afratioitem
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afratioitem [2008/01/29 13:46] twdorris created |
afratioitem [2008/01/29 13:49] twdorris |
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| ====== Estimated A/F ratio ====== | ====== Estimated A/F ratio ====== | ||
| - | The A/F Ratio display item causes more confusion than any other. But it's really very simple. It's basically taking __mass__ airflow data reported from the datalog and dividing it by __mass__ fuel flow data. The calculate __mass__ fuel flow, the display item uses injector pulsewidth data from the datalog and the flowrate of your injectors along with the specific gravity of the fuel you're running. | + | The A/F Ratio display item causes more confusion than any other. But it's really very simple. It's basically taking __mass__ airflow data reported from the datalog and dividing it by __mass__ fuel flow data to arrive at an estimated A/F ratio. To calculate __mass__ fuel flow, the display item uses injector pulsewidth data from the datalog and the true (more on this below) flowrate of your injectors along with the specific gravity of the fuel you're running. |
| What's confusing many times is that you have to **TELL** the A/F Ratio display item the flowrate of your injectors. It doesn't know and can't assume that the global fuel scalar is correct. You configure the A/F Ratio display item the same way you configure other display items. Right click on the A/F Ratio label in the graph legend and select "Props". Fuel specific gravity data will be available from your fuel supplier. C16 race fuel, for example, will have a very different specific gravity than regular Exxon pumpgas. | What's confusing many times is that you have to **TELL** the A/F Ratio display item the flowrate of your injectors. It doesn't know and can't assume that the global fuel scalar is correct. You configure the A/F Ratio display item the same way you configure other display items. Right click on the A/F Ratio label in the graph legend and select "Props". Fuel specific gravity data will be available from your fuel supplier. C16 race fuel, for example, will have a very different specific gravity than regular Exxon pumpgas. | ||
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| ===== IMPORTANT 1G NOTE ===== | ===== IMPORTANT 1G NOTE ===== | ||
| - | From the factory, manual transmission 1G DSMs came with a base fuel pressure of 37psi. The ECU, of course, knew this and calculated fuel delivery based on the assumption that you were running 450cc injectors at 37psi. Most injectors are rated at 43.5psi, however. Including those 450cc injectors installed on the 1G DSMs. So that 450cc/min rating is not the actual flowrate into the engine. The actual flowrate is closer to 415cc/min: | + | From the factory, manual transmission 1G DSMs came with a base fuel pressure of 37psi. However, most injectors are rated at 43.5psi, including those 450cc injectors installed on the 1G DSMs. So that 450cc/min rating is not the real flowrate into the engine. The actual flowrate is closer to 415cc/min: |
| 450 * sqrt( 37 / 43.5 ) = 415 | 450 * sqrt( 37 / 43.5 ) = 415 | ||
afratioitem.txt ยท Last modified: 2024/03/15 11:16 (external edit)
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