I hate the "bad" rev limiter. You know the one... Its the one where you decide not to shift because the next corner is coming up and rather than just go "pop pop pop pop ..." the car tries to throw you out. (I guess it though you should have shifted )

Some people call the "bad" limiter the "wall."

Now don't confuse this with the engine too cold "wall." I'm talking about the ~9k limiter.

Why is there a bad limiter? Like all of the other car's I've ever driven just have a regular old pop pop pop limiter. Some have had longer duty cycles than other - but still - the power came on and went off and came on again. They never just shut the car down.

Why is it random? If I always got the "bad" limiter I would adjust my driving to make *certain* that I never hit it. But sometimes I just want to bounce the limiter a few times down a short straight - and it usually will just bounce.

So what is it? It is a limiter - or some engine safety thing? And if its and engine safety thing - what are the sensors that make it go off?

I know that you guys know your stuff... what's going on in that ECU?

Thanks!

-r

 

hmm, I've hit the limiter of the S2000 a couple of times... and it wasn't anything too dramatic... it's like the limiter on my B16 in the CRX... da da da da da da

 

There are a number of places on the track where a pace can make it is too early to brake and to late to shift.. I learn them and when I can anticipate just feather the gas a little. Does not make a notable difference in lap time and is probably easier on the car. I only experience the limiter in third so do not experience the 'wall' which I think has to do with the multiplication of engine braking by the lower gears.

 

There is probably a 2 stage rev limiter in our ECU. I'm assuming the S2K's ECU software works like some engine management software that I am personally very familiar with.

The first stage is a rotary misfire, either cutting fuel or spark or both (spark is the fastest reacting, most sure way, though). This is known as a soft limiter. I'd guess it cuts 1-2 cylinders per engine cycle (2 revs), and alternates cylinders. Stage two is a complete fuel cut. This is known as a hard limiter. Stage two exists in case you somehow get through stage 1. The hard cut is there to keep you out of valve float or spring surge.

I'm guessing you found stage two when trying to hold 1st gear. I belive that, other than going down a steep hill, you probably won't encounter stage 2 in any other gear (you would be the first I've heard of). I think that under some conditions, in first gear, the firing cylinders can work up enough of a hit to carry you through to stage 2. Then you hit the fuel shut off, and there is a bit of built in hysteresis to carry you down a couple hundred revs before turning the fuel back on. In higher gears, you have much more inertia to accelerate, so it should be very hard/impossible to blow through stage 1.

I've recorded some tach data during a short rev limit ride in 2nd gear, and the data shows the engine cycling between about 8950 and 9100 rpm. I'd guess the hard cut is just past 9100, maybe 9125 or 9150.

 

[QUOTE]Originally posted by Windscreen
[B]...
I'm guessing you found stage two when trying to hold 1st gear.

 

I've hit the 'hard' second stage many times in 2nd gear on autocross courses. In fact, it might be the culprit for my victory-robbing spin on my last Saturday run at the Peru Tour (after the finish lights.) I had a clean run up until that point, and then during a long fast accelerating left-hander I just spun when I think it hit the hard limiter (fast corner, but not at the limit). I hit two cones after the lights, among other damage.

To quote a friend 'I snatched defeat from the jaws of victory, as that run was over .5 faster and I lost the event by .1'

Needless to say I hate the 'hard' limiter... and the fuel starvation I had on Sunday! Man, what a weekend.

 

*BLEH* that's a better name than "bad"...

So yeah - I've hit the *BLEH* limiter in second too - and so have my co-drivers.

And I'm with JZR on the prediction issue. The fact that it does it - well it sucks - but there's nothing we can legally do for B Stock *except* understand why it happens. (Which is why I posted this.) I think if we understand it we can avoid it. So JZR I'd like to *try* to prove otherwise...

So Steve and Jason say 2 stage limiter - and that sounds about right. The hysteresis induced delay on the *BLEH* is brutal. It seems like -f o r e v e r- before the engine pulls again. AND the 2nd stage limiter does feel the same as a fuel starvation (I also hate long left hand sweepers - but that's a separate post )

So if someone has info about what variables the ECU is using to choose the BLEH that would be really useful.

As for prediction, I've noticed this:
If there's a portion of the course that induced the BLEH on the first run - it will do it again at that same portion on the next run.
AND if there's a portion of the course that induced the BA BA BA on the first run - it will do it again at that same portion on the next run.

Neither of these help you avoid the BLEH on the first run... But I have learned that if it hits on the first run that I should expect it to hit on the next - and that I should change something to avoid it. I used to think that it was random - and it was just bad luck on the first run. Then I'd get it again on the 2nd run. DOH!

-r

 

I've noticed that to be mostly true, but I've had BA BA BA areas on the first run become BLEH areas on the second... mainly when I nail the corner before the straight and get a better run going. Momentum seems to be key in the equation. I've found it hard to predict, so much so that I'm going to try a proactively avoid the limiter more. (not going to be easy)

 

Yes, I agree that we will never be able to predict which limiter is going to engage. There's probably a good chance, though, that you will encounter the stage 1 limiter for at least a few cycles before hitting stage 2.

Any ECU limiter that I've ever had the pleasure of calibrating was purely speed based. That said, I suppose it is possible that the ECU may look at rate of RPM change to predict how fast you're approaching the limiter. Consider too, that if the ECU samples RPM just as a cylinder fires, the instantaneous speed will be quite a bit higher than the actual mean speed for a given engine cycle (maybe 50 - 100 rpm). So, if you get unlucky enough to have an RPM sample occur at just the wrong time, blamo, stage 2.

Hmm, maybe its possible that I've hit it in 2nd and just don't remember. It's more likely that in top of 2nd gear situations I was driving like a wuss and didn't have my foot planted.

At this late hour, that's my theory and I'm sticking to it...for now


...and Jason, the Mistress thanks you for being proactive in this matter!

 

For the record - I hit the *BLEH* limiter in 3rd yesterday (getting on the fwy)... I don't think I want to try to hit it in 4th

Jason - I agree that if you change something (like nail a corner) you can change what limiter you get. But if I take the same corner the same way I'll get the same limiter. I've been bit too many times to think that it's random.

I'd like to be more proactive as well - but I don't think I'm good enough. I figure we have 2 options:
1) shift up - then downshift back at the next corner (if appropriate)
2) feather the throttle to hang right under redline

For 1) - I think I'll probably go shooting off the next corner trying to get back down a gear -- maybe too many things to do for me. If I decide to leave it in the up gear I'll probably get a wicked bog exiting the next corner. (Remember that I originally wanted to just BA BA BA on entry so I could power out of the next corner.)

For 2) - I run the risk of not accelerating fully - like feed in the gas too slow trying not to get to the limiter. I guess I could practice this one on the street - annoy the neighbors... race up to redline in first - feather just short of redline - hold at redline. But I'm betting that this would be a mess if I try it. I'm also betting that it would be faster to just bump the limiter... course I'd have to be bumping the BA BA BA to be faster - the BLEH ruins everything - thus the post.

ANYHOW

So can anyone point me to some documentation on how our ECU is working? Like what sensors its using and where the thresholds are for coming on and going off? I'm doubting that Honda published this - but its worth asking. Maybe some of the dyno guys have bumped the 2 different limiters on the rollers and know the rpm on/off points.

And don't let me overlook Windscreen's stuff... good stuff - and most probably what our ECU is doing - I just want to know more...


[QUOTE]Originally posted by Windscreen
[B]
Hmm, maybe its possible that I've hit it in 2nd and just don't remember.