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Rotational Idle & Cats

GTS-t VSPEC

By GTS-t VSPEC,
in Engines & Forced Induction

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GTS-t VSPEC Grand Master

GTS-t VSPEC

Posted
Posted

Hi Guys,

I am planning on running rotational idle with my engine management system, I have been told that in order to do this I have to remove my cat(catalytic converter, not the furry variety). I was wondering whether anyone knows if this is true and secondly why.

I believe rotational idle works by not firing a cylinder, and it does this in on different cylinders for every full crank rotation. The reason you do this is that by not firing the cylinder it aids in cooling the engine and the turbo. If anyone has more info or a correction then please let me know.

See'ya:burnout:

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https://www.sau.com.au/forums/topic/9032-rotational-idle-cats/
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MetBlue_GTST Community Regular

MetBlue_GTST

Posted
Posted

I'm actually running rotational idle on my car right now and i have a cat... Runs beautifully!!!! May i ask where you heard such nonsense???

Also what engine management are you running??? I've got Autronic SM2 v1.94...

And yeah your right about how the rotational idle works...

gtrken Grand Master

gtrken

Posted
Posted

Nothing wrong with rotational idle per se' but when the cylinder is not firing the injector still is. What it's doing is dumping raw fuel into the exhaust which helps cool the turbo but then eventually ends up in the cat.

I would suggest that over an extended period of time it will be to the detriment of the cat.

Also , it would never pass an idle emissions test.

Ken

kjb_r33 Experienced

kjb_r33

Posted
Posted

not evren close, if the engine is wired up for sequential injection, which it should be, you would cut out injection pulses, not spark pulses...... no fuel, no damage to cat...

and its would be the unburnt/unburning air that cools.....

same way that from the AU falcon up, you could run the engine with NO coolant at all, it stops injection on alternating cyl's, the air passing straight through kewls the engine....

GTS-t VSPEC Grand Master

GTS-t VSPEC

Posted
  • Author
Posted

I was pretty sure that the fuel was still being dumped into the cylinder, you get flames coming from the exhaust so I assume that is unburnt fuel being ignited when it exits the exhaust.

Ken, I'm not too worried about passing an emmisions test, the rotational idle will be on a switch, and I'll keep my orginal muffler and cat in case I need to replace it for the pits.

See'ya:burnout:

GTS-t VSPEC Grand Master

GTS-t VSPEC

Posted
  • Author
Posted

MetBLUE_GTST,

Thanks for the info, I'll be running it on my Wolf Ver4, it has both rotational idle and anti-lag now, with launch-control coming aswell. It will probably work OK with a cat in but does it destroy the cat's function?

I don't mind removing the cat, but I'd be happier to keep it in, then the cops have nothing to worry me about. It is a high-flow cat anyway, so if I don't have to remove it then I won't.

See'ya:burnout:

MetBlue_GTST Community Regular

MetBlue_GTST

Posted
Posted

There aren't any flames out the exhaust, it cuts the injectors, the idling engine is only idling on 5 injectors....

And yes the benefits are huge!!! During tuning of my autronic and power runs with the ambient temp of 37degrees inside the dyno shop the engine was running really hot and after a period of 30 seconds to a minute the engine temps went from 90+degrees down to 80degrees...

GTS-t VSPEC Grand Master

GTS-t VSPEC

Posted
  • Author
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MetBLUE_GTST,

On the car I saw it running on there were small flames popping out of the exhaust, and they said this was normal.

It's good that it does cool the car down quickly, more sensible than a turbo timer.

Thanks for your help.

See'ya:burnout:

gtrken Grand Master

gtrken

Posted
Posted
Originally posted by MetBlue_GTST

The Autronic management shuts down the injectors, not the spark... If you have a look at the monitor all function in the software you can see all the injector pulses shutting down and coming back up in a rotational manner...

Oops , MetBlue is correct and I am wwwrrooo.. , I am wwwwrrooonnn....... Bugger , I ain't right.

Was getting a bit mixed up with antilag. Checked with the guru ( who tuned Mets car ) and he straightened it out.

What it does do is the throttle is open a certain percentage all the time and it's the unburnt air passing thru that helps cool it down quickly.

Cheers

Ken

gtrken Grand Master

gtrken

Posted
Posted
Originally posted by MetBlue_GTST

The only way flames could be coming out would be from anti-lag, but anti-lag doesn't work while the car is idling....

I wouldn't throw away the turbo timer though...

Antilag can be set for a certain time period after the throttle is shut ( ie. idling )

With the Group N subarus we usually run it for about 10-15 secs before it resorts to rotational idle.

Thats maybe where phptf saw it , especially if it's set for a long time.

Now THAT will bugger the cat.

Cheers

Ken

Roy Grand Master

Roy

Posted
Posted

If unburnt fuel is passing into the exhaust manifold, am i right in assuming that it will ignite in the hot exhaust manifod, ie an exhaust pulse will still propogate thru the exhuast spinning the turbo, ie similar to anti-lag.

Dont know exactly know how rotational idle works but i assume only air passes thru the head whereby doing the cooling, not fuel???

Another question, have they refined anti lag systems so that they dont chew thru turbos, or is this still a side effect of boost at idle.

[

GTS-t VSPEC Grand Master

GTS-t VSPEC

Posted
  • Author
Posted

Thanks for the further info guys. So it sounds like rotational idle is good to cool then engine back down, but what about the anti-lag? Is it good/bad for the turbo, and when should it be used, on the track or drags?

See'ya:burnout:

MetBlue_GTST Community Regular

MetBlue_GTST

Posted
Posted

Yes the butterfly in the throttle body is open, its open about 15% but the ecu TPC is reset to 0%... This allows the engine to suck in the large volume of air required.... Rotational idle is awesome and sounds awesome too! Takes a bit to get used to when city driving...

That Subaru group N anti-lag delay can be setup in the autronic software or off a switch, personally i prefer the switch for the coppers (although i can't run anti-lag at the moment, read next post)...

Okay for a good explaination of rotational idle is the second paragraph of GTS-t VSPEC's first post... The way that the cylinder is not "fired" is through an injector being turned off.. EG. ECU turns injector 1 off and runs injectors + spark for cylinders 2 to 6, then it turns injector 2 off and runs injectors + spark for cylinders 1, 3 to 6, then turns injector 3 off and runs injectors + spark for cylinders 1, 2, 4 to 6 and etc. continually until the throttle is opened more than 1% then the engine runs normally...

GTS-t VSPEC Grand Master

GTS-t VSPEC

Posted
  • Author
Posted

For an anti-lag setup thay tend to use a kicker on the throttle body, which is a solenoid which opens the throttle body 10-15%. The extra airflow causes the exhaust wheel to spin and spool up the turbine, therefore the car is always ready to produce boost with no lag. Is that right?

See'ya:burnout:

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