Fuel mileage improvement success!

After a new distributor with an adjustable mechanical advance, a new timing chain along with advancing the cam 2°, a set of correct heat range plugs and some carb adjustments I've achieved my goal of 10 MPG well actually 9.89 MPG. Close enough! Still have some very, very light spark knock under a load even with 89 octane fuel, but it isn't anything down shifting to a lower gear won't cure. I'm happy with it.

Attaboy - for that last .11, air the tires up, and imagine an egg between the gas pedal & your foot.
Might even ponder some aero, like smaller mirrors or an air dam, if it suits you.
On my Dually, I lift early approaching anything I might have to pick up the throttle from afterwards; makes a difference.
Coasting 5500 or so pounds instead of charging into the future, so to speak, helps.

did you check your afr? i would look at the carb next, get yourself a big spreadbore so you have the power when you put your foot into it but only sip the fuel at part throttle on the primaries. are you running vacuum advance? that helps alot at part throttle.

Oh yeah, I'm sure I could eek out a few more tenths if I really tried.

Not changing carbs, don't have an O2 sensor and I'm not running any vacuum advance. The mechanical is set at 12° BTDC at idle and 36° total all in by 1700 RPM. I know a vacuum advance might help some along with delaying the full advance but I'm not messing with it for now, it runs way too good. I started at 7.3 MPG I think, so I'm pretty happy with it.

I have found some low hanging fruit on old carb/distributor engines with a little vacuum advance, not a ton but a little bit goes a long ways.

there is a reason the factory ran vacuum advance, and no it is not for emissions, my 51 Plymouth has one.

Run one, it will help.

Sometimes yes, other times no, depends on the combination but might be worth a try. If it starts surging or misfiring you have added too much

Good job on the ‘74

There in your driveway you have two “Bookends” of the crisis years of oil production
from 1974 to 2019

The vacuum advance is adjustable on this distributor so I may hook it up to the ported vacuum source. The engine doesn't make a ton of vacuum, even though the cam is mild it has a 108° LSA, 60° of overlap IIRC.

Guitar there is likely improvement to be had in your mileage using a vacuum advance. The more part throttle cruising you do on the highway, the bigger the difference in mileage will be. At some point I would revisit it, but can I certainly understand enjoying your ride as is for now.

X3 on vacuum. Also do you have EGR passages? Lots of EGR and advance at cruise can help.

No EGR and the truck spends very little time cruising on the highway. The mileage I recorded was with 28 miles on the highway at 2K RPM out of 125 miles of driving. And the A/C was on.

EGR does not help MPG, it is strictly there for emissions. It actually lowers MPG and is the reason manufacturers are going away from it. Air is 21% oxygen and you need that oxygen to burn fuel and you need to burn fuel to make power and move your car, that fuel needs to burn extremely fast and the less oxygen in the air/fuel mix because of exhaust dilution the slower it will burn and more likely it is to continue to burn after the exhaust valve is open and it can no longer push on the piston so it is wasted and statistically less of the fuel molecules will actually burn in the cylinder and it will reduce efficiency. At 20% EGR you have reduced the oxygen available to burn any particular molecule by 20% and there is only now 16% ish oxygen in the combustion chamber so our fuel molecule is less likely to find a partner and if he does find one it is more likely to happen after it has a chance to add pressure to the cylinder. You are also going to increase carbon deposits in the intake trac including the throttle body or carb, intake manifold, intake valve, piston top and combustion chamber. You are also pumping more molecules through the engine further reducing efficency, that is why the new hemi shuts off 4 cylinders and not just the fuel to them but the air that would otherwise continue to flow.

Yes EGR slows the burn, that's why you add timing. It can also help with pinging as it lowers peak pressure.

Add even more timing so you can do even more work against the rising crank.... got it.

>> The mechanical is set at 12° BTDC at idle and 36° total all in by 1700 RPM.>>

That is already a good amount of advance.

If there is a slight audible pinging when climbing a highway grade the timing “might” need a bit of tweaking.

I have run with an Actron ODB-I scantool hooked up on a 1995 360V8 and seen as much as 47 degrees of ignition advance at 1600 rpm on a level Interstate,
but the 1995 has Magnum high swirl heads, EGR and SMPI. I do not remember the manifold vacuum when that happened but would guess 10 to 12 inches of Mercury.

It does have magnum heads on it I've tried running more timing but it doesn't like it. 35-36° seems to suit it fine.

What I used
http://www.mopar1.us/engine2.html

35 - 36 seems to be the max mechanical that a magnum head likes but they do like more at light loads and that is where the vacuum advance should come on. They seem to like about 17 - 18 at idle and mechanical should come on pretty slow, this is one of the reasons the factory magnums got such bad MPG, way too low advance at lower engine speeds and idle... that it jumps around a ton at idle, not steady at all and I'm guessing it was done to make it sound a little more powerful because when you put a carb and dizzy on a stock engine they idle a lot smoother than the factory EFI setup.

I think we all need to remember that it takes a certain amount of energy to move the mass when operating any vehicle, car, truck, boat or airplanes.
The faster you go the more fuel it will use and the quicker it will get to where you want to go
I remember talking to some SCTA (Southern CA Timing Assoc.) land speed racers at El Mirage on how fast they could make cars stock street go back in the mid 1970s, the replies were anyone can go 125 MPH, some can go 150 MPH but once you get above a certain speed, usually 150 MPH, you have to double the HP to go 175 MPH in the same car with no other changes
I had that example made to me while flying my 1960 Piper Comanche 250 home too SO CA from the Tacoma ,WA area after visiting our grandkids. I was flying at 11,500 above a solid cloud cover, the outside air temp was right at +5 F, I had the airplane trim out to fly straight and level at 2400 RPM with the mixture set at 50 F rich below peak EGT, the ride was very smooth and basically boring so I thought I will try slowing the prop RPM down to try and save some fuel, I use the prop controller to slow it down and then retrim and reset the mixture for that RPM and that stupid dang airplane went from 148 knots ground speed up to 162 knots I didn't believe that at all so I redid that test twice in the next 20 minutes, it repeated Got their faster and saved fuel, went from 10.0 GPH to 9.6 GPH at 13 knots quicker ground speed
I am not a weather guru or know anyone who is but I ended up thinking that the colder denser air at that altitude that day was pushed more efficiently by my prop at 2300 RPM versus 2400 RPM
Testing paid OFF
Your right foot determines the fuel mileage, a vacuum gauge can help you get the best mileage on long trips by using the lightest pedal pressure you can to maintain the speed you want to go that day on hat trip

I wasn't trying to get a maximum mileage figure just something that would be representative of what it would get driving it like I would normally, well except for not stabbing the throttle a couple times

On a gasoline engine this isn’t true, EGR helps with milage due to the reduction in pumping work and it moves the timing needed to make peak torque for any given speed/load. The engine bsfc will improve with modest amounts of EGR in the cruise range.

The vehicles that don’t have EGR now usually have variable cam timing on both the intake and exhaust, and they accomplish EGR by moving the cams in relation to each other.

I've found that MPG gains are always improved most by dropping RPM.
I guess that Piper had a flat 6? Thats a 300 combustion cycles per minute drop in fuel use. Having pitch control on the prop was a huge advantage, since you could adjust the load.

I found MPG in an adjustable PCV valve. My 99 Dakota with the 5.9 dropped more the 100 RPM at idle, and that helped city mpg quite a bit.
The OEM pcv design is inaccurate and inconsistent. I put one on my 73 Ford and the adjustment range let me set the idle at 550 to 600, and it gained around town as well.

I wondered how a Magnum would do with a well programmed 8 speed, so that cruise RPM could be held around 1800 or so

Leaning out the mixture will do all the same things. Also running a leaner mix does not decrease the statistical probability of a fuel molecule finding and reacting with an oxygen molecule in a timely fashion but a lean mix don't get along with a cat used for reacting remaining carbon in the exhaust stream with remaining oxygen. It also does not reduce peak temp as much as EGR that causes NOX, it is the more emissions friendly way but not quite as efficient MPG wise as leaning out the mixture. Also new hemis don't have EGR and don't change the intake and exhaust cam separately, they merely retard the whole cam to reduce cylinder pressure under certain conditions. I have tested many vehicles with and without the EGR hooked up and every. single. one. got worse MPG with it working including my current 92 dakota with a 318.

With a camshaft of those specs,
at low rpm and part throttle, the engine is probably creating at least 5% “internal EGR.”

If the exhaust valve stays partially open past top dead center when intake manifold pressure is low, it naturally pulls in exhaust gas.

Lean air to fuel ratios improve fuel economy by raising raising intake manifold pressure.

Exhaust gas recirculation improves fuel economy by raising manifold pressure
- but too much EGR can cause ignition missfires to increase.
A single sparkplug with low swirl cylinder head design will begin ignition missfire earlier than dual sparkplugs with high swirl heads.

Since this engine has a carb it would be relatively easy to leak some air air around the carb to lean it out - airplane style.

My 75 B300 camper van (360 2BBL) would run way rich at 9,000', so I added a 3/8" bleed line to the carb base and a valve where I could reach it. Just left it open whenever in Utah.

My Geo Metro TBI 3 banger runs poorly without the EGR functioning perfectly, and get 52mpg highway when it is.

I blocked the EGR on my dads 97 metro 5 speed he bought brand new and it did better. It would do right aroun 50 MPG on the highway with and about 52 or 52 without it under identicle conditions but it did make the CEL come on with an insufficient EGR flow code so I took my block off plate and made a tiny hole so it could still get just enough flow to keep the light off and it settled right down around 50 and 51 mpg.

I been making a spacer for my 92 dakota to block off the exhaust and instead open up to introduce fresh air when the valve opens, I expect the O2 sensor will just "fix" the AF ratio but figure it is worth a try in my free time.

How much fuel mileage gain did you find?

Curious how that would work since the IAC valve would adjust for different idle speed wouldn't it?

All driving about 2 or 3 mpg.
The IAC does compensate, but I guess the PCV design is very consistent across all throttle positions and loads. The adaptives in the computer respond with more accurate fuel/timing profiles.
It's just a swag on my part.
The idle drop takes several miles (or startups) to occur though. But that's just with a computer reset.

Consensus on GMF is that EGR is best if all else is stock
https://geometroforum.com/viewtopic.php?p=766586#p766586
The ECU map is fixed and programmed for it.

https://geometroforum.com/memberlist.php?mode=viewprofile&u=9543

Ha, and I just saw my old post on carbon cleaners https://geometroforum.com/viewtopic.php?p=706381#p706381

I have considered adding a new IAC to the 71 413-1 (Holley 4150) so I could go leaner with a dash switch, but I'm not sure what size to get, or what is the biggest flow out there. One can always reduce the flow if too much.

You can reduce EGR flow by relocating the EGR tapping point in the exhaust farther toward the tailpipe.

The longer pipe carrying this exhaust gas back to the intake manifold will also act as a gas cooling “radiator”.

Cooled EGR will raise intake manifold pressure, but WITHOUT increasing combustion chamber tendency to knock/ ping/ detonate.

I have thought about doing this using Cunifer metal tubing and designing all curves with long radius elbows to make periodic carbon deposit “rod outs” cleaning easier.

If you scientifically care about such things,
cooled EGR reduces NOx even more than hot EGR.
That is why OEM’s put those high $ EGR radiators on that clog up so bad.

I first saw a “water scrubber” on coal mining “scoops” and “Ramcars” with diesel engines in the 1970s.
These water scrubbers are the ultimate in exhaust gas cleaning but require clean out of “black gunk” and water refill at least every two days.
I have also pondering building a 2x2x2 foot water scrubber in the bed of my pickup to super clean and super cool the exhaust gas for EGR.

Ray there are "stand alone" stepper motors/ iac valves that can be installed using a vacuum line rather than trying to attach directly to the carb. Maybe a manual rheostat could be used to control the opening at part throttle cruise? With your computer knowledge though I am sure you would fashion something a little less crude.

Yeah I was thinking a new port under the carb - I have a 1" spacer that I could drill and tap.
A stepper solenoid would be cool but I don't have the Pi touchscreen going yet, too many other paying projects.

I've been saying for years that the EGR should be picked up after the cat to keep from picking up all the raw carbon that gets deposited in the intake tract. Also it would reduce or eliminate the need for EGR coolers that are so troublesome.

How about a vacuum switch to open it? This would only allow it to open under high vacuum that happens when the engine is fully warmed up and under decel conditions when it don't need fuel at all. Ideally an adjustable one where cut on and off are both adjustable. This is sort of how the bypass thingy on the back of some thermoquads was sposed to work.

Good idea, but the problem I've had at 9,000' is that it always needs leaning, which is what the later T-quads had built in - Holley never did.

My 318 in the old Chinook wouldn't even start at Brianhead unless I held the choke wide open.
I have also considered manual choke which my 68 F100 had. The Holley electric "automatic" is time-based electric heat rather than eng temp based.