and this is exactly what I was refering to when I said,,,
'getting the right vacuum operated power valve in the 2300

I have a holley 2280 that has, along with the acelerator pump a mechanical power valve and a vacuum power valve,, I have an intake vacuum gauge and an a/f gauge, had noticed that at low rpm situations, while in 3 or 4th gear in city or highway,, and accelerating,, the vacuum would be low and the a/f would be full rich..

modified the 2280 to eliminate the vacuum power valve,, in city and on highway have picked up a full mpg,, ( ignoring SSD's comments that everyone on .org that reports fuel economy is either a fool or is a liar)

this has not come without some consequence,, previously there was absolutely no bog when the throttle was stomped,, now there is,, very light but present,,
a rich fuel mixture overcomes a lot of errors,,\
originally I had a 195 thermo, then put in a 160 then a 180,, as the temps went down, so did the engine shaprness.
Currently running a 180,, plan to go back to the 195 this spring and see what that does for the bog,, if that does not fix I am looking at modifying the 2280 internally to have the vacuum PV activated mechanically along with the existing mechanical PV,, to get additional fuel only when the throttle is wide open,, and not on near full throttle - low vacuum

remember the concept,, a rich fuel mix overcomes a lot of errors,
poor mileage and good drivability,, you are probably too rich,,
good milage and good drivability,, you are probabily optimized,,

I've had slants that got as low as 16 and as high as 24 highway. I don't think my dad's '61 Savoy ever got less than 20. My '75 Valiant 225 was the one that made 16, and I traded a '68 Fury 318 for it hoping to get better mileage on my long commute. The Fury got 22 on the highway, so the Valiant was very disappointing, since the gutless wonder spent most of the time in 2nd gear trying to get out of it's own way...one reason it sucked up so much gas.

After two years I traded the Valiant for a '77 Monaco 318, expecting the Fury's numbers, but it never got better than 14 under any conditions! Can't win sometimes....

Tuning for mileage has always been a mystery to me. My current '64 Valiant averages between 18 and 20 for all driving conditions, and with only Ethanol spiked fuel available around here, that's fine with me.

Bad wiring with old, high resistance connectors will kill gas mileage. Look for voltage drop between alt, batt. and high side of resister. Anything more than .5 volts indicates problems with wiring and/or connectors. When I first got this car, it delivered 13 mpg. All I did was replace connectors and wires in primary ignition circuit and it jumped to 18. Adding MSD ignition pushed it to 20. A super six swap yielded 22, and the 833od put me consistently in the 25 mpg range, daily driver, working car. Best tank ever was 29. That bbd was the best.


Everything everybody else said is important as well.

Sam

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Some thoughts on your questions......
Yes, it makes a big difference! A cast stock aluminum manifold heats up quicker than the cast stock iron and is even better if your counting on better mileage in the first few miles from the house in the morning. I also use electric cooling fans (which are off in the morning) just so it will warm up even faster. I also adjusted the stock automatic choke so it kicks off about a mile from the house.
How warm does your intake get under the carb? If not 180 to 200 degrees, use a heat shield to help keep it warmer which also helps keep the carb cooler from heat soak after shut off.
Only if it is constantly pinging. I have a real fast curve up to 55 degrees, but I keep it balanced by unscrewing the vacuum canister from 2 to 5 turns so it never pings with either distributor, the 042 or the 876. I run both at 12 degrees initial.


When you get it too hot.....it will ping and mileage will go down but so does the power. You end up putting your foot in it to compensate and the power valve comes on and just dumps loads of extra fuel........thus poorer economy.

There is some real good advice given from the guys....cam timing, using ported vacuum, manifold heat, wiring and even doing the HEI mod....(you need it with that 350 carb) I also agree your compression is too low. Dan is right, a lot of these cars off the show room floor didn't get much over 18 mpg unless you had the Feather Duster (lighter cars and the more aerodynamic body styles) and a overdrive with real good tuning and some good gas.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I can add my 2 cents.

Completely tuned up slant 6, fresh exhaust (only a glasspack), 2 barrel intake & carb. Engine has either 136k or 236k miles (Your guess as good as mine), in a 86' Dodge D100 pickup.

A833 4 speed with overdrive. 2:94 rear gear. Factory tire size.

I drive everyday 56 miles, 48 via highway & 8 in town. I keep her 65mph on the highway, because those RPM's climb 70mph+ I noticed.

In a 4,995 lb truck with me 150lb...

I manage a lowest of 15.5mpg to my highest of 16.8mpg every week, and my odometer matches perfectly mile marker to mile marker.

I would hope a car 1000-1500 lbs lighter could possibly achieve 18 - 20mpg if in top shape, driven intelligently, on my same route.

That's just me.

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1986 Dodge D100, short bed. 225 /6, A833 4 speed.

Big Blue,

Are you sure your truck weighs that much or was 4,995 lbs a typo?

I have an 86 D100, short bed, SL6, A904 too. I took a load of scrap to the junk yard today and my empty weight was 3,880. I weigh about 160 and have a tool box in the back with probably 100ish pounds in it.

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1970 D100 "Dude"
SL6 / 3 speed manual

My 82 D150 longbed weighs 3540 with 10 gallons of gas in it.

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--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

Maybe 4995 is the GVM

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Richard (aka Fingers)