August 4, 1997
This FAQ is based on my experience in building a six cylinder 3.1
liter Z car engine. I am by no means an "expert" on this subject,
so this FAQ is not the final authority. Any comments, new
information or additional questions are always welcome.
You may e-mail them to: Steve Golik (goliks@knox.pcec.philips.com)
*How can you build a 3.0 liter (or larger) Z engine?
All the 3 liter (and larger) engines are based around using a
crankshaft with a longer stroke in an L28 (280Z) block. The stroke
of a stock L28 crank is 79mm. Nissan did made an L series six
cylinder crankshaft with a stroke of 83mm. In the USA this crank
was only used in the 1981 (7/80 production date) through 1984
(9/83) diesel Maxima with the LD28 block, hence it is commonly
referred to as "a diesel crank". The Nissan part number for the
diesel crank is 12201-V0790.
*What bearings do you use with the diesel crank, 280Z or diesel
*Maxima bearings?
The dimensions of the connecting rod journals and the main bearing
journals of the diesel crank are the same as the L28 crank (and
L24) crank so you can use Z car bearings. This also means that any
of the L engine series connecting rods will fit on the diesel
crank.
I used standard size Z engine main and rod bearings (either 240,
260, 280, or 280ZX, they are all the same). The diesel bearings
appear to be the same as a Z engine, but the rod bearings have a
different part number.
*Do I have to "prep" the diesel crank any?
The diesel crank has a locating dowel on the rear where it mounts
to the flywheel. You must remove this with a hack saw or grinder.
A Z car flywheel will then bolt up. The Z car harmonic balancer
will bolt up with no problem. There is a hole for a pilot bushing
as well, so don't forget to check for it's presence if you are
going to use a manual transmission.
Check the journals for scoring. Very light scratches can be removed
by polishing. See your machinist for details. Inspect the thrust
bearing surface at the center of the crank for wear. The crank can
be checked for straightness with Vee blocks and a dial indicator,
again, your machinist can perform this. However, from what I
understand, Nissan cranks are extremely rugged. You should make
sure that none of the threaded holes are stripped, although this
can be repaired if your machinist has the right equipment.
I had my crank polished, inspected and measured for about $35. My
machinist recommended this before balancing the bottom end, which
I do recommend doing (although it cost me around $100).
*When using the diesel crank, do you have to notch the block so the
*connecting rods clear correctly?
It depends. I had no clearance problems when I built my 3.1 liter,
but other people have. The diameter of the bore is a factor, a 89mm
diameter bore will give you more clearance than a 87mm bore. The
9mm connecting rods have less clearance than the 8mm rods. And
there are probably slight differences in the L28 block due to
tolerances and changes to the casting molds during the production
run of the L28.
So, you must expect to check this during engine assembly and take
appropriate measures if necessary (get the die grinder out).
*How much should I expect to pay for a good _used_ diesel crank?
According to a recent survey of people who had purchased one, they
go for between $300 to $400. One individual said he paid only $150
for one. In my case, I spent $300 for an entire diesel engine. The
junkyards I talked to would not disassemble an engine just to sell
a crank.
*What size (displacement) engine can one get?
That depends on what you decide to bore the block out
to:
| bore(mm) | stroke(mm) | displacement(liters) | notes |
|---|---|---|---|
| 86 | 79 | 2.753 | stock 280Z |
| 86 | 83 | 2.893 | 5.1% increase |
| 87 | 83 | 2.960 | 7.5% increase |
| 88 | 83 | 3.029 | 10.0% increase |
| 89 | 83 | 3.098 | 12.5% increase |
| 90 | 83 | 3.168 | 15.1% increase |
As you can see from the chart, you can't just drop a diesel crank
in a stock bore L28 and honestly call it "a 3 liter". You must at
least bore it 1mm over.
*It can't just be a "bolt in" job now can it?
Well, most of it is. The problem is that now since you have
increased the stroke by 4mm, a 280Z piston when installed on a 280Z
rod would extend over the top of the block by 2mm! Now I have heard
of people milling the tops of the L28 pistons by 2mm to correct
this, but Ron Johnson of Nissan Motorsports said that if you mill
the stock cast pistons this much the top compression ring could get
too hot and eventually fail.
To resolve this dilemma you must use a rod and piston combination
that will allow the piston to protrude the correct amount or just
slightly more so that the pistons can be safely milled. There are
also head gaskets with different thickness available to assist in
this. You also must maintain some amount of piston to head
clearance at TDC.
Another item which must be addressed is the compression ratio. Even
if you obtained the same "deck height" as a stock 280 set up, the
compression would increase because you have increased the sweep
volume of the engine.
*So how do I know if my combination of rod and piston needs to be
*machined, and by how much?
I went through this in detail when I built my 3.1 liter, using a
spreadsheet program. The figure of concern is what I call the
"installed piston height". It is the maximum distance between the
centerline of the crankshaft to the top of the piston with
everything assembled.
Or:
installed piston height =
[piston pin height + rod length + stroke/2]
Piston pin height is the distance between the centerline of the
piston pin to the top edge of the piston. Rod length is measured
between the centers of the two circles formed by the big and small
ends.
The installed piston height along with the height of the block will
determine the "deck height" which tells you how far the piston will
be relative to the block at top dead center (TDC), or:
Deck height = Installed piston height - block height
This number can be positive or negative. A positive deck height is
where the piston extends above the top of the block. Because of the
thickness of the head gasket, this can occur without the piston
making contact with the head.
Since most people use the L28 block with the diesel crank the
height of this block becomes important. This height is 207.9mm.
For example, in a stock L28 (280Z) the installed piston height is:
38.1mm + 133.3mm + 79.0mm/2 = 207.9mm
And the deck height is:
207.9mm - 207.9mm = 0
You should keep in mind that if you are going to use the diesel
crank then you have changed one of the parameters in the "installed
piston height" equation and must be aware what are the
consequences. What you end up doing is using a rod and a piston
with the correct pin height or one close enough so that you can
mill the top of the piston to maintain clearance to the head.
*What are the important dimensions of suitable pistons?
Here is a chart of most of the Nissan L series pistons (all of
these are cast, not forged):
| Engine | pin height(mm) | piston diameter(mm) | application notes: |
|---|---|---|---|
| L28 | 38.1 | 86 | 280Z |
| LZ22S | 35.0 | 87 | 720 truck 6/79 to 10/82 |
| LZ22E | 32.5 | 87 | 200SX 7/81 to 10/83 |
| LZ24 | 34.0 | 89 | 720 truck 11/82 to 10/85 |
| KA24E | 34.0 | 89 | 240SX |
*What about connecting rods?
The lengths of the L28 and L24 connecting rods are 130.3mm and
133.0mm respectively. There was a 140mm length rod that was used in
the 2.0 liter six cylinders (the Fairlady Z engine), but this
engine was not imported to USA, and it also only had the 8mm
diameter rod bolts. All the other L series rods are too long to be
of any use.
*Why should I use 240Z rods?
240Z rods are recommended because they are longer than the 280Z
rods and the theory is that a larger [rod length]/[stroke] ratio
should produce more horsepower. Since you have increased the stoke
of an L28 you should increase the rod length to maintain a more
optimum ratio.
Of course you use the later 240 rods which have the larger 9mm rod
bolts and weigh less than the 8mm rod bolt connecting rods. Early
L24 engines (up to serial number L24-096181) have the 8mm rod
bolts. Therefore, the changeover to 9mm bolts happened sometime
near the end of 1972 model year, so only a 1973 240 engine would
definitely have the 9mm rods.
*Why can't I use the diesel rods?
For several reasons you cannot (and should not) use the diesel
rods. The piston pin diameter is larger than the L series pistons,
it is longer in length than a rod that an L series uses (I don't
recall by how much) and being designed to be used in a diesel
engine, it is considerably more massive than a rod for a gasoline
engine.
*Ok, so what pistons/rods can I use to build a 3.0 liter?
There are a few options: One is to use 240Z rods and LZ22S pistons
(87mm diameter) which were used in the Nissan 720 truck from 6/79
to 10/82. The part number is 12010-06W11. These have a dish of
9.3cc. The installed piston height is:
35mm + 133.0mm + 83mm/2 = 209.5mm
And the deck height is:
209.5mm - 207.9mm = 1.6mm
In other words, the pistons will protrude about .063" (1.6mm) above
the top of the block when everything is assembled and installed.
As a result, you must use the 2mm thick HKS head gasket. This
results in a compression ratio of 9.6 to one with an N42 head
(44.6cc combustion chamber volume) and 9.9 to one with an E31 head
(42.4cc).
Another option (especially if you want more compression) is to use
the 280Z rods, 280ZX (flat top) pistons (in a +1mm, or 87mm
diameter), and the 2mm thick HKS head gasket. If the pistons are
milled 1mm the compression ratio with an N42 head becomes 10.6:1.
Yet a third option is to use the LZ22S pistons with 280Z rods and
the stock 280Z head gasket. The installed piston height is:
35mm + 130.3mm + 83mm/2 = 206.8mm
And the deck height is:
206.8mm - 207.9mm = -1.1mm
In other words the pistons will have a negative .043" (1.1mm) deck
height so the compression ratio will only be about 8.6 to one (with
an N42 head). The top of the block can be milled to increase the
compression ratio, but several concerns must be addressed: the
timing chain slack will increase, the heads bolts might bottom out,
the oil passage restrictor plugs would have to be pressed further
down into the block, and the keyholes used to position the head in
the block would have to be re-machined, etc, etc. Needless to say,
this is not a popular approach, but it has been done.
*What about a 3.1 liter?
To build a 3.1 liter you must use 89mm diameter pistons and the
"Big Bore" head gasket. Use either KA24E pistons or LZ24 pistons.
The 280 block must be overbored by 3mm (about .120"). Again, use
240Z rods. All of these pistons have a 34.0mm pin height.
The installed piston height is:
34.0mm + 133.0mm + 83mm/2 = 208.5mm
And the deck height is:
208.5mm - 207.9mm = 0.6mm
So, both of these pistons will protrude, but only about .025"
(0.6mm) above the block.
*Isn't a 3mm overbore risky?
Nissan Motorsports recommends that you have the bores "sonic
tested" or measured for thickness, but only before you take MORE
than a 3mm "bite" out of them. It's still probably something you
might consider doing. Sonic testing will check to see if any
shifting of the sand molds occurred during manufacture. You may
have to contact several machine shops to get this done, as it is
not a standard automotive machine shop operation.
I have heard of overbores of 4mm (.160")! without hitting water
passages. The real problem is how much flexing you can tolerate.
All engine blocks flex during operation. Removing metal from the
bores reduces overall block rigidity, allowing the rings to stop
sealing. This is mainly a high rpm phenomenon.
I really don't know what is the minimum thickness you need around
the bores for a Z engine. Rick Voegelin in "Engine Blueprinting"
recommends a minimum of .180" wall thickness for a small block
Chevy. He says what you want is consistency from bore to bore.
Measure the wall thickness in four places (ninety degrees from each
other) near the top and bottom of each bore.
*Tell me more about the LZ24 pistons?
These are the pistons I used in my 3.1 liter. As I said above, when
installed in an L28 block with 240Z rods these pistons extend about
.025 inches above the top of the block. I did not mill the pistons
to reduce this. This piston has a fairly large "dish" of 15cc.
The calculated compression ratio with an unmilled N42 head is 9.3
to one. Using an E31 head would increase this to 9.6 to one. I used
a milled N42 head to obtain a 9.4 to one ratio.
The Nissan part number for the LZ24 piston is 12010-30W01. They
were used in the 720 truck built from 11/82 to 10/85. They list for
$38.50 each. The part number for the ring set is 12033-30W10. They
sell for $91.39 for a set to cover four pistons. You must order two
sets of rings for a six cylinder engine!
A problem with using these pistons is that there is insufficient
clearance between the top "eye" of the rod and the piston pin boss.
However this is easily solved by removing a very small amount of
material from both sides of the small end of the connecting rod. Of
course re-balancing is necessary.
*Tell me more about the KA24E pistons?
This piston was used in the 240SX. This piston has a floating pin
and clips to retain the pin. There are two versions of this piston,
a "dished" and a "flat top", but both have the same piston pin
height.
Part number 12010-30R10 has a 2.8cc volume dish and part number
12101-40F10 has no "dish" and hence one could obtain a higher
compression than with the dished KA24E piston. These are the
pistons that Nissan Motorsports sell in their "3.1 liter kit".
However, with a N42 head and a 1mm thick head gasket, the
calculated compression ratio would be 12.0 to one! Using the 2mm
thick HKS head gasket would lower this to 10.6 to one. Milling the
tops of the pistons by .025" would reduce this further to 10.0 to
one.
There is another part number, which was used on the truck
(Hardbody) version of the KA24 engine, part number 12010-86G20.
This piston is also a "flat top" and appears to be very similar to
the 12101-40F10 piston (it also has the same pin height). I have
been told that it uses a pressed piston pin rather than a floating
one.
*Can I build a motor even larger than 3.1 liters?
You can get both the L24Z and KA24E pistons in a 1mm oversize
(90mm). This would give you 3.168 liters of displacement (usually
rounded up to 3.2 liters). But according to two sources, a 4mm
overbore is very risky. A 3mm overbore is the practical limit.
*Why should I use a lightened flywheel?
Most everyone who has built a stroker engine recommends using a
lightweight flywheel (10 lb. or less) to prevent failure of the
harmonic balancer or the crankshaft key due to cracks.
I used the HKS flywheel, sold by Motorsport Auto (phone 800-
633-6331) and others.
*What if I use the stock L28 crankshaft and bore the L28 block out
*3mm?
This will result in a displacement of 2949cc. Using 240Z rods and
the KA24E pistons would result in a calculated compression ratio of
9.6 to one with an N42 head and the 1mm head gasket. The deck
height is a negative .055". Again, the block could be milled to
increase the compression ratio.
*What about stroking an L24 block?
I have not actually done this, nor do I know anyone who has but,
according to a "paper design" you could use the diesel crank with
a bored L24 block, 280Z rods, stock 280Z head gasket, unmilled E31
head and unmilled LZ20S (PN 12010-W4001) pistons. This would result
in a compression ratio of about 9.9 to one. The L24 block would
have to be bored out 2mm to 85mm, giving you an overall
displacement of 2826cc's.
*Tell me more about this "Big Bore" head gasket?
This gasket is made by HKS (phone 310-328-8100) and is available in
either a 1mm or a 2mm [compressed] thickness. It is sold by Nissan
Motorsports and Motorsport Auto for around $100 for the 1mm version
and $125 for the 2mm one. The Nissan part numbers are 11044-91MM1
(1mm) and 11044-91MM2 (2mm). You can order it through any Nissan
dealer. The Motorsport Auto part numbers are 10-2456 (1mm) and 10-
2458 (2mm).
This gasket is a all metal, multi-layer design with the pieces
being riveted together in a "sandwich" configuration. The rivets
are outside the engine, so they do not interfere with the head-to-
block seal. However, one of the rivets does interfere with the rear
heater hose brackets on the right side of the block.
You MUST use this gasket if you bore is increased to 89mm or more.
The bore size of the stock head gasket measures about 89mm and
should only be used in engines with a bore of 88mm or less. The
bore diameter of HKS gasket is 91mm.
BTW, the compressed thickness of the stock L28 head gasket is
1.2mm.
*Does the engine run hotter (water temp) in the 3 liter?
I have had no problems with the engine water temperature being any
hotter than before. I use a four core radiator with only the stock
fan and clutch unit.
*What about the stock induction system and stock exhaust. Can they
*handle the increased air flow of the larger engine?
Well, I am using the triple Weber carb setup with the Motorsport
Auto "6-into-1" header and a 2 1/2" exhaust system, so I'm can't
answer your question, but even if you retain your stock induction
and exhaust with your 3.0/3.1 liter, you will still benefit from
the increased lower rpm torque as a result of the larger
displacement and longer stroke.
*What about the performance of a 3 liter engine?
In my 260Z a 3.1 liter with 9.4 to 1 compression replaced a 1mm
overbored L28 block I had in the car which had just over a 10 to 1
compression ratio. In my opinion the horsepower is the about same.
There does seem to be more bottom end torque, which is what you
would expect. I did not dyno either engine, however. Bowling's
horsepower computer program, shows that both engines should
produce
almost exactly the same peak horsepower.
*How much did it cost you?
It does take a LOT of money to build a 3 liter. I did not pay
anything for the L28 block. It came out of a friend's car and he
just gave it to me after we installed another engine in his 280Z.
I paid $300 for a used crank, $100 for the head gasket, and $220
for the flywheel. I got a deal on the pistons, only $15 a piece.
Then there was $35 for piston rings (another good deal) and $60 for
a set of good used 240Z rods.
I spent around $350 for the machine shop work. Of course, if you
are going to bore an L28 block just 1mm over, the machine shop
costs are the same. The only "extra" shop charges was the work done
to the rods and the re-balancing. There was $50 for new bearings
and $25 for the gaskets I needed. Let's see, that comes to a grand
total of $1,230!!
Of course if one were to rebuild an L28 using oversized pistons the
cost differential would be only be around $650 or so.
*Who sells a 3 liter "kit"?
Arizona Z's (phone 602-844-9677) latest catalog features a 3.1
liter kit. The crank is a custom made from 4340 chrome moly. It has
a 83mm stroke, the same as the diesel crank and sells for $2395.
The pistons likewise are custom made. They are forged, 89mm in
diameter, with a flat top (no dish) and have a zero deck height
when installed with 240Z length rods. The piston pin is a full
floating design that is 1mm smaller in diameter than a L series
piston. The pistons run $95 a piece (includes rings). They also
have chrome moly rods that are lighter than the stock 240 rods.
These cost $169 each. Total kit cost is $3979.
I would think that you can utilize a used diesel crank and used
240Z rods and save some money. They will sell you the pistons
separately. The rods would have to have a bushing pressed in by a
machine shop and then machined, but this is a fairly standard
procedure.
They are also working on a 3.2 liter kit which will feature another
set of custom pistons and rods and a crank with an 85mm stroke. The
rods will be slightly longer in length to maintain the rod
length/stoke ratio, and this of course, means a different custom
piston with a relocated pin. No price info yet.
As I said above, Nissan Motorsports (phone 310-538-2610) sells the
diesel crank, 240Z rods, flattop KA24E piston and rings for their
"3.1 liter" kit. Part number is 99996-28BBK. The cost is $1800. You
can also order the exact same kit from Motorsports Auto for the
same price.
There was a 3.1 liter and a 3.2 liter kit offered by Jim Cook
Racing that are no longer available. They used custom made pistons
in either 89mm (3.1 liter) or 90mm (3.2 liter) diameters.
*What is the cheapest route?
I would get the following from a junk yard: the diesel crank, a
280Z (or ZX) block, late 240Z rods and a 240 flywheel. Use
aftermarket versions of the pistons (and rings) suggested above. If
you build a 3.0 liter and you can use the stock 280Z head gasket,
Felpro makes an excellent replacement, and it's cheaper than the
factory one.
The 240Z flywheel must be lightened by a machine shop. I doubt they
can safely reduce the weight down to 10 lbs, but every bit they
take off will help. The machine shop work for either a 3.0 liter or
a 3.1 liter should be about the same, IMO. Both versions must be
bored and honed, and although you must remove more metal on a 3.1
liter, most shops charge a flat rate for boring jobs.
****************************************