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I'm trying to fix someone else's work and learn so please go easy on me.
Q. What is a safe amount (maximum) of timing used in boosted applications at low load? I have a map I'm working with and it has 48o of timing at high rpm and low load.
What's a typical range you are used to seeing on 4 cylinder turbo.
I've never setup a timing map from scratch on any ECU but I've never seen anything run more than 38o of timing on a distributor or a timing box.
Thanks in advance.
Tune it the same as the rest of the ignition map, you give it whatever produces best torque without knock. You often wont even have any knock limitations at low load. 40-55 BTDC in cruise and overrun regions is common with road car engines, but every engine is different.
As Adam said, tune it to what it needs - at higher rpm and light load engines need a lot of timing because
a/ as rpm increases the fuel burns at the same rate, but has less time to do so, so the ignition point is advanced so the pressure curve best matches best torque needs.
b/ less dense air-fuel mix burns more slowly and so needs the ignition to start earlier, for the same reason.
Back in the days of distributors, understanding the ignition needs was a bit of a tuners' 'black art' with the former being catered for by initial timing and mechanical advance curves, and the latter by careful selection of vacuum advance diaphrams.
