Stroker Myths and Legends Revealed!
~ by Bob Hanvey
I hope that on this page, I can successfully get across all that I learned while building my 3.1L.
I researched lots of sources, including many people who have built a stroker motor.
Through all my trials and tribulations, I think I finally have a good idea on how someone else
can successfully tackle what is really a monumental buildup.
First, as on all these pages, I need to start with a discalimer. 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!
I originally thought, "Hey, just pick up a diesel crank, and some 9mm 240 rods, and those 89mm pistons, and abra-cadabra, lots of power!"
The thought process was fairly sound for the most part, for what appeared to be a minimal investment, i.e. a few hundred dollars,
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 wanted to see how people had done the mighty stroker motor. I was checking to see if it would be worth my time
to get the LD28,(stroker), crank and the bigger pistons. The rods and pistons were actually a moot point for me,
since I had to replace mine anyway. So the only real cost difference to me,(as I first saw it), was the cost of the crank.
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 info, 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 240, which greatly increase it's performance for a small outlay in money. I consider this a must stop for those
of you looking to improve your performance.
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", etc... Carl Beck has done an excellent job of pulling from the many
knowledgable 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 anticipated.
I deceided that I would stay with the stroker combo, even though I began to see just how much it was going to involve.
I figured that if I was going to spend that much money to do it right, I might as well have the best out there!
Crank
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 Maxima Diesel. What it offers is a slightly longer stroke,(83mm vs 79mm). There is a fair
amount of math, thermodynamics, and basic engine stuff involved, the end result is more power.
Pistons and Rods
How much more 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 the same 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! While you could
mill those pistons, you are just asking for all kinds of trouble. First, you have an odd rod/crank ratio, which is not very
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. But wait! You say. Why, then
would I want to put the longer 240 rods in there, theoretically, since they are almost 3mm longer than the 280 rods,
the piston would now stick up almost 5mm! That is why you need to find a piston whose pin height, (where the "pin" goes
through the piston and rod, connecting the two), is less than the stock 280's. The pin height of the stock 280 piston is
38.1mm. The two most common used pistons in 3.1 buildups, the 240sx piston, and the 720 truck piston, have pin heights
of ~34.5 mm. Problem solved. The amount they stick above the deck is managable.
I have had many people ask why the 9mm rods, and what does the 9mm stand for? First the 9mm is the bolt size.
The later 240 rods had 9mm bolts, and that is why they are called the 9mm rods. Being the evolution in design, they were
lighter, and stronger. This is why they are the prefered choice for a performance build up. Your motor will survive if
you can only find 8mm rods, but I would reccomend two things, one, replace the rod bolts with stronger ARP bolts, or
order the set from Motorsport Auto that will replace the 8mm bolts with 9mm ones, and two,(nice run-on sentence I have now),
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, and that is why they were chosen, because
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.
Block
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 deceided that it was the better part of valor to go with what is supposedly a stronger
block. The turbo block is the F54 block.
For clarification purposes, the F54 block, which is often refered to as the "Turbo" block, is actually the block that
replaced the N42, and you will find it in both turbo and 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 could see 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 told me that in-between each cylinder, in the
water jackets, they made an extra re-inforcing near the center of each bore. This was designed to strengthen the block
in anticipation of the added stresses of the turbo. Remember, Nissan over-engineered most of the Z parts.
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 taking off. 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 the normal L28 block, and bore it out that much,
you are greatly decreasing its rigidity. What will happen, is as you start to produce power, the block will deform
slightly, and you will lose power. By using the stronger F54 block, you minimize your deformation, and keep some of
your power, as well as extend the life of your engine. I consider this, after balancing, to be the most important
part to do.
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. By doing this, the engine will last
longer and likely will produce more power. In a nutshell, by boring the block with the torque plate on, your are cutting
holes in the block when it is stressed as it will be when you reassemble the motor. When you torque down the head, you
distort the cylinders, and if they were bored without a torque plate, you will actually make them slightly out of round
when you reassemble the engine. 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. 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. Actually,
this is one of the most important choices as well,(there is a list at the bottom). A bad bore job can ruin a rebuild,(and
waste a lot of money). I didn't use one, and my engine is one of the strongest out there, but as is the theme here, it
cost a lot of money to get there. We have all heard the term, "Speed costs money, how fast do you want to go?"
Head
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. Those three heads,
which I talk about on my Head page, are basicly of the same design. Their biggest advantage is the squish combustion
chamber. It is a heart shaped design, which helps put all the fuel/air mixture around the spark plug, promoting better
combustion. The P-79 head, however, has those "Evil Exhaust Liners". People have tried to take them out, and few have
succeded. My engine builder spent countless hours after they had removed them, trying to get decent flow, but never
could get it to work for his high HP race motors. However, as Bryan Little says, it is great for the street enthusiast.
The P-90 heads have the same square exhaust as the early style heads, (E-31, E-88, N-42) and they flow much better.
So I went out searching for some turbo heads, to see if they were worth a try. Once I saw them, I knew they were.
Unfortunatly, 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 about a 9.6:1 Compression ratio. I shaved my head slightly to get 10:1. I am not going to discuss the heads much
on this page because it is covered thoroughly on the head page.
So what is left? You have the block, crank, rods, pistons? Lots. Rings, bearings, new oil/water pumps, timing chain,
clutch/flywheel, induction, exhaust, camshaft selection. 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 nescessary for
your newfound power, brakes, tires, rearends, transmissions, etc...
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 feel
it is worth it. Then of course, as with all headers, you will have to pay for a exhaust system. That ran me about $270,
and was well worth it. 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,(basicly a better glasspack), 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. 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, and it runs 3 in the rest of the way back. There is often debate on 2.5 in vs 3in,
and I am not going to get into it. I have always wanted a 3 in system, because I belive the stroker benefits from it,
(better breathing etc...). In addition, noone in the area could do mandrel bends,(no crimp or indentation in the tubes),
so if I chose the 2.5 in, when you factor in the indentations, I have a system that is smaller than 2.5 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.
Camshafts
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, noone has taken the time
to dyno multiple camshafts and find the best one. I had a shop in Califoria 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 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. There are many cam grinders
out there, from Crane to Schneider, and many inbetween. You look at how you will drive the car 90+% of the time, and I
mean MOST of the time. Sure a 500 lift, 300 duration cam is really cool for 5000+rpm driving, but it sucks around town.
Look at how you will drive and go from there. 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,
so I am happy. I am also running the hydrualic head, which slightly increases the effective duration, because the
lifters lock up a little sooner. But again, we have no way of knowing how much the stroker part contributed, the cam,
the induction,(which is 40mm SK's, similar to webers), exhaust, etc...
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 cabability, 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. 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) Balance, Balance, Balance. Enough said.
2) F54 block. 3mm overbore is HUGE! Keep some of that strength.
3) The best machine shop you can find,(not afford, find, for if you can't afford it, then you are throwing money away).
4) 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!
