3.1 litre stroker: The Machine Shop
Now that you have disassembled the parts of the 280 engine and cleaned them. Lets do some basic cheap improvements. These improvements may save your engine later in life. The first is to debur the internal crank case area. When all cast iron blocks are made, the molten iron is poured into a sand form. When the block was first used, Nissan cleaned the block as best as they could. They missed some sharp lips where the different layers of the forms meet. These lips are called surface risers. These lips have a tendency to chip under high RPM conditions. If this small chip gets into a cylinder, the damage would be catastrophic. The process of deburing the block is simple. It does require a small high speed grinder. This task could take as little as one hour or as long as three. Take your time. There are two areas you do not want to touch with the grinder. The first is the bottom of the cylinder bore. The other is the bearing seats. Both of these area are machined to a fine tolerance. The second improvement to the block is the main oil galleys. These galleys deliver oil to the main bearing surfaces from the oil pump. If you upgrade to a higher PSI/volume pump these galleys need some minor modifications. When the block is assembled these galleys are open at both ends of the block. Nissan uses small steel plugs to close the system. These plugs will pop out during high PSI/RPM conditions. This is another one of those catastrophes we want to avoid. The way around this problem is to remove both of these plugs. Then using a proper size tap, cut threads into both holes. Install two hex head plug into the newly threaded holes. Be sure to use the permanent version of Loc-tite (do not install the plugs until the block has been returned from the machine shop). The third modification is to remove the oil filter check valve bye-pass. This check valve allows oil to bye-pass the filter in the event of a filter clog. A problem is created when you use a high PSI/volume oil pump. The oil will seek the path of least resistance through the valve not through the filter. Since you change your oil and filter every 3000 miles you will never have a clogged filter. Before you attempt any of the modifications discussed above, read and understand these processes discussed in the "How to modify your Nissan/Datsun OHC Engine", or talk to someone who have done this before.
The machine shop you choose is important. Talk to lots of people who race or who builds engines. They will know the shops to use and the ones to avoid. Its decision time again. During the process of locating a good machine shop, you need to ask if they have a torque plate. If they don't know what a torque plate is, find a new machine shop. This plate is attached to the top of the block where the head normally sits (you will also need to use a head gasket for this task, then through it away). The plate is tightened to the same specs as the normal head. When the plate tightens down it will distort the cylinder slightly. If you bore the block under a torque condition, you are guaranteed the cylinder will be perfectly round when you install the new head. This will add $50 to $75 to the cost of boring the block, but its worth it! Its generally a good idea to have one shop do all of your machine work. Do you remember those 240-Z rods you bought at the junk yard? Its time to do some work on those. The first process is to magnaflux all six rods. Magnafluxing checks for small cracks and faults in the metal. Once you know the rods are good and safe. All six rod need to be balanced and shot peened. Shot penning increases the strength of the rod by compressing the surface. Once again this is not necessary but its $50 well spent. The crank shaft will need to go to the machine shop along with the block, pistons, and rods. But, before we send the crank out we need to improve on the Nissan part a little. Like the block, the crank has oil galleys. This provides lubrication to the main bearings. These galleys are drilled at angles then plugged just like the block. If you plan to use an improved oil pump these plugs must come out. Then these holes are taped and new threaded hex plugs are installed with Loc-tite (do not install these plugs until the crank comes back from the machine shop).
Its time to talk about the cylinder head. Horse power is made in the
head. And like other parts of the engine, there are several recipes to increase
horse power. Eric and I used the N42 head because of the larger intake valve
diameter. This head will also offer you better options regarding your compression
ratio. Once you have cleaned and disassembled the head. Think about matching
ports and polishing these surfaces. Match porting eliminates the slight
difference between the intake manifold and the head. This will allow the
fuel/air mixture to flow with fewer restrictions. Eric and I took this process
to an extreme. Eric cut an old N42 head into cross sections. These cross
sections allowed us to map the water jackets the cooling system uses to
cool the head. We knew how much material we could remove. By enlarging and
straightening the intake and exhaust chambers, the engine breathes better.
Thus making more horsepower. Be careful, too much grinding and you will
trash the head. Thereís a company on the west coast call Extrude
Hone. You can ship your head and manifold to them. They will match port
and polish both parts. They inject a compound that looks like silly putty.
But, it's abrasive. It will open up the ports slightly and radius the corners.
The finished surface is as smooth as glass. They claim up to 25% better
flow across the surface. For more information check Grassroots Motorsports
Magazine for their number. When you call, be prepared for a long explanation.
I thought I was talking to NASA! As it turned out, the founder got his start
at NASA using this process on rocket nozzles. Some of their many customers
include, several Indy teams. They hone the internal vent surfaces of brake
rotors. Better air flow equals better cooling. Two important points, if
you plan to race this engine, beware SCCA only allows certain parts to be
ported and polished. Second, don't just start grinding away thinking it
will improve your performance. Consult with a machine shop that can flow
bench the head before you start. This starting point is called a base line
spec. As you proceed check your progress on the flow bench. If you plan
to port the head yourself. Ask lots of questions and read the entire section
under "Cylinder Head" in the sacred tablet ("How to Modify
your Nissan/Datsun OHC engine"). Eric and I were lucky to have access
to a flow bench. Eric designed and built a flow bench adapter for the Z
head. As we removed material we could see the benefits as the numbers increased.
Another trick process you can blow some bucks on are the ceramic header
coatings. The days of using header paint are long gone. These coatings are
sprayed on then baked. They coat the inside and the outside surfaces. There
are two benefits. First your headers will last twice as long. Second, it
looks cool (Cobb's rule #4: No matter how trick or high tech your parts
are, someone will always discover a better more advanced part. CHEAPER!!!
The Machine Shop
Cranking & Debugging