All about brake bias and big brakes

Posted by & filed under Automotive, Suspension / Brakes.

I posted this on the DGTrials board, thought you all might want to see it too.

Since there’s some discussion on various big brake upgrade kits, Erik asked me to do some calcs and make a post on what’s important for brake systems.

First, some assumptions:
1) The F/R brake bias set by the manufacturer is ideal, or close to it (this may or may not be true, but it gives us a reasonable target to shoot for)

2) All pads have the same coefficient of friction

Now, some general info:

The #1 thing to remember about bigger brakes is that the main goal is NOT to stop your car quicker! If you can lock up your stock brakes, you won’t see much, if any, improvement in stopping distances with larger brakes. Larger brakes are used for their heat capacity, in turn giving improved fade resistance.

Also, more pistons does not equal better braking! The main benefit of more pistons is the ability to use a larger pad, which will last longer and have more heat capacity. An exception is when you go to 8 pistons or more, which typically use two separate pads — supposedly the pad edge ‘bites’ a little better than the rest of the pad.

Ok…so if you want to figure out what effects various brake setups will have on the brake

bias, the key is brake torque. How do you calculate brake torque? Easy:

Torque = Force x lever arm

Force in this case is the pressure in the brake line multiplied by piston area of the caliper and the coefficient of friction of the pads.

The lever arm is how far out on the rotor you apply the force. For these calculations, we use the center of the pad as the “effective” rotor radius. And then you compare between front and rear, or various different caliper/rotor combinations,etc.

A few things to note:
1) I already said earlier, we’re assuming the coefficient is the same in all cases, so if we stick to just comparing different setups, then it doesn’t matter (it’s just a scale factor)

2) same with factors of pi, or 4 (from, say, using the diameter instead of the radius of the pistons to calculate area) — as long as you’re consistent in your calculations (i.e. as long as you’re wrong consistently!), the results will still be valid. I’m going to leave out factors of pi and use the piston and rotor diameter instead of radius.

3) A sliding caliper has effectively TWICE the number of pistons as it actually has. So a single piston sliding caliper acts, in hydraulic terms, as if it were a 2-piston fixed caliper. The reason is because the piston presses directly on the inboard pad, but the caliper body itself acts as an “inverse” piston and pulls on the outboard pad via the pad frame (the part that arches over the top of the rotor). At any rate, there’s a factor of
2 you have to remember if you want to compare sliding calipers to fixed calipers.

Ok…so lets throw some numbers out here.

Stock 240sx non-ABS front brakes (CL22VB):

– Single piston sliding caliper
– 54.0mm piston diameter
-252mm diameter rotor
-45mm wide pad (‘width’ is the radial dimension of the pad, following the terminology in the FSM)

effective rotor diameter: 252-45 = 207
effective piston area: 54^2 x 2 (<-sliding caliper) = 5832
“brake torque” = 1207224

Stock 240sx rear brakes (CL9H):

– Single piston sliding caliper
– 34mm piston diameter
– 258mm diameter rotor
– 40mm wide pad

Effective rotor diameter: 218
effective piston area: 34^2 x 2 = 2312
“brake torque” = 504016

front brake bias = 1207224 / (1207224 + 504016) = 70.5%
rear brake bias = 1 – front brake bias = 29.5%

So those are our baseline numbers.

To compare, let’s see what happens if you put 300ZX brakes on the front of a 240sx…

300ZX front brakes (OPF25B)

– 4 piston fixed caliper
– 40.45mm piston diameter
-280mm diameter rotor
-50mm wide pad

effective rotor diameter: 230mm
effective piston area: 40.45^2 x 4 = 6545
“brake torque” = 1505350

front brake bias = 1505350 / (1505350 + 504016) = 75%
rear brake bias = 25%

Now if you put the 300ZX rear brakes on too, what happens?

300ZX rear brakes (OPZ11VB)

– 2-piston fixed caliper
– 38.1mm diameter piston
– 297mm diameter rotor
– 36.5mm wide pad

effective rotor diameter: 260.5mm
effective piston area: 38.1^2 x 2 = 2903
“brake torque” = 756231.5

front brake bias = 1505350 / (1505350 + 756231.5) = 66.5%
rear brake bias = 33.5%

Just for completeness, Q45 brakes (2-piston sliding, 43mm pistons, and 280mm diameter rotor) and stock rear brakes give 78.5% front brake bias.

I don’t have piston sizes, etc, for the Altima/180sx brakes, unfortunately.

OK. So that gives us a range that we can work with — 67% to 75% front brake bias. I’d be wary of using any less front brake bias than ~67% because that could cause the rears to lock before the fronts — not good.


Suppose you want something bigger

Let’s do an example. For concreteness, let’s assume that we’re going to use 4-piston fixed calipers at each corner with equally-sized pistons in each caliper (but different front and rear), 323mm (12.72″) front rotors, and 309.7mm (12.19″) rear rotors (those are commonly available sizes from vendors such as Wilwood, Coleman, etc).

What piston sizes do we want in order that the front brake bias be, say, 70%?

Well, of course it’s just the reverse of what we did up above.

front brake torque: FBT, rear brake torque: RBT

FBT / (FBT + RBT) = .7

One equation, two unknowns…how do we solve it? The astute reader will notice that the equation above is insensitive to multiplying both FBT and RBT by the same constant factor (say multiply everything by 1.5) — this amounts to either scaling up the rotor size on each end by that factor, or scaling the piston areas on each end by that factor.

Let’s constrain the piston areas so that the TOTAL piston area is the same as 300ZX front brakes + stock rear brakes (this is probably the limit where you’d get too mushy a pedal if the total piston area gets any bigger)

So we have:
front piston area + rear piston area = 6545 + 2312 = 8857

let’s solve for the rear piston area and we’ll use that to eliminate the rear brake bias term in the previous equation.

rear piston area = 8857 – front piston area

and remember our equation for brake torque is:

brake torque = effective piston area x effective radius

first let’s rearrange the brake bias relation to solve for FBT:
FBT = 2.33 x RBT

plugging in for FBT and RBT (and assuming a 50mm pad width):
(front piston area x 273) = 2.33 x ( (8857 – front piston area) x 259.7)

front piston area = 6103

or, front piston diameter = 39.06mm (1.54″)

now we can find the rear piston area = 8857 – 6103 = 2754

or, rear piston diameter = 26.24mm (1.033″)

Of course, you can’t get calipers with just whatever piston sizes you want, so you’ll have to juggle available piston sizes, rotor sizes, etc, etc to determine what will work. For instance…the combination above won’t work because the piston sizes are too small (nobody I know of makes a caliper with 1″ pistons), for example. Conclusion: In this case, you either allow the overall piston area to increase, thus likely requiring the use of a bigger master cylinder for proper brake feel, or you can leave the rear brakes alone and recalculate for just a front big-brake upgrade that would give the proper brake bias.

Wow, I hope I got all the math right.

Ok, now try it yourself! It’s fun, I swear!


Degreeing cams/setting valve lash in the 240sx

Posted by & filed under 240sx.

Setting Valve Lash
First off, I’m doing his Write-up because I feel that there just isnt information on these subject matter, all in one place. I do not take credit for much of what I am about to write, I am just condensing all the random information into one place.

Valve Lash
The purpose of setting valve lash is to bring your cam lobe to bucket shim clearance into the correct specs per the FSM. Valve lash needs to be checked when either:
A. Valve noise is audible.
B. Installing stock cams or the “91 Hot cam swap”
C. General Maintenance and Rebuilding

In a bucket cam motor such as the KA, valve lash is defined as the space between the bucket shimpad and the cam lobe. In other applications it maybe the space between the valve and the rocker arm, or the rocker arm and the hydrolic lifter.

Setting Valve Lash

Setting valve lash is pretty straight forward. You will need the following tools.

1. Feeler gauges
2. Micrometer or Digital Caliper (Which can be purchased at your local autoparts store or a tool store such as Harbor Freight.)
3. Pen and paper
4. Calculator
5. 1 1/8″ or 28mm socket
6. Torque wrench or breaker bar

Step 1. With paper and pen (obviously) write down Intake, and below it write 1-8 in decending order. Do the same for the exhaust side.

Step 2. Remove spark plugs. This makes turning the engine easier.

Step 3. Slowly rotate the engine in the direction of operation, Use the feeler gauge set to measure the tolerance between each lobe and shim, and write the number in Inches or MM in next to the corresponding number.

Step 4. If the clearance is not between .33 -.41 mm (.013-.016” inch), then a new shim is needed to correct this. If the clearance is to large, use a shim that is thicker than the original shim by the amount needed to correct the clearance.

Removing Shims
Basically you have 2 options when doing this. You can either A. Remove the cams B. Google Valve Adjusting Tool Kit – Nissan J-38972 and prepair to be raped in the butt.

Most people who are doing this will probably opt for A.

To remove cams, I suggest going here as it is aleady complete with instructions and pictures.

When measuring each shim. double check that your caliper or micrometer is set to 0. Be sure to set it to MM before measuring. After measurement, write the correct number beside the corresponding tolerance you measured with the feeler gauges. Do this for all 16 shims.

Here are some examples of the process.

My worksheet.

Once once have all your measurements written down, its time to do some math. First you will have to calculate all of your lash numbers to metric if your feelers dont have the metric reading stamped on them. I used this site.

As per the FSM the equasion to find your new shim measurement is: New Shims= Old shim + (lash – .35mm) Add note 2/27/10: To find the new shim for aftermarket cams with different then stock lash, use the new equasion I have listed at the bottom of this post.

So, for example my new #8 intake shim will be 2.21mm + ( .2794mm – .35mm) =N So, my new shim shoud be 2.134mm.
But since shims only come in even numbers, You want to round either up or down according to the last numbers or numbers. >5 round up <4 round down. In this case, a 2.12mm shim was needed. This equation gives you a tolerance of .0138" so you have a little room to play. As you can see, I had a 2.11 in the exhaust #8, so I will switch that. Once you have all your new shims calculated you can easily look to see if you have a shim that will work for what you need. I was able to achieve this Intake Exhaust 1 E1 New 2 I6 New 3 I4 Good 4 E6 E5 5 Good New 6 E4 Good 7 I3 Good 8 E8 New Out of all 16 shims, only 4 new were needed. Now, install your cams per the FSM's requirments. And enjoy properly clearanced valves. Note, all aftermarket cams call for a different valve lash to be set then stock. If you are installing aftermarket cams, This spec is listed on the cam card that came with your cams. If you didn't receive a cam card, you can either visit your cam manufacturer's web site, or call them directly to receive a cam card. Add note 2/27/10: If trying to find the new shim for an aftermarket cam with different lash then stock you can modify the FSM's equasion. To do this convert the new lash (inches) into new lash in metric. Brian Crower lists .008" intake. This is .2032mm. So to find what shim we need for a .008" clearance our new equasion looks as such. New Shims=Old Shim + (lash(mm) - .0232mm) To change the size lash needed, just change the specified lash to metric. The basic equasion for finding the correct shim is: Old shim + (old lash - target lash) = new shim Note this can be done in metric or standard but the new shim must be converted to metric if measurements are taken in inches. ========================== Degreeing Cams
There seems to be a lot of confusion on this subject, and I am by no means an expert, but I know enough to help you get your cams dialed in properly.

Let me start this by saying that I’m still learning, just like alot of you, my information I believe is correct, so I have decided to share my experiences with you. There are a lot of How-To’s on this subject matter all over the net, but I feel that none of it goes into great depths with visuals, on a cam on bucket motor; specifically the KA24DE.

When degreeing-in a camshaft, you’re insuring that valve opening and closing events are in accordance with specifications, regardless of the cause. Actual valve opening and closing events are influenced not only by accuracy with
which a cam was ground, but also timing chain stretch, keyway position in the crankshaft, crank timing sprocket, and dowel pin hole position in the cam sprocket also play a major role.

The most accurate way to set camshaft position is to properly degree the cams. This way you can be sure the cams are in the right position regardless of engine variations, deck heights, and cam gear marks. Cam degreeing can also be used to check valve opening and closing positions, durations at various lifts, and peak lift measurements.

Note using the centerline method to determine valve events is NOT an accurate way to degree your cams. Your engine does not care where the centerline of your cams are. What will determine your power band is your actual valve opening and closing points.

The intake valve’s opening point and your exhaust valve’s closing point are the most important specs to follow. These two openings determine two things, lobe overlap and lobe sepatation angle.

The link below is to a glossary so you can know what all this jargon means.…

To degree your cams you will need a few items and tools.

1. A degree wheel. (There are many of these that you can print off for free on the internet. I bought mine from SummitRacing. Note, if you are doing it with the engine in the car, or with the water pump on, you will need a 7inch wheel. Most degree wheels will not clear the waterpump. This is where I got mine…)

2. A dial gauge and a sturdy base. A magnetic base will not work on our heads, because well they are aluminum. I got my dial gauge again from SummitRacing.

3. A solid pointer. Coat hanger, welding wire, or something else like this will work fine.

4. A breaker bar or Torque wrench.

5. A 1 1/8″ or 27mm socket to turn the crank bolt.

6. A Thick medium length Flat head screw driver

7. 4-6 inch long, THIN dial gauge extension. Pointed is preferred.

8. Pen and Paper

9. a set of Adjustable cam gears (Found here…

10. 24mm or 15/16 socket

11. 1inch adjustable wrench

First we need to loosen the crank bolt. The way I do this, is to wedge a screwdriver behind the radiator support and a slot in the crank pully. Using a breaker bar, loosen, but do not remove the crank bolt.

[b]Start off by finding true TDC. To do this, turn your crank till you have it at the approximate tdc mark on the pully. This mark is the 2nd one on the left.

Remove the crank pully and install the degree wheel. You will need to use the washer for the crank bolt and the correct bushing to be able to clear the stock timing needle. Place a large brass washer on the front of the wheel so you can turn it later on. Take care when tightening the crank bolt that you dont turn the crank past tdc too much, and not too loose that the degree wheel flops around.
Now turn the wheel to match the TDC on it to the stock needle.

Now install your pointer. You can mount it on pretty much any bolt you want. I find there is a nice spot on the right side of the water pump. Bend it and point it in line with with the stock timing needle. Bend it in the angle of the TDC mark so you can easily read your findings.

The method we are going to use here to find TDC is with a dial gauge. You can also use the piston stop method, but with older engines or engines with looser then normal tolerances, meant for racing, this can impose some mathematical errors.

You can use the piston stop method, but I chose not to.The method will not be discussed here, but is easily found by Googling “degreeing cams”.

Now unscrew the base off of your dial gauge. There are 2 holes in the very front of the head, between the cam gears that is the perfect thread to mount in. Screw in the shaft and tighten it slightly with a pair of pliers or vice grips.

Install your extension into the shaft of your dial gauge. Line up the dial gauge in the center of the spark plug hole, and drop the gauge down, preloading it just a little bit. After this is done, set the face of the dial gauge to 0.

Now slowly turn the crank in the direction of rotation, you will notice the needle on gauge will spike then fall back down. Do NOT turn the engine backwards from this point forward. Complete one full cycle of the engine, back to approximate tdc. Keep turning the engine until the point where you see the #1 piston dwell at the top of its stroke. Set the gauge to 0 again. Complete 1 more full cycle this time stoping at .010″ before TDC.

Go to your degree wheel and document that number. Now slowly turn the engine again till the piston peaks and starts to fall. Once you reach the same .010″ after TDC, stop again. Document this number.

Example: The first number you wrote down was 4 before tdc. and the next was 8 degrees after tdc. Add these 2 numbers together and devide by 2. 4+ 8= 12 /2 = 6. TDC is half way between the 2 numbers. Turn the crank to this number. Set your degree wheel to TDC. This will be true TDC. Set your dial gauge to 0 and make another full revolution, ensuring that 0 is read on the dial gauge when TDC is reached on the degree wheel. Repeat the steps above until true TDC is reached. You will not turn the degree wheel after this point.

Degreeing the cams

This is probably the hardest part. You need to set your dial gauge to the one of the lobes on the intake cam for the #1 cylinder. It is very important to make sure to keep the dial gauge parrallel with the angle of the valve! Geometrical errors will be incurred if this is not maintained. Note is takes a little work to get the angle you need, while keeping the point of the gauge on the shim pad.

At this point you want to make sure your extension is as thin as possible, with a pointed end.

I found it was helpful to slide a feeler gauge between the 2nd cam lobe and shim to extend the veiwable angle of the bucket.

Make sure the engine is at TDC and there is no load on the shim pad. You can verify this with a feeler gauge. Preload the dial gauge to about 1.5″ then carefully set the dial gauge to 0.

Now, slowly turn the crank 1 full revolution past BDC and back to TDC and verify that your dial gauge goes back to 0. If it doesn’t keep messing with it till you achieve a good contact and motion. Also be sure the tip of the extension stays on the shim!

Once you are sure that the dial goes back to 0 everytime, its time to check our timing events.

Slowly turn the engine the engine forward so the intake valves start to open.When the needle on the gauge gets close to .050″ slow down, and stop on .050″. Go to your degree wheel and document this number. The first number your write should be labeled After TDC or ATDC

Now slowly turn the engine forward again, past the cam’s peak lift, toward intake valve closing point. We are looking for .050″ right before the valve closes completely. Once you have this, and it may take you a few times to get the timing right, document this number. This number should be labeled ABDC

Just write down the number you see, dont try to over complicate things by trying to add stuff to the numbers.

Now just do the same with your exhaust cam.

Once you have your numbers, you should have something like this written down
Note your numbers will probably vary from mine, which is ok. Lots of factors come into play here as discussed at the beginning of this How-To.

Intake Open ATDC: 18.5
Intake Close ABDC: 49
Exhaust Open BBDC: 44
Exhaust Close BTDC: 14

Now plug your numbers into this cam calculator

You will need to place a – in front of the opening values of the intake if the reading is ATDC and also before the exhaust closing readings if its BTDC.

It will tell you everything you need to know about the profile of your cams. From here you can start playing with your cam gears.

Example: My cams have an Overlap of -32.50 degrees and has in Intake Duration of 210.50 degrees @ .050″ lift.
The Exhaust Duration is 210.00 degrees @ .050″ lift.
The Inlet Cam has an Installed Centerline of 123.75 degrees ATDC.
The exhaust cam has an Installed Centerline of 119.00 degrees BTDC

Again, as stated above, your engine does not care where your cams centerline is. It is not accurate to use the centerline to determine cam timing. The real way to degree your cams is to set your intake valve opening and your exhaust valve closing points. BC calls for the intake to open @ -12 atdc and the exhaust to close at -9btdc.

As you can see, with my lash set to stock, I am a little off off. Adjusting lash on BC v2’s nets around 1 degree per .001 of lash. It can be different for all cams, because this number depends on the cam profile.

My first lobe is @ .014 and BC calls for .008. Thats .006″ of lash to be tightened, which translates into roughly 6 degrees.

If you look in the posts below, the CORRECT BC cam card is now listed below and the How To was updated accordingly. You can see the post that solved this problem here —>…

So we can say -18.5-6= -12.5 degrees which is perfectly within the margin of error and my cams will be pretty much spot on to spec. From there I can degree them to where I’d like the powerband to be.

Now when I tighten my exaust lash from .014 to .010 that should give me around 4 degrees of duration back on my cam. This should also move my timing from -14btdc to -10 btdc.. which is only 1 degree off from the cam card and is perfectly acceptable, which is GREAT news for all the guys wanting BC cams.

(Updated 6/12/2010)

Determining overlap
To find your cams overlap you simply add the intake opening + exhaust closing point.

Using the BC cam card we can say the intake opens @ -12 atdc and the exhaust closes @ -9bdtc. So -12+-9= -21 degrees of overlap.

Determining Lobe Sepatation Angle
This is basically the distance in degrees, as measured on the cam, between the point of peak lift on the intake lobe and the peak lift on the exhaust lobe.

The LSA is calculated by adding the intake centerline and the exhaust centerline, then dividing by two. For example, a cam with a 106-degree intake centerline and a 114-degree exhaust centerline has a lobe separation angle of 110 degrees (106 + 114 = 220; 220 2 = 110)

The BC V2’s have an LSA of 119.5 which is fairly wide compaired to high overlap N/A cams, which means that power is going to hang on a lot longer but give up a little torque.

If you still have some confusion, check out this video and it will help some also:

If anybody needs any help getting their setup dialed in please PM me with the type of cams you are running, your current valve lash, how much boost you are running, and the size turbo you are running. Also let me know where you want your power band to fall.

Enjoy! I hope this helps clear up some of the confusion dealing with degreeing cams on the KA-DE.

If I missed anything or if you would like me to add something, let me know so I can update this asap!

Thank you to everyone in the community that has had a hand in providing information for everyone’s learning experience.

240sx LSD Swap

Posted by & filed under 240sx, Automotive.

The lowdown on 240 rear end swaps:

with legal LSD


First things first, what is an LSD? 
It stands for Limited Slip Differential, 
why is this important? Because it allows your car to get an incredible
holeshot due to increased traction.   The
differential is the thing in the rear of the car that splits the power coming
from the driveshaft up between the 2 rear tires.  

Now the factory 240 (with a few exceptions) use what’s called an ‘open
rear end’.  In this setup both tires
are basically free to spin at whatever speed they want to, this has one good
side and a bad side.  The good side
is that when going around a turn the tires don’t ‘scrub’ or ‘hop’ around since
they will be traveling at different speeds (outside tire has farther to go so it
spins faster).  If you had a solid
axle (or welded the 2 halves of the differential together) you would have killer
grip in a straight line but handling would be extremely bad.  
The bad side of the open rear end is that since both tires are free to
spin at whatever speed they want, whichever tire has less grip (the one
spinning) will get more power transferred to it which will cause it to spin
more, which will cause it to loose more grip and spin more which………….
anyhow it’s not a good cycle. 

The LSD comes into play right here, LIMITED SLIP comes to the rescue by
stopping the loss in grip by recognizing that one tire is spinning and then
transferring the power to the other wheel that has grip.  
The type of rear end I’m using is called a Viscous LSD which means it
uses silicone and 2 plates to operate.  
The simplified explanation of how this works is that there is a plate
stuck on the end of each shaft.  These
plates spin at the same speed as the wheel they are attached to.  
When one wheel looses grip and starts to spin faster it creates friction
between the two plates due to the difference in speed. 
This friction heats up the silicone floating around causing it to expand. 
When the silicone expands it pushes on the other plate ‘locking’ it to
the one that’s spinning.   This
locking is what causes the other wheel to push.   

The fact that both wheels are now pushing is VERY apparent while driving. 
My friend’s turbo 240 dropped a full second off his quarter mile time
after I installed an LSD from an Infiniti J30 into it. 
My car can be launched at 5,500 RPM’s by sidestepping the clutch and
flooring it with almost no wheelspin.  
But this isn’t just useful to dragracers, the difference while
autocrossing is even more pronounced.  The
car can start accelerating earlier and harder out of corners than you could ever
hope to do with an open differential.  
Lastly the car is much smoother to drift (but it dose take a lot more
power to get the rear end to start coming around).

Now that you know what an LSD is I’m sure you want to know where to get
one.  The easiest way is to find a
240sx with one on it already and take it.  
There is a lot of talk about what year and options a 240 has to have to
be equipped with an LSD.  From what
I’ve heard SE’s with ABS, HICAS, or S14 5 lug SE’s w/ ABS all should have the
LSD.  Canadian 240’s also have VLSD
(all of them).  The easiest way to
check is that  the LSD will have an
orange sticker above the fill hole that identifies it as an LSD. 
Also if you turn one side the other should turn the same direction.  
You’ll also notice that the LSD is harder to spin by hand than the open
differential.    If your
like me you can’t find a 240 in a scrap yard anyplace with an LSD in it, so you
have to improvise………. here comes the fun part.  
The R200V (VLSD) differential is used in the Infiniti J30, and Z32 300zx.  
The Infiniti one has an ABS sensor at the front which adds about an inch
to the length of it.  The flanges
for the halfshafts (the shafts that go to the wheels) are the same pattern for
the 95 and up J30’s (pre ’95 used a different pattern at least on the ones I saw
in the yard)  Also if you own an S13
(89-94) you will need to get a new differential cover gasket and swap the rear
cover off your R200 (stock diff) onto the new one.   The S13’s used a different bolt pattern (4 bolts) than
the S14 (2 bolts).    The
90+ 300zx one also fits but takes more work. 
First thing DO NOT get the twin turbo diff, it’s got different gear
ratio’s in it and it will really slow your car down (3.86) 
The NON turbo has the same ratio as the 240 (4.06).  
The 300sx also uses the 2 bolt rear cover so if you own an S13 you’ll
need to switch it.   The biggest problem with the 300zx  is that the output flanges are different. 
The look like a ‘5 star’ flange where the 240sx uses 3 sets of 2. 
The parts to convert a 300 to a 240 can be had for around 200-300 new.  
I got mine at a scrap yard for 150. 

The M30 and Q45 diff’s also work with the same basic modifications I
mentioned earlier.   The big
thing to look for is the flanges, they need to be the 3 sets of 2 or you will
have to replace them.

I have heard rumors that the J30 differential requires you to shorten the
driveshaft by an inch due to the position of the ABS sensor but my buddy hasn’t
had any problems with his when he installed it in an S14.   It’s only been on for 2 weeks and the fit is tight but
it works.

The install is pretty straightforward, just unbolt the stock diff and
then stick the new one in.  The hard
part is getting the new diff up and in place so you can bolt it on (these things
are HEAVY).  I needed another guy to
help me and 2 jacks to get the thing where I wanted it.   
Care must be taken when tightening it down that it’s level when you start
tightening so that you don’t’ crack the cover.   I hung it in the back by sticking the studs on the
cover through their holes and then lining up the bolts in the front and
tightening them down then I put the nuts on the rear. 
After that put on the 6 bolts on each side that holds the flanges to the
driveshaft.  Finally bolt the
driveshaft to the differential.  

While you have it out I highly recommend changing the fluid in diff while
you have it out since it’s a major pain to do it while it’s still in the car. 
You MUST use either a fluid designed for LSD (royal purple or Redline) or
add the LSD additive (this additive contains the silicone I mentioned earlier
that heats up to make the differential lock up).  
Another thing you might want to do at this point is take the bottom drain
plug off the stock diff and put it on the new one at the filler point. 
The bottom plug has a magnet on it that picks up metal shavings floating
around in the case, it’s not really necessary but since your throwing the other
diff out anyhow you might as well keep the magnet for the new one to help keep
stuff from floating around the case.

and modifications required:

240sx W/ LSD
No mods needed if it is NON ABS
300ZX  90+ Non Turbo Needs new output flanges
90+ Turbo
Needs new output flanges and gears are
J30 95+
No mods needed*
J30 pre 95
Needs new output flanges
No mods according to Infiniti of
Melbourne FL*
Infiniti Q45 No mods according to Infiniti of
Melbourne FL*

*might need to have driveshaft shortened one inch due to ABS sensor but
this isn’t’ confirmed and my
friend has no problem with this setup

Written by Paul 

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AEM F/IC Documentation Link

Posted by & filed under AEM F/IC, EFI Tuning.

I’ve been researching the AEM F/IC for a 1JZ single turbo tune I have coming up.

AEM FIC Tuning Tips

Posted by & filed under AEM F/IC, EFI Tuning.

AEM FIC Tuning Tips

There has been a lot of questions about tuning the FIC. I’ve went through a lot with the FIC and this is what I came up with.

Special thanks to JeffTsai, TeckIS300, and the community for this post

So you have a vvti 2jzge? decided to go FIC with it? Double checked your wiring? You are half way there. Make sure you update the latest firmware and use the latest software to give you less headaches.

The FIC tuning tip document supplied by every FIC unit is a must read. It will give you a good insight on how piggyback tuning works.

Use the stock Bank 1 Senor 1 o2 sensor, and hook up the FIC skew to it (don’t forget the resistor). Then wire the B2S1 sensor signal to the B1S1 sensor. You would also want to run a dual-output o2 simulator for the Sensor 2s. Except for B1S1, use a resistor on all the heater circuits (if the circuit is present). Do not splice heater circuits to each other because this will cause a drop in resistance, and trigger CEL.

Calibrating your MAF in its new environment

Before anything, you compensate in the MAF voltage map (not the MAF fuel map). Stock intake pipe diamater is 2.75″, and more than likely you are running a 3″ MAF charge pipe. To compensate for this difference, add 9% to the entire MAF voltage map. I had the worst problems with idling because i neglected this step.

Select All -> Right Click -> Set Value -> Enter “9” -> Press OK

You are done with the first step.

Update: the MAF pipe from stock is about 2.75″, not 2.5″, so 9% would be the sweet spot to get your fuel trim smack on [(3-2.75)/2.75]

MAF Clamp

Next step is MAF voltage clamp. Your MAF tells your ECU how much air is flowing, thus the ECU adds fuel accordingly to your MAF reading. Don’t think your MAF just sits there and does nothing; that is how your ECU tunes its AFR. Our ECU tunes the way how we want our AFR to be already; NA IS/GS300s do hit 11.5:1 on WOT.

There are several points where you can clamp your MAF voltage, but I recommend letting your MAF operate as much as possible. You want the stock system to be in control for as much bandwidth as it can handle. Good place to clamp is 4.7V. No need to hide boost from the stock ECU. As far as it’s concerned, it’s just more air and it will pair fuel with whatever it reads accordingly.

MAP load fuel map

MAP Fuel map lets you:

1. change injector size.
2. create a base fuel map (for those that are clamping MAF from seeing boost)
3. fine-tuning.

My AFR is on target by letting my MAF doing most of the work. I also don’t have to worry about fuel trim related issues because that is all worked out between the MAF and the stock o2 sensor.

O2 Skew

To keep the fuel trim +/- 3%, here’s a very simple rule that has worked out for me so far.

Lets say i need to add 3% on the fuel map because of a lean spot, at the same cell, I would put -3% on the O2 skew map. When you are 3% more on the fuel trim, you want the o2 sensor to see 3% leaner.

Can’t really tune this unless you are on a dyno with kick-ass knock sensors hooked up. But if you know you are knocking (and your CR is kinda high), then pull some ignition timing.