Interesting thread. I have a question about the optimal cruise rpm. What is the reasoning behind the peak torque rpm being the optimal cruise rpm?
Peak torque rpm is determined at full throttle. Cruise is done at fairly light throttle. Why would peak torque rpm be the optimal cruise MPG rpm - theory-wise?
-Shupe

You're running points on a car you're trying to get mileage from?

Been haveing some drivability problems, the nylon cam block on the points was disentigrateing and finally came off in the middle of a busy intersection in a torential down pour this morning. Put in new points in the mc-donalds parking lot and it has not run this good yet. In the search for the problem I tried a 600AVS and built a completly different thermoquad that I set up just for this motor. I was going to a budys shop that I knew was exactly 30 miles from my house. It was a level drive with mixed driving conditions. I filled up a block from his place and drove home in a constant down pour when the weather let up I went and filled up at the gas station 1/2 mile from my house and it only took 1.12 gallons to go 30.5 miles, or 27.2 mpg

I was hopeing for 25mpg hwy with it now so this even surpriesd me

I still have a few other things up my sleeve includeing an OD tranny, electronic ignition, vacume advance is not hooked up yet and I want to try the tourque-plus gaskets with screens. I need to get the speedo cable fixed so I can start makeing more of these MPG tests now to back things up.

As a reminder my previous best with the origninal bone stock 318 2bbl was 22 on strictly highway driveing.

Dave, Dave, Dave...those points have GOT to go...especially considering the goal in mind here.

OK guys...I think Dave needs a Pertronix or an OE electronic ignition. Who's sending it to him?

That sounds like a great start, but checking mileage on such a short trip introduces all kinds of potential for error that can really influence the calculation. Getting 400 miles out of a tankful would be a better indicator of what's really going on. I track the mileage on my new Honda Fit, and I can see a difference when I fill up at a station where the car doesn't sit level like my usual station. It's enough to see 28 or 33 if I fill less than 1/4 tank, and I'm pretty sure it's all due to fitting more (or less) in the filler neck than normal.

Clair

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For the lack of time and money I have in this I am very happy. I have an electronic distributer (several actually to get parts for recurving)and a wiring harness but no ECU yet.

I have just been cautious with the vacume advance as I don't want pinging on my hyper pistons. I will probably hook it up today.

I know things can be scewed by where I fill up. However I made sure every thing would be real close here, Both stations were level and unlike a fit or any other newer car there is no overflow tank or expansion tank in the cuda. When it is full it is full you can see every drop of fuel in the filler neck. Next time I get a few dollars I will get a new speedo cable and fill up and make a new check. The motor is still loosening up a bit too, it doesn't warm up near as fast as it was at first.

Adjusted the valves properly today and it (and a couple other things) really made the power jump up. a few intakes were loose a few were tight and of course all the exhausts were tight.

I realized since it had been sitting a few months the tires lost preasure from cold and just sitting I aired them up from 25 to 50 today. Tires say 51 lbs max.

I also bumped the timing up to 20 initial and 30 total and still no pinging

I bought and installed a speedo cable but it is not working

I also picked up an ECU so I have a complete ignition conversion kit to install next time I get some time.

Between airing up the tires, the valves and timing adjustments it really woke up today.

If I can ever get the speedo working I will get some more MPG numbers.

Use a portable GPS unit it will give you actual miles traveled and MPH as well.

Nice job on the project so far.

Tom

is the speedo pinion indexed properly? just a thought

If your trying to pull mileage out of a 318 2bbl
upgrade to electronic ignition or better still
a computer ignition system like MSD or Jacobs
(Jacobs mileage master comes to mind)...
rebuilt your front end, get steel belted radial tires and run them at max pressure...

I have a 318 B-Body and I have gotten before
(and still get) 15-16 city and 20-22 on the highway.... (hiway mileage is ONLY if I do the speed limit)above that (say doing 70-75) and I
won't break 20mpg at all!!!!)

In either case b-body or A-body your not going to do much better than that...

Remember (points aside)an A-Body 318 or B-Body 318 wieghts in the range of 3300+ pounds...

Just to make it more convenient to me....

Any updates?

Dave

My wife and I went to the Atlantic Nationals in Moncton, NB in July '06. We drove almost 2000 miles round trip and some site seeing. We averagerd 23.6 MPG. Not bad for a big car.

'68 Sport Fury vert.
318 2 bbl 727 auto
276 ratio
235/70/15 tires
2" dual exhaust
points ignition

But what's the BSFC for an engine at part throttle? I still haven't seen a good explanation of this aspect of engine/drivetrain design. My gut tells me it's not reasonable to say that because my 340 has it's peak torque at 4000, I should set my highway cruise at 4000rpm for best mileage. Somehow a 400hp Corvette can pull mid-high 20's on the highway while turning maybe 1500rpm. Torque peak on a Z06 sure isn't below 2Krpm. Until I can sort out how VE relates to a throttled situation, I'll stick to thinking that best economy is going to come at the lowest possible engine speed that you have good fuel control.


Clair

a engin will make peak torque @ say 4000 wide open put with less throttel opening mabe 10% throttel the torque curve moves down to say 1800 because theres not enoufgh air fuel to push it much higher. fo example drive in 1st gear at 2000 ad watch your peadel then 4000. it will take at least dubel the throttel to cruise @ 4000 because the rotating mass of the engine is limiting the rpms when you dont give it much fuel. wide open is another story

yeah, but since there is no way to measure where your peak torq is at part-throttle you're just guessing. Depending on the engine, IMO usually 1700-2000rpm is ideal for MPG. Much below that and your engine will really start to lug, especially if you hit a bit of wind. Much above that and you're revving higher than necessary.

If your cruising was done at wide open then yes you would get best MPG at peak tq. But really who cruises at full throttle? For best MPG you need to figure out where your part throttle peak tq is, I garauntee it will be lower than the full throttle pk tq. My car cruises about 2200 now and feels like it is way past a shift point, when I let off from steady cruising it vaccume brakes hard.

I did get the speedo working yesterday and filled it up again to get a fresh new reading. I have just been driving it around town so next fill up should be a good city miledge test but it will probably be a few days.

I will wait till I get those results before changing any more like installing electronic ign. or even hooking up the vaccume advance.

I think our 1/8th mile track opens in about a month and I will test it up there for the fun of it, any one want to make a guess on that? I will not change anything from the street tune.

I just filled up again, the rubbing block on these points are driving me nuts. This one fell apart and makes the car run like crap. I put another set in yesterday and checked my miledge (20 MPG city only and lots of cold starts and warm ups idleing and points screwing up). I wanted to try the vacume advance so I put in the shortest advancing can I had (10 degrees) and was going to go for a drive but as soon as I hit the gas the car would buck and cough violently and not move. As soon as I let off the gas it would idle perfectly. I jumped out and pulled it off and all was fine again. I tried adjusting the can to reduce when it cam on and didn't get any better, I guess it really don't want vacume advance at least not 20 degrees

If I get the time today I will put the electronic ign on. It has a 6.5 advance can on it so mabey that will work better. I was going to set up the curve useing the springs from my points dizzy and set the advance slot to the same length but the guts of the advance mechanisim are totally different in the mopar perf distributer so I will get it as close as I can.