3.1 l Stroker Myths and Legends Revealed!

Contributed By: Bob Hanvey, IZCC #4545

As of 20 March 2002


This page was originally written in 1996/7 as I finished the extensive buildup of my 3.1L Motor. Over the years, I have continued to refine the setup, and have received numerous e-mails with questions regarding the stroker motor. I will attempt to answer many of those questions that were not originally addressed.

First, before you venture into any project of this magnitude, you need to sit down and answer some crucial questions. First, what are you trying to build? Do you want basic improved performance out of your 240/260/280Z/ZX? Are you looking to build a motor to power down the drag strip or road course? Will this car be used exclusively as a track car? Is this your daily transportation? Autocross? Show car? Monster truck? (Hint, this is the wrong car to start with÷but it has been done!). Ask two people, and you will get four answers. Your desired end result makes a huge difference in how you get there. Installing a stroker motor in your Z is no small project, in money or time. Realize up front that few people have built the stroker, and each have approached it in a different way. I will walk you through how I researched and built mine, but realize there is more than one way to skin a cat.

First, as on all these pages, I need to start with a disclaimer. While I am offering up this information for all to share, and I am a mechanic, (although on the side now), I am by no means an expert. I have just spent a lot of time researching and working with the Stroker setup. I cannot promise you will see the same results. Any forage you take into this project, you take of your own free will, and soon to be empty wallet!

Ok, why a stroker? To be honest, I was na've. I originally thought, "Hey, just pick up a diesel crank, and some 9mm 240 rods, and those 89mm pistons, and abracadabra, lots of power!" I felt the thought process was fairly sound for the most part. What appeared to be a minimal investment, i.e. a few hundred dollars more, the over all re-build cost would be about the same, right? WRONG! Well, as I started gathering my parts for the re-build, I also, (thank God, in hindsight), started to do a little research. I began checking to see if it would be worth my time to get the LD28, (stroker), crank and the bigger pistons and what exactly was involved. The connecting rods and pistons were actually a moot point for me since I had to replace mine anyways. As I saw it, the only real cost differential to me was the used diesel crank. It is funny how little I knew.. The bottom line is you would build a stroker for more than just a higher horsepower figure. A stroker motor tends to produce more torque,(torque is what directly affects acceleration), and over a larger powerband. What this means to you is the car will be easier to drive.

A good example of how torque can make a difference is the current Honda S2000 vs a 98-00 BMW Z3 //M Roadster/Coupe. The //M Roadster and Coupe are the "muscle" versions of the Z3 convertible with the same motor as the 96-99 M3. Both the S2000 and the //M Roadster/Coupes have 240 hp and are within 200 lbs of each other. However, the S2000 produces about 150-160 ft-lbs of torque, while the BMW's have nearly 240 ft-lbs. The 0-60 times and 1/4 mile times are fairly close, with the BMW's being on top. But if you drive both, they are two worlds apart. Sure the S2000 will go 0-60 in under 6 seconds, (5.9), but you have to rev the motor to nearly 9000 rpm and drop the clutch. A more reasonable launch at say 3-4000 rpm will put 0-60 in the hi 6 to low 7 second range. Now, the BMW's can be coaxed to near 5.0 seconds 0-60, but the average person can almost always produce a sub 6 second time. It is a function of the extra torque and that it is available lower in the powerband. It begins to accelerate the car sooner. While these two are not Z's, they are two extreme examples to show you that 240 hp is not equal to 240 hp.... So how much more torque in a stroker? That depends on how you build it. My motor produced about 2-30 more ft-lbs than a similarly built 2.8. But what is far more revealing is the plot of the torque. It was nearly the same from 3500-6500. That means my motor is much more flexible and easier to drive. It is the area under a power curve that will tell you whether you must rev to the high heavens, or can get away with lower rpms.

So, I began my quest for knowledge. I started in my trusty book,How to Hod Rod and Race your Datsun by Bob Waar. While that had a lot of great information, 1) it was somewhat dated, and 2) it didn't really answer my questions. So I turned to the Internet and magazines.

The Internet has been, by far, the best resource I have used/found yet. Two pages in particular were especially informative and useful: "The Datsun Garage" by Bryan Little. He outlines many simple upgrades for the Early Z's, which greatly increase its performance for a small outlay in money. I consider this a must stop for those of you looking to improve your performance in any 6 cylinder Z. The IZCC, or Internet Z Car Club, has an excellent web page with everything from a mailing list to pages on "How to modify your L6", extensive history, etc. Carl Beck and many others have done an excellent job of pulling from the many knowledgeable sources on the net and put it all in one place.

As I continued my search, I called many engine builders, camshaft grinders, etc... The list goes on and on. As I began to get the full picture, I realized that there was a whole lot more than anything I had initially anticipated. I decided to stay with the stroker combo, even though I began to see just how much it was going to involve. I have a slight obsessive disorder; I must have the best out there. And I was single, and had no significant bills. Something I wish I still had! I started by giving my L28 block to the builder to start on. I then set out to find a LD28 crank.

The LD28 crank was offered in the early 80's Nissan/Datsun Maxima Diesel. It was known as the Datsun 810 in the late 70Ės with Maxima being a high trim level. In 1981, the 810 became the Maxima, and for the first time, a 2.8L 80hp diesel was offered. The diesel was not a very popular option and was discontinued in 1983. As you can see, only three model years offer a possibility of having the diesel motor, which carries the LD28 crank. You can buy a new one from Nissan, but be prepared to spend close to $1000, (might be more or less - depends on your source). What the LD28 crank offers is a slightly longer stroke or how far the piston moves up and down, (83mm vs. 79mm). There is a fair amount of math, thermodynamics, and basic engine stuff involved; the end result is potentially more power. I say potentially because you can always mess it up!

Many people ask how a diesel crankshaft will work in a non-diesel motor. And if it works, why not use the connecting rods as well? First, Datsun had essentially the same block for their diesel as the gasoline cars. It turns out that the bearing diameters for and the overall dimensions are identical to a L28 motor, (except obviously the stroke). However, you DO NOT want to use any other parts from the diesel. A diesel is designed to combust the air/fuel mixture by compression instead of by spark as in a gasoline engine. This means that much larger forces are placed on the connecting rod and pistons. If you see a connecting rod from the L28 diesel, you will see how massive they are. Heavy rotating parts do not contribute to high power production. Bottom line, use only the crankshaft from the diesel.

So how much more power will I see? How much more power you produce depends on what other things you do. Just putting a LD28 crank in an L-28 block will increase your stroke, and increase your compression ratio. You now have a greater swept volume, i.e. the pistons travel a longer distance in the bore,(that would be the up and down). So with some geometry, you now have a greater start volume, and a smaller end volume, result - a higher compression ratio. However, if you left the stock 280Z rods and pistons in place, they would stick above the deck about 2mm. The stock head gasket is thinner than 2mm! While you could mill those pistons, you are just asking for all kinds of trouble. You now have an odd rod/crank ratio, which is not as good for power. You need a longer rod to take advantage of your increased stroke. By putting the LD28 crank with the stock L28 rods, you have a fairly large rod angle, (the maximum angle the rod forms with the vertical). The larger this angle, the more force the piston will exert on the side of the cylinder, and less gets forced down, which turns the crank. By using a longer rod, the rod angle is reduced, and more of that newfound power can be utilized. So the key is to find a rod/piston combo that puts the top of the piston in the right place. ĪBut wait!Ķ you say. Why would I want to put the longer 240 rods in there since they are almost 3mm longer than the 280 rods! The piston would now stick up almost 5mm above the deck! This is why you need to find a piston whose pin height, (from where the "pin" goes through the piston and rod to the top of the piston), is less than the stock 280's. This is commonly referred to as the piston compression height. The piston compression height of the stock 280 piston is ~38.1mm. The two most common used pistons in 3.1L buildups, the 240sx piston, and the 720 truck piston, have compression heights of ~34.5 mm. Problem solved. The amount they stick above the deck is manageable

Next are the connecting rods. I have had many people ask why the 9mm rods, and what does the 9mm stand for? First the 9mm is the connecting rod bearing cap bolt size,(say that three times fast!). You can use either of the two types of 2.4L connecting rods. The early 240Z motors came with what is commonly referred to as the 8mm rods. The later 240Ės came with a revised connecting rod, which had a larger 9mm bolt. Being the evolution in design, they were lighter, and stronger. This is why they are the preferred choice for a performance build up. Your motor will survive if you can only find 8mm rods, but I would recommend two things. First, replace the rod bolts with stronger ARP bolts, or order the set from Motorsport Auto that will replace the 8mm bolts with 9mm ones. Second, don't run the daylights out of your motor.

Now I have this really cool LD28 crank, and some nifty used 9mm rods. So now time to order some 240sx pistons. Incidentally, the 720 truck and 240sx pistons both have a diameter of 89mm. That, coupled with the 83mm stroke, yields a displacement of 3098cc, or 3.1L. For the part numbers and other options for combinations, look at the IZCC homepage, under How to modify your Z for more HP under the section about building 3.0 and 3.1L engines. Steve Golik did a lot of research on part numbers and combinations, and put it all together in a FAQ, saving us all lots of time and effort. And Walter Fath of the Z car club of Sydney put together a great Windows based program which calculates various engine combinations called L Engine. You can try a 280 crank in a 240 motor with 89mm pistons and a E31 head. It will tell you the compression ratio, displacement and other valuable information. It allows you to try different combinations quickly without the cumbersome math. I am currently asking for permission to post the program here. Also, if you are a programming/web whiz, let me know if you think you can put this program online via a java applet or otherwise. It would be great if people could just pull it up on the web. My e-mail address is at the bottom. Z Owners of Northern California or ZONC currently have the program on their web page.

Now I want to dispel some myths about the stroker setup. Some of the most commonly heard ones are issues such as: It won't produce much power over 5000 rpm. They are inherently unbalanced. You will destroy front harmonic balancers. As I stated at the beginning of this article, building a stroker is not a cheap way to get more power. Almost every time when I talked to someone who had problems with their stroker setup, it was related to cutting corners. This was almost universally the cause of problems. Here is some food for thought: When a motor comes from the factory, all parts are designed to work together. Each piece has a certain tolerance for weight, dimensions, and function. The entire rotating assembly is balanced to work together. With the stroker setup, you are taking a crankshaft from a diesel, connecting rods from a 2.4L motor, pistons from a Nissan truck or 240SX motor, and an engine block, which had none of the above originally. Each of these parts was manufactured with a certain tolerance in mind. That is no longer valid in your new setup. You Must thoroughly balance the entire rotating assembly. This should include the flywheel and harmonic balancer if possible. You can get away without the balancer and flywheel, but the internal rotating assembly MUST be balanced. For some of the connecting rods, we removed several grams of material. If you fail to balance the rotating assembly, you are giving up an unknown amount of power. On my builders L6 race engines, he had seen up to a 15 hp difference in power on a 330 hp race motor. Now those were 2.8L motors which had parts they were originally designed for. I would venture so far to say that an unbalanced 3.1L stroker could lose up to 25% of its power. The L6 crankshaft is very long. It develops some extreme harmonics as we approach and exceed 7000 rpm. Now take 6 connecting rods that might vary by as much as 5 grams and throw them around with pistons on the end, which could be off a few grams as well. Now you are talking about a significant effect. Any builder will offer to balance your motor, but be VERY WARY about who you have balance your assembly. It is an art, and the machine used is a variable as well. If you already have a shop and are unsure, find the most successful racing shop in town and ask them where they send their winning motors to be balanced. It is not uncommon for engine builders to send their rotating assemblies out of town to a reputable balancing shop. Don't be afraid to do this. Matching the connecting rods and piston weights is not hard. The hard part involves the balancing of the crank to those weights. There is a clear theme throughout this article. Building this motor costs money. The most important choice you can make, more important than which head to use, or which combination of parts, is the machine shop. Choose the best shop you can find. Not the best you can afford, but the best you can find. If you skimp on this it will just hurt you in the long run. 5-20% more in cost now is worth it in the long run, (not having to rebuild the motor in 5-10k miles).

One of the myths mentioned earlier concerned breaking harmonic dampers. The dampers for the Datsun L6 motors are two steel pulley's bonded together with rubber. Over time this rubber will begin to break down, especially if it is in contact with oil, (i.e. a leaky motor). Now take this damper and put it on a stroker setup which was not balanced or was poorly done. It is almost guaranteed that you will destroy the rubber bonding btw the two steel parts, it is just a matter of when. And even motors that are built properly, they dampers are nearly 30 years old, and are now being sent to 7000 rpm on a regular basis. Good common sense dictates either a new one, or an old one in really good shape for your freshly rebuilt motor. Bad balancing will contribute to all of these problems. And bad balancing can also cause a motor to not produce much power above certain rpms.

The last myth concerns the lack of power above 5000 rpm, or that they won't even rev above 5000! Likely the single largest contributing factor to this myth/problem is fuel delivery, of a more apt description, fuel starvation. I know many people who put their 240Z SU's on their freshly rebuilt 3.1L motor. This is just fraught with problems, especially if you add an aftermarket camshaft, which you most likely did! Think about this, those carbs were originally built and designed for a 2.4L motor, its fuel requirements, and volumetric capabilities. You have just put it on a motor with 40+ more cubic inches, different volumetric efficiency, and a completely different fuel requirement! If you make no changes to the SU's, they are going to run out of capability to deliver fuel to the 3.1L motor somewhere around 5000 RPM. Above that RPM, the carburetors cannot supply enough fuel to continue producing more power, and power will drop dramatically. There are several options when you want to use the SU's from the 240. This can include different fuel needles, different springs in the piston assembly, and a larger bore, either from a different motor such as a Jaguar, or boring out the carb,(hard to do, only Rebello does it as far as I know).

The bottom line is many of the "myths" about the stroker result from improper building and parts selection.

So here I am all ready to go, and then I hear that the turbo block is stronger than the stock L28 and should be used for the 3.1 stroker! Why?!?!?! No one could tell me. Having a friend that had a spare turbo motor, (and the fact that he wanted my "spare" 240 motor), I decided that it was the better part of valor to go with what is supposedly a stronger block. The turbo block has F54 cast on the intake/exhaust side of the motor, (on the block). For clarification purposes, the F54 block, which is often referred to as the "Turbo" block, is actually the block that replaced the N42, and you will find it in both turbo and some non-turbo motors from 81-83. There was a period where Nissan was using both blocks, and you can find some turbo motors that have the older N42 block. About a month later, I was finally able to find out the difference between the two L28 blocks. When I was de-burring the block, (a process where you smooth out the casting ridges in the block, helping eliminate potential stress areas, and possibly future failure areas), I saw no difference between my old L28 and the F54 turbo block. I didn't know if it was just made with a different material or what. Finally a Nissan technician and rebuilder told me that in-between each cylinder, in the water jackets, they cast an extra re-enforcing near the center of each bore. This was designed to strengthen the block in anticipation of the added stress of the turbo. Remember, Nissan over-engineered most of the Z parts. Some racers donĖt believe it helps a non-turbo motor. I wanted to be on the safer side. In my opinion, the F54 block is the only block you should use for anything with a 3mm overbore! Many sources will tell you that the 3mm overbore is risky, and it most certainly is! Remember, that is ~.120" of metal you are looking at removing from each cylinder. For those of you familiar with V8 rebuilds, .040 or .060 over is considered a large overbore. So three times that most certainly is. If you take any block and bore it out that much, you are decreasing its rigidity. What will happen as you start to produce power, the block will deform slightly, and will produce less power. By using the stronger F54 block, you will hopefully minimize your deformation, and keep more of your power as well as extend the life of your engine.

At this point, I feel some comment should be made about boring with a torque plate. What this involves is bolting a plate to the block that simulates the cylinder head being on the block and torqued down. In a nutshell, by boring the block with the torque plate on, you are cutting holes in the block when it is stressed as it will be when you reassemble the motor, (I am assuming you also have the main bearing caps installed as well). When you torque down the head, you distort the cylinders. If they are bored without a torque plate, they will become slightly out of round when you reassemble the engine. How much depends on how strong the block is, how much the cylinder head bolts deform the block and the quality of the boring job. We have already said that the block is less rigid than a stock block, so this effect is only magnified. So, as some of you may ask, who has these plates, and what if I can't use them? I am sure there are more, (please e-mail me if you have knowledge of any), but the two I know of are D.L. Potter Racing, and Rebello Racing. You can ship your engines to them, and expect to pay a fair penny for them to work on them,(Rebello will only bore your block for you if you wish). So what if you don't have access to these parts? You can still do it, but make sure your machine shop really knows what it is doing. This is one of the most important choices anyways, (there is a list at the bottom). A bad bore job will ruin a rebuild, (and waste a lot of money). I didn't use one, and my engine is still very strong, however it is unknown how much power I am losing because I did not use a torque plate. At the time, I couldnĖt find anyone who had a plate we could use.

So now we have a stroker crank, the 9mm rods, the cool pistons, the ultra superman block. So where from here? The head. This is another area I feel strongly about. While I was researching, on "The Datsun Garage" , Bryan Little talked about modifying a P-79 head. He also briefly discussed the turbo heads, the P-90 and P-90A. He has since added pages about the P-90, selecting it as I did. Those P series heads, which I talk about on my Head page are basically of the same design. Their biggest advantage is the combustion chamber. It is a heart shaped design helps put all the fuel/air mixture around the spark plug, promoting better combustion. The P-79 head has exhaust liners. People have tried to take them out, and few have succeeded, and it is completely unnecessary. It is a common misconception that the exhaust liners hurt airflow. The opposite is true. With a more gradual angle out to the exhaust manifold, and a better design, it will actually outflow the earlier heads! The P-90 and P-90A were the last evolution in design of the L series heads, and incorporated many of the best design features. However, all P-series are excellent choices for the stroker motor. If you want a slightly higher compression ratio without resorting to excessive shaving of the head, the N-47 and N-42 are excellent choices. I would personally choose the N-47 among those two. Again, reference my Head page and Paul RuschmanĖs comments about that head. The P-90 heads have the same square exhaust as the early style heads, (E-31, E-88, N-42). So I went out searching for some turbo heads, to see if they were worth a try. Once I saw them, I felt they were. Unfortunately, these heads are not very good for smaller displacement engines, for the combustion chamber is much larger than the early style heads. But for the 3.1, it is the best you can get. Coupling the P series heads with a 3.1 motor yields just above a 9:1 Compression ratio. I shaved my head slightly to get closer to 10:1. I am not going to discuss the heads much on this page because it is covered thoroughly on the head page but I will address shaving the head. When you shave the cylinder head, you are decreasing the distance from the crankshaft to the camshaft. The timing chain is a set length. The tensioner can only take up so much of that slack. However, that is generally not the problem. The problem is the cam timing is now retarded, i.e. valve opening and closing is happening later than it is supposed to. This will affect power production, mainly on the top end. There are three adjustment holes to account for this, but even they may not be enough. So what is the fix you ask? You need to shim the cam towers up so the distance between the crankshaft and camshaft remain the same. This involves buying shims the same thickness as the amount you shaved the head. They go in-between the camshaft towers and the cylinder head. However, there is now a larger gap between the camshaft and the followers. This can be adjusted two ways. One is to put larger lash pads, (this goes on top of the valves), and the other is to just adjust the lash adjusters up. Does that make sense? Basicly you are moving the pivot end of the follower, (goes from the adjuster to the valve, is what the camshaft touches), up to the proper distance beneath the camshaft. What negative effect does this have? Well, you are biasing the camshaft contact point away from the valve. This serves to open the valve more for a given camshaft lift, (think of a lever, the closer you are to the pivot, the more the end will move). This is fine as long as all the valves have the same contact point, and most importantly the wipe pattern doesn't go off the contact surfact. The wipe pattern is the area where the camshaft contacts the follower.

So what is left? You have the block, crank, rods, and pistons? Lots. Rings, bearings, new oil/water pumps, timing chain, clutch/flywheel, induction, exhaust, camshaft selection, gaskets, ignition, and lots more. This is what tends to nail people as far as budget planning goes. Those parts alone added up to several thousand for me. And that doesn't get into upgrades that are now necessary for your newfound power, brakes, tires, rear ends, transmissions, etc...

Let me start with the exhaust. I personally chose the Nissan Motorsport 6-2 large diameter header. I think it is the best available, and many shops will support this claim. However, it is not cheap, it is about $300. I personally felt it was worth it. Again, it is a personal decision. As with all headers, you will have to pay for an exhaust system. That ran me about $270. I had them run the two pipes back until the back of the transmission, then join them together, (from two 2.5 in to one 3 in). I then put a Walker race muffler, (basically a glorified glass-pack), then the two 90 degree bends, into a Ultraflow muffler. Even with the two mufflers, it is loud. The race muffler in the drive tunnel serves to help cut down on the resonance famous in Z cars. Actually, by running the two pipes back as far as I could, that helped as well. Keep in mind that somewhere down the line you may want to remove the transmission, either for a clutch job or otherwise. You would be well advised to have the shop weld on flanges near the motor/tranny interface and behind the tranny. This will allow you to remove the exhaust or a portion therof and remove the tranny. Or you can do like I did the first time around and have the flanges welded just behind the transmission. This means you must remove the header assy. to remove the tranny. No fun. Let me say the exhaust shop that worked on my Z did some excellent work, for the pipes don't hang down, (except near the rear lower A-arm), and that is impressive considering there is not room for two pipes to run down the side of the transmission. There is often debate on 2.5 in vs. 3 in, and I am not going to get into it. I have always wanted a 3 in system, because I spend my time at ĪhigherĶ rpmĖs. In addition, no one in the area could do mandrel bends, (no crimp or indentation in the tubes), so when you factor in the indentations, I have a system that is smaller than 3 in. In the end, it is an individual choice. With the 3 in system, expect to drag your exhaust once in a while, especially if you lowered it and drive on bad roads.

I have saved camshafts for the very last, because that will vary dramatically regardless of who you are. First, there are no "Stroker" grinds out there. There is so little demand for the stroker motor to begin with, few have taken the time to dyno multiple camshafts and find the best one. I had a shop in California tell me he had done so, and gave me the specs and the shop that ground it. I ordered that grind, and when we ran the engine dyno and tried several difference cams, I found it didn't produce the broad range of power, or even the peak, as the one I ended up with. It did well, but not as well. I ended up with the Motorsport Auto 2003 cam. It is a 0.460 lift, 270/280 duration cam that is advertised to produce power from 2000-6000. It does exactly that, and even up to 7k. Schneider actually grinds the cams for Motorsport Auto. They are well respected and have worked with L6 motors for some time now. You look at how you will drive the car 90%+ of the time, and I mean MOST of the time. Sure a 0.500 lift, 300 duration camshaft is really cool for 5000+rpm driving, but it can suck around town. Look at how you will drive and go from there. If possible drive other peoples cars and see what you think. Find one you like and go with it. I don't really want to address how the stroker affects the cam specs, because I don't fully know. Mine works great and I am happy. I am also running the hydraulic head, which slightly increases the effective duration, because the lifters lock up a little sooner, (they sent me a non-hydraulic cam). But again, we have no way of knowing how much the stroker, the cam, the induction, (which is 40mm SK's, similar to webers), exhaust, or other components affected the power output. I will soon be trying a Sunbelt Motors new grind - when they make them publicly available.

Bottom line, plan on over 5K to do it right. You can do it for under 2k, but you take some chances of reducing your longevity, power producing capability, etc... With stroker motors, it is a crap shot. For those looking at turbo strokers, I will tell you, NOONE has built a good turbo stroker, because it costs too much to do both well. Well, apparently there are some getting close to doing both well, but that is still up in the air. Those that did try, skimped in the stroker part, because the turbo is what produces easy to see power. If you want a turbo, stick with the L28, unless you just have money to throw around, and want the ultimate power. In that case, throw a few grand my way! So what is important for the stroker? In order of importance, in my humble opinion:
1) The best machine shop you can find, (not afford, find, for if you can't afford it, then you are throwing money away).
2) F54 block. 3mm overbore is HUGE! Keep some of that strength.
3) Balance, Balance, Balance the rotating assembly. Enough said.
4) Money, lots of money.
With those, you will have a good start. Do lots of research, and pick the brains of everyone you can. You will start to get a clear picture when you do. - Good Luck!
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(c) 1997-2002 rehanvey@yahoo.com Please don't e-mail looking for an immediate response. The Navy keeps me really busy, so it may be up to several weeks before I can respond.