Not to be particular, but you contradict yourself in the message preceding this one: "knocking it back to 10 RETARDS the spark throughout the rev range and will lose you power. Retarding makes it fire closer to TDC - the spark goes off before the piston reaches top of stroke." 1) Of course spark goes off before piston reaches top of cylinder. Have NEVER heard of an engine timed ATDC. Takes time for explosion to fill cylinder. If you shoot spark too close to top, by then mixture is decompressing. That's whole purpose of spark advance -- to compensate for constant, and rather slow, physics of explosion at high RPM's. Again: have NEVER heard of an engine timed ATDC. Does DeLo scale even go ATDC? My Lincolns only go 5 or 10 degrees. 2) Advancing time moves spark closer to bottom of compression stroke -- cuts power (but does give longer & cleaner burn. That's why American manufacturers kept advancing throughout '70's, dropping HP along the way). Also lets you burn ever lower octane fuel. ABSOLUTELY 100% GUARANTEE YOU'LL NEVER GET A HIGH COMPRESSION ENGINE TO RUN ON TOO LOW OCTANE WITHOUT ADVANCING SPARK. Stop by my house on way to Pigeon Forge and I'll prove it: Have an 11:1 460, built for 97 octane. Factory timed at 10 degrees, which it will ONLY do with octane boost in 93 fuel. Will NOT run without knocking so timed without the boost. Got tired of buying additives, so I've moved to 12 degrees to run on 93 alone. Only complains when I stomp on accelerator AND DROP VACUUM ADVANCE BEFORE CENTRIFUGAL KICKS IN. Usually defer, but in this instance I'm right. Bill Robertson #5939 >--- In DMCForum@xxxxxxxxxxxxxxx, Martin Gutkowski <webmaster@xxxx> wrote: > > You get cack all power. I've watched Darren tune up a car retarding the > ignition back to 6 degrees because it was knocking. I am not making this > up. Read www.pumaracing.co.uk and learn about how the spark actually > timed. Timing advance is the time before the piston reaches the top of > its stroke that the spark goes off. Too much advance and the fuel will > combust too quickly trying to push the piston back down before it > reaches the top. Retard the spark, ie reduce the advance and the spark > will go off when the piston is nearer the top of the stroke allowing > full combustion to occur after TDC. Bill. I'm right. > > Buggerit - here's some text for you. > > http://www.sdsefi.com/techcomb.htm > > And now, Taken wholly from www.pumaracing.co.uk full credit to Dave Baker > > > Ignition Timing > > It takes one or two milliseconds from the time the spark occurs until > all the fuel/air mixture in the cylinder is fully alight and expanding. > The spark plugs therefore need to be fired a little while before the > piston reaches Top Dead Centre so as to get the fuel mixture burning at > the right time to push the piston down and generate power. When measured > in crank degrees rather than seconds this time delay is called ignition > advance. The perfect time to trigger the spark depends again on engine > speed and throttle position. Cars used to use a mechanical distributor > to set the spark timing. Nowadays it is normally done by the ECU in a > similar way to how the fuel mixture is controlled. The ECU stores > another map on its chip of how much ignition advance is required which > operates just like the fueling map. Copyright David Baker and Puma Race > Engines > > The amount of ignition advance required depends on the engine design. > Average figures would be between about 10 crank degrees at idle to about > 30 degrees at peak rpm. The required advance usually increases with rpm > up to about 3,000 to 4,000 rpm and then stays fairly constant. It also > needs to increase at low throttle openings and reduce again at full > throttle. If the spark is fired too early (over advanced) then the > mixture starts to burn too soon and tries to push the piston backwards > down the way it came before it reaches TDC - very bad for power and a > major cause of engine damage. If the spark is fired too late (retarded) > the piston has already gone part of the way down the bore on the power > stroke before the mixture is alight and much of the effectiveness of the > energy released is lost. > > If I had £1 for every person who thinks that more ignition advance is a > good thing in its own right I'd be a rich man. Like most other things, > more advance is only good if there isn't enough to start with. Excessive > advance is just as detrimental to power output as insufficient advance > but it's also potentially much more harmful to the engine. In fact the > better the engine design the less advance is required and other things > being equal, an engine that requires less advance will produce more > power. Copyright David Baker and Puma Race Engines > > ------- > > Martin > > > > > > > > > > [Non-text portions of this message have been removed] Yahoo! Groups Sponsor ADVERTISEMENT <http://rd.yahoo.com/M=194081.4074964.5287182.1261774/D=egroupweb/S=170512 6215:HM/A=1754016/R=0/SIG=11pv1u2ju/*http://www.ediets.com/start.cfm?code= 30529&media=atkins> click here <http://us.adserver.yahoo.com/l?M=194081.4074964.5287182.1261774/D=egroupm ail/S=:HM/A=1754016/rand=500353837> To unsubscribe from this group, send an email to: DMCForum-unsubscribe@xxxxxxxxxxxxxxx Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> .
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