The Quest for more Power using the L-Series
by Ben Pila Jr, Member at Large
Part one of this series has got you interested in how you can build a more powerful L-series engine. In this month's article, I will try to clarify info listed in the charts and explain which parts are best to use in the build-up.
There are many engine combinations that will get more power. Which combo you choose depends on what your goals are. What kind of induction system you will use are also things you will have to decide. For those with turbocharging in mind, any of the choices that keep the compression ratio close to 8.0:1 will allow more turbo boost and that will make more power. Generally speaking, lowering the compression ratio in a turbo engine helps to reduce the threshold of detonation. This is the point at which the fuel mixture begins to detonate or ping. You can hear the dangerous knocking sound when you drive up hills under load and/or have some low octane fuel in your tank. While under a load and at higher rpms, this uncontrolled knocking can damage pistons and destroy your engine. So to make power and do it safely, choosing the correct compression ratio for your engine is important. For normally aspirated (non-turbo) engines, staying under 10.0:1 would be advisable for today's Premium fuels. If you choose a ratio that is in the mid 8.0:1 range, you might be able to still use the lower grades of fuel. To keep throttle response up you would want to pick the highest ratio that you can get away with. This will allow more power in a normally aspirated configuration.
The various cylinder heads available for L-series engines each have their own benefits. Perhaps some of the best choices are the N42 and the P90 cylinder heads. The N42 head was used on the 75-76 and some early 77 280Zs and has the square port exhaust configuration. The advantage of this head over the 240Z heads is that it has larger intake and exhaust valves. This head has bolt holes for either the carburetors or fuel injection manifolds. The P90 head was used on the 81-82 280ZX Turbo and has the same features as the N42 but with a larger volume combustion chamber. That larger volume will help to lower the compression ratio necessary for a turbo engine. If you were to have the valves changed in a 240Z head then those cylinder heads could be possible choices. With the plan of creating a larger displacement engine, larger valves will allow more air and fuel into the engine.
The best crankshaft choice is probably the one from the 1981-83 Maxima Diesel. These Maximas had a diesel option (LD28 engine) and the crankshaft from these engines is one of the keys to building a big Z engine. If you look at the charts you see a chart that lists the pistons, rods and crank combos. Most of the combinations listed use the LD28 crankshaft.
Which block is best for boring out to a larger size? 1975-81 non-turbo blocks are the best. These have siamesed cylinders. What this means is that between each of the cylinders, there is solid metal between them. The blocks to avoid if you will bore big are the 1981-83 turbo blocks and the 1982-83 non-turbo blocks. These blocks have an open casting area between the upper half of each cylinder, which could collapse if bored too large. With overboring to 89-90mm, you should pay the extra money to have the block sonic tested before the block gets bored. This will determine if there was any sand casting shift or thin areas (when the block was formed,) that could possibly lead to a collapsed cylinder wall.
Connecting rod choices are either the L24 or the L28 depending on what combo you pick. One thing to remember is that the early 240Z rods (up to 4/71) had 8mm rod bolts and the later 240Z rods (5/71-6/81) had 9mm rod bolts. You want the rods with the 9mm bolts. You should buy and replace all the rod bolts and nuts with new Nissan parts or use ARP brand bolts and nuts. The ARP company makes racing hardware that is very good.
Piston choices like the other items, needs to be decided based on your desired configuration. When buying your pistons, pay the extra for Nissan factory if possible and definitely use Nissan factory rings. Custom forged pistons are good if you plan to run high boost. Also use Nissan factory bearings if you can. The quality of the factory parts is best and many race engines have used these bearings. On the piston chart, where is says cut .5, this means having the top of the piston milled or cut down .5mm. This keeps the piston top or deck from sticking out of the top of the block.
The head gasket chart (See table in Part 1) shows three choices. The HKS metal head gaskets are available from Nissan Motorsports. Although a bit pricey, these are the only gaskets to use when boring the block for larger than 88mm pistons.
In the next part of my series, I will discuss the preparation of the rotating engine parts and the cylinder head work needed. I will pick some favorite engine combinations and comment on induction choices and flywheel/clutch combinations. If you have any questions at this point, feel free to e-mail me.