Ais removal and Cat

[paulius]

Hello from Lithuania! What a great forum - helped me a lot with all the bulldog mods.

Just have one question which I can't seem to find the answer to.

I have recently installed Topham / Mikuni kit with a bigger air inlet, 132.5 main jets, and also size 20 pilot jets. The exhaust has also been upgraded with the krause end pieces (big thanks to Eddie! ).

Then I also thought about removing the AIS from the bike. Just on the same occasion, before adjusting CO. But. It is a 2006 bulldog with the CATalyst in the exhaust system. And I've read on the VStart site that removing AIS and leaving CAT makes the exhaust getting too hot - something about AIS cooling down the CAT?

Here, under AIS removal: http://www.sloneservices.com/SilverBack ... 05.htm#AIS
they write: "WARNING: DO NOT Remove or Plug the AIS system with bikes having catalytic converters still installed. Doing so could cause a fire!!"

So. My question is - should I leave the AIS in peace? Anyone has the experience with CAT without AIS?

Thank you,
Paulius

[Axman]

Hi Paulius,

we haven´t heard (yet?) of fire caused by the catalytic converter getting too hot because of the AIS system being removed.
But it seems to be logical : the AIS-System blows fresh air into the exhaust manifold after combustion, thus "diluting" and "leaning" the exhaust gases. As the catalytic converter is inside the silencer-cans, you can only circumvent this problem by fitting aftermarket silencers (BOS is the most popular here but you can fit whatever you like if it is made for the Bulldog)

Or leave the AIS in place..

By the way..removing the original silencers with the Cats does not in any way influence the engine performance as the cats only have a "alibi-funktion"

greets

Axman

[paulius]

Thank you, Axman! Nice to hear an expert opinion.

OK, I see - Cat sits in the exhausts, and replacing them to aftermarket ones solves the issue.

But I will not be buying another exhaust anytime soon I think - I am very happy with the Krause / Eddie end pieces I've got installed.

But I wonder - maybe with those bigger exhaust outlets and a better air flow it is not a problem after all?

I've got everything I need to remove AIS, so I might try just for fun to remove it, and then if it gets too hot.. put it back on. Some temporary heat wouldn't ruin anything right?

Regards
Paulius

[Axman]

Hi Paulius,

removing the AIS and getting everything airtight afterwards is not as easy as it seems..but, to tell you the truth..I really don´t understand all this "AIS-removing-hype" The AIS is on the bike for a reason..removing it doesn´t improve anything.

As the cats are inside the silencers the ehaust gasses have to pass it first... putting on the Krause-endcaps will definitly not cure the overheating..except the sound..that will definitly be much better.

Greets

Axman

[paulius]

Hi,

Well, if the reason for the AIS would only be the emission control law, I would remove it.
But now when it seems that for the exhausts with cat it has a better function too, it is maybe wise to leave it.

Again something about catalytic converters - from a general mechanic site:

"Necessary oxygen required for catalytic reaction is provided to the converter by air induction system. ... Any engine malfunction that will expose the catalysts to excessive amounts of unburnt fuel will severely overheat the catalyst and impair its efficiency and its life."

http://mech-power.blogspot.com/2008_09_01_archive.html

Regards,
Paulius

[Axman]

Again something about catalytic converters - from a general mechanic site:

"Necessary oxygen required for catalytic reaction is provided to the converter by air induction system. ... Any engine malfunction that will expose the catalysts to excessive amounts of unburnt fuel will severely overheat the catalyst and impair its efficiency and its life"

Regards,
Paulius[/quote]

Hi aigain,

that´s exactly it! there is a big difference in "regulated" and "unregulated" cats. Regulated cats - they only work with fuel injection - have a Lambda-Sensor in the exhaust that controls the "quality" of the exhaust gases. If they are off a preselected chart, the injection computer changes the amount of fuel (in relation to air) and the ignition timing till the composition is right and the cat has the best cleaning effect. This whole matter is much more complicated than my attempt to explain it, but you get the gist..I hope

Unregulated cats - like on the Bulldog - only work when the composition of the exhaust gases are accidentally right..they have an efficiency rate of max 15%. Which leads some people to say, that it is better than nothing. But it isn´t..from the factory the Bulldog comes with carburetor settings thar are much too lean. I´ve seen engines that have to run with 0,8% of CO while the correct setting is 4,5 to 5,0% That is why the correct setting of the CO has to be done using the studs on the exhaust headers (not in the silencers!) and with the AIS disconnected.

I hope I didn´t bore you with these explanations, but people keep asking me, why I say that the Bulldogs cats only have a alibi function..

Keep up the good work

Axman

p.s.: are you coming to the "9th International Bulldog Meeting" in June?

[paulius]

Thanks for the explanation, it is good to know.

Yes, I would love to come to the international meeting. But probably next year - have to plan it a bit earlier. I checked - it would take 2 full days of riding only to get to saarland.Thats is without getting lost and so on.

See you then,
Paulius