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curtis73 02-04-2008 12:28 AM

cam LSA and CA smog
I'm pretty new to the CA smog thing, so I have some questions. The car in question is an OBD2; a 96 Impala SS. I'm building my LT1 into a 383, 11:1, ported aluminum heads and a GMPP 846 cam (222/230 with 112 LSA). Many of the guys in the SS clubs have done this and it will pass the sniffer just fine with careful tuning.

After some careful searching, I really want to install the ICL at 107 to be ideal, but that puts the exhaust lobe too far ahead. To do it "right" would be to use a 108 LSA, but that's too narrow for a street EFI car with power brakes. I thought about having Crane custom grind me that cam on a 110 LSA to split the difference. Desktop Dyno sure likes it :)

Does CA test idle sniffer, or just the 15 and 25 mph? How will a narrower LSA affect the 15 and 25 mph tests?

kwopper07 02-04-2008 11:29 AM

that new of a car you will have to smog forever.i whouldnt custom grind anything i whould get one with a carb e.o. number i know you dont want to hear that but smog here is no fun to fight.

curtis73 02-04-2008 01:29 PM

the 846 cam seems to be a slam dunk with the sniffers in its as-ground LSA. I just wonder what the 110 LSA would do to cruise emissions.

oldbogie 02-04-2008 02:12 PM


Originally Posted by curtis73
the 846 cam seems to be a slam dunk with the sniffers in its as-ground LSA. I just wonder what the 110 LSA would do to cruise emissions.

Emissions go up as the LSA gets smaller. But if you're running sequential injection this can be managed by when you inject fuel. Holding off till the overlap is finished will not degrade emissions. But reducing the LSA degrades manifold signal which neither EFI or carbs deal with well. Typically to make up for lost signal the injection or carb is run excessively rich. This isn't good for emissions, mileage, or upper cylinder lubrication but it does improve power a bit.

Typically factory engines are significantly better at emissions than they need to be, because the law put meeting emission standards on the factory for a 100,000 miles without the owner maintaining the motor. You can eat into that cushion with hot rod mods, but then you have to stay on top of the state of tune and the wearing condition of the engine to remain legal.


rreruption 02-04-2008 03:50 PM

its not an easy one I got my buddys 98 yukon to pass with his 383 and his was only 9.5:1 with about the same cam size but ground at a 112lsa with a 108 intake centerline I had to send the computer to be programed to handle this new set up the truck runs awesome now though

curtis73 02-04-2008 05:21 PM

Some guys on the Impala forums actually passed with the 846 cam in a 355 or 383 without touching the computer. It was a little on the rich side, but it still passed. After some proper tuning they're very clean. Not sure why its so different between the LT1 and the Vortec... unless he did it on stock heads. If his heads were stock it might have made things a tad rich, or if his knock sensor started pulling too much timing out. Those things have been known to happen.

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