how high can you safely rev a stock F20c?
10-25-2010, 10:11 AM
#2
I think that depends on the tune, and how you plan to drive it. I would bet that a stock S2000 might reach 9200 with the stock ECU in 1st gear, since the ECU's calculated RPM lags behind the actual crank speed. So basically, if you will be doing lots of 1st gear romps to the rev limit, you'll need to lower the rev limit. If you tune the ignition and fuel maps very conservatively at the end, so that the very top of the RPM range doesn't have as much power (to prevent overshoot), and you are carefull in the lower gears, then you can put the limit a bit higher.
10-25-2010, 04:12 PM
#4
Thread Starter
Originally Posted by gernby,Oct 25 2010, 10:11 AM
I think that depends on the tune, and how you plan to drive it. I would bet that a stock S2000 might reach 9200 with the stock ECU in 1st gear, since the ECU's calculated RPM lags behind the actual crank speed. So basically, if you will be doing lots of 1st gear romps to the rev limit, you'll need to lower the rev limit. If you tune the ignition and fuel maps very conservatively at the end, so that the very top of the RPM range doesn't have as much power (to prevent overshoot), and you are carefull in the lower gears, then you can put the limit a bit higher.
40k miles with AP2 retainers
10-25-2010, 06:03 PM
#6
Originally Posted by chris_barry,Oct 25 2010, 08:32 PM
Not true. The ECU calculates the engine speed down to parts of a revolution. If it didnt it wouldnt be able to fire the individual ignition coils or time the fuel injectors to fire when the valves are open. There is no lag in the ECU's calculation of crankshaft rpm.
Do you want the datalogs?
10-25-2010, 06:25 PM
#7
BTW, I do agree that there is at least 1 part of the ECU that knows how fast the crank is turning with GREAT accuracy. If not, the injector phasing and ignition timing would be all over the place. What I doubt is that the main processor of the ECU really knows.
When I developed my 1st piggy back ECU back in '03, one of the most challenging parts of the project was getting a good RPM calculation. The timers available in the processor just didn't have the resolution for calculating it with precision, especially at high RPMs.
I may be wrong, but I believe the OEM ECU has hardware based timer circuits for the injectors and ignition coils, and I think the ECU just sends parameters to those circuits based on its lookups.
One thing that sort of cemented this in my mind was that would be the only reason why I think you would want or need ignition timing by gear.
When I developed my 1st piggy back ECU back in '03, one of the most challenging parts of the project was getting a good RPM calculation. The timers available in the processor just didn't have the resolution for calculating it with precision, especially at high RPMs.
I may be wrong, but I believe the OEM ECU has hardware based timer circuits for the injectors and ignition coils, and I think the ECU just sends parameters to those circuits based on its lookups.
One thing that sort of cemented this in my mind was that would be the only reason why I think you would want or need ignition timing by gear.
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10-26-2010, 06:25 AM
#9
One thing that I thought of last night is that the accuracy of the ECU's RPM calculation will be much higher at low RPMs than it is at high RPMs, no matter what. So the biggest error in RPM will be at the rev limit. When I calculate the effect that it would have on ignition timing and fuel injector phase, it seems to just have the effect of retarding the ignition and injectors by about 8 degrees. Since the injectors are already spraying at about 90% duty, most of the time, they are spraying on closed valves anyway.