The Datsun L Series engine has undoubtedly been one of the most popular engines used in Australian rallying for the past 50 years. Simon Gardiner tells us how to go about obtaining strong, reliable horsepower from Datsun’s venerable workhorse. * * * * * The Datsun ‘L’ series engine has developed a great following in Australia since its release in 1968 in the Datsun 1600 (known internationally as the P510). These 4-cylinder engines have been at the heart of club level and fully blown rallying for over 30 years. The great appeal has been that most of us can afford to buy one, modify it and have a go at rallying or racing, then drive it to work again on Monday.

Nathan Reeves and Scott Spedding in action in their Datsun 1600 in the Begonia Rally in Victoria.

These are a rugged and well thought-out design. Look at the other engines available in that era like the Mazdas, Ford Pinto and Chrysler - no other manufacturer’s engine had the Datsun’s potential. A well sorted, naturally aspirated one is capable of producing in excess of the magic100 hp/litre, in a range of capacities. As always it’s critical to define the engine’s end use. Is this going to be a championship Group Nc 1600 screamer or a family Autocross 2200 that needs to last five seasons? If the class rules allow, you often can’t beat cubes. People get sucked into wanting small, high revving engines. Consider a really well developed L16 might have 130 ft/lbs of torque, where a mildly modified L20 could be 150 ft/lbs, and the 1600 might get over 170 horsepower and the L20 close to 180.

Standard (bottom) and steel conrods from a Datsun L Series engine.

In rallying you spend a lot more time in the middle of the rev range and the L20 will be a lot cheaper to build. An engine’s potential is always the sum of all its parts. A well sorted set of reasonable parts, tuned well, will always beat an expensive mish mash of odd parts. We see a lot of engines on the dyno that go backwards when the latest part is bolted on. This is heartbreaking - we all know of people who have won championships with fairly stock machinery. That’s how they did it, making sure they have ‘The Package.’ These Datsun engines have the advantage of being able to swap over various combinations of crankshafts and conrods to create a variety of capacities. The L16 and L18 are the short blocks. Some of the harder to get L18s come with siamese bores between cylinders 1 and 2, 3 and 4. If you are feeling brave and get a good one, you can sometimes take them out to a 90mm bore. The L20s are a taller block and easily identifiable by the extra bolt in the front timing cover. The Japanese 200B blocks were never as good as the Australian-manufactured blocks, which often could be safely bored to 89mm. The Australian-made blocks only had one dipstick hole. With planned big bore engines, always sonic test the block. Often there isn’t metal where you really want it. We like to see a minimum of 3.0mm in the finished bore wall thickness on naturally aspirated engines. No matter what the engine is, I try to find a clean un-rusty block to start with, it will transfer heat to the cooling system far more efficiently.

A billet 94mm Datsun L18 crankshaft.

Cranks have two main bearing sizes – L16 and L18s share the same main size and the L20 runs the larger mains. Warm road motor cranks run as is. For competition the crank can be lightened and heat treated. It is a good idea to dowel the flywheel to the crankshaft. For big strokers you can fit Z22 or Z24 cranks into L20 blocks with varying amounts of work. For some of the special L18, 94mm stroke race engines, we fit a steel billet crankshaft and a special rod combination so you don’t get too close to the main oil gallery and therefore squish all the parts under the rocker cover. Ultimate engines get a billet conrod. If it is a good competition engine we stick with a prepped set of the Datsun rods with the larger 9mm rod bolts (for 1600s). To up-rate these we crack test, polish the beams and detail around the rod bolt holes then shot peen. Often we will bore out the little end and fit a fully floating gudgeon pin. Then to top it off, fit a set of ARP rod bolts, resize and balance the rods. If the revs and grunt are to be kept lower then the standard rod bolts are fine if they are crack free. In most applications of competition engines we fit a set of forged pistons. We tailor them to suit the rod-stroke combination and compression ratio. Some L18 applications, where we are chasing capacity, require the gudgeon pin right up close to the ring land. In a lot of applications for warm to hot road engines, you can get reliable horsepower from a good set of cast pistons.

Standard shape and forged pistons from a Datsun L Series engine.

Most engines though, need a bit more compression ratio and squish. If the head gasket thickness permits then the piston crown can sit above the block by around 0.015”. This has the benefit of not only raising compression but also improving combustion. We make a vernier cam gear to allow the cam timing to be accurately adjusted. You cannot just bolt a camshaft into an engine and expect the cam timing to be optimal - you must check the cam timing. Typically most engines will like the camshaft slightly advanced. One common trap is that people increase the compression and fit a bigger cam and the valves hit the pistons. Always check the valve-to-piston clearance with the cam timing set during the engine’s dummy assembly. It is nice to see over 0.060” clearance on the inlet valve and over 0.080” on the exhaust valve. The valves get closest to the piston either side of TDC, so this is where to check it. There have been a lot of engines over the years with broken camshafts from this. The most neglected thing when people raise engine compression is that they’ve not calculated what it is. We saw a motor recently that was over 12:1 and it was expected to run on pump fuel. This engine needed zero degrees of ignition advance or it pinged. I wonder why?

Datsun L Series chamber filled with plasticine.

Always calculate your compression ratio. The combination of the compression ratio and cam duration, go hand-in-hand. Typically, the hotter the cam used the higher the compression ratio, possibly this is because the effective amount of inlet charge captured varies with cam duration. It’s interesting to note that a mild cam at 9.0:1 may have the same compression pressure (entrapment) as a race cam at 10.3:1. Lubrication often gets my attention. Most competition engines I build get a high volume oil pump. This has a longer rotor than the standard item and hence pumps more oil per rev. We usually plug the oil filter bypass hole so that all the oil has to be filtered rather than some allowed to escape. It’s good to open up the oil feed hole (that is pressed into the block) for the cylinder head so that the cam and valve train see more oil flow to keep it cool. This is pretty important to get right as too much flow takes away oil pressure from the bottom end at low rpm. With the big grunter engines with big camshafts we make up a spray bar to add extra lubrication to the camshaft to keep the surfaces cool and slow down wear.

Welded water ways in the Datsun L Series head.

We also fabricate special baffled sumps for competition engines to reduce oil surge. There are a lot of different cylinder heads. They have a variety of combustion chamber shapes, chamber volumes, valve sizes and port diameters. This is great because there is usually something that can be modified to do the job. The Datsun heads do have a couple of common problems. They are old and can be badly corroded around the water passages. They can be welded and resurfaced to save them and this leads to problem number two. A lot of heads have been cooked from running in air cooled mode. When the head gets too hot it looses its temper and strength and usually warps. They warp mainly because a flame thrower is being shot at the chamber side of the head without the water to carry the heat to a radiator. So we hardness test all alloy heads and re-heat treat them if they are too soft. If the head is going to require heat treating it may be a good opportunity to do some welding repairs or modifications. If the rules allow and you are chasing compression then you can add material around the valves to improve the squish and aid low lift flow as the valves come off the seat.

Damage from valves hitting the pistons.

Port sizes will vary on the spec of the engine and may go from a 32 to 39mm inlet port, depending on the output. We usually err on the small side. The old FIA heads had around a 40mm port and for years people copied this, but it is giving away power. Big is not always better. I would rather have a higher gas speed in most circumstances for better drivability. As with all performance heads, having a good three or four angle valve seat job is important to aid flow of the air from the valve throat over the valve seats to the combustion chamber. Even different angles on the backs of the valves can make a difference to air flow. Because there were so many different specifications of engines produced there are a range of valve sizes. So for most applications something can be adapted to give an increase in valve area if required. Just as ports are often too big, so are the valves chosen. Small equals more gas speed. For applications where valve lift is to be kept under 0.500” the standard valve lengths and common aftermarket spring combinations work fairly well.

Lash pads sitting in retainers.

For special big lift engines we use a longer valve so we have more room for a longer valve spring. This has the added advantage that with a big cam you don’t have a lash pad as thick as a house brick. Setting up the cam wipes onto the rocker arms is very important. We see so many prematurely stuffed camshafts and rocker arms caused by incorrect setup. If the rocker arms, camshaft and or lash pads are pitted, replace them. We always fit-up cams, rocker arms and lash pads as a set on each head we assemble. The contact patch of the cam to the rocker arm affects the cam timing and the rocker ratio. I like to get the contact patch about 0.040” (1mm) in from the pivot end of the rocker arm pad. I smear a small amount of blue on the cam and arm, set the tappet clearance and check the contact patch. Then optimize it by fitting different thickness lash pads. If the lash pads start to get very thick we use a set of high side retainers to support the lash pad. Don’t guess the lash pad thickness, check the wipe or there is a good chance the cam and rockers won’t last.

Short height Datsun L18 piston.

Timing chain slop is a common L Series problem in modified engines. We see a lot of engines that have huge amounts of chain backlash and a tensioner that is about to fall out of its block. Some occur because the engine is just flogged out after years of entertainment. Others need to have the whole chain and bondage thing addressed. If you surface a heap from the block and then you surface another truck load from the head, the camshaft could be 0.080” (2.0mm) closer to the crankshaft. What are you going to do with the 0.160” (4.0mm) of spare timing chain? When you are building the engine, before the front cover is fitted, it’s a good idea to sit the head on with a gaset, and dummy assemble the timing chain, guides and tensioner. By modifying the guide mounts you can better position the chain to get rid of the play and keep the tensioner close to its seat. Check that you have the clearance required inside the front cover. Do this and you are a long way ahead of the opposition. We all know that camshafts are a black art not fathomable by anyone other than the cam grinders. But the original Datsun ‘works’ grinds had a fairly simple numbering system. They took the advertised duration of a camshaft and divided it by four. Hence a ‘works’ 68 degree cam that will work well with SUs is a 272 degree advertised duration cam. A ‘works’ 72 degree cam is 288 degrees advertised etc., right up to the ‘works’ 80 degree cam that has a whopping 320 degrees advertised duration. For large capacity engines we will often use a 76 or 78 degree hi-lift cam so that we get the valves open as fast and as far as possible without getting too crazy on duration. If in doubt go milder in the camshaft choice, it’s all about the package.

The finished welded up head.

A common competition setup for the L Series engine is the use of sidedraft Weber carbies. We still make the L Series (Datrally) Powerplay inlet manifold; these have a medium sized runner that can be matched up to most applications. We also make a competition manifold gasket to suit the manifolds and extractors. Extractors have become harder to get over the last few years as aftermarket production has dropped off. This is especially the issue for smaller capacity engines where, to get the runner sizes that we require, something may have to be hand made, or again there will be too little gas speed. The engine is all about the whole package. Measure and check everything. Do dummy assemblies to check piston to valve clearances etc. Check your compression ratio and cam timing. Keep the air speeds high in the inlet manifold, head and exhaust systems. Above all else, tune it properly. It is easy to get fooled that an engine that goes like gang busters when it finally comes on the cam at 6,000 rpm is a cool performer. Most of us mere mortals can’t feel 10 horsepower blasting around on the road, yet most gains come in less than 5 horsepower increments on a dyno. Sorting and testing your package is as important as the initial build.
  • Originally published in RallySport Magazine, December 2005

A completed L Series engine ready for rallying in a Datsun 1600.


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