I just failed the idle part of my emissions (barely passed on the cruise portion, but did).

I had 1229 PPM of HC, and the limit is 220. So it wasn't even close. It's a 396 LT1 w/ 236/236 cam, long tube headers and no cats.

I leaded it out as much as I could for the retest (I have a FAST system with wideband) and the headers cooked my brake booster which now leaks (Arrrgh!). That only brought it to 1000.

Given that it got a little better when I went even leaner, I don't think it’s a lean misfire.

I'm running 28 degrees of timing at idle. I think I can improve some by doing down to 20 deg. I can add a gallon or two of alcohol to the tank, but I don't think that's going to help.

Anything else I can do to get a moderately big cam and no cats to pass at 220 ppm?

Thanks!
- Dave

 

nope

 

That was useful. Do you know this authoritatively? I can find posts that claim running 10-20% alcohol it will pass... but if your post contained actual content based on prior experience, I'd love to hear more detail.

 

try some cats.....they may be useful.

 

Dry some cats? You mean like with a blow dryer? What do I do with them once they're dry?

Any useful posts welcome...

(oh, I see you edited your post, so now I have to too)

 

I doubt you'll get anywhere without cats, but having had the same problem I can tell you that having the engine temp up to normal or stock levels (I have 180 stat) by turning fans off, helped me a lot. In fact, I think the main cause of my failure to pass on the first try was having the engine too cool. For insurance purposes, I retarded the timing to 12 degrees advance for anything beneath 3000 rpm, I bumped the idle up to 1150 rpm, and i put a full gallon of methyl hydrate in an almost empty tank. This did the trick for me.

 

i wasnt tryin to talk poo.....why dont you get some cats you can bolt in and out?

 

Does it have a blower or not? Does it have a "blower" cam (114 or greater LSA)? Overlap can be an issue, but not with a blower cam. How did you do on CO?

 

Yes, my cam is on 114 centers.

So you're recommending that I get cats with collectors on each end so I can replace them with an "off road" pipe?

 

yeah, whatever it takes to pass the test. just have some off road pipes to run untill smog time comes. i may do it later when i get some cash. it will lengthen the life of my cats too id imagine...

 

You needs cats and an emision tune or cash to get you a sticker. But no way in hell is that thing going to pass with no cats.

 

Well, with timing and alcohol I got it down from 1200 to 570, but that's still a ways from 220. Made an appointment with the local muffler shop to look at putting cats on it this Thursday...

 

I think the Cats are really going to help you out on this one. I don't see how there was anyway, even with alcohol you were going to get a 396 with a cam to pass. Where do you live?

 

Hydrocarbons is unburned crpa in the exhaust. Something cats would be more then happy to burn off/deal with. That's why you pass at cruise and not idle, overlap and big duration means lots of excess out the tailpipe at idle

 

If you were in CA I doubt you could pass at all with that cam. You may
have a chance with cats. Good luck.