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Message: <blockquote data-quote="rz5.0" data-source="post: 1219866" data-attributes="member: 12700">[h=2]Timing 101[/h]by Michael Decipha PonthieuxLast updated: 9-10-2013 [h=3]Premise[/h]Ignition timing makes torque, and torque makes power! at low loads idle and part throttle you can usually demand a crap load of timing, i've often put sbf's at 50 degrees during cruise and 42 at light acceleration, 40 at moderate acceleration and 38-36 at heavy acceleration, and idle at 34+ above 1k rpm, the most significant factor to determine ignition timing will be the combustion chamber/cylinder head design, this can vary significantly, an MBT reference chart is listed at the bottom of this page. over advanced timing at very low loads is often confused for valve train rattle, DO NOT CONFUSE THE TWO, it may not be subtle at first, but with time may poke its head, if you are heavily advanced at very low loads and hear what sounds to be a valve train rattle, verify it is the valve train by removing the spout, or pulling out 10 degrees of timing during that condition WOT timing will be significantly effected by the cylinder head, reference the chart at the bottom of this page for more details, just remember there's no point in demanding any less than the amount of timing you demand at WOT for part throttle at the same rpm as that's just reducing torque, the amount of timing at WOT should be the absolute lowest timing the engine should ever see at that rpm other than idle now keep in mind cylinder head, stroke ratio, intake design, cam profile, runner length, plug type, coil strength, gearing, and a bunch other variables will directly affect the safest amount of spark you can demand, the largest influence will be the OCTANE LIMITIATION OF THE FUEL YOUR BURNING also keep in mind where your peak efficiency is (where the engine makes peak torque) at max efficiency you'll typically need to pull out 2 or 3 degrees to prevent detonation (if your are running timing on the very edge), this can be easily observed on a dyno or by feeling and listening to the engine now this might not exactly apply to those in california or other states that have to pass emissions, but for the sake of being politically correct, the tune you use for emissions testing should be labeled 'emissions tune' Note: retarding timing reduces emissions, its not uncommon for folks to LOCK OUT timing to 10-15 degrees for emissions testing. [h=3]MBT - Maximum Brake Torque[/h]the biggest mistake a bunch of tuners make is thinking that more timing=more power, that's correct to a point, but like everything it's a trade off, the idea is to get as close to MBT as possible, MBT in the context i'm using it for is max brake torque, just because an engine can handle more timing doesn't mean that the additional timing is helping, over advancing an engine is a common mistake that i see often, so keep that in mind MBT is defined as the MINIMUM amount of ignition timing that results in the MAXIMUM amount of engine torque increase For clarification, this does not mean the maximum amount of ignition timing that equals the aboslute maximum amount of torque. MBT is the point where removing 1 degree of timing will result in a greater torque loss than increasing 1 degree of timing. For example: lets say at 3000 rpm and 70 load you make: 258 ft lbs @ 26 degrees 275 ft lbs @ 27 degrees 292 ft lbs @ 28 degrees 296 ft lbs @ 29 degrees 281 ft lbs @ 30 degrees Although 29 degrees created the most torque, 28 degrees is MBT since decreasing to 27 results in -17 ft lbs lost and increasing to 29 degrees only results in a gain of 4 ft lbs MBT can be summarized as when pulling a degree has more of an effect than increasing a degree. there's been quite a few times where i've pulled timing and picked up mph's in the 1/4 its not uncommon so be warned on a dyno you can easily find where MBT is by using the method described in the above example, on the street it may be harder to tell, typical dyno loading allows for an engine to hit MBT where that's not possible on the street with actual loading as it will almost always result in pinging thus detonation before getting there when i hear an engine ping lightly i pull out at least 2 degrees, if its a hard knock i yank out at least 4+, to each their own, this is just my quick adjustment method a low load knock is by far the hardest for an untrained ear to hear, it will to the normal person sound like a valve train rattle, it will most notably be present during decel, keep this in mind if you think you have a valve train issue as it could very well be over advanced idle spark or low load spark knock you can verify by pulling the spout a boosted engine is an animal of a different color, boosted engines don't tend to knock or ping for very long instead they detonate with a loud rattle or even a bang, don't get too greedy on a boosted engine, its been said before that the general rule of thumb to be safe is to pull out 1/2 degree for every lb of boost, that is not the end all method to all at all, thus the need for tuning. as stated previously there are many factors that come in to play when dealing with ignition timing, any one of those factors can be significantly aggravated with boost, although pulling out 1/2 degree per pound will result in satisfactory results more times than not i always yank out a couple degrees more at first and work my way up rather than over advancing and working my way down on a dyno its pretty easy to tell when your under advanced as its typical to gain 35-60 rwtq for every degree when heavily under advanced, when you get to the point that adding a degree reduces tq minimally you know your at MBT, on boosted engines I typically stay at least 3-4 degrees away from MBT regardless, unless I know I have enough octane that detonation is not going to ever occur on a boosted engine i always use the timing at max engine efficiency 0 vac and 0 boost as my reference, as I transisition into boost i yank out timing linearly until I reach my desired advance at the highest load the engine can reach for that specific amount of boost, once again listen and feel, the two most important tools in any tuners arsenal if you find yourself surprisingly under advancing the timing to prevent pinging you should start investigating, don't rely on the fuel to be what its advertised to be, it wouldn't hurt to try to clean out some carbon by heating the engine up and sucking small amounts of water through the engine using a small diameter vac line, question the base timing and double check it its not uncommon for the harmonic balancer to be slipped especially on older vehicles modular's typically handle boost better than sbf's so you can typically get away with pulling out less timing for boost than with a pushrod. But keep it safe.</blockquote>