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Original Message
RE: Still looking for theory on advance timing.
By Gerry Proctor - 06/04/2004 6:43:34 AM; IP 207.133.188.254
You're well into the range of theoretical operation where you blend pure science and engineering...in other words, a think tank that includes engineering, chemists, and physicists and I'm none of those.

A specific answer to your question would require knowing where the cylinder pressure spike occurs. A small bore/long stroke engine will have a different optimal timing curve than a big bore/short stroke engine. There is also the combustion chamber design to consider. Every engine is different and that’s why tuning is so important and you can’t go by ballpark numbers other than to create a baseline.

There is a direct relationship between cylinder pressure (combustion energy) and oxides of nitrogen…the higher the pressure, the higher the nox emissions. Having the spike occur before TDC can create very high cylinder pressure (and associated nox) but a lot of the thermal energy is actually going into fighting inertia by trying to force the piston back down the bore. This isn’t always noticeable at idle other than through MAP but once the manifold vacuum has topped out, you’ve gone as far as you can. This doesn’t mean the engine will run well off idle with that much initial advance. As to a cold engine liking a lot of advance…were really talking primarily emissions issues. The higher limit only exists briefly and by a lot we’re talking in a range of five to eight degrees over the hot idle base timing.

So, with the timing numbers you’re stating are you sure the numbers are accurate? There are notorious ways to be misled with timing an FE. Those include a slipped inertial ring on the balancer and using a chain cover/timing pointer incompatible with the balancer mark. Have you verified that indicated TDC is actually TDC?

I'll have to run and record a datastream on my wife's car this weekend to map the numbers through transition. My cars are all CAN and my wonderful and expensive scanner is now useless.
This thread, so far...
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Collapse <a href=../ForumFE/reply.aspx?ID=21694&Reply=21694><img src=../images/reply.png width=30 height=10></a>&nbsp;<a href="#" id="anchor21694" onclick="return false;">More questions on timing...not answered below</a>&nbsp;-- <font color=#0000ff>Walker, <i>06/02/2004</i></font><script type="text/javascript"> new HelpBalloon({ dataURL: 'replyb.aspx?ID=21694', contentMargin: 60, icon: $('anchor21694') }); </script>  More questions on timing...not answered below -- Walker, 06/02/2004
Collapse <a href=../ForumFE/reply.aspx?ID=21698&Reply=21694><img src=../images/reply.png width=30 height=10></a>&nbsp;<a href="#" id="anchor21698" onclick="return false;">RE: More questions on timing...not answered below</a>&nbsp;-- <font color=#0000ff>Gerry Proctor, <i>06/03/2004</i></font><script type="text/javascript"> new HelpBalloon({ dataURL: 'replyb.aspx?ID=21698', contentMargin: 60, icon: $('anchor21698') }); </script>  RE: More questions on timing...not answered below -- Gerry Proctor, 06/03/2004
Collapse <a href=../ForumFE/reply.aspx?ID=21700&Reply=21694><img src=../images/reply.png width=30 height=10></a>&nbsp;<a href="#" id="anchor21700" onclick="return false;">Why: it's DIS, so 'vacuum advance' is now MAP adv</a>&nbsp;-- <font color=#0000ff>Walker, <i>06/03/2004</i></font><script type="text/javascript"> new HelpBalloon({ dataURL: 'replyb.aspx?ID=21700', contentMargin: 60, icon: $('anchor21700') }); </script>  Why: it's DIS, so 'vacuum advance' is now MAP adv -- Walker, 06/03/2004
Collapse <a href=../ForumFE/reply.aspx?ID=21701&Reply=21694><img src=../images/reply.png width=30 height=10></a>&nbsp;<a href="#" id="anchor21701" onclick="return false;">RE: Why: it's DIS, so 'vacuum advance' is now MAP adv</a>&nbsp;-- <font color=#0000ff>Gerry Proctor, <i>06/03/2004</i></font><script type="text/javascript"> new HelpBalloon({ dataURL: 'replyb.aspx?ID=21701', contentMargin: 60, icon: $('anchor21701') }); </script>  RE: Why: it's DIS, so 'vacuum advance' is now MAP adv -- Gerry Proctor, 06/03/2004
Collapse <a href=../ForumFE/reply.aspx?ID=21702&Reply=21694><img src=../images/reply.png width=30 height=10></a>&nbsp;<a href="#" id="anchor21702" onclick="return false;">But at STARTUP? need some explanation/theory</a>&nbsp;-- <font color=#0000ff>Walker, <i>06/03/2004</i></font><script type="text/javascript"> new HelpBalloon({ dataURL: 'replyb.aspx?ID=21702', contentMargin: 60, icon: $('anchor21702') }); </script>  But at STARTUP? need some explanation/theory -- Walker, 06/03/2004
Collapse <a href=../ForumFE/reply.aspx?ID=21703&Reply=21694><img src=../images/reply.png width=30 height=10></a>&nbsp;<a href="#" id="anchor21703" onclick="return false;">RE: Now it gets complicated.</a>&nbsp;-- <font color=#0000ff>Gerry Proctor, <i>06/03/2004</i></font><script type="text/javascript"> new HelpBalloon({ dataURL: 'replyb.aspx?ID=21703', contentMargin: 60, icon: $('anchor21703') }); </script>  RE: Now it gets complicated. -- Gerry Proctor, 06/03/2004
Collapse <a href=../ForumFE/reply.aspx?ID=21704&Reply=21694><img src=../images/reply.png width=30 height=10></a>&nbsp;<a href="#" id="anchor21704" onclick="return false;">I thought RETARDING the timing raised temp's</a>&nbsp;-- <font color=#0000ff>Walker, <i>06/03/2004</i></font><script type="text/javascript"> new HelpBalloon({ dataURL: 'replyb.aspx?ID=21704', contentMargin: 60, icon: $('anchor21704') }); </script>  I thought RETARDING the timing raised temp's -- Walker, 06/03/2004
Collapse <a href=../ForumFE/reply.aspx?ID=21705&Reply=21694><img src=../images/reply.png width=30 height=10></a>&nbsp;<a href="#" id="anchor21705" onclick="return false;">RE: We're working many different things.</a>&nbsp;-- <font color=#0000ff>Gerry Proctor, <i>06/03/2004</i></font><script type="text/javascript"> new HelpBalloon({ dataURL: 'replyb.aspx?ID=21705', contentMargin: 60, icon: $('anchor21705') }); </script>  RE: We're working many different things. -- Gerry Proctor, 06/03/2004
Collapse <a href=../ForumFE/reply.aspx?ID=21706&Reply=21694><img src=../images/reply.png width=30 height=10></a>&nbsp;<a href="#" id="anchor21706" onclick="return false;">Still looking for theory on advance timing.</a>&nbsp;-- <font color=#0000ff>Walker, <i>06/03/2004</i></font><script type="text/javascript"> new HelpBalloon({ dataURL: 'replyb.aspx?ID=21706', contentMargin: 60, icon: $('anchor21706') }); </script>  Still looking for theory on advance timing. -- Walker, 06/03/2004
Collapse <b>RE: Still looking for theory on advance timing.</b>&nbsp;-- <font color=#0000ff>Gerry Proctor, <i>06/04/2004</i></font>RE: Still looking for theory on advance timing. -- Gerry Proctor, 06/04/2004
 I was surprising myself every new cold day... -- Walker, 06/04/2004
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