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Some
time in the year 2000 my neighbour gave me a cylinder head (AB7)?
It
was off a Nissan 4 cylinder L series engine.
A
friend of his gave me a 1983 bluebird wagon with a faulty carbie.
I
used the block out of this car for my 1983 Bluebird sedan.
In
my spare time I ported this head and a manifold that I had.
In
2002 I installed the good block from the wagon and the cylinder head into my
1983 Bluebird.
It
fired up ok took it for a test drive wow it was really responsive.
I
had 33 cc in the chamber approx compression ratio 12.5:1
I
found just by depressing accelerator to the floor I was able to create wheel
slip in 2nd gear, going around a typical right-hand corner at normal
speeds I was pleased.
But
the timing was really out when the revs where up past 3000.
This
engine had a very short life.
I
ended up destroying this high compression engine, because of the timing
characteristics that was needed to run it.
The strange
characteristics.
I found by revving this engine with no
load above 3000 Revolutions Per Minute (RPM) it made a terrible
knocking/banging sound like all the bearings were not there, but the block was
in good condition before.
The
knocking/banging sound was constantly there when driving the RPM was over 3000
RPM.
I
had plenty of power under the hammer I was pleased with my work.
The
correct spark plugs for this engine would only last 3 days.
I
started replacing the all the high voltage components; the result was a slight
improvement but short lived.
I
ended up reducing the compression ratio to 8:1 in 2002 I did know what else to
do.
I
had discovered a way to run a spark ignited (SI) internal combustion (IC)
engine several degrees After Top Dead Centre (ATDC), all thought I did not
realise at the time.
I connected timing light
and started to investigate.
I
found the only way to silence the noise was to retard the timing back to 3 to 4
degrees Before Top Dead Centre (BTDC) this was when the engine revs were over
3000 RPM, with no load on my engine.
With
the standard mechanical advance it then caused the timing at idle to be totally
wrong.
When
at idle which is ~22 degrees less this engine would not idle, because it was
being fired ~18 degrees After Top Dead Centre (ATDC) which is extremely too
late in the power cycle to achieve Peak Combustion Pressure (PCP).
I
now know from my 2nd engine the vacuum advance needs be approx in an 18 degrees
range.
I started to think.
I
could make a computerised ignition system I had a Laptop.
I
built up an interface for the printer port.
I
built the first interface with 2 transistors and 2 leds 6 resistors on a piece
of veroboard soldered on the end of a DB 25 way connector .
I
bought 2 kits from altronics to try and tune the engine.
1
was the high-energy ignition kit and a programmable ignition controller that
would allow a negative slope, however I found this was not good enough for my
Engine.
I
then started to write a program in BASIC, the first one was just to delay the
spark.
It
didn’t work very well but it did stop the knocking above 3000 RPM.
I
worked on the programs all night to try and overcome this timing problem.
I
quickly got a program to work and have been improving it till now (7
years later).
I
had to grind out the locating keyway on a rotor button to allowing the timing signal
to be advanced so the computer could takeover
I
had to manually enter the timing every 25 RPM into data statements.
I
gathered data over the next 8 months after lowering the compression to 8:1 in
2002.
My engine died and I threw out but I should of kept the head.
In 2005 I had a go on another head this was off a 1986 Bluebird wagon.
The secret is out now.
After porting my head and manifold I was going to have the compression raised by welding up the chamber I was talked out of it and had it shaved heaps the ratio ended up at approx 10.5:1 this how ever left the chain to the overhead cam rather sloppy, I used a plastic cutting board to take up some of the slack, later on I ended replacing the chain and up moving the chain guide by welding some more plates to it and drilling new mounting holes, at this time was when someone had put silicon into my engine oil and it blocked the oil way to the cam it damaged the cam and also damaged the bearings.
One night we had to go from Maddington to Bunbury and back at that stage I had a 92 deg c thermostat fitted my engine was not tunned up very well because it would knock slightly when under light loads, under highway driving conditions, I did approx 400 km on 14 L of fuel cruising around 80 km/h in overdrive very rough figures 80 mpg (3.5 L/100km).
I then added a second vacuum sensor made out of a aircon pressure sensor, I reversed it and by chance it was adjustable and this provided my computer system with another signal for when the load was higher to retard the timing.
I used to do regular trips approx 220 km at 80 km/h in overdrive and achieved around 45 mpg 6.28 L/100 however I could be pushing my engine too hard.
If you put your foot down it uses heaps of fuel too because the vac sec are fully open at 2000 rpm now, when I first fired this engine up I had quite a lot of HP until I cooked it I can only guess at the power gain, I have never had enough money to dyno it or when I have asked the shops they just laugh at me.
Another strange thing is my engine still runs when the spark is fired 65 deg BTDC at idle.
see https://www.youtube.com/watch?v=Oydmh5hX8dM
The video clip starts with the timing at 65 then I slowly bring it back to 10 note there are two timing marks on the pulley and there 20 degrees apart.
I think a normal engine would normally stall I would be good if some one else could test this would be good
Another thing my engine needs is a linear timing curve I can only guess why that is.
The city fuel consumption, I have no idea because my Speedo is broken and I don't drive it that much any more.
I did a city test in sep 2010 using www.whereis.com as a mileage guide, I did 12 laps around a block, also have a tacho graph as well the result was 40.13 MPG 7.04 L/100km and I did some stats on my engine data, time idling 7.41% I think this is a bit low, 9.94% for above 2500 rpm 82.61% above 1000 rpm to 2500 rpm.
I investigated the data a bit further and used engine acceleration to calculate time spent in lower gears it was 19.49% the other 80.41% was driving and idling.
Idle fuel consumption is around 12cc/min @950 rpm, approx 55% less.
Peak combustion pressure
(PCP)
needs to be achieved by the time the crankshaft is 17-19 degrees ATDC according
to research I have done on the Internet.
The
second engine is now running with an advance is approximately 15 degrees BTDC
at 3000 RPM with WOT.
The
timing drops with carbon build up thus is very unstable in the long term but if
it keeps going we will end up firing after top dead centre (ATDC) again.
From
Information stated that a knocking engine will quickly destroy the pistons and
bearings etc
Yet
I was not able to melt my pistons even with 22-25 degrees to much advance.
My
engine was run with extremely heavy knocking AT WOT up to 6500 RPM through the
gears to over 120 km/h on a hwy lots of times and never melted anything,
But
I was hammering the life out of the crankshaft and other parts below.
After
suffering many personal hardships.
I
then moved to my sisters in Huntingdale and continued to improve my timing
program.
In 2005 had the
courage to start this project again.
To
work a head and manifold on another L series engine.
I
got it all together in the 3rd quarter of 2005.
Now
with the second engine a mild version, the data that I have gathered it now
indicates that there is approximately 30 degrees of vacuum advance, on a cold
night.
I would need to build
a 3rd engine and do more tests.
Assuming
current data would be similar in range on previous engine at Wide Open Throttle
(WOT) the original head may have been timed (fired) as late as 14 degrees ATDC
above 3000 RPM and still achieve Peak Combustion Pressure (PCP), it’s a rough
guess at best.
But it’s a slippy slope estimating timing on the down side of the power stroke when no one has done it before.
Cam (STD)
Carbie (STD)
Compression
38-39 CC in chamber approx ratio 10.5:1
Fuel U.L.P
60 MPG@80 km/h
Minimal
porting, but my original coating
Matched ports
2 inlet valve
inserts have lips (didn’t repair)
Port surface (restricted information)
~ 6 degrees
BTDC below 750 RPM
~12.5 degrees
BTDC, 3000 RPM
~24 degrees
BTDC, 5500 RPM
Controlled
leaks for vacuum advance 13.8 Degrees.
Absolute
vacuum advance 12.8 Degrees.
~ 1.1 degrees
BTDC below 750 RPM
~ 9.33 degrees
BTDC, 3000 RPM
~18.2 degrees
BTDC, 5500 RPM
~33.2 degrees
BTDC, 10000 Rpm
Controlled
leaks for vacuum advance 8 Degrees.
Absolute
vacuum advance 10 Degrees.
Ignition (STD)
Bosch module interfaced to printer port
Distributor
modified with 62 degrees maximum advance.
2008
Distributor replaced.
Laptop running
my program written in Microsoft’s QuickBasic.
Special power
supply for Laptop (reduces the risk of a flat battery) lasted 1 year aux power
supply.