I made a sort of informal poll in another section of this board regarding people with larger cams in their LT1's and if they passed emmissions or not. Just from looking at the completely unscientific responses it seemed that guys running a 383 were able to pass emmissions no problem while the stock displacement guys were failing.

The reason I am making this thread is that I am about to have to start over with my motor. The block cracked due to an overheating issue and I have a clean slate to start with so to speak. The only catch is that the car has to pass TN emmissions. I was able to pass no problem with the HOTcam and ported heads. If a stroker will make it to where I can run a bigger cam and still squeeze by the emmissions standard I would like to do so, because with the new motor I want to go larger than the HOTcam anyway.

So tell me, does a larger displacement motor put out less hydrocarbons and carbon monoxide than a smaller displacement motor, holding all things beside displacement equal? Keep in mind the emmissions testing is done at idle with the car in neutral.

 

I'm not 100% sure, but i think a longer stroke will help your cause.

and emissions is PPM, not total sum; just FYI

the big thing is calibration, calibration, calibration.

you'd be suprised what will pass with propper calibration.

please note: calibrations is NOT 3 pulls on a dyno

 

All else held equal, I beleive smaller bore motors have a natural advantage from what I have heard. Flame front has less distance to travel away from the plug to consume the A/F mix completely and efficiently. Of course, things are never "equal" in the real world.

Look at just about any modern engine and you'll notice that the bore/stroke ratio is lower than a lot of older engines, even if they are still only using 2 valves per cylinder. For instance, compare the LS-1 to an earlier 350. 4-valve engines often have a stroke that is equal to or GREATER than the bore. They can still get good flow from the heads on a small bore engine becuase they have 4 valves to work with. Not all, not always, but it's often true.

 

A larger engine can tolerate more overlap with the same effect on power band and emissions. Mostly, a larger engine has more swept volume which allows it to still pull a decent vacuum…

Past that, crevice volume, chamber design, compression, tuning… all have a major affect on emissions.

Be warned, if the enviro idiots have their way new standards that set maximum CO2 limits will hurt big engines since more displacement results in more end gasses no matter how clean the engine is and CO2 will go up with displacement. If this does come to pass, I suspect that they will set standards for older vehicles based on their original displacement, and since almost no cars (no cars?) came with a displacement greater then 350ci in the 80’s/90’sI suspect the limit will be somewhere in that range.