Stock, Original Cars at Today's Interstate Speeds?

Sure fooled me...

 

Jeff.. first off, I'm not trying to be argumentative when I say that this has never, ever, not even once, been my personal experience. Lower throttle angles and slightly less rpm's ALWAYS means less fuel needed so long as the amount of torque is sufficient to move the car along. Always and without exception.

Now, if you are suggesting that a car uses more gas.. or more to the point that the AFR goes to hell in a handbasket while running along in the IFR(remember that idle feed restriction feeds the idle holes AND transition slots of both barrels), than it would while running at higher rpm and leveraging the boosters?.. then you may need to revisit your understanding of the circuitry and the overlaps that exist between them. Or at least explain and help me better understand where I may be off target about how these particular carbs may differ substantially enough in their circuit designs that I may be completely wrong here. Don't think I am wrong though, can't understand how I could be because I've "supertuned" a hell of a lot of them through the years and it's far more than just theory or something I was told or read about. In fact, all the cars I tune will typically exhibit very touchy throttles(extremely fast "tip in") and tire chirps during gear changes in cars with shift kits/higher line pressures under very light throttle angles. Never have I heard anyone complain about the increase in light throttle torque and all have gained cruise efficiency.

In hopes of helping the OP better understand what I was getting at in my previous post I will explain a bit further. The idle circuit consists of the IFR(idle feed restriction) that controls the maximum level of fuel flow to the idle holes and the transition slot which is leveraged to fill the fuel mixture void created as the throttle is opened further and the boosters start to come into the picture. What happens at idle and off-idle(high idle/up to about 2,000 rpm as the throttle blades are opened a bit further) is that all the fuel is coming through these orifices. As you pass a certain point you will see the boosters start to dribble and drip. And despite not being located inside the venturi portion of the bores they(IFR) are still considered to be an "on demand" type device.. ie; they will never flow more than the manifold demand of the engine dictates in relation to the size of the IFR, mixture screw adjustment location and throttle angle. While atomization may not be on par with the fuel mixture coming out of the booster at higher rpm's.. it is not without sufficient ability to get the job done at such low throttle angles due to the simple fact that the air velocity is quite high at a nearly closed throttle positions. So, in effect..AFR can be and IS quite consistent with the higher rpm ranges associated with the boosters operation. If the mixture ratio is going substantially out of whack at very low throttle angles then there are more issues at play, most likely relating to the spark advance and manifold vacuum level.

But here's the kicker. They(all orifices related to the IFR) do NOT quite contributing to the overall fuel curve once the boosters come into play. They are still in effect and the fuel coming out of the boosters ends up hitting the edges of the partially closed throttle plates and breaks up remixes with the IFR's same and ongoing initial contribution anyways. Also keep in mind that the fuel coming out of the boosters is typically just an erratically positioned dribbling effect at those more closed throttle positions.. not more finely atomized as it is during full load at WOT. Cruising at 2,000-3,000 rpm will never result in the throttle blades being sufficiently removed enough out of their way, thus providing an additional shearing effect and still leveraging the increased pull out of the IFR's orifices. The ONLY time a booster becomes most effective at contributing to an increase in mixture refinement(improved atomization effect or "mixture homogeneity") is when the engine is at much greater throttle angles nearing WOT when the blades have moved almost completely out of the boosters way. Anything short of that causes the throttle blades to shear the mixture and further promotes mixing/homogeneity. IFR and main well/main jet flow are constantly intertwined, quite literally, at lower/intermediate throttle angles by virtue of their design. Keeping the throttle blades in a more closed position while still maintaining proper AFR helps improve mixture response and increase manifold vacuum levels which equates to more power capability at reduced throttle angle requirements to get up to and maintain cruise speed. Throttle angles may not be drastically reduced, but every little bit helps and points towards more power production and improved efficiency if you can manage keep your foot out of it while attempting to enjoy the increased acceleration potential.

Point of all that? What is the negative result of leveraging the IFR to greater extent with a more closed throttle angle.. than expecting less from it and more from the main jets themselves at a more open throttle angle? The engine will only take and demand what fuel it needs to make xx amount of power anyways and one way makes more manifold vacuum than the other. Easy to see with a gauge in the car.

Here is the reality. This car is light and the power needed to cruise down the highway at static speeds is much much less than most may realize. I have a link to a good calculator somewhere, must be on another computers storage disks, but can't seem to locate it right now so this one will have to do in a pinch. As you can imagine there are many variables to consider for the calculation. Either way you split the numbers rarely should it take much more than about 30-35 horsepower to get you along a flat roadway at highway speeds.

http://ecomodder.com/forum/tool-aero-rolling-resistance.php

So, my original point still stands. ANY way you can help the engine make more power at peak torque rpm and especially everywhere under that point(from idle on upwards) will undoubtedly allow you to use lower throttle angles to get up to and reach any given speed while still allowing you to cruise at slightly lower throttle angles. BSFC's numbers will improve and that in itself denotes improved fuel efficiency. And again, the timing curve is one of THE biggest area's of gain in these old smogger motors because Ford specifically warranted timing reductions to reduce NOx which were/are far more damaging to the environment than having more raw unburned and wasted fuel coming out the tailpipes. Increased part throttle timing lead also helps contribute to lower operating temperatures as well. Which is why utilizing full manifold sourced vacuum advance on your distributor is better than a ported source which does nothing at idle/off-idle engine speeds.

 

Also something to consider is RPM vs internal friction... Think of internal friction as similar to wind resistance, as engine speed increases a portion of the HP developed must be used to overcome frictional increases... Luckily HP increases several times that of friction, but it still takes more gas to spin the engine at a constant 3000 RPM vs 2000... If not, the fuel delivery system has some serious issues... Of course if engine isn't spinning fast enough to create good vacuum(maybe due to performance cam) efficiency takes a hit... There are no doubt numerous pieces to this puzzle, key is getting each one optimized...

 

Mine is a bone-stock 200/C4/2.79:1 combo. When I bought the car back in 2012, I drove it to work maybe a half dozen times. I put around 1000 miles on it for the month that I drove it. My commute is 30 minutes highway each way. The car seemed to be happy around 60mph. When it got to 65mph, it started feeling like I was pushing it. I don't have a tachometer, so I don't know exactly how fast the engine was turning, but the other thing to remember was that my car came with P185/70R14 tires on it when I got it. I'm sure the smaller diameter tires didn't help. I now have P215/70R14 so maybe with the taller tires, it will be able to stretch its legs a little more. Maybe I'll even break into the 70's (mph)....

...and YES, I am talking "miles", not Kilometers (even though I'm in Canada).