[theunchosen]

wow, good thread Bruce!

I had been wondering this myself but never got around to asking.

RK I'm sure knows more than I do as he is/was in the engine import business, but the grill block on cat side causes the lean burn to last longer because its making sure the cat stays at high enough temperature. During lean burn you are not emitting hydrocarbons at anywhere near the rate of stoich. So the cat is not really burning anything and is therefore cooling.

I would gamble that before the grill block your lean burn cycled on and off somewhat consistently?

The reason for this would be Honda had to make sure the vehicle would pass EPA under all driving conditions in all modes so if it starts getting too cool for the cat to function properly it kicks back over to heat it back up. The Grill block allows for more heat soak to the cat.

I'm not completely solid on its emissions scrubbing for NOx and SOx under lean burn so I can't say whether or not it needs the heat for those processes or whether its just keeping it toasty should you all of a sudden need to gas it and drop out of lean burn and emit HC's.

update: After searching I was unable to locate anyone actually talking about how the cat scrubs NOx and SOx or if it does that effectively. Everyone else just wants to know how to switch to standard cat so they can put performance headers on. I could have searched for the wrong tags, but the threads I hit all involved that issue even if they wer mistitled to describe how it worked. If anyone has an owners manual it may be in there and that would definitely be the easiest place to look as it has a table of contents and isn't as misguided as most forums.