You're right, modern engines of course are computer controlled. But that isn't the question. The gasoline, after all, has no way of knowing any of this.

The characteristic of NOX emissions in particular, which spike (relative to HC and CO) when the engine tuning and air fuel ratios are optomized for power and economy is well known, this is what the early smog regulations were designed to address. They basically crippled the motors with compression reductions, late valve timing - and lots of ignition timing jiggery-pokery.

Modern EFI especially means engines can run very lean air fuel mixtures, far leaner than any carbureted engine, I get that, but I'm still curious how they were able to reduce NOX emissions to acceptable levels, the kind and amount of pollutants is a basic characteristic of fuel combustion, regardless of how it gets there.

They don't need to retard the ignition timing anymore, they have reasonable compression. They can run maybe 18-1 AFR on the highway. This should make the NOX worse, not better. See where I'm going with that? Again, I figure it must be in large part due to better catalysts.

It would be interesting to see what the engineers thought back then trying to meet all the federal clean air rules. The basically traded power and economy to reduce NOX, and then burned all the wasted fuel in the tailpipe in the catalyst. Not the most elegant solution.

Actually, excessive NOX is as a result of a too lean mixture and/or calibration(s) out of sync -
- https://www.smogtips.com/failed-high-NO-nitric-oxide.cfm

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It's probably just aggregate improvements over the past 40 years or so.  Fuel management, as well as the overall engine, drivetrain and body design has improved.  Lot's of small changes over time result in big changes.


Lawrenceville, GA

Nox is formed when you introduce high heat and unburned fuel listed as HC.  So when you pump exhaust back into the engine via EGR systems it reduces cylinder temperature as well as reducing the amount of air/fuel which helps lower the production of Nox.  In modern cars there are some converters that actually combat Nox as well which is why many cars dont even have EGR valves now a days.

I have read that in some instances you can get a an egr effect with reversion with some cam designs which is quite interesting but for me I just got a plain old truck/tow cam from Crane in roller form with specs of 216*/224* @ 0.050" lift 112* lobe separation 107* intake center line and .520"/.542" lift.  Its more of an efficient setup and not so much focused on emission reduction.  I cant focus on emission reduction as Holley strongly stresses to not use emission systems with their EFI setup which is EGR, and catalytic converters.  So I am deleting my air injection pump, converters were gone long ago, egr will be gone which is why I am having the distributor recurved as it was curved for a emission era engine.  Only emission systems I will retain is my evap mainly to reduce raw fuel smell from my fuel tank and the PCV system.  As far as emissions goes I would be interested to do a snifer test on my truck once I am finished cause being that its fuel injected now the reduction in unburned fuel in theory should reduce the amount of Nox formed even with higher compression.  It is from my emission classes I took for work years ago that taught us that older high performance cars didnt produce as much Nox as they were high compression and had a more complete fuel burn.  The lower level of HC resulted in less Nox being formed, so with this in mind the FI setup should create lower Nox production due to a more efficient fuel delivery system even though its a TBI setup and not true MPI.

But that is why emission era engines can benefit from gutting emission systems and a big reason why I am doing that to my truck as the small block ford is just gimped too badly to the point it just doesnt feel that powerful.

1956 Ford Fairlane Town Sedan - 292 Y8 - Ford-O-Matic - 155,000 mi

Quotes From The Referring URL In My First Post -

1. Lean Fuel Mixture - Lean fuel mixtures cause high NOx. A lean fuel mixture exists when less fuel then required is delivered to the combustion chambers or when more air then necessary is added to the fuel. In either case the lack of gasoline needed to cool the combustion chambers down is not present. Combustion temperatures increase causing high nitric oxide emissions. A lean fuel condition may be due to a vacuum leak/s and/or defective fuel control components, such as the Air Flow Meter, Engine Coolant Temperature Sensor, and O2 sensors.

5. Engine Overheating - Inadequate engine cooling can will high NOx. If your vehicle's cooling system is not working efficiently, (i.e. bad radiator, thermostat, hoses) high NOx will be created. Remember high NOx nitric oxide is created when an engine's combustion chamber temperatures reach over 2500F. You will want to make sure your vehicle's cooling system is working properly, and your vehicle's temperature gauge is always indicating normal.

Too fat of a fuel curve will create excess HC and most likely overheat the CAT(S) and burn them.  

You say HOLLEY? Is it the SNIPER?

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See they are simplifying their whole "lean fuel mixture".  Lean fuel mixture will create higher combustion chamber temperatures and higher temperatures in the cylinders help to create Nox.  Even running a lean mixture there will still always be some unburned fuel in the cylinders.  A rich fuel mixture actually results in a cooler combustion chamber which is why I personally am going with the Holley fuel injection on my truck as I can have my fuel map set to go rich when under load which will reduce cylinder temperature and help prevent detonation.  A rich fuel mixture can help prevent Nox forming due to reducing combustion chamber temperatures but who would want to get worse gas mileage to offset the formation of Nox.  Thats where the EGR comes into play as it takes up cylinder space resulting in unburned HC being pulled back into the engine to give them a second time to burn and you are now squeezing less air/fuel into the cylinders reducing the temperature of said combustion chamber helping greatly to prevent the formation of Nox.

Like wise too rich will burn out your converters by making them run too hot.  You will know this is happening as you will have a rich sulfur smell which is the converters overheating.

Yep the setup I got for my truck is the Sniper, but I got the Stealth 4150 that looks like a holley 4150 dual feed carb.  I went with this one in the traditional gold finish as it was the only offering Holley has that comes with the ford kickdown to retain my C6 kick down rod without having to convert to a cable.  These units are great and Ive personally installed 7 of them at work in the last 3 years and the options that you can make this do is amazing as well.  I can set up idle speed to not just idle up when cold and idle down as engine warms up but I can also do like ford did with their temperature switch for vacuum advance to switch between manifold and ported at 225*F to idle the engine up to help cool the engine down by spinning the fan faster.  I can have the sniper do this as well.  Like wise I can wire in my A/C so the IAC will idle the engine up to a new idle speed setting when the AC is switched on and I can also program a TPS percent where the sniper can also cut the AC compressor circuit at wide open throttle like a late model car.  All of these features I will be using on my truck to get the most out of it, I am also going to invest in the AN flaring turret for my Eastwood flaring tool I have as I am thinking about pulling the entire 5/16" OE carb fuel line off my frame and running a new stainless steel 3/8" OE style fuel line and chop it up and AN flare it for my FI setup.  I can also use this to form a metal hard line from the simulated 4150 carb down to where the mechanical fuel pump would be and then use a small short piece of push lock hose to connect frame to engine.  More work but would help reduce the amount of rubber hose in the end.

Its why I wish Holley would make more retro looking FI setups, if they offered a Holley 4000 style FI setup I would seriously consider it for my Fairlane just because of the functionality of unit and the best part is no float issues with this ethanol blended fuels.

1956 Ford Fairlane Town Sedan - 292 Y8 - Ford-O-Matic - 155,000 mi

You really do not have to worry about being EMISSIONS COMPLIANT with just a CFI FUEL SYSTEM do you?

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Here is a basic tutorial describing timing advance -
https://www.hotrod.com/articles/set-ignition-curves-create-optimal-performance/

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Here in Texas like most states except for california once a vehicle hits 25 years old, such as my F150 which is a emission era truck but its over 25 years old you dont under go emission testing as its just a safety only inspection but by law your emission systems have to visually be there but they are not tested for functionality.  Most people doing state inspections today werent around when these vehicles were new so they wont know what has and hasnt been gutted and majority of the time they just pop the hood do a quick look and move along and dont act crazy about having systems on the vehicle.

States like California how ever they do emission testing back as far as 1975 I believe it is last time I checked unless they changed that.

Thats why for my truck I am gutting all emission systems as they do nothing but hinder the efficiency of the engine and lets face it in the grand scheme of things my single truck being driven daily racking up some 6,000 - 10,000 miles a year is not going to put out polution in any kind of level to have any real negative impact.  Its why most states do do emission testing on old vehicles as the first thing is there are so few 25+ year old vehicles still on the road and the second thing is they dont drive as many miles in a given year compared to a newer vehicle.

But to ensure I dont run into any issues with some inspector that wants to be a stickler for the rules, I am trying to make my truck look as OE as possible.  Im even going so far as working on a reproduction emission decal for my truck in Photoshop to put on the new hood latch panel I have to reflect the changes to my truck.  Firing order is different, spark plug number is different, and vacuum hose routing is different as well and I figured since I am making these changes to reflect my truck to help some mechanic in the off chance I ever do let someone else work on it I figured I will omit emission systems I no longer have.  I know many have told me its illegal to do that but I think the legality aspect comes in for getting around emission testing which I am not as I dont have to under go emission testing.

1956 Ford Fairlane Town Sedan - 292 Y8 - Ford-O-Matic - 155,000 mi

But to ensure I dont run into any issues with some inspector that wants to be a stickler for the rules, I am trying to make my truck look as OE as possible.

OK, I understand now.

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