User 121020

There has been some discussion in the R&C forum: SCCA STR prep thread about how the stock ECU limits the revs. A lot of us regularly hit the rev limiter or even drive on it momentarily during auto-x events.

We've noticed two different behaviors with the limiter -

1. If you approach it at part throttle, say in 1st gear, you'll get a "ba ba ba ba ba" response from the engine when you reach the limiter.

2. If you approach the limiter at full throttle, the response is different - "buuuuuuuuh ba ba ba..." (Yes, I know. My descriptions are very techinical.) The extended power cut seems to happen when you've reached an RPM above where the high frequency limiter keeps the engine and will continue to cut power until the RPM drops enough.

I'm hoping someone here has more intimate knowledge of the stock ECU programming and can explain how the rev limiter works. Does it use timing retard initially and fuel cut if the revs are greater than the timing retard RPM limit? That's my theory...but I'm definitely not an expert...

Thanks!

Gernby

I'm not certain about this, but looking at the dalogs from my FlashPro, it seems to just be a difference in "overshoot" based on throttle position. The throttle plate does not close, and the ignition doesn't appear to be altered. What does appear to happen is that the injectors are simply not spraying when the RPMs go above 8K, but they do spray at full duty below 8K. Since there is some delay in RPM calculation, the full throttle "spray" event in low gears can cause the RPMs to shoot over 8300 RPMs even after the fuel has been cut. This means that the RPMs have to fall over 300 RPMs before the injectors will fire again. Basically, I believe hitting the rev limitter in higher gears or at partial throttle just results in less overshoot of the rev limit, so it doesn't seem as abrupt.

Gernby

This brings up a question about raising the rev limit. If I've raised my rev limit to 8500, then hitting the rev limitter at full throttle in 1st gear may result in the motor hitting almost 9K. That sounds pretty dangerous. Should the rev limit not be gear dependent?

User 121020

Interesting...

So there is no timing retard that occurs at the rev limit? Fuel cut is the only method it uses to control the RPM. My only means of logging timing advance/retard hasn't proven to be response enough to characterize the limiter events.

Thanks for the response.

Hondata

Hitting the rev limiter is bad - it puts a lot of stress on the engine.

Edit the rpm index so that you have a tuning point 100-200 below your rev limiter. Above this point retard the ignition as much as it will go. eg if your rev limiter is at 8200 rpm, insert a row at 8100 rpm. Then edit the ignition at 8000 to -20 degrees. This softens the rev limiter and reduces the stress on the engine.

Elroy

Learn something new everyday around here!

J

spectacle

Kpro docs state the launch control functions the same as the rev limiter...so is bouncing off that just as 'bad'?

Gernby

[QUOTE=Hondata,Dec 17 2009, 07:18 PM]Hitting the rev limiter is bad - it puts a lot of stress on the engine.

Edit the rpm index so that you have a tuning point 100-200 below your rev limiter.

Gernby

Would there be similar benefit in increasing the fuel for that last 100 RPMs of the rev range by ~10%?

prelude99

Hitting the rev limiter is bad is news to me. So does this mean the re-flash and flashpro pre-tuned maps with the 8600rpm limiter has retarded ignition at 8400rpm? So technically there's no point to going past 8400rpm which effectively makes your rev-limiter 8400rpm and not 8600rpm even tho the "bounce" occurs at 8600?