I had to decide what to do... go 6 bolt 1st gen short block, rebuild my short block, or go with replacement 7 bolt short block?
I toyed with this for a few weeks talking to many different people and shops. Needless to say, I got different answers from each person.
I realized that I needed to do some self evaluations (The same thing I tell many people who e-mail me regarding parts for their cars) It
was time for me to follow some of my own advice.
I first needed to decide on a 7 bolt or 6 bolt motor. In the DSM tech. world, when we talk about 6 bolt verses 7 bolt, we are referring
to the number of bolt holes for the flywheel in the crank. 6 bolt motors are found in 90-early 92 turbo cars, and 7 bolt motors are
found in the late 92-99 turbo cars.
So what are some Pros and Cons to the 6 and 7 bolt motors in a 98 GSX ?
7 bolt:
So now I have a few of the Pro's and Con's of both set ups. Trust me there are a lot more, but I don't have the time to get
into all of them.
But wait... What about Race Short block verses Stock Short Block!?
I thought this Pro's and Con's list was supposed to make things easier!
Ok, race verses stock... how much HP do I want to make?
Time for some self evaluation... At the HP levels I want, and want to run reliable, I will need to go with a built motor. At this
point I will have to start addressing the $$$. I keep telling myself, if I am going to do it, I need to do it right the first time.
I have to decide, am I going to go 6 bolt or 7 bolt race short block? My answer will probably shock you so I will explain...
I am going with a 7 bolt race short block... Yes, that is correct, and it isn't a typo! 7 bolt race block!
The number one concern people are thinking... What about crankwalk? It is a 7 bolt motor, you are wasting your money!
Here is my "PERSONAL" feelings on the matter of crankwalk. 1st generation motors get it too! Both 6 bolt and 7 bolt short blocks
can get crankwalk. I am sure there are more then a few 6 bolt motors with crank play that is out of spec, but the owners don't
know it because the cars don't have crank angle sensors to kill the motor. After looking at my short block in the car, I had
7 thousandths play in the crank. At 9 thousandths the thrust bearing needs to be replaced. I also noticed that the crank was also
very close to hitting the collars. I was not able to measure the amount of play before contact with the collars but it was very,
very small. I believe that not only in mid 98 and 99 did Mitsu put in different thrust bearings, they also limited the space
between the crank and the collars. That way they could catch crankwalk before it did severe damage. So would my car have gotten
crankwalk? I don't know and will never know. But I would be very curious to hear from some 1st gen 6 bolt owners, how much crank
play they have measured with their oil pans off!
If my theories are correct (not saying they are) then the best choice for me is to go with a built 7 bolt race short block. If
I get one that is built to withstand 600+ HP, I should be able to run 450 HP all day long with no worries. Plus by going with a
built race short block, I will be replacing all of the weak stock parts with stronger ones. Including the rods and rod bearings!
So now the bigger question... Who is going to build my 7 bolt race short block for me???
Brief History:
On August 4th 2001 on my way home from the track I developed Rod Knock. - See
Rod Knock Videos and Raw Pictures -
6 bolt:
Pro: 6 bolt motors have a larger journal on the crank to accept a larger rod. This makes them more forgiving if minor detonation occurs.
Major detonation will hammer any rod bearing. Hmmmm... Larger rod... Spun bearing! The 6 bolt are felt to be a stronger bottom end, but
this is in stock trim.
Con: The 6 bolt motor has a lot of structural differences to the 7 bolt motor. The 6 bolt motor doesn't have a crank angle sensor
which is on the 7 bolt motor. (there is a work around using a 1G crank angle sensor.
http://www.magnusmotorsports.com/ ) There have
been a few people who have been having some problems with the 1G cam angle sensors and stock 2G ECUs. They get a random misfire,
check engine light RMCEL. This occurs when the stock ecu detects the crank angle sensor (which is not there anymore) out of sync with
the cam angle sensor. This RMCEL causes the car to go into a limp home mode until reset with the gas pedal. It was designed into the
OBDII specs. In order to get the 6 bolt motor to work in a second gen, there is a long laundry list of parts you need in addition to
just the short block. They are listed on Magnus's web site. Also the 6 bolt motor would require a 6 bolt AWD flywheel. Remember I
already have a 7 bolt aluminum dual disk clutch and flywheel assembly!
Pro: The 7 bolt has a lighter rotating assembly. That means less mass for the motor to spin in order to transfer power to the wheels.
It also creates faster revs. Also the 7 bolt short block is a direct replacement for my 7 bolt with a spun bearing.
Con: The 7 bolts can spin rod bearings easier. Due to the differences in rod bearings. 95-99 model year cars are known to get
crankwalk. That is where the crank wears out the Thrust bearing also known as the crank bearing. This bearing is on the drivers side
with the pulleys. As the bearing wears out, it allows the crank to move outward. (Remember the 2nd gen Eclipses have the crank
angle sensor) The crank has what is called a key on the crank, two different sized plates. When the crank starts to move outwards,
the key will eventually make contact with the crank angle sensor and the car dies!
Answer: 450-500 HP - for now ;-)
Well, I know my Frank II turbo is only good for about 450 HP, so there is no need to go beyond that without my 3rd turbo upgrade.
Again, I started talking to the experts to get their opinions. I was told that the stock bottom ends are unpredictable. Some will
hold 500 HP others will let go at 300 HP. It is the luck of the draw. The consensus is that the stock 6 bolt short blocks seem
to be more stout because of the larger crank and rods.
There is a catch... I am going with a 1993 1st gen 7 bolt short block. Since you are scratching your head, I will explain why I am
doing what I am doing.
Now please keep in mind that this is my personal opinion. There are others that believe that crankwalk is caused by bad cranks,
bad blocks, bad machining, bad bearings, bad oil passages... the list goes on. But I do find it interesting that crankwalk magically
appeared once Mitsu started installing crank angle sensor on the cars...