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Discussion Starter #1
Hi all! I didn't want to hijack the other thread I was looking in so I thought I'd start a new one. As others in that thread stated they are getting at least 20 mpg, but after some calculating I did when I filled up on Monday I found out I'm getting about 11. I don't have a lead foot, but will occasionally floor it just for fun, but it's not every time I drive it. Here's my setup:
1965 coupe
1968 302
Edelbrock 3027 top end kit
Autolite 4100
C4
3.0 gears

So what are everyone's thoughts? 11 mpg seems really low for such a light car, and just casual driving.
 

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Generally speaking, when people a stating mileage numbers in the 20-24 range, they are referring to open highway use. It sounds as though you are comparing those numbers to your street use mileage or a mix of street and highway. If you're getting 11 mpg on the open road, you have some issues.
 

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Discussion Starter #3
When I take it out it's almost always on the freeway/highway.
 

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I've had the same questions. I remember getting around 20mpg when I first bought it back in '86. And with the rebuild a few years ago, and getting it back to the 4 bbl it was supposed to have (first rebuild before I bought it converted to 2 bbl), I thought I should be getting close to that, since I'm not driving with a lead foot. Was only getting 13-14 last year. Put a new distributor on it since the old one had a broken vacuum advance, and went with an electronic one, but only got 16 out of it since. Stock 289 4bbl (Edelbrock), headers, super-coil, electronic distributor. I keep wondering if I need to take it to a specialist to fine tune it, but ain't sure if it's supposed to be better.
 

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I only get 11-12 mpg myself
Rebuilt 289 with 500 cfm carb.

Go figure.




.
 

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I ran that cam in a '73 302 back before there were any aftermarket top end kits. It ran well and with a plain 'ol 1850 Holley 600 I pulled down 16~18 mpg with 3.00 gears. First thing I'd check is your initial, total and vacuum advance timing. I once forgot to hook up my vac advance after doing some work and lost 5mpg instantly.
 

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The phrase "Your Mileage May Vary" applies here. Under optimal conditions with a standard vintage power train, I would expect that a small block V8 would likely return mid to high teens. A big block likely would return low to mid teens.
Under less than optimal conditions (ie: stop and go driving, prolonged idling, a heavy right foot, worn out engines, low tire pressures, ethanol gas, etc) the actual numbers can be less. Don't obsess about it, just get in and enjoy the ride!
 

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Around town I get about 16 MPG in my Mustang 64 1/2 D Code, 289, Autolite 1.08 4100, T5, Engine isn't stock. Speedpro flattop pistons, Crane Energizer cam, .456 lift intake and exhaust, engine bored .040 over, heads port matched, 1.94" intake, 1,6" exhaust, Edlebrock 289 Performer intake, 2 1/4" dual exhaust. On the highway in 5th gear at 70 MPH I get 24 MPG. I think I have a 3:0 rear but it seems lower than that.

That 65 Custom that I had that got 22 MPG was mostly highway. It was bone stock and had a 2.80 rear and a C4 transmission.
 

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Discussion Starter #9
Been a long time since I looked at the timing, but I think with the vacuum advance hooked up it sits around 37-38 (seems to like it higher than what's in the book.) I also have 15" wheels, rather than 14". Not sure if that makes a huge difference.

byteme, oh I do enjoy the ride, but it was just a concern that when I finally take it out on the road trip I'm planning that I would have to stop and fill up a lot more with that mileage.
 

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Been a long time since I looked at the timing, but I think with the vacuum advance hooked up it sits around 37-38 (seems to like it higher than what's in the book.) I also have 15" wheels, rather than 14". Not sure if that makes a huge difference.

byteme, oh I do enjoy the ride, but it was just a concern that when I finally take it out on the road trip I'm planning that I would have to stop and fill up a lot more with that mileage.
Is your fuel gauge accurate or how are you calculating out your mpg? Are you going roughly 160 miles when the gauge shows close to empty and then dividing by a 16 gallon gas tank to get roughly 11mpg? If so, as stated before, is your fuel gauge accurate? I've had several go bad on me where they would show an empty fuel tank on the gauge but then you could still hear half a tank or so of gas sloshing around in the back of the car. That and when it would say the tank is full you'd only be at about 8 gallons total. I'd look into that first as it's a very common problem and if you're dividing by 16 gallons when you've still got 4-5 gallons left in the tank well then your mpg is going to be way off of what it should be and through no fault of the engine.
 

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Discussion Starter #12
Is your fuel gauge accurate or how are you calculating out your mpg? Are you going roughly 160 miles when the gauge shows close to empty and then dividing by a 16 gallon gas tank to get roughly 11mpg? If so, as stated before, is your fuel gauge accurate? I've had several go bad on me where they would show an empty fuel tank on the gauge but then you could still hear half a tank or so of gas sloshing around in the back of the car. That and when it would say the tank is full you'd only be at about 8 gallons total. I'd look into that first as it's a very common problem and if you're dividing by 16 gallons when you've still got 4-5 gallons left in the tank well then your mpg is going to be way off of what it should be and through no fault of the engine.
The fuel gauge is part of a Dakota Digital cluster so I'm not sure how accurate those are. In my old cluster it was way off, even after trying 3 different senders. I'm calculating by taking the mileage reading on my trip meter and dividing that by the number of gallons I put in until the nozzle shuts off. If this helps I drove about 160 miles, but after that my gauge showed I used up 3/4 of a tank.
 

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It is nice to see you have the Dakota Digital instruments. I have their VHX gauges in my '68. It is nice having an accurate speedo and trip meters. Anyway, if you want to have an accurate measure of your carb tuning, ie your AFR (air to fuel ratio), then you should think about installing an AFR gauge which will use a wide band O2 sensor. I have an AEM model 30-0300 X-Series gauge installed. Using it you can tune to carb to ensure you're not running too rich. I had to reduce my secondary jet one size and my primary jet 2 sizes to tune my carb.

 

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I don't know anything about the dakota digital gauges or how accurate they are but if you went approximately 160 miles on 3/4 of a tank, or 12 gallons if you have the stock 16 gallon fuel tank, then you're averaging about 13.3 mpg. I'm guessing that if you do any in town driving that it's going to likely bring down your overall or combined mpg. The next time you fill up your tank, do so all the way until the nozzle clicks off, then record how many miles are on your odometer and run it dry over the next couple days or however long it takes you to go through a tank of gas and then record your final number on the odometer. But have a spare 5 gallon gas can with you when you're getting towards the empty side of your tank. That way you can get an exact number of miles without having to guess if there's any fuel left in the tank and you can see if your gauge is also giving you a correct reading at the same time while also not running out of gas without a few gallons to get you to the nearest station.
 

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Discussion Starter #15
I had planned on doing that, but decided that doing it the way I did it would be sufficient. Guess it won't hurt anything to run it until it's empty. It's not like it's a diesel.
 

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Using your trip meter and the amount of fuel required to fill the tank is sufficient to accurately calculate your MPG. This is assuming that you properly calibrated your speedo. Does your speedo reading match your GPS or your smart phone?
 

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I was definitely referring to highway mpg. City driving is probably somewhere around 16 or so, but I haven't checked in a LONG time. Don't know the condition of your engine, compression, leakdown, timing and advance, tire width and pressure and whether your carb is jetted and tuned for max efficiency or running rich, etc, but you should be able to get at least in the high teens on a tank of highway driving. Also, are you carrying extra weight around in the trunk, etc?
 

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Discussion Starter #19
Using your trip meter and the amount of fuel required to fill the tank is sufficient to accurately calculate your MPG. This is assuming that you properly calibrated your speedo. Does your speedo reading match your GPS or your smart phone?
To within 1 mph.
 

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Discussion Starter #20
I was definitely referring to highway mpg. City driving is probably somewhere around 16 or so, but I haven't checked in a LONG time. Don't know the condition of your engine, compression, leakdown, timing and advance, tire width and pressure and whether your carb is jetted and tuned for max efficiency or running rich, etc, but you should be able to get at least in the high teens on a tank of highway driving. Also, are you carrying extra weight around in the trunk, etc?
Just a spare and extra fluid.
 
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