<div dir="ltr">Remember the intake valves stay open for a bit past BDC as the piston starts up, also to get the mixture to go from flammable to flat out explosive the charge has to be compressed. so those factors tend to limit how much effective timing you can have. <div>Going a little deeper when you are using a mechanical distributor with weights there is only so much refinement you can get in your advance curve. Once you get into fully electronic ignition systems, there are systems that have upward to 70 degrees of range from fully retard to full advance (they may not use it in all applications, but the capability is there in the electronics)</div><div>Rick</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Apr 2, 2020 at 11:33 AM Max Heim <<a href="mailto:mvheim@sonic.net">mvheim@sonic.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="overflow-wrap: break-word;">Well, I mean, it would be true at some extreme — for example, igniting the spark at the very beginning of the compression stroke. But I suspect Barney was getting at something else.<div><br><div>
<div style="color:rgb(0,0,0);letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div style="color:rgb(0,0,0);letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div style="margin:0px;font-size:13px">--</div><div style="margin:0px;font-size:13px;min-height:16px">Max Heim</div><div style="margin:0px;font-size:13px">'66 MGB</div></div></div>
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<br><div><blockquote type="cite"><div>On Apr 2, 2020, at 11:24 AM, Richard Lindsay <<a href="mailto:richardolindsay@gmail.com" target="_blank">richardolindsay@gmail.com</a>> wrote:</div><br><div><div dir="auto"><div>Max that might be true if the ignition pressure from the combustion didn't build so long after the spark...within reasonable limits.<br><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Apr 2, 2020, 12:11 PM Max Heim <<a href="mailto:mvheim@sonic.net" target="_blank">mvheim@sonic.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="overflow-wrap: break-word;">Well, it seems to me that if you advance the spark to a point on the compression stroke where the piston is still coming up, the expanding ignited mixture would be fighting the piston, and it would actually reduce power. I’m not sure if that is what you are talking about, though.<div><br><div>
<div style="letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div style="letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><div style="margin:0px;font-size:13px">--</div><div style="margin:0px;font-size:13px;min-height:16px">Max Heim</div><div style="margin:0px;font-size:13px">'66 MGB</div></div></div>
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<br><div><blockquote type="cite"><div>On Apr 1, 2020, at 8:17 PM, Barney Gaylord via Mgs <<a href="mailto:mgs@autox.team.net" rel="noreferrer" target="_blank">mgs@autox.team.net</a>> wrote:</div><br><div><div>Okay, let's see if anyone knows the answer to this one. Why is it that "You do eventually get to a point where no more advance will help". Why do we stop spark advance at ~32d BTDC at road speed, and keep the advance the same for all higher engine speeds?<br><br><br>At 07:56 PM 4/1/2020, Richard Ewald via Mgs wrote:<br><blockquote type="cite">It takes about 3ms to burn the fuel in a cylinder from when the spark ignites it. The engine designers want the peak pressure to occur at between 5-10 ATDC.<br>At idle speed 3ms is about 15 degrees. Â<br>So if you want your peak pressure at 5 ATDC, your base timing is 10 BTDC, if you want your peak pressure at 10 ATDC your timing is 5 BTDC.<br>If you look at tune up specs for non smog controlled engines, most have base timing in the 5-10 BTDC range.<br>Now if you double the engine speed, it still take 3ms to burn, but to keep the max pressure at 5-10 ATDC, you have to light the mixture sooner.<br>You do eventually get to a point where no more advance will help. That point varies with the engine design, cam profile, combustion chamber design, headers etc. Â<br>Rick<br>....<br></blockquote><br>_______________________________________________<br><br><a href="mailto:Mgs@autox.team.net" rel="noreferrer" target="_blank">Mgs@autox.team.net</a><br>Donate: <a href="http://www.team.net/donate.html" rel="noreferrer" target="_blank">http://www.team.net/donate.html</a><br>Suggested annual donation $12.75<br><br>Archive: <a href="http://www.team.net/pipermail/mgs" rel="noreferrer" target="_blank">http://www.team.net/pipermail/mgs</a> <a href="http://autox.team.net/archive" rel="noreferrer" target="_blank">http://autox.team.net/archive</a><br><br>Unsubscribe: <a href="http://autox.team.net/mailman/options/mgs/mvheim@sonic.net" rel="noreferrer" target="_blank">http://autox.team.net/mailman/options/mgs/mvheim@sonic.net</a><br><br></div></div></blockquote></div><br></div></div></blockquote></div></div></div>
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