lithium
14th July 2008, 06:24 PM
i know a thread about this got closed yesterday - i just thought people might want to know *why* those ebay resistors don't work
the basic principle behind N/A ECU tuning is to optimize two factors - how much fuel is going into your engine at a given RPM vs Load pair (air-fuel ratio) and how many degrees before TDC the spark is delivered, at a given RPM vs Load pair (ignition timing)
generally, to produce maximum power, the air-fuel ratio should be within a certain range (eg. 12.5-13.0) and the ignition timing should be as advanced as possible without detonation. compared to the conservative factory settings and when running high octane, this usually means we need to *lean* out the fuel and *advance* the timing.
now to the ebay stuff. the resistor hooks to the intake air temp sensor fooling the ECU into thinking the air coming in is much colder than it is. a factory ECU will usually do the following based on air temp:
cold air: *richer* fuel mix, *advanced* timing
warmer air: *leaner* fuel mix, *retarded* timing
so the first reason it doesn't work: as you can see, this doesn't do what we want. cold air does advance the timing, but it will also richens the fuel instead of leaning out the fuel. will this still result in a net power gain? who knows, but what you will find is that over time the extra fuel will cause extra wear on your piston rings, and in a very bad case burn out your cat.
the second reason it doesn't work: and perhaps the more important reason - for maximum power the A/F ratio and timing must be optimised *at every RPM vs Load* point for the engine; in other words, at all different driving conditions. for example, we might want to enrich the fuel mixture at low RPMs, and to lean the fuel mixtures at high RPMs. a resistor cannot adapt and will enrich the fueling at *every* point, under every driving condition, even the ones where doing so will result in reduced power.
this is why the utimate in ECU tuning is always done on a dyno, so the fueling and timing can be optimised under all the different driving conditions, for *your* specific engine, in its current state of wear and manufacturing tolerance. good power gains can also be seen with a replacement map (aka ECU flashing) that contains more aggressive fueling and timing settings
this is at least this is my understanding of the process. someone who is an actual tuner can probably correct anything wrong i've said above :)
the basic principle behind N/A ECU tuning is to optimize two factors - how much fuel is going into your engine at a given RPM vs Load pair (air-fuel ratio) and how many degrees before TDC the spark is delivered, at a given RPM vs Load pair (ignition timing)
generally, to produce maximum power, the air-fuel ratio should be within a certain range (eg. 12.5-13.0) and the ignition timing should be as advanced as possible without detonation. compared to the conservative factory settings and when running high octane, this usually means we need to *lean* out the fuel and *advance* the timing.
now to the ebay stuff. the resistor hooks to the intake air temp sensor fooling the ECU into thinking the air coming in is much colder than it is. a factory ECU will usually do the following based on air temp:
cold air: *richer* fuel mix, *advanced* timing
warmer air: *leaner* fuel mix, *retarded* timing
so the first reason it doesn't work: as you can see, this doesn't do what we want. cold air does advance the timing, but it will also richens the fuel instead of leaning out the fuel. will this still result in a net power gain? who knows, but what you will find is that over time the extra fuel will cause extra wear on your piston rings, and in a very bad case burn out your cat.
the second reason it doesn't work: and perhaps the more important reason - for maximum power the A/F ratio and timing must be optimised *at every RPM vs Load* point for the engine; in other words, at all different driving conditions. for example, we might want to enrich the fuel mixture at low RPMs, and to lean the fuel mixtures at high RPMs. a resistor cannot adapt and will enrich the fueling at *every* point, under every driving condition, even the ones where doing so will result in reduced power.
this is why the utimate in ECU tuning is always done on a dyno, so the fueling and timing can be optimised under all the different driving conditions, for *your* specific engine, in its current state of wear and manufacturing tolerance. good power gains can also be seen with a replacement map (aka ECU flashing) that contains more aggressive fueling and timing settings
this is at least this is my understanding of the process. someone who is an actual tuner can probably correct anything wrong i've said above :)