Stock 302/2bbl/C4 est MPG?

[Handegard 10]

I'm hearing mixed opinions on what to expect.

 

My grandfather swears he got about 20mpg in my 69, and I've heard a few people say I should expect 15+ out of the car.

 

My girlfriend is averaging 8.2mpg. A bunch of work was just done by a local shop, rebuilt the carb, I put a new disty in and they timed it, and then they dialed in the carb.

 

So, now I'm wondering if I should go back and say "hey, I'm getting bad mileage" and get them to do a tune again, or if all the claims I've heard about MPG are exagerated.

 

Oh yeah, I get a solid 9+ mpg from my F250 with 4bbl 460 and a C6. I really want the car to get better mileage than the truck ya know ;)

[69RavenConv 286]

You should be getting something in the teens, eight is way too low. It could be a carburetor problem like a stuck choke. You don't say what shape your engine is in. Are the plugs fouling? Is the compression down? It could even be something like a dragging brake, or a bad tranny or rear axle/differential. Does it roll easily in neutral? Have you checked for a leaky fuel line or gas tank? Does the car get to warm up, or do you only take it for short little trips? Troubleshooting these cars can be loads of fun!

[Handegard 10]

I don't have any other reasons for suspecting anything else. The car is in pretty good shape, and was expertly cared for (the car belonged to the owner of a shop I used to work ins Father-in-law, and my boss took care of it)

 

After I first took in it for the carb rebuild, I was getting 2 MPG!! I was blackening the ground when I let it warm up. I took it in, he replaced something, and it ran much better, and the MPG was up to the now-8.2.

 

I've been meaning to compression check the car for awhile just to see. It's got brand new plugs in it, I suppose I can go take a peek to see if they've discolored yet.

 

And these aren't hack jobs working on my car. These guys have been doing performance tuning for years, they do incredible work, building blown Hemi Chargers and 'Vettes and stuff like that. It's always weird, when I pull up in the parking lot in the Mustang, I'm actually usually in the crappiest car in the parking lot...

 

I don't doubt the work, I'm wondering if they just tried to get the best power, at the expense of mpg or maybe just made a mistake. I just want others opinions when I go back in so I can say "I've spoken with x number of people, the consensus is I should be getting XXMPG"

[Angel 24]

my car doesnt roll easily in neutral. what does that mean?

[69RavenConv 286]

my car doesnt roll easily in neutral. what does that mean?

 

Probably nothing. But a lot of rolling resistance will hurt your gas mileage, like driving around with your parking brake on. I was just offering up some troubleshooting ideas....

[69RavenConv 286]

I don't doubt the work, I'm wondering if they just tried to get the best power, at the expense of mpg or maybe just made a mistake.

 

That sounds logical, it sounds like they're performance guys. Still, a stock 2bbl can only be tuned so far; 8 mpg still sounds low but I guess it's possible. I might suspect a rebuild problem (leak) but then you'd be dumping raw fuel down the intake and the mystery to me is why doesn't your car run like crap?

 

Are you sure no one's siphoning your gas tank at night?:scared:

[sleek98 12]

I just took a trip from Kansas City to Des Monies for the good guys show, I have a 69 302/2bbl/c4/3.00 gears. It has newer plugs wires, fresh oil in the motor, trans, rear end. I got 18ish going up there garmin said my average driving speed was 66.2 mph with a high of 80 for a bit. And around 15 while driving around town and around the show.

[mikem 13]

I bought my 69 mustang two years ago. It was a stock 302, 2bbl carb, with C-4 with 168k original miles without ever having the heads off. It got 14 mpg combined mileage and it had a burnt valve on #8. I had the engine long blocked, balanced, mild porting on the heads, replaced the intake and carb with Edelbrock Performer and Holley 670 cfm carb, headers and Com Cams 268 cam. It runs very well and now only gets 10 mpg in town. You have a problem. I honestly believe that with a 2.79 gear ratio, and 2bbl carb on a stock 302 that is in good shape, you would see 20 mpg on the highway.

[Pakrat 1,043]

I've always been puzzled by folks claiming good mileage in these cars, I don't doubt them, just puzzled by them. My car is far from stock but it's no beast either. It got the general upgrades of 4V carb, intake, cam, headers, pertronix etc. with a 3spd manual and 2:79 gears. When I drive it normally "which means spirited" I get 8mpg, I did an experiment one summer and drove it like grandma would, I got a best of 11 and it was no fun at all so wasn't worth it to me. This was mostly city BTW, at a steady cruising spped on the highway I'm sure it's better.

 

I have two daily drivers, 1) a 2000 Dakota 3.9 V6 and 2) a 2004 Grand Cherokee V8 and both of them average no better than 17.4 all highway or 15 mixed with city, that's mainly why I get puzzled by claims of 40 year old V8's pulling teens or better on a carb.

[sleek98 12]

I've always been puzzled by folks claiming good mileage in these cars, I don't doubt them, just puzzled by them. My car is far from stock but it's no beast either. It got the general upgrades of 4V carb, intake, cam, headers, pertronix etc. with a 3spd manual and 2:79 gears. When I drive it normally "which means spirited" I get 8mpg, I did an experiment one summer and drove it like grandma would, I got a best of 11 and it was no fun at all so wasn't worth it to me. This was mostly city BTW, at a steady cruising spped on the highway I'm sure it's better.

 

 

Crusing on the highway up there i would only need to barely push on the gas to keep the speed. I was actually suprised by how good of mileage it got. I was expecting 13ish.

 

BTW, My dads 67 390 4bbl vert gets like 5-6 mpg, I think the 4bbls just suck more gas period, both city and highway.

[Angel 24]

I got a 351w with 650 speed demon, rpm intake, ignition and exhaust. I leak and burn oil like no other. block has never been rebuilt, to my knowledge at least. and its been in my fam for well over 10 years. ive got 2.75's in the 9" and an aod off of a 90's mustang. on a good day, with a clean air filter, i average about 15-17 mpg highway. on the street its about 12mpg. and like i said, burning oil. so theres really no reason why you shouldnt be getting better gas mileage than me.

 

aerodynamics plays a big part too, on the highway at least. my girlfriend lives an hour away and i normally drive out there about twice a week. so mpg is important. i installed the chin spoiler because i thought it would help the car handle better on the freeway since it improves aerodynamics. i thought it might help my gas mileage but i was very surpised after the first round trip. before the aod and spoiler, it took about 2/3 a tank to get there and back. 50miles each way. after the aod, it took a about 3/8 tank for round trip. the spoiler got me down to 1/4 tank round trip. so not only does the spoiler look good, but its also functional.

[69gmachine 15]

I certainly didn't build my car with economy in mind, and when I'm playing with the throttle I don't even bother to calculate the mpg. I know it's low. But when I go for a long trip out on the highway where i can cruise over 60 mph for a while, I drive like i would in my DD, and I do want to know what it's capable of getting.

 

My engine is still pretty fresh since the last rebuild, but even with big everything the combination of an OD tranny, annular boosters in the carb and a fresh engine have consistently yielded 17 mpg on the highway without trying. If I'm really trying to get max mpg I have to drive on a straight level road between 60 and 65 mph in 5th gear to get just a smidge under 20 mpg. It's not very fun driving that slow if I'm out on the open road, so it usually drops down to 17 because I usually speed up to at least 70. A C4 must be a fairly inefficient trans that's costing a lot more power than a manual does. Also, aerodynamics does start playing a role by the time you get to 70 mph. Lowering the car helps and so does the goofy little plastic spoiler up front. I think by keeping air flow from going under the car it makes a noticeable improvement when you're going that fast.

 

Having said all that, a stock 2bbl 302 with 2:80 rear gears should have no problem getting 20mpg on the freeway. Something is wrong. There has to be a leak somewhere.

[Handegard 10]

Wow, lots of response here ;)

 

Ok, so to address a few things that were brought up.

 

Car rolls easily in neutral (very easy)

 

Car runs very, very good. Vibrates a little at a stop, but it's runs nice and smooth. Plenty of power too, far more than I would have expected.

 

Driving habits- This is my girlfriends daily driver. She doesn't drive in any way you could describe as "spirited". She drives like a grandma, and so do I.

 

I am planning to hook a vacuum gauge up this evening and see what I see there, and I'm going to jack the rear end up and see what gear ratio I have (I'm sure it's factory, but I'll check)

 

And I understand those who think it's dumb to expect good mileage out of these cars, but when my 5k lbs truck with a 460/4bbl gets better gas mileage towing a boat, I realize there is something wrong. Even if I don't care about the gas, I want to correct whatever is wrong before it damages something or gets worse...

 

I have a appointment with the shop that did the work on Tuesday, they'll be checking it out again...

 

Thanks guys!

[Justafordguy 10]

I have a 351W with a 600cfm 4bbl, mild cam, dual exhaust, FMX auto tranny, 2.73 rear gear, 25.7" tire. I can easily get 18 - 20 MPG on the open road running about 60mph with the A/C on. You should get that with a 302 2bbl with stock gears/tires easy. Something must be wrong.

 

I get 16 city-19 highway with my 8000+ lb 4x4 crew cab F-250. It's a diesel but it's 3 time heavier and a 4x4.

[LSG 15]

Chris, it sounds like at least one of your guys doesn't have a clue. I'm not meaning to be harsh, but 8 ?! Something is wrong, very wrong. I have a '69 FB with a 302/C4/3.00 axle. When I bought the car, back when there was a 55 mile an hour national speed limit, I got 22 mpg driving the car from Nashville back to my place. After the purchase, I removed the two barrel and iron intake and installed an aluminum Edelbrock and Holley 600. The best mileage with that combo was 17, the very worst, driving drag strip style, was 11. After a few years, I decieded the 4V didn't give enough extra power to justify the mileage loss and I sold them and put the factory 2v and iron intake back on. A fuel injection setup doesn't offer any inherant advantage in fuel economy over a carb. The fuel injectors are just easier to tune. Either your carb is way way off, or your ignition timing is not advancing properly, or you have fuel leaks you're not aware of, you should be able to beat 15 mpg without even trying. LSG

[Handegard 10]

Yeah, I know that something is wrong, I just wanted to hear others say it so I could walk into the shop and tell them "ten other people that have the same combo get xx mileage"

 

What does everyone agree is best for timing on this setup? I think it's at 12* but I might just be talking out of my ass. It's at whatever the Chiltons recomended for that combo...

[Pakrat 1,043]

In my experience these cars run best bewteen 10*-15* BTDC, every car is different though and you should give your car as much as it likes and not just what someone tells you to set it at.

 

If it is set to what Chiltons says right now then that is probably what factory stock is and that would be 6* BTDC, a very enemic setting at best.

[70Mach03 12]

Wow, no wonder the world is experiencing a gas shortage (LOL). I had a 1970 Fastback Mustang that I bought new in 1970 with 302-2V, auto and 2.79 gears. When it was new and I drove it like an 18-year old kid did back in 1970 it got 15 to 19 mpg. Over the years I added dual exhaust, dual point distributor, and finally a Holley 500 CFM two-barrel carb. My gas mileage when I sold it in 1992 with 186,000 miles on a never rebuilt motor was still 15/16 around town and I had gotten as much as 23.6 mpg on the road driving the speed limit. Plus I always ran my timing anywhere from 10 to 16 degrees advance.

 

Something ain’t right and it may be as simple as the choke is stuck partcially open. Even my present 351C-4V gets 11 to 13 mpg around town and much better on the highway.

[Handegard 10]

Two things that should help-

 

The mark the on the crank pulley wasn't anywhere near where I thought it was. I took a wire wheel and ground all the rust off so I could read the whole thing, marked zero with a new paint pen, and re-timed. I'm at 11* now, and I believe it was about 5* off before, but I didn't catch what way.

 

I went to the shop that did the carb work today, he came out and played with it for a minute on a gas analyzer, noticed that my choke tube (the one from the manifold up to the choke) had snapped off at the bottom, backed my choke off a little, and rejetted it.

 

I watched HC at cruise fall over 50% when he made his changes, so I'm pretty happy that it'll get better mileage.

[relic1864 10]

Just took my 69 coupe on a 3 hr. trip one way. All stock 302 automatic 2 bbl. Going down i went 60 to 65 mph and got 15.8 MPG. Comming home I drove 65 to 70 and got 14.3MPG Whats other people getting?

[rangerdoc 22]

Back in the day when my engine was stock I could get about 20mpg on the freeway with my 2bbl 302 and 2.89 rear end. In the city that would drop dramatically. I have no idea what I get now, nor do I care.

[dzahm 10]

I have a 69 vert- pure stock 2 bbl, not even rebuilt just a valve job- c4 and 2.79- I am 18-22 mpg driving interstate (around 75mph) I drive it easy as it is orig, and its a cruiser- I have no spoiler, can't really tell if theres a difference top up/top down- in terms of mpg (though its a vert- who cares if its worse with top down- it would be worth it if it cut mpg in 1/2 IMHO) That all said- something ain't right with yours- My F250 4x4 crew cab V10 gets 12 mpg- it weighs in around 6200 empty (so in terms of HP/engine displacement and weight) even realizing new technology helping the truck's mpg.........there still has to be something wrong

[MustangChuck 16]

Back when it ran, my mildly modified 302, 4 barrel carb and 4 speed top-loader (3.20 rear gears) would get 14-15 mpg on the open road (70 mph-ish). It turned about 3000 rpms at 70 mph.

 

Chuck

Edited October 19, 2012 by MustangChuck
I didn't have an automatic, it was a 4 speed top-loader -- What was I thinking???

[danno 128]

Wow, this is an interesting read. The numbers are all over the place. I have the 302 with stock carb also, and get around 12mpg in town. I never take it on the road to know what it would do, but maybe 15 mpg driving it like my turtle's grandmother. I installed the AOD, but they will not help much in town.

 

I have tried everything to fix the problem. Everything is new or double checked. Nothing works. My car starts and runs perfect. I just figured it would never do better, then I read these posts. I had even thought of switching to a 5.0L from a 1992 car, they got federal rating mpg of 23.

 

Maybe there is hope afterall for my 302? There should be an article written about the steps someone should go through to troubleshoot these issues. Thousands of articles about how to get more power, I have never seen one on how to get more mpg.

 

What does testing with a vacuum gauge tell you? Is there a way to find out if it is running rich?

[dsc2 10]

Not a lot information out there on MPG for classics. Driving style and modifications will play a big role. I found this site listing some data........

http://www.aboutautomobile.com/Fuel/1979/Ford/Mustang

 

I would agree with 15+ MPG is reasonable to assume with a 302, C4, 2.79 gears.