355, 4 speed , 3.73 gears. 3900# car (OT) 265 70 R 15's, 600 CFM 4 hole Holley, Slight cam, headers and flowmasters pulls 17 on highway. I'd look at your distributor's mechanical advance. If the weights aren't advancing, your power will be down and your throttle more open to compensate. I installed a Moroso weight kit in the distributor years ago. I think I'm running the mid weight springs.
Nope Make sure that you are not running with your secondaries open. Pretty much any 4bbl can be adjusted to run on the primaries until you need all 4. Then make sure that you are properly tuned. IE proper valve lash (mechanical) or preload (hydraulic). Points set correctly or if you are running a GM HEI get rid of it, or find a decent electronic if you must (I like a mallory unilite personally). Timing set correctly. large open air filter. Proper operating temp. Choke not partially closed. Part of your problem could be those big assed tires. If they are narrow maybe you are OK. Big tires and low torque motors don't mix. Even with the 3.55:1 gear with a 283 you really want a 28-30" tire. If you want to run that tall of a tire it would help your mileage to go deeper with your gear, like a 3.73 or even a 4.11. I know it sounds backward, it is not. You want your engine to be operating in your torque band to optimize mileage. Not lugging and not overworking. OK TMI right? I am only trying to help.
Wow! I guess I have a problem with this post too. The title clearly says the topic is fuel mileage. I don't remember seeing anything in the "rules" requiring that everyone has to read every post, or respond to it. For those not concerned about fuel mileage, I can't figure out any reason why you would even want to open this thread, let alone read it into the 2nd or 3rd page, and then add a smart azz comment to keep it on top of the message board. Of course, if each of you want to send him $100, he would probably not mind buying the extra gas, but he would probably still give his car a better tune up. If he spends less money on gas on his trip from MN to TX, maybe he can buy more fun or important stuff like: hot rod parts, more beer, or food. Fortunately, the guy has gotten several useful comments, and has things he plans to look into.
People who tune for power assuming a decent engine, get MPG’s as a side benefit and their engine and motor oil lasts longer. Apparently some here don’t have to concern themselves with practical matters.
a good tuner/builder makes power by making the engine more efficient. real builders are few and far between and tuning is way more then points and plugs. Right?
Mileage is somewhat inversely proportional to power output. The higher the power output number, the lower the mileage number. It's a trade off we hot rodders are happy to live with. Any gain in one will cost you in the other. Not so much when it is backwards. The guy's 283 sounds like a stocker, and will have limited power levels. That's fine, until you take on board that it is running 12-13 mpg to give him that power. How many of you out there would be happy with that. All the "that's what hot rods are" crap talk doesn't apply here. I'm sure he would be happy with 12-13 mpg if his engine pushed out 500+ horsepower. I think the OP would just like to be paying a reasonable price at the gas pump for the HP output he is getting. Makes perfect sense to me. And most likely, if he solves the gremlins that are causing the woeful mileage from his near stock 283, he will gain some giddyup as a result. Win - win. Been there and done that..........
I was staying out of this thread until I got pinged. As one poster mentioned, the low fuel mileage MIGHT be masking a much more serious issue. Lots of GOOD guesses, but guesses cost money. Why not some testing??? I may have missed it, but was a vacuum value posted? I know it is a rebuilt engine, but a compression test would tell you if there is a valve too tight, or low compression pistons, or??? If the compression test shows everything normal, then an ignition test would be useful. Not all ignition components like each other I personally would not have used the carburetor of your choice; but it is your choice, maybe you can make it work. Possibly, if you have a friend that will loan you one, swapping out the unit you have for a factory WCFB or 4GC as a test to see what happens. Finally, tire pressure, dragging brake(s), clogged exhaust, more testing. Jon.
Finally, compression is mentioned. The OP said he has double hump heads which increases combustion chamber vol. by 4 cc unless he has the very early 62 cc heads. If he had all early (57,58) parts, I.E. 4 valve relief pistons, 58 cc heads and steel shim head gaskets, he might be around 9.2 C.R. Using commonly available rebuild parts, his engine could easily be around 8.7 C.R. Dropping C.R. is giving away torque, which a short stroke engine can't afford. I would be checking cylinder pressure. As pointed out already tuning is about increasing efficiency; building an engine is about using the parts that will allow efficient tuning.
Since I'm being included in these, guess I need to clarify my end of it. BTW thanks for the lectures boys. My comment was not pointed at tracking down a performance issue......why the hell would I have a problem with that? My comment had to do with the @gene-koning original post....so it must be Karma that his second post has to do with me. Thought I had quoted his original post with my original comment but was in a hurry, so I'll do it now. Not ragging on anybody. Just a "tongue in cheek" observation....but he offered help and I didn't.....so my bad. "I can get 2 mpg - 3 mpg better mileage then my wife can get from the same car, on the same day, on the same drive, at the same distance. Driver style has a lot to do with gas mileage. Traffic flow has a big effect on driving as does the speed, the road surface, and the terrain your driving around in. The 318 in my truck gets 10-12 mpg right now. Its suppose to snow tomorrow, in 4x4 around town it might get 8 mpg, but next summer it will get 15 around town and near 20 on the highway. Shouldn't I be getting better mileage? Based on last summers numbers, yes, but it isn't summer, the gas isn't formulated the same as it was last summer, and the truck isn't getting used the same way it was then." "For a second there, forgot this was a hot rod forum."
I had a '49 Chevy pickup that I put a fairly low mileage 305 in with a TH 350, 3.0 gear, 235 70 15 tire and the Rochester 2 bbl carb. It got about 18 mpg. When the engine got tired, I rebuilt it and went with an RV type cam (stock cam had some very flat lobes), 500 Edelbrock carb and a new HEI distributor. I lost 2-3 mpg. I went back to the old distributor, bought the tuning kit for the carb and tried about every combination there was. No improvement. I know I made a lot of changes at once, but I always blamed that carb and never used one again. Gary
When that happens, it's usually too much camshaft. Probably the biggest mistake people do on street driven cars. Probably not the original posters issue.
Stock 283's need about 2300 rpm to be happy. 70 mph is pushing it because your pickup is not aerodynamic. The best carb I ever used on a 283 was a Q-jet with it's triple venturi primaries. Between 2200 and 2400 rpm I got 23 mpg driving like a little old lady on flat roads with a 3 speed stick at about 56-59 mph. Overdrive transmissions are not for every engine, low rpm's do not mean better milage on many older engines. Get your rpm's fixed first, then worry about cams and other things. imo
B...S..., tell that to the NASCAR guys. They do anything they can to improve mileage and make their engines perform at their max.
I'm with @carbking on this, guesses can get expensive and waste time. We won't get readings and looks at parts since the car is not being used rt now. All was revealed on that score. Guessing can be fun too, I guess. My guesses are that there seems to be something inducing excess parasitic losses not just in the engine but somewhere from carb to tire contact patch. Another is that I'll assume this is at least cared for well above the "It's just a lease..." mentality so maybe the issue is something aside from jets, timing, tires, yadda be boo bah. Something easy to miss or unknown by the engine builder like the wrong timing chain components could have cam timing out to lunch. Low compression was already mentioned too. Maybe the builder grabbed the wrong head gaskets and added unwanted volume to the chambers with excess bore and thickness. All beyond the pleasure of tuning a hot rod and feeling change when engine internals are on hiatus in perpetuity. We all hope something silly like a dist vacuum pulling the plate the wrong way, stuck weights, or the damper ring moved and it's way off. Or the wrong pointer (more often on Windsor Fords than others), or the timing light is hinky. I think the O/P has ability but again some stuff...?
I get 15 mpg in my 31 roadster on 32 rails with a 671 blown 396 with duel 750 Edelbrock carbs, a 400 turbo and 3:50 gears with 30" tires. I also have a 32 coupe with a gutless 145 hp 350/350 and 2.79 gears and I get the same mileage on it as with the blown big block. It doesn't make a lot of sense.
Clearly you must be forgetting the part in Henry Gregor Felson's book HOTROD where they had to run around the track and see who could go the farthest on a gallon of gas? If Bud Crane can be challenged about fuel economy....
Except gas hasn't averaged $0.25 per gallon since 1947, which is equivalent to about $3.48 today. In 1965, gas averaged $0.31 per gallon, or about $2.97 in todays doll hairs, which is what I paid last week. Obviously local tax schemes affect the spot price, but as a general rule, gas prices have followed inflation closely, rarely deviating from the average over the long term. We are just spoiled as most other "consumer" items have gotten cheaper relative to inflation over time due to increased manufacturing efficiency, technology improvements, etc, add in the fact that 5 out 4 Americans don't understand math, and you get the incessant whining about the price of fuel.
Yep, and I was making $2.50 an hour before taxes which translates to $23.78 today. Gas around here is running $3. 31.
However, to be completely comparable, in 1965, you could pull into a Sunoco station and buy 100 octane fuel. How much is that now?
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