Can anyone workout the gains of firing the piston closer to TDC than normal?

[Smokingwheels]

I need someone to help me calculate the improved efficiency in theory, maybe post a question at a physics forum or a mechanical engineering forum.

Thanks in advance but do not mention smokingwheels...Please..

The figures I have measured at various RPMs.

3.76 Deg ATDC eg -3.76 Deg for 750 RPM at Wide open throttle (WOT).
10.57 Deg BTDC for 2970 RPM WOT.
27.2 Deg BTDC for 5565 RPM WOT.

The raw calibration data is on sound cloud https://soundcloud.com/smokingwheels...ation-jan-2013
You will have to convert the MP3 files to WAV files (eg CDEX freeware) then look at the pluses in a wave editor and measure them. The firing pulse has a duration of 1 mS usually the top trace.
The distributor offset is approx 62 Deg BTDC when looking at the sound files.

[mechman600]

I think if it was that simple, everyone would be doing it already.

[Smokingwheels]

Originally Posted by mechman600

I think if it was that simple, everyone would be doing it already.

I have told everybody quite a few years ago now, but I cant find any evidence on the net of any story's of successes or failures.

I would like someone to try my method maybe boring out like a cylinder hone pattern who knows what will happen.

No one thinks its actually possible I guess.

I have a 280 ZX with EFI and oneday I will port it.

There has been mostly good advice on how to improve my methods.

Anyway here is the pic again...

[mwebb]

i do not understand your question , then again
you do not have a question

your statement is false do not proceed with your experiment .

the answer is
AVERAGE
peak combustion pressure must happen at about 14 degrees after top dead center

not so important at idle as at every other condition of engine operation
spark duration is almost always longer than 1ms but the combustion event itself takes much more time than the time for the spark event
the spark event will end before the combustion event

the timing advance / change for the spark event
changes
with rpm and load and temperature
and
the spark event is timed so that the combustion event produces peak pressure at 14 degree after TDC
=================
if
peak combustion pressure does not happen at 14 degrees after TDC because someone tampers with base ignition timing
peak power and peak efficiency are reduced / decreased
emissions increase
and
if base ignition timing is advanced enough so that some random combustion events get to peak combustion pressure before TDC
the engine will be damaged .

do not frack with it

[pete c]

what ^^^^^said. combustion takes time. that is why ignition always takes place BTDC, never after.

[mechman600]

Originally Posted by mwebb

peak combustion pressure must happen at about 14 degrees after top dead center

Is this true will all engines? Four stroke/two stroke? Gas/Diesel? etc...
Just curious. I have never heard the 14 degree ATDC figure before.

[gone-ot]

...something to remember, ignition STARTS ahead of TDC, takes a finite amount of time (combustion flame rate) to happen, all while the piston rapidly slows its upward motion until it passes through TDC, and then begins to rapidly increase its downward motion...in coincidence with the peak combustion pressure (~14º ATDC for gasoline; other fuels alcohol & methanol, etc. are different -- does NOT apply to diesel).

[Smokingwheels]

Originally Posted by mwebb

i do not understand your question , then again
you do not have a question

your statement is false do not proceed with your experiment .

the answer is
AVERAGE
peak combustion pressure must happen at about 14 degrees after top dead center

not so important at idle as at every other condition of engine operation
spark duration is almost always longer than 1ms but the combustion event itself takes much more time than the time for the spark event
the spark event will end before the combustion event

the timing advance / change for the spark event
changes
with rpm and load and temperature
and
the spark event is timed so that the combustion event produces peak pressure at 14 degree after TDC
=================
if
peak combustion pressure does not happen at 14 degrees after TDC because someone tampers with base ignition timing
peak power and peak efficiency are reduced / decreased
emissions increase
and
if base ignition timing is advanced enough so that some random combustion events get to peak combustion pressure before TDC
the engine will be damaged .

do not frack with it

Well I did Frack with Twice now the first one died a bad death, spark plugs would only last 3-4 days before they carbon-ed up and stopped working while with heavy knocking.

Here is a video I made in 2002 sept

http://www.youtube.com/watch?v=XnwJuNbvULY

I thought the fuel had ruined my engine but
I patched up the bottom end an lowered the compression to 8:1 and discovered some strange engine timings.

On this page New Page 1 the bottom graph has a red trace, these values came from my timing computer just before the patched bottom end died again.

Yes I understand about Peak Combustion Pressure (PCP).

[Smokingwheels]

Originally Posted by pete c

what ^^^^^said. combustion takes time. that is why ignition always takes place BTDC, never after.

Yes But in a normal engine it is like that.
I have modified mine.

My engine needs to be fired -3.67 Deg @ 750 Rpm eg 3.67 Deg ATDC to avoid knocking.

I measured what my computer was doing and the Trigger and Firing pluses have been stored on a MP3, anyone can download them and convert the MP3 to a Wav file, then use a good sound editor to work out the timing.
Note: the offset is 62 Degrees BTDC and the Degrees between pluses is 180 for a 4 cylinder 4 stroke engine.

Timing confirmation jan 2013 by smokingwheels on SoundCloud - Hear the world

The file name stores the info.
750-rpm-65-7-d-3-67-set-2-1
rpm =750
total timing = 65.7 deg
d = -3.67 (Actual timing 62 offset)
set = -2.1 (what the computer is tring to run the engine at with 62 offset)

[Diesel_Dave]

Originally Posted by mechman600

Is this true will all engines? Four stroke/two stroke? Gas/Diesel? etc...
Just curious. I have never heard the 14 degree ATDC figure before.

I don't know about gasoline engines, but it's not necessarily true for commone rail diesels. I've seen the same engine have peak pressure locations everywhere from TDC up to 20 dATDC. It all depends on the operating condition.

...something to remember, ignition STARTS ahead of TDC, takes a finite amount of time (combustion flame rate) to happen, all while the piston rapidly slows its upward motion until it passes through TDC, and then begins to rapidly increase its downward motion...in coincidence with the peak combustion pressure (~14º ATDC for gasoline; other fuels alcohol & methanol, etc. are different -- does NOT apply to diesel).

Yes, ignition doesn't necessarily start before TDC in a common rail diesel. This is particularly true for some of the newer ones that have special operating modes intended to create heat for the aftertreatment (DPFs SCRs, etc.). In these modes, the combustion is intentionally delayed so that less heat gets extracted during the power stroke and more heat gets sent into the exhaust. In some cases the injection doesn't even begin until after TDC. As long as there's enough compression, there will still be enough heat to cause ignition. I've seen some operating conditions where combustion doesn't even start until 10 deg after TDC.