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Message: <blockquote data-quote="shiroitenshi" data-source="post: 3154907" data-attributes="member: 27518">It's actually the timing, div. if you advance enough, the peak pressure is achieved just as the exhaust valve opens fully. That's causes higher exhaust speed which goes out the exhaust giving you the sound. But with higher timings, comes higher risk of knocking. How fast would the fuel burn (the burn rate) given the conditions dictate how much timing is optimal. That's why some people would say increasing fuelling would give you the 'louder' sound, while some would say the 'timing'You can actually run lean settings to get power on NA, but it's not really without risk.Why I say this is because you can observe from the original mapping of factory ecus, that the peak rpm has higher AFR recommended mixtures is because a speed density system only estimates the amount air coming in, based on MAP and IAT, the ECU calculate the density of the air coming in (the TPS is there for another reason). The inherent inaccuracies in this type of system means we have to 'allow' some safeguards in the tune.In fact, if you notice, when we floor the accelerator, there's usually a quick lean spot (how lean is based on the part throttle tune), even though we can see on the ECU mapping that it's already reading the high load portion of the ECU. I'd have to wait a few moments for the AFR to stabilize, and tune from there. Adjusting some other cells also affect the adjacent cells, so it's up to the tuner to figure out which cells are involved, in order to get a good tune out. Sure, you might not get that ultimate power tune, but when reliability is involved, it pays to play it safe.That's why tuning is a matter of being able to get reliable AFRs out, and estimating the timing needed to get the most out of the engine without incurring too much risk.But it seems to me that your AFR would swing so wildly from the day to the nights.Usually it's 12+ for me in the day, 13+ at night. About one point difference only.from 11.5AFR to 13.8 AFR, you must have really hot/humid days and really cold/dry nights. NICE!If anyone wants to read about AFR and don't want to pay for the SAE research papers, this is something I dug up from google.. I also have the book, lol. http://books.google.com.my/books?id=RYsglAO9f8gC&pg=PA133&lpg=PA133&dq=humidity+air+fuel+ratio&source=web&ots=bT7Kz_hO9y&sig=9JC4QiDF0ToZnvk4GgGgW0R0nvA&hl=en&sa=X&oi=book_result&resnum=2&ct=resultPage 134 is a gem (make sure your engine is healthy and tunable) LOL. Doesn't apply to Malaysian s though.. I saw cars being tuned in less than healthy conditions.But some of his info is outdated or a little inaccurate due to the fact that somethings have changed from during his time, which include engines that can exceed of 8,000 rpm by A LOT 'unworkable' rod stroke ratios (in his time) which influences the leverage, hence the peak pressure point is no longer the claimed '15 degrees' ATDC. and also the fact that EMS have more cells and faster processors now.Not to say that he is wrong.. he is right in his time, but with new engines and new technologies, some rules have changed. But most basic stuff is there, and they're all supported by SAE white papers (if anyone have ever bothered to check)</blockquote>