing that no extended pre-ignition occurs.
For use with a single dual throat down draught carburetor, or a single side draught carburetor, the heads to use in order from most desirable to least desirable are:
1. XN1A (or XN6 with XN1A inlet manifold), or Argentinian XMA or XC fuel injection head fitted with a special inlet manifold.
2. Early style of XN1 or XC5/XC6/XC7/XM/XM7 machined and filled to give four separate 36mm inlet ports and fitted with a special inlet manifold.
3.Square port style of XN1.
4.Early style of XN1 or XC5/XC6/XC7/XM/XM7 with welsh plugs removed and fitted with a special inlet manifold.
5.Early style of XN1 with standard inlet manifold.
For use with a twin carburetor system, the heads to use in order from most desirable to least desirable are:
1. XN1A, XN6, Argentinian XMA, or XC fuel injection head.
2. XC5/XC6/XC7/XM/XM7 or early style of XN1, machined and filled to give four separate 36mm inlet ports.
4. XC5/XC6/XC7/XM/XM7 or early style of XN1 with inlet welsh plugs removed.
For use with a high performance fuel injected engine, the heads to use in order from most desirable to least desirable are:
2. XN6 or XN1A
3. Early style of XN1 or XC5/XC6/XC7/XM/XM7 machined and filled to give four separate inlet ports.
4. Square port style of XN1 fitted with a special inlet manifold and one or two injection throttlebodies, or early style of XN1 or XC5/XC6/XC7/XM/XM7 with welsh plugs removed and fitted with a special inlet manifold.
Later heads (after mid 1970s?) have a venturi shaped inlet valve seat insert which is much better for low rpm flow than the earlier parallel insert. It should be possible to purchase these valve seat inserts and fit them to an earlier head.
Only high speed steel or tungsten carbide cutters should be used on aluminium alloy heads (don't use grinding stones).
On all pushrod Peugeot engines the ports are already larger than optimum, so making them any larger will make things worse. It is best just to smooth out the area within 10mm of the valve seat, without taking much material away. The valve guides can be pressed out to allow you to remove the excess alloy in the vicinity of the guide, so that the roof of the port makes a nice smooth curve. Before refitting, the guides can be tapered in a lathe, but care must be taken not to leave a sharp edge on the guide, otherwise steel from the guide can break off and fall into the engine. Care must also be taken not to reduce the size of the radius from the valve seat to the bottom of the port. The 140hp 504 factory rally cars used 44.5mm inlet valves, so I would consider this the maximum safe limit for road use.
Not much material can be removed from the exhaust ports because the water jacket is in close proximity to the port. It is best just to smooth out the port within 10mm of the valve seat, clean up the roof of the port in the vicinity of the valve guide, and have the valve guides tapered, taking the same caution as outlined in the paragraph above. Care must also be taken not to make the small radius from the valve seat to the bottom of the port, too sharp. The 140hp 504 factory rally cars used 37.5mm exhaust valves.
The best exhaust manifold for road use is the long big bore 4-2-1 type fitted to some 505s and some late model 504 coupes and cabriolets. Alternatively the similarly designed small bore manifold fitted to many 504s, 505s and 404s can be fitted with a custom made longer bigger bore engine pipe.
For ultimate power on engines with a long duration camshaft the best type of exhaust manifold to use is a long (800mm+) 4 into 1 type. There are atleast one or two companies in France that make these (does anyone know their contact details?), but they cannot be fitted to cars that have the steering column on the right hand side (neither can the nice but rare Argentinian 504TN/GRTN manifold as shown in the picture at the top of the page).
Lightening Components to Reduce Inertia
-Approximately 2kg can be removed from the flywheel without adversely affecting its strength or flywheel effect.
-The cam followers can be lightened by shortening them by approximately 6mm (0.25").
-The rocker arms can be lightened a tiny bit by removing all the rough casting from the outside, and the springs between the rocker arms can be replaced by spacers to reduce friction.
-The pushrods can be replaced with ones made of a lighter material that has a similar coefficient of thermal expansion (titanium?).
|to go to a page with drawings of modified heads|
|Engine and gearbox from the Argentinian 504GRTN|
|The XN1A engine with four branch inlet manifold
(thanks to Mauro for the pic)
|The Argentinian 1.8 litre four branch inlet manifold.
(thanks to Mauro for the pic)