360 gas mileage

[Klowd_13]

http://water4gas.com/ This might help, i was planning of finding the book and using it on my 360. They're made in a Mason jar so 3 or more shouldnt be too hard to tuck under the hood.

Cheers,
-John-

[flyboy2610]

I don't have any hard numbers, but I'm positive that when I had my '68 F100 with the 390 and 4:10 gears, it got better mileage than my '69 F250CS with a 360 and 3:73 gears does.
Maybe the Pertronix Ignitor # 1281 Electronic Ignition Conversion Kit I order 5 minutes ago from Amazon will help. Also going to replace cap, rotor, plugs and wires.
Couldn't hurt.

[Salty]

For what it's worth, when I got my truck it was getting 8mpg, gave it a tune up and now it's up to 8.5mpg. For what I'm using it for, it's not a huge deal, but it does make me think twice before driving it long distances.

[cdeal28078]

A friend of mine has a 65 F100 short bed stepside, warmed up 390, headers, 325 gear and gets 14-15 on the interstate running 70 mph.
These trucks can get better than 8 mpg. It takes tuning and the right parts.
My 71 F100 longbed mild 460, headers 600cfm Holley and 3.25 gears gets 14 MPG around town.
I have spent a lot of time tuning the Holley and the distributor. I am running 18 BTDC initial and around 35 total with the vacuum advance tuned also.
They can get better than 8
clint

[Salty]

Yeah, I would assume that with the right combination of parts you could get much better than 8mpg, considering that there are plenty of carbed engines in the 350-400ci range getting 12-15mpg. It'd really be nice to know which parts are causing the problem though, even if internal. I imagine fuel injection would help a lot as well.

[sideoilerfe]

I prefer the taller gears in my trucks as I use them as trucks. the 3.25 gears in the half tons might help a bit as The 1/2 tons are lighter anyway.

[Salty]

I prefer the taller gears in my trucks as I use them as trucks. the 3.25 gears in the half tons might help a bit as The 1/2 tons are lighter anyway.

Yeah, I've got 3.25's in my truck and still only get 8.5mpg. On the highway it feels like it's barely off idle (although I don't have a tach to verify).

[cdeal28078]

I prefer the taller gears in my trucks as I use them as trucks. the 3.25 gears in the half tons might help a bit as The 1/2 tons are lighter anyway.

I might not haul 10k every day like some but my truck has worked almost all of it's life. Dad bought her new and hauled many loads of rocks for landscaping and we heated with wood so there is no telling how many loads of firewood it has hauled.
Still heat with wood but I use a trailer now
clint

[sideoilerfe]

Yeah, I've got 3.25's in my truck and still only get 8.5mpg. On the highway it feels like it's barely off idle (although I don't have a tach to verify).

Yeah, I don't but the 15 MPG in and FE.

[Salty]

Yeah, I've got 3.25's in my truck and still only get 8.5mpg. On the highway it feels like it's barely off idle (although I don't have a tach to verify).

Yeah, I don't but the 15 MPG in and FE.

Come again.

[Montana71-F100]

When I overhauled the 360 in my 71 f100 I took it on a road trip and was disappointed with the 11-12 mpg I was getting. After reading the posts, I guess I should have been thankful. In town I get around 6 mpg. I didn't realize it at the time but the diaphram in my vacuum advance had a hole in it and wasn't working at all and there must have been a vacuum leak. I replaced it not long ago but haven't checked the mileage yet.

I wonder if it has something to do with the timing curve. At 600 rpm I set it at 6 degrees btdc. At about 1750 rpm it was 36 degrees btdc and with the vacuum advance, it was 50 degrees btdc at 2000 rpm. It seems to be pretty early to be "all in" but I wonder if it's helping my gas mileage. Since my vacuum advance wasn't working when I checked the mileage it must have been advanced 36 degrees at highway speeds. I don't know for sure since I don't have a tach in the cab and don't know the rpms in relationship to speed. Has anyone done any research as to the best timing curve for fuel economy for in town and highway driving?

[cdeal28078]

Only way I know of tuning for vacuum advance is to add more vacuum advance until you start getting spark knock on a long incline with steady pressure on the gas. Back of the advance until it goes away. That is after you have gotten your initial and mechanical advance working the way you want it and have your carb dialed in. A lean carb will cause spark knock and make you think it is timing related some times also.
I still have an allen wrench that fits the vacuum canister in my center console
clint

[GSequoia]

Just to add a bit more data to this thread...

1971 F250CS
390, C6, 4.10s

Engine is a bit tired and has a big manifold leak on the passenger side. Autolite 2100 is freslhly "rebuilt" (parts store kit, no new jets and such). Distributor is new and timed to factory spec.

Around town if I'm driving normally (not hard on the pedal) I get between 7 - 9 MPG.

Semi-highway (when I commute to work, good bit of traffic here and there so it's not dedicated highway) I adverage 10 MPG.

I haven't really taken it on any real highway runs since I've been working on it (I've gotten 13 MPG in the past but that was a rare set of ideal conditions of empty highway, 55 MPH, flat, and about 60 degrees out). My plans for the immedate future are to rebuilt a different 2100 I have (Just have to make sure it is a big bore 2100, I have no idea what it came from) taking more time to verify jetting and that the thorttle shaft isn't leaking a bunch of air and possibly putting a Duraspark distributor in (I have two or three Duraspark modules in the garage, might as well use one, right?). I'll also replace the manifold gaskets and properly block off the old air injection crap in the manfolds (California truck). I expect a slight improvment after that, I will report my findings here if I remember to.

[cdeal28078]

If you put one of the Durapsark Distributors on there you really need to check the timing curve on it. Some of them, depending on what it came off of can have a lot of vacuum advance added to them causing spark knock. When that happens people start backing off the initial advance to get rid of the spark knock and there goes the economy and performance.
Some of them also have very stiff springs and can really inhibit performance and economy also.
Here is a pretty good tech article explaining all the different timing issues. I think it covers things pretty well if you read all of the side bars.
http://www.fordmuscle.com/archives/2000/03/timing/
Clint

[R.Smith]

When I got my 70 CS it got about 12 mpg on the 100 mile trip home over highway and 2 lane country roads. It's a 390 C6 setup.

The guy I bought it from said it had a "mild" cam in it although I don't know the specs. It' does go "budda bump...budda bump...budda bump at the light but, nothing obnoxious. Anyway, it still had the original carb and intake on it. The prev owner had installed headers dumping into a large single pipe running out the pass side.(spare gas tank=no dual exhaust...yet) I put an Edelbrock perfeormer intake and a Holley 600 cfm 4 bbl on it and now it's actually getting almost 14mpg on the highway and 11 around town. It's stayed pretty consistant. I know this because the gas guage doesn't work and I have to write down the gallons in and out. I'm constantly doodling and figuring out my milage.

I don't know what the rear end ratio is. Maybe I should find that out.