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Building a 3.1L Stroker Motor for Your Z

Original Article by Lee Cobb


Introduction: "Boy! This sounds like a great idea!"


I am one of a rare breed; I have owned my Z since it was new. It celebrated its 23rd birthday this year. For those of you mathematically challenged, itís a 1973 240Z. Ever since I bought the car, the factory Hitachi carburetors coupled with the crude attempt at exhausts emissions kept the car from really performing.

About a year ago I attended our monthly Z car club meeting. During this meeting one of our members brought a diesel Maxima crank shaft. This crank was a work of art! The edges had been knifed and polished. The total weight had been reduced by 26%. I though to myself, ďWow! I bet this makes his Maxima really haul butt!Ē Then it was explained to me that this crank would also fit into a 280-Z, improving the stroke and horsepower over the stock specs. The club member was Eric Chapman. Eric runs Z-Quip, a machine shop in Newnan GA. Z-Quip builds one-off parts for Z cars. During this same meeting another club member (Steve McCarley) mentioned he had built an engine using this same technology. Steve mentioned that a person with reasonable mechanical skills and approx. $3,000 could build such an engine. Boy! This sounds like a great idea. Steve outlined the basic concept of a 3 liter engine.

As I listened, visions of racing at the front of the Indy 500 started to run through my mind. After all $3,000 is a lot of money. Little did I knowÖ As Steve proceeded with his information dump, I was frantically writing down every syllable that came out of his mouth. During this information dump, Steve would say, ďSince you're doing this, you really should upgrade to this and that.Ē So, by the end of the meeting, I had gone from not knowing what a 3 liter was, to spending $3,000 to build one, to upgrading to this and that. As near as I can tell somewhere between ďYes, I can spend $3,000Ē and driving home, I spent an additional $2,500 on upgrades.

During this article I hope to share with you the ups and downs of building a 3 liter stroker engine. I am not an expert. The technical part of this article will be handled by Eric Chapman. Between the two of us, you should have a good idea whether or not you want to tackle such a project.




Getting Started: How Fast Do You Want to Go?


When starting any project, you need to have a game plan. A good starting point is to ask yourself this question "How fast do I want to go?" Since how fast you go is directly related to how much money you spend, this is a good starting point. Unless your last name is Gates or Trump, you will need to set a budget. This will let you know just how much you need to lie to your spouse. It will also serve as a reality check (Cobb's Rule #1: Building a 3 liter engine has no basis in reality!). Another major dilemma is can you do it yourself, or do you pay to have it done? I have a moderate amount of technical ability, but I didn't have any of the necessary tools. So I did a mix. Eric and I decided to build his engine and mine side by side. This allowed me access to Eric's knowledge and some really cool tools. My advice is to ask club members and others with more technical ability than you have. Another source of excellent information is what Eric and I call the ďsacred tabletsĒ (the Nissan Shop Manual and How to Modify Your Nissan/Datsun OHC Engine). Both of these books are critical to engine modifications and assembly. These publications are available through several sources. The tools and technology required to do this type of work will require the services of a machine shop. How much you send to the shop depends on your access to specialized tools like pneumatic grinders, valve spring compressors, and mic gauges.

Building a high performance engine is a lot like cooking. The right ingredients, blended together correctly produce a great end product. Locating the necessary parts to send to the machine shop is a project by itself. The single hardest used part to locate will be the diesel Maxima crank. Nissan only produced this option for a few years. Because of that, they are few and far between. I chased down three people with these cranks. The first was a person who wanted $500 (I don't think so!!!). The second was a junk yard. The car had burned to the ground and because of the heat, the crank was warped. Finally, I located a crank out of a car with only 54,000 miles on the engine for $150. This single task took over six weeks. You could also go to a Nissan dealer and purchase the crank and rods new for $450. Next, plan to purchase a 1975-1978 280-Z engine, unless you plan to use your own engine. I bought a complete 1976 engine with the correct head (N42) for $250. I sold the fuel injection and manifold to a club member for $50. While you are at the junk yard, pick up a set of 240Z rods. Remember there are two different types of rods for the 240Z. One has 8mm main bolts and the other has 9mm bolts. You will want the 9mm bolts for the added strength.

Now is probably a good time to make a few hard decisions. Since some of these parts will take three to four weeks for delivery; the first decision is where do you plan to drive the car? This simple question will help determine the correct parts to order. There are trade-offs when making these decisions. As an example, if you plan to drive this car on the street all of the time, then a milder cam and lower compression would work best. On the other hand, if low speed drivability is not an issue and you want more power, then you may want to get a little more aggressive on the cam and increase the compression. At this point, start thinking about improving your ignition system and your life insurance. Now if you're tired of listening to your bitchy neighbor talk about how fast his 5 liter pony car is (yawn), then a cam that kicks in around 4500 to 5000, triple 44mm Mikuni carbs, competition valves and matching springs and a different piston to up your compression to around 10.5:1 would be the ticket. Oh by the way, you can kiss ever using pump gas good-bye. You're now an octane junky. Remember: itís only money. (Cobb's Rule #2: You can never go too fast!) The bottom line is simple. How will the car be driven? Then, build the appropriate engine. There are many sources for the right recipe. Talk to people in the club that race. Parts suppliers like Motor Sports in Orange CA, offers cams with good information on driveability and RPM ranges. Some of these companies also offer their own 3 liter kits. These kits offer convenience, not flexibility. As for the three engines that Eric and I built, we used an aggressive cam with 510 lift and 300 duration. Attached to the cam are Nissan swirl cut and tulip valves with hardened competition valve springs. The intake manifold has been extensively ported and polished (see the "Machine Shop Section" for more details). At one end of the manifold are triple 44 mm Mikuni carbs. And at the other end are six JE forged pistons with moly rings. The compression comes in around 10:1 (93 octane or higher required). The factory ignition system was replaced with the Electromotive Crank fire system. At one end of the crank is a HKS eleven pound flywheel and the other end is a Fluid Dampener harmonic balancer. The lubrication system uses a 90 PSI high volume oil pump sucking oil from a 9 quart competition oil pan. (Cobb's Rule #3: Keep telling yourself, ITS ONLY MONEY!)

You don't have to use parts produced by NASA to build a fast engine. The early SU side draft carbs (1970-1972) can be modified to offer good performance at a reasonable price. Cast pistons instead of forged can be use to help cut cost. The factory ignition system and many other OEM parts will work fine. Which parts you use are up to you. Now you need to decide how far to bore your engine. Up until now I have used the term 3 liter generically. Letís define just what I mean. I bored my block 40 thousandths over stock to get a 3.0 liter engine. Eric on the other hand bored his to a 3.1 liter or 120 thousandths over stock (3.0 uses 87mm pistons and a 3.1 uses 89mm pistons). So order your pistons now because the machine shop will need these to bore the block.

Now that you have ordered the correct parts, itís time to disassemble the 280 engine and prepare it for the machine shop. When I was a kid, I could take apart anything. Putting it back together was always the hard part. I always had extra parts left over when I was finished. This part of the project is fun and does not require special tools. However, it does require some organization, because some of these parts may be used again. You will need some type of parts organizer. You can buy an engine organizing tray from a parts house or use milk jugs, heavy-duty 8"x10"envelopes or coffee cans. Once you remove a part label or tag it. You DO NOT need a hammer to disassemble an engine. The head is aluminum and the block is cast iron. Both are brittle, and do not react well to being hit with a hammer, since the newest engine you can use was built in 1978. The use of liquid wrench is recommended. The bolts for the water pump and timing cover will snap if forced. The use of penetrating oil will help removing these bolts. There are two very important parts to label (the cam towers and the main baring caps). As you take one off, label the location. These parts look identical. They are not! These parts must go back into the same location you took them from. Parts like the old cam, crank, timing chain and gears do not need to be kept. Spend a few minutes inspecting the head bolts, cam towers, and main bearing caps for damage. Thoroughly clean all parts with an automotive de-greaser. This will make the inspection process much easier.


The Machine Shop: I Thought I Was Talking to NASA!


Now that you have disassembled the parts of the 280 engine and cleaned them, letís do some basic cheap improvements. These improvements may save your engine later in life. The first is to de-bur 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 de-burring 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 areas 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 bypass. This check valve allows oil to bypass 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 has done this before.

The machine shop you choose is important. Talk to lots of people who race or who build 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 throw 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 itís worth it! Itís 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? Itís 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 rods need to be balanced and shot-peened. Shot-peening increases the strength of the rod by compressing the surface. Once again this is not necessary but itís $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).

Itís time to talk about the cylinder head. Horsepower 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. There is 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!!! ).


Engine Assembly: A Clean Engine is a Happy Engine


Now its time to get anal! Break out the mic gauge, torque wrench and assembly lube. Itís time to start assembling all of those new parts. The first thing you need to do is unwrap all of those nice sparkling clean parts and clean them again. Especially the parts returned form the machine shop. Never assume that because a part is new or just machined that itís clean. A clean engine is a happy engine. For this stage you will need to have lots of clean, lint-free rags, newspaper and cardboard. Carb or brake cleaner does a fine job removing the small particles and the old grease. The use of taps to clean up the bolt hole threads is a good idea. Blow any foreign material out of the holes with brake cleaner then compressed air. If you plan to use the original head bolts, take a few minutes to clean and inspect them. Both Eric and I upgraded to an ARP performance bolt kit. These are the same bolts that most of the NHRA teams use. Use your compressor to blow the parts dry. Pay close attention to the block. There are several places where metal shavings can hide. Once you have thoroughly cleaned the parts, coat them with WD40 and wrap them in clean news paper. This will keep them from rusting. The cylinder surfaces will rust quickly if left unprotected. Use the cardboard to cushion the heavier parts on the bench or shop floor. At this point some engine builders paint the internal surface of the block (crankcase only). This serves as another layer of protection from sand dislodging from the block surface. The paint Eric and I used is called Glyptol. This paint is manufactured by General Electric. GE uses Glyptol to coat the inside of high voltage transformers. It has a high temp rating and is almost impossible to remove once it has dried. Now itís time to paint the outside of the block. Standard engine paint works fine. Be sure to mask off the machined surfaces with tape. Locate those oil galley plugs we discussed early and install them. When installing the plugs for the main oil galley, be sure that you donít block off the feeder port to the bearings.

The block is now ready for assembly. I'm not going to walk you through the entire assembly process. That where the sacred tablets come in. Follow the standard steps for the block, then the head. Be sure to use generous amounts of assembly lube. To avoid dust contaminating the block and head, use a clean trash bag to wrap the block. Just like the disassembly, you do not need a hammer to assemble an engine. Take your time and always torque to the manufacturers spec. Some manuals will give the dry (non-lubricated) torque spec, and some the wet (lubricated) spec. And some just give you a torque spec. In the case of the ARP kit they provided special moly-lube for their bolts. By using this type of lube the bolt turns easier thus requiring a low torque spec. This is where a good torque wrench is critical. If you plan to purchase one, be sure it will torque up to 150 foot pounds. This will cover all the parts to torque in your engine.

Once you have installed all the parts for the valve train, be sure to set the cold valve clearance. This will get you real close for the initial engine crank-up. If you have never set a Z-carís valves before, have someone show you how. The Nissan shop doesn't do a great job of explaining the procedure. Please take your time. The golden rule is when in doubt, ask someone. I drove Eric crazy asking questions.


Cranking and Debugging: Oh My God, Where's All That Oil Coming From?


Now that you have finally buttoned up your engine, it's time to fire it up! Remember this is a new engine. We have all been told to take it easy and break in your new car. Even that engine has been broken in before you pick it up at the dealership. Following a few basic steps will allow the engine to be broken in correctly. The only thing keeping you from hearing metal on metal is the assembly lube you coated on those parts. Do a final check of all hoses, bolts, and wires. Add a good quality grade of oil to the crank case. Be sure not to use a low cost oil filter. This first oil and filter set will be used to break-in your engine. This filter will catch any foreign material you missed during the cleaning process. I would recommend pre-lubing the engine. To do this, simply remove the spark plugs and turn the engine over until you have oil pressure. This insures that your oil pump is working and that oil is circulating through the engine.

Fire it up (A small prayer would be a nice touch). Once the engine starts, DO NOT OVER-REV. Let the engine idle while you check for several things (oil pressure, leaks, water temp, and odd noises). Both Eric's and mine fired up on the second try. The night I fired mine up, Eric had gone home early. So I fired up my engine and did my checks. The temp started to climb a little too high so I decided to shut it down. This is not uncommon in new engines. But, just to be safe, I called Eric. Eric agreed this was normal, especially since I was using a stock radiator. So I hung up with Eric and walked back into the shop to find a large puddle of new oil under my engine. Oh my God, where's all that oil coming from? I had a sick feeling rush over my body. Then the illness passed and was replaced with stupidity. I had installed the flywheel without installing the rear main seal. So instead of finishing the break-in process, I got to pull my transmission and install the seal. The lesson is this: Don't get in a hurry. Once you have broken in the cam and rings (two 20-minute sessions at 2000 to 2500 RPM allowing the engine to cool between each). Adjust the valves again while they are hot. Take this opportunity to inspect the valve train. Once the valves have been adjusted, take the car for a short LOW SPEED drive. Let the engine cool. During this time check the condition of the spark plugs (lean or rich). Once the engine has cooled, check the coolant and oil for level. Now itís OK to drive the car a bit faster. During this period, fluctuate the RPM range you drive at. After about 100 miles change the oil and filter, then again after 500 miles. This should remove any foreign material and assembly lube.

If you have kept the trick parts to a minimum, debugging the engine will be relatively simple. On the other hand, this could be the hardest and most frustrating part of your project. In my case, it drove Eric and I crazy. The introduction of the Mikuni carbs required the services of an expert of epic proportions (Alan Smith). Alan has an amazing understanding of how to make Z cars move. Alan did in two hours, what four knowledgeable people couldn't do in six weeks. Alan had built a GT2 Z car with a truly amazing engine. His experience with Mikuni's solved my problems. Mikuni uses several different types of jets to tune the carbs. The factory jetsí ranges were not delivering the performance the engine was capable of. Remember the factory settings are great if you're building a factory engine. Once Alan had identified a few problems the car finally started to really move.

Well that's it. This is one way of approaching an engine project. It is definitely not the only way. I made lots of mistakes a long the way. I hope this article helps your project turn out as well as mine did. As for my partner in crime, Eric Chapman: Thanks for your knowledge and your friendship. I could never have done it alone. This information isn't a secret, it can be found each month at your local Z club meeting. Now, that sounds like a great idea!