If the combustion chamber is different, then why did you use it as data in a compression discussion? We're not comparing apples to apples if you bring up different chamber designs...

 

Let me see if I understand this...I've heard folks say that a stroker will swallow up a small cam and some folks even have said that a pretty choppy cam in a 350 will sound pretty mild in a 383. Does that necessarily mean that because of the extra cubic inches, I can go up on lift, or duration, while being able to stay within the emissions limits? Which has more of an effect on emissions? Lift or duration? I was considering the gmpp 846. Has anyone used this and passed the sniffer test? Thanks again for the replies.

 

Duration. The longer the two valves are open at the same time, the more unburned fuel enters the exhaust. That will in turn boost hydrocarbon and carbon monoxide content.

 

I passed emmisions with a cat convertor, without it, I didn't even come close. My exhaust is flanged to pull the cat in and out and put a gutted one or straight pipe in when I want more air.

 

What Doc mentioned, regarding stroke, or more accurately the increase of same, reducing the severity of a larger cam is understood. I believe he is, in the same 'breath', leading one to equate that the increase in stroke will also make it easier for a larger cam to pass emissions. This is also a fair and understood comment. However, it is little more than a generalization. Big Dave, it looks like you (or someone) will need to test for the different effect on emissions of the 383 with the 224/230 cam to say, the 230/236 cam, with the same overlap, lift and rate of lift. (This would be necessary to reduce the variables to one, duration.) I state this, cuz I'm confident you really would like to know how big, (to utilize as much of the 383 potential as possible) can you go, and still pass the emission requirement. You are not alone.

As alluded to in my statement above, not just duration having an effect on emissions, but also overlap, and lift, or rather the rate of lift, which will affect the area under the duration curve, will affect emissions. There was a relevant thread in LT1 Tech in the past week that touched on this topic.

 

I'm not sure I believe that you could go another 10º @ .050" with a 383, but it is 9% more cubes, so mebbe you could, but it will clean up a cam no doubt, proven here in CA.

 

Maybe a person could 'backdoor' it by asking/knowing what duration/overlap at .050" will pass a Cal emission in a 350. Or, at least get a closer approximation in a 383, by realizing what passes in a 350. So, what is known to pass with a 350 in Cal?

 

Problem is, that stuff depends on the ability of the tuner, and whatever tricks might be used. A 305 or a Hotcam will easily pass provided again tuning and car is up to snuff, some have passed larger.

 

One of the cams I was considering was the gmpp 846 which has the same duration and lsa as mine (222/230, 112) but has a bit more lift. (550ish/560ish) to my (.533/.544)This is why one of my questions was whether duration or lift would have a more negative effect on emmisions.