[Cut & pasted this paragraph up here to suggest potential diagnosis before ears shut...] Before your knickers twist totally off body, consider this startling possibility: perhaps Andrew's distributor hold down nut has worked slightly loose. Force of camshaft may have rotated distributor enough that he is now OVER ADVANCED!. Happened to my little AMC once... Have I *EVER* disagreed that over advancing will cause pre-ignition? Go back and re-read Message #9261. I *SPECIFICALLY* stated that over advanced ignition will cause rattling of valves (and bearings) as RPM's increase (when timing mark is jumping off scale, duh). THAT MAY BE WHY INCREASING OCTANE TO 93 DOESN'T SEEM TO HELP ANDREW. Even his 104 racing fuel may not help if timing of spark is problem. And yes, I do know what "advance" means. Don't you remember our last tiff? Whole issue of 13 degrees vs 10 degrees had *NOTHING* to do with timing mark jumping off scale BTW (my 10 degree PRV jumps off scale too, thank you very much. It just starts closer to TDC and doesn't jump as far). Has everything to do with how much pressure exploding mixture exerts against piston as it comes up. Advancing spark exposes compression stroke to more of it. Haven't researched Volvo part numbers yet, but can assure you Ford Motor Company used SAME distributors on same engines throughout late 70's as they specified each year to time ingition farther and father from TDC. And what a coincidence -- HP dropped each time. Bill Robertson #5939 >--- In DMCForum@xxxxxxxxxxxxxxx, Martin Gutkowski <webmaster@xxxx> wrote: > A lot of the time, I have no idea what you're going on about - eg the > first paragraph in your e-mail below. I take issue with sweeping > statements that are often just plain wrong. I quote them in my replies. > You then seem to attempt to blind me with science but contradict > yourself at the same time. I'll sign off with simply repeating for the > umpteenth time: > > Over advancing will cause problems with pre-ignition > Retarding will correct but going too far will lose you power. > > These are basic principles, not tied to any particular engine. For more > info, read www.pumaracing.co.uk > > Martin > > PS You do realise that advancing means increasing the number of degrees > before top dead centre? ie set the DeLorean timing to 13 degrees, rev it > and the timing will jump off the scale as the spark is sent more and > more in advance of TDC because the time taken for combustion to > propagate in the cylinder by and large doesn't change, but with the > speed of the engine increasing you need to light it up further and > further away from TDC..... > > content22207 wrote: > > >My point is: PRV drops from 17 down. Race engine drops from something > >closer to 0 down. That's why we have vacuum advance diaphragms and > >they don't. That's why we can time closer to TDC and they can't. > > > > To unsubscribe from this group, send an email to: DMCForum-unsubscribe@xxxxxxxxxxxxxxx _____ Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/DMCForum/ * To unsubscribe from this group, send an email to: DMCForum-unsubscribe@xxxxxxxxxxxxxxx <mailto:DMCForum-unsubscribe@xxxxxxxxxxxxxxx?subject=Unsubscribe> * Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> .
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