So I have this 1982 regal with an unoriginal (originally a diesel) oldsmobile 307 in it, with a thm350, a holley carb, a4 intake, 2.4 lsd rear, 5a heads, and I need to improve my mpg. It's totally slow and gets about 11mpg, but all I hear is 307 regals getting 17-18. I have a cold air intake, stock exhaust (Which i know will help about 2mpg), but what else could I do to increase the mpg, even if it means hurting my (extremely low) horsepower? What do that have different??? This is my daily driver and 13 highway mpg is getting unbearable. Thanks!
Olds 307 mpg improvement
- Thread starter Bladecatcher82
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Well, I got about 17mpg with my 307. It's because I have an overdrive transmission. An OD gear really helps the gas mileage. Idk if there were ever any BOP pattern 700r4 transmissions, but you could find yourself a 200-4R to use with your 307. It might cost you some money but if you drive the car a lot then it will eventually pay for itself in gas money. Just a suggestion.
A tune up cant hurt if it hasn't been done in a while and the carb might need a rebuild too. I would also suggest using mid grade gasoline, even though its 10 cents higher/gallon because it will burn cleaner and produce a bit more power. Remove all the weight that you don't need in the trunk. Also, if you drive with a lead foot, that's a big part of it. If you live in a hilly area, you will burn a lot more fuel. Change out the o2 sensor if its old and keep the tires full of air. That's all I got....Bladecatcher82 said:
Are you sure the carb is set correctly? Things like the squirter nozzle size, even the pull off number for the power valve, and obviously the jet size can have a big impact on fuel economy, most guys set a carb to run well and stop, but they usually can go much leaner when concerned about mileage, even the idle screw setting has a very small impact on fuel mileage. Timing also plays a big role, the more timing advance a motor will take the less fuel it needs to run. The 260ci in my car makes even less power stock than your 307 but with some playing around and a good tune up, my car gets nearly twice the mileage you are getting, I have a slightly lower gear (2.29) but same trans. Things like EGR, driving the air pump, emissions timing calabrations, and catalytic converters all helped emissions but hurt the fuel economy. I am in the process of eliminating all this stuff on my car to try to get it even better, I drive my car nearly 40 miles everyday so every bit helps
the fact your block started as a diesel is probably the entire problem, so the answer is to think outside the box: buy a new engine, or get a new car. It's just not going to happen for you w/ that setup. You can change plugs, think about getting a new trans, buy some new shocks ... w/e you would do this month to try getting better mileage will exceed the cost of a car payment on something else. So if you're spending money to save money that doesnt make any sense - does it?! & you do want to save this car - but, if you can't afford 13mpg then you can't afford to save / restore this car, therefore you will only fall further behind in maintenance until you've dug a hole so big the only way out is to sell the car, and I'm sure you don't want to do that or you wouldn't be here on this forum. So consider dropping a deposit on something else to drive to work until you've saved enough to fix this situation. If I were getting 13mpg there had better be @ least 300 hp on tap or that doesnt make any sense - it's 2013
pencero said:
Wow, that's what you got from reading his post?
The dude said it's a 307 in place of the original diesel.
Hey Bladecatcher82, One, which Holley carb do you have? If it's not a spread bore,(Throttle plates have small primaries and large secondaries) then that is one of your major issues.
Two. Is the engine in good tune? A lot of times the motor's timing could be off by a hair and it just won't deliver the torque it is supposed to have. Has the timing chain ever been changed?
Your set up is fine. The TH350/2.4:1 rear end was used in a majority of 307 cars because only the 307 and the Olds diesel could pull those gears.
The only thing on your set up that sounds fishy to me is your carb. A TH200R4 will hurt the mpg because it used 2.56:1 and up gears. The overdrive put it right where your car is now. So don't change your set up. Concentrate on the motor's tune.IMO
T
I don't see how an overdrive gear would hurt that much with just a .16 difference in the rear gears. :?: And the 200-4R's 1st and 2nd gear ratios are a tad better for getting the car going. Is the TH350 a lighter load on the engine? I'll admit that a trans swap would be pretty involved. You'd have the trans, crossmember and extension, T.V. cable, driveshaft, correct speedo gear, trans lines, and maybe linkages and wiring to worry about. Pretty big project for a DD.jetsetw31 said:
I agree with the tune up, though, especially on the carb. I was running a rebuilt square bore Holley as well. I know the square bore/spread bore adapters rob CFM, but it still ran much better than my worn out Q-jet. Not saying the Holley is better by any means, but I am saying that a well-tuned carburetor can do you a world of good. So x2 on the tune-up.
pencero said:
Or you could do that, $30,000 on a new car vs $150 for a tune up, and a weekend if playing with the carb, and dialing in the dist. These cars can get very good mileage they were designed more to curb emissions and some of that stuff actually hurts mileage, look at all the things that are no longer used on new cars to make them more efficient, air pumps, mechanical fans, carbs, dist., low compression, low coolant temp, heavy weight oils, friction cams, all of these things make a motor less efficient, therefore they burn more fuel to do the same job. Granted unless you want to EFI your motor you can't compete with a brand new car but you can get very close, like I and the other guys said start with the carb, then the dist. I get between 17-21 MPG out of my car, it still has the original 2bbl on it for now but it has a good tune up, eliminated the temp controlled timing retard and set up a curve for the dist, that's it
307 Regal said:
TRUE, the difference isn't much and the 200-R4 has the launch advantage. I was thinking of the overall drive ratio. The overdrive would turn that 2.4 way lower. But the most obvious difficulty is that it won't fit without a extension welded to the frame for the the 200-R4 crossmember. The 200-R4 started in G-bodies in 84 or 85 I think. X2 too many changes for a DD.
Is your lock up torque convertor working? If it is the original trans, it will be a TH350C, it will lower highway rpm 200 to 300. Get a Qjet off a late 70's Olds 350. It will be jetted very close to where you need it. The stock exhaust does suck but I have achieved double to triple your mileage with a very similar set up in a heavier 81 Delta 88. Biggest difference was a good Qjet and proper timing curve set. Where did you set your base timing?
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