This section will detail some power and speed
(Click on pictures to see larger version)
Change of Final Drive Ratio
While the overall gearing of the automatic transmissions
is an improvement over the manual F20's 1st gear is still a bit short to
be of any real use with any sizable increases in power. To combat this I
will be changing the drive chain sprockets in the transmissions from
32\38 teeth to 35\35 teeth from a different variant used in the US on
the larger engine capacity vehicle, this will change the final drive
from 3.91:1 to 3.26:1. This will also aid in top
gear cruising ratio's, the table below shows the outcome of the change.
4T40E (3.26:1) mph
4T40E (3.91:1) mph
6500RPM \ Gear
Hmmmmm, that would make an interesting top speed now of
178mph at 6500rpm which would be which may actually be achieveable with over
700hp despite the poor aero of the mini. :) (6500rpm is
conservative on the engines, should be able to do 7500rpm fairly easily
on the setup which would be 205mph or even 215mph on the 225's but can't
see that somehow lol)
||4T40E (3.91:1) rpm
Top Gear 70mph Cruising
These are the 35T sprockets that will be used during the
rebuild to change the FD ratio. Will add a picture of the
originals for comparison once removed.
Limited Slip Differential
The options for this item are extremely limited for
these automatics, the majority are simple sprung plates which work
against the spider gears in the open differential to emulate a plate LSD
function but relies on friction between the spider gears and the casing.
The other option is similar but a modified solution which fits small
clutches between the spider gears and the casing which is a little more
enhance that the basic sprung plate design but the same pricipal.
There is quite a significant price difference between the options so
still investigating which to go with on a low mileage use car.
Based on my research into these options I will be going
for the Team Green LSD, while this is the more basic option it appears
to be fine for the purpose required. If the car was a daily use
vehicle expected to see high mileage then the more expensive clutch
converted item would have made more sense. Will add more pics when
Internals in the Transmission
The pysical side of the transmission is already fairly
robust and should cope with the amount of power that will be thrown at
it in a car of this weight, the weaknesses are primarily in the clutch
friction material and the torque convertor. Due to this I will as
part of the rebuild source uprated clutch packs and an uprated torque
Once the engines are rebuilt I will be wanting to run
likely around 1.5bar of turbo pressure for the planned 300-350hp output.
In order to do this in a controlled manner I have opted to purchase a
couple of digital boost controllers, in this case the newer Greddy
Profec. I used to have an Apexi AVC-R in the Skyline which was
brilliant but the greddy is so compact it was much more suitable with
little dashboard space remaining available for yet more gadgets.
These will then allow me 3 different boost setting off (actuator
pressure) low and high along with a scramble boost setting should I want
to add a timed overboost option. This unit also has the capability
to perform as per the Apexi with variable boost against rpm with an
additional module added but for now the default will suffice.
All installed ready to go, have removed the old
mechanical boost gauges too which looks much tidier and they were
blocking visibility a bit too when there were four mounted on the side.
This is a quick video of the startup sequence, if it
keeps getting more gadgets it will soon rival Knight Rider lol
I have also now purchased the map module upgrade for the
boost controllers, this will allow RPM and TPS based boost mapping
similar to an ignition\fuel map. This may enable more boost to be
run at higher rpm ranges where the higher compression currently won't
cause pre-ignition but such a boost level at a low\mid RPM could cause
The engines were already strengthened in the original
build so this will primarily be a refresher build with the addition of
new pistons to complete the setup by lowereing the CR to around 8:1.
Bits and Bobs
The dashboard was looking a bit scratched up after quite
a few years and also still very prototype looking. In the sun it
also had quite bad glare off the top panels. Was originally going
to make new panels from carbon fibre but this wouldn't be cheap and also
quite time consuming so opted for now to use carbon wrap.
Doesn't look too bad actually, much better than
scratched up aluminium.