??s on EFI on controlling emissions

[tcbnj]

I searched this topic and did not see any reference from a prior post.

Assuming that tuning a factory EFI can 'pre-select' the air fuel ratio for a predetermined RPM and engine load:

Is it true to say that a good tuner can reduce the potentially higher emissions that would otherwise result from installing a bigger camshaft and/or higher ratio rockers arms?

If this is not true, could someone explain why not?

My question is the result of hearing that bigger cams and/or higher ratio rockers arms pass more fuel past the valve, but if an EFI is correctly tuned, these mods should pass more "fuel mixture" pass the valves which under light load and a cruising RPM should be ~ 14.7:1 which therefore would not result in higher emissions.

Isn't this what that factory is doing with motors such as the LS6 vs the LS1?

[squirrel]

Re: ??s on EFI on controlling emissions

I think the problem is that you get too much mixture dilution at low rpm because of the long overlap with a big cam, which causes the engine to misfire, and have high HC emissions. Nothing you can do about this with tuning, notice that all our old carb equipped cars idle rough no matter how we set the idle mixture screws.

[TheSilverBuick]

Re: ??s on EFI on controlling emissions

The LS factory cams still run a 116-117 LSA to keep overlap to a minimum and prevent raw fuel from going straight into the exhaust at low rpm (keeps emissions low). Too much overlap and the car won't idle at 14.7:1, unless the idle is set pretty high. It all comes down to overlap and engine speed, leaning it out will only cause a rough running engine that probably will still mis-fire enough to spike the HC's.

[dieselgeek]

Re: ??s on EFI on controlling emissions

Yep, it's the physical nature of the cam design - optimized for power at high RPM, trades emissions and "best" operation at low RPM, idle etc.

If you were to just lean out the mixture to where the exhaust shows stoich, the mixture will be too lean in the combustion chambers to run the engine.

-scott

[CDMBill]

Re: ??s on EFI on controlling emissions

That said the ability to more precisely control mixture as measured by AFR does give you better response and much better part throttle cruise and idle stability plus MPG. I have seen huge gains (+20-60%) after my carb to EFI swap. My carb was pretty well dialed in with air bleed and emulsion well feed adjustments made on a chassis dyno. Its the adjustability of an EFI set up like Mega squirt or in my case EMSPro that gives you much finer control over the full range of parameters like you would with accelerator pump cams and squirters, bleeds, well jets etc. all without having to disassemble the carb for every little change.

I have a pile of money in jets, power valves, air bleeds, squirters, pindrills blah blah blah, and now I can make a cam change or manifold change or whatever and dial it in with the keyboard driving down the road. Some new technology is worth the time money and learning curve.

[squirrel]

Re: ??s on EFI on controlling emissions

Do you have to pass a smog test with your Mustang?

[tcbnj]

Re: ??s on EFI on controlling emissions

The LS factory cams still run a 116-117 LSA to keep overlap to a minimum and prevent raw fuel from going straight into the exhaust at low rpm (keeps emissions low). Too much overlap and the car won't idle at 14.7:1, unless the idle is set pretty high. It all comes down to overlap and engine speed, leaning it out will only cause a rough running engine that probably will still misfire enough to spike the HC's.

To all that responded - this is good stuff - the unfortunate concerns of a junkie with late model junk.

A) Following up on TSB's response - It should be true then that increasing the rocker arm ratio while the keeping the stock LS2 cam should not impact cruising emissions, correct?

B) If (A) is true then a LS2 performance cam with a ~ 116 LSA should also not impact cruising emissions, correct?

C) If (B) is true, what aspect of a performance cam other than LSA affects emissions - lift and/or duration and at what point do they become a problem?

Thanks

[TheSilverBuick]

Re: ??s on EFI on controlling emissions

The LS factory cams still run a 116-117 LSA to keep overlap to a minimum and prevent raw fuel from going straight into the exhaust at low rpm (keeps emissions low). Too much overlap and the car won't idle at 14.7:1, unless the idle is set pretty high. It all comes down to overlap and engine speed, leaning it out will only cause a rough running engine that probably will still misfire enough to spike the HC's.

To all that responded - this is good stuff - the unfortunate concerns of a junkie with late model junk.

A) Following up on TSB's response - It should be true then that increasing the rocker arm ratio while the keeping the stock LS2 cam should not impact cruising emissions, correct?

B) If (A) is true then a LS2 performance cam with a ~ 116 LSA should also not impact cruising emissions, correct?

C) If (B) is true, what aspect of a performance cam other than LSA affects emissions - lift and/or duration and at what point do they become a problem?

Thanks

My understanding of cam spec changes to how they effect other parts of the valve timing, namely overlap is very poor. But I would think with a larger rocker ratio you only open the valves faster, so the net overlap doesn't change much. I believe at cruise it is easier to lean out the engine to a 14.7:1 and keep it running decently with some overlap and HC emissions would be kept in check, but I think leaning it out too much will up the NOx.

As for "C", I'd check the specs on cams offered for your engine (like from comp, crane, etc) that are certified for emission legal and see what boundaries they push. Might just be faster ramp rates with more lift to still keep overlap at bay, but at the same time they may be fudging in some more overlap and still pull under the emission requirements.

I'm currently trying to figure out the same things, only I want HC's to be low for fuel mileage instead of emissions and I'm completely ignoring NOx for now (to run lean while cruising and run more timing). That way if I ever move back to a place that does emission testing I'd just be two cats, an electric smog pump and a software tweak away from tail pipe emission compliance (granted the 1977 regulations are much looser).