Reving past the limiter

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Mobne_s13
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Reving past the limiter

Postby Mobne_s13 » Thu Jan 10, 2019 5:11 am

I have noticed in my logs that my engine can rev past the limiter.

I use fuel soft cut with the limiter at 8000 rpm.
Full sequential injection.

I often hit 8200rpm.

Is this normal? I now have to set it at 7800 to get it to stop completely at 8000.

Any ideas?

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HaltechMatthew
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Re: Reving past the limiter

Postby HaltechMatthew » Thu Jan 10, 2019 1:48 pm

It is always possible for this to occur with a fuel cut because fuel is sent in long before the spark event, so fuel is still present for an engine cycle after you cut it.

Mobne_s13
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Re: Reving past the limiter

Postby Mobne_s13 » Sat Jan 12, 2019 11:45 am

How come you can’t enable both fuel and ignition cut at the same time?

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Re: Reving past the limiter

Postby HaltechMatthew » Mon Jan 14, 2019 11:27 am

Because you will still get the delays when resuming power if you cut fuel, so nobody asks for it. For motorsport it is almost always ignition cut.

Mobne_s13
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Re: Reving past the limiter

Postby Mobne_s13 » Thu Jan 17, 2019 7:57 am

HaltechMatthew wrote:Because you will still get the delays when resuming power if you cut fuel, so nobody asks for it. For motorsport it is almost always ignition cut.


Yes but the s54b32 have issue with valve shims coming loose when cutting only ignition and a lot of excessive fuel ignites in the manifold.

If you could cut both I would of guess the exhaust bangs would be minimal because of the small amount of fuel left in the runners with sequential injection?

I’m not pleased with “no body asks for it”. I asks for it lol. I feel I often get that response and to me it just don’t feel right. There is so many different engines with its own issues so making it possible for the user to customize would be the best.

Many other ecu offer that kind of sulutions for rev limiting.
Please make it possible for the user to decide. There is no draw back with it I guess.

Please add in future firmware. Can’t be many seconds of programming.

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HaltechMatthew
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Re: Reving past the limiter

Postby HaltechMatthew » Thu Jan 17, 2019 12:47 pm

The problem with "no-one asks" is it gets knocked down the priority list compared with "everyone asks" requests. What you are asking for makes complete sense so I am not fighting you on it in any way. No request is ever ignored and it always goes into the database for people far higher up the tree here to make decisions on what the engineers will work on. Just often there are much larger priorities that not everyone knows about.

Have you also tried feeding more retard into the appropriate table when you are near the limit? This will also slow it down to prevent overshoot with a fuel cut.

Mobne_s13
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Re: Reving past the limiter

Postby Mobne_s13 » Thu Jan 17, 2019 4:41 pm

I know you have limited resources with the engineers.

But often the things I have been asking for is fast adjustments and not to remake the whole ecu.
Like the to add the canbus protocols for cam angle targets and error over canbus. That was like 1 year ago and still not added in the latest update.

Because “I’m the only one in the world” that want to log cam angle actual value against target with an motec dash.......


Atm i think its retarding about 10-15 degrees about 200rpm before redline.

This did make the egt rise some 50 degrees. I can try more retard. What is your suggestion?

Should the effective timing be close to zero to have an real impact?

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HaltechMatthew
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Re: Reving past the limiter

Postby HaltechMatthew » Fri Jan 18, 2019 10:19 am

You are more than welcome to apply for a job here and show everyone how quick it is to make a simple change. :D

There is far more going on than you may think and any time spend needs to be warranted. Especially when there are thousands of individual requests for functional changes and every one of them someone claims it is life or death for them. A good example lately has been trying to add support for the 86/BRZ CAN system which has maybe 100x people waiting and would take priority over the request for cam position data over CAN. It is not ignored, just priorotised together with how vital it is to keeping a vehicle running. In short we too want a perfect ECU but the closer you get to the pavement the more cracks you see and the bigger minor imperfections appear to be.

Just keep in mind that an EGT rise is not necessarily a combustion temp rise or dangerous to engine internals. You are just sending energy out the exhaust rather than the piston. So whatever retard is necessary for the short amount of time you are on the limit to get it under control I would not be too concerned about a 50C jump in the pipes. Getting near to TDC under these conditions is normal depending on the engine.

Mobne_s13
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Re: Reving past the limiter

Postby Mobne_s13 » Fri Jan 18, 2019 7:46 pm

I’m aware of that less timing is more gentle to the piston but runs the turbo hotter.
The manfold is made out of “black steel” piping.
That material is also a bit sensitive on high egt.

Now this is for such a short time. So you think running close to 0 advance about 50 rpm before final redline is a normal timing condition for what I want to do? And that it would limit my over shooting issue a bit? How high manifold temps can I ignore? Up to a 1000deg?

How come I don’t as a lean spot before the redline if the engine is running on left over fuels? I would expect it to go really lean then?

Mobne_s13
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Re: Reving past the limiter

Postby Mobne_s13 » Fri Jan 18, 2019 7:51 pm

HaltechMatthew wrote:You are more than welcome to apply for a job here and show everyone how quick it is to make a simple change. :D


That would be like a dream come tru mate ;)

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HaltechMatthew
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Re: Reving past the limiter

Postby HaltechMatthew » Mon Feb 04, 2019 2:11 pm

It is not a lean amount of fuel, it is the right amount of fuel over the last cycle of the engine.

Mobne_s13
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Re: Reving past the limiter

Postby Mobne_s13 » Mon Feb 11, 2019 9:33 pm

HaltechMatthew wrote:It is not a lean amount of fuel, it is the right amount of fuel over the last cycle of the engine.


Does it not cut all cylinders at the specified value?
If all injectors are cut at 8000rpm. How can it get fuel to go to 8200? What is driving the engine?

I still don’t really understand this?
It’s not a waste spark config so it should not get any fuel unless injected?

Or is this a soft cut issue? It starts to cut first cylinder at 8000 and it will then rev past target because of that?

Should I use injection hard cut instead to solve this?


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