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Location:
Sydney
Registered:
May 2002
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Location:
Terrigal
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Tue, 27 May 2003 12:25
 
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I might be wrong, but thought an engine would run like a bag of poo if you fired it ATDC.
Only half know the theory in this so will let someone else explain who knows more about it 
I think you want to ignite the air/fuel though while its being compressed and more power is made firing BTDC.
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Location:
Hornsby, N.S.W
Registered:
September 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Tue, 27 May 2003 13:05
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i hear about this all the time, it would be great if some could verify the correct meaning/purpose.
justin 
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Location:
Perth
Registered:
September 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Tue, 27 May 2003 17:41
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i had an 85 pulsar
timing was to be set 10 (or 5) degrees ATDC
go figure that one
but she purrred when i set it
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Location:
Canberra
Registered:
December 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Wed, 28 May 2003 00:04
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It will purr like a kitten because you have nothing opposing the piston on its way back up, but wouldnt you loose alot of your torque becaus the fuel wont have time to reach its full potential when it explodes in the cylinder?
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Location:
Perth
Registered:
September 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Wed, 28 May 2003 02:01
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well, the manufacturers ID plate said to make it ATDC as standard timing
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Location:
Brisbane, Queensland
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Wed, 28 May 2003 02:52
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a lot of ignition timing has a lot to do with compression ratio's and the type of fuel your using. (fast or slow burning fuel).
If you have High compression then you want a slow burning fuel.
and vica versa.
You'd be supprised at how many "know-all's" don't know anything about this matter.
If you have an old car with slightly low compression, you don't go and put ultimate fuel in it!, you want to put in a lower grade fuel that burns faster so that you'll get some what of the same expected performance out of the motor.
This all comes down to when you ignite the fuel and what power your going to get out of it where the piston is in the bore.
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Location:
Sydney
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Wed, 28 May 2003 09:23
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i can understand your low/high compression thing Benny
But if your gonna set high compression and then set ignition time ATDC....whats the point of setting such a high compression ?
Ta
Mani
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Club Member
Location:
sydney
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Wed, 28 May 2003 10:25
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Im not sure where youre reading this information from (ATDC) but they could be referring to a twin spark engine where one plug is fired before TDC and then the next is fired after TDC to get the maximum burn/power by making sure there is no residual unburnt fuel after the first ignition...its a fairly common idea .. in fact alfa still use it on there engines.. just look for there coupe that has a twin spark badge on the boot
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Location:
Sydney
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Wed, 28 May 2003 10:41
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Michael....thanx for that....that helped a bit
but the engine that is saw it on was NOT a twin spark engine
4 cylinder....horizontally opposed....flat.....Volkswagen
only had 1 ignition...and that was ATDC....well atleast thats the only one it showed on the specs sheet
Ta
Mani
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Club Member
Location:
sydney
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Thu, 29 May 2003 10:43
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In that case are you sure theyre not referring to it as At Top Dead Centre????
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Location:
Sydney
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Thu, 29 May 2003 11:18
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no im positive it was AFTER TDC
i found out today what its for
its only set like that for idle....purely for emmisions reasons
once u rev its BTDC
i forgot to ask HOW it helps emmisions but yeah for some reason it lowers the nasty nitric emmisions
i should have asked how but anywas thats the reason
Thanx
Mani
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Location:
South Australia
Registered:
July 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Thu, 29 May 2003 16:02
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You'll find that the distributor has a counterweight set-up hidden away that operates on centripetal (or is it centrifugal, can never remember) force that generates advance as the revs increase.
Robert Bosch wrote a good reference book on fuel & ignition systems, but I can't remember it's name, will look it up next time I go to uni. Unfortunately, to say that having ATDC improves emissions in general is a bit of a fallacy. See generally with lower nitric emissions, you will get greater carbon monoxide emissions...it's one of those equillibrium/catalytic systems, you shift something one way then the other goes the opposite.
I think it's to do with available oxygen being spent one way or the other. Would look it up, but year 12 chemistry is a distant memory that I don't want to re-live!!!
I leave my road ignition settings to the engineers, and my race settings up to the dyno
Ignition advance does generally equate to greater power/torque due to there being more time to burn, and also the fuel gets burnt during a period of higher compression. There are of course, hazards to ignition advance, and it varies alot with different modes of operation (over-run as Bosch calls it, full throttle, temperature of the intake charge etc can also be factors). Quality of fuel is also important.
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If you have an old car with slightly low compression, you don't go and put ultimate fuel in it!
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I'm not sure I'd believe that (but I'm not a know-it-all), fast burning fuel will require ignition timing that is more retarded (not in a spastic sense), whereas a slower burning fuel (higher RON) will be able to advance the ignition over standard, giving better torqure down low, and at least equivalent upper-rev range performance as well.
I think having faster burning fuel has some heating issues as well, but I'd have to find that book to confirm that. More energy gets converted to heat rather than kinetic energy maybe? Not sure. Also if there is an issue with heat, that can change the equillibrium in the whole emissions equation. It's a way too complex an issue to remember everything, maybe I'll get that book and hit this post again  (In a way I'm admitting I'm not an ultra-reliable guru on this subject).
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Location:
Sydney
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Fri, 30 May 2003 08:46
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Yes the person who answered me this question i found out today was wrong
so ignore this thread
this person generally gives poor quality answers so no more questions for this guy
and the ingition timing was set at 0 degrees ATDC....which means right at TDC.....all i saw was the ATDC.....so yeah i dont think there is such thing as ignition after TDC
sorry for the confusion ppl
im sik of ppl answering things they dont know about
Thanx
Mani
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Location:
Branxton
Registered:
January 2003
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Location:
Canberra
Registered:
December 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Fri, 30 May 2003 22:37
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| Doctakay wrote on Sat, 31 May 2003 08:20 |
I would hope not, I hope you are reffering to someone you spoke to about this off line. The best advise I can give you is do a bit of basic research yourself before starting a thread, you might find that you learn things quicker and with more fact by hitting the books instead of the forums.
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Agreed, research is good and you will learn alot more generally now that ive said that it is also good to get the opinion of the toymods community that way you can get all the data and compile it into some useful info. This aside not all reading material is useful and to the point.
PS ive read some of the above books and they are extreamly good.
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Location:
Sydney
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Sat, 31 May 2003 07:43
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Yeah the person i spoke to about this was offline
in reference to researc.....i find the best way to do so is by asking live ppl as u get a better xplanation
and i do so offline AND online...so stop your assuming
If it is wrong for me to ask these tech questions online.....could a moderator PLS tell me to stop it as im so sik of ppl liike u with nothing better to do than whinge constantly whinge about doing research
if the moderators have no problem with it then im gonna keep asking these questions .... as like i said....i ;like to get a wide variety of responses.....and on top of that questions like these help other ppl too
once again if the moderators find my questions annoying PLS PLS PLS PM me and let me know
Thanx
Mani
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Location:
Hornsby, N.S.W
Registered:
September 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Sat, 31 May 2003 12:03
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this thread has become very informative.
justin 
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Location:
Canberra
Registered:
December 2002
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Location:
Sydney
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Sun, 01 June 2003 07:56
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Thanx Jase
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Location:
Cairns
Registered:
May 2002
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Re: ATDC (After top dead centre ) ??? Pls xplain ?
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Mon, 02 June 2003 07:02
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The only silly question is the one you don't ask.
The only person you insult with a flame post is yourself.
Let's all enjoy the benfit of everyone's different life experiences dealing with the automotive world. Isn't this the fundemental idea behind a tech and conversions forum?
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