Best BUDGET Fuel Economy Combo Advice

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QS442

Master Mechanic
Sep 20, 2011
294
148
43
DE
I am looking to see what combo members have for best fuel economy outcomes. I just picked up a 78 Olds Roller that I would like to make a daily driver. I am very open to any combos for the car. Im not a fan of putting Chevys in Olds, however this Olds was originally equipped with a Chevy 305 engine and is still set up for Chevy. This is the only situation I would consider putting a Chevy engine in an Olds since I am looking for fuel economy, it originally had a chevy engine, it's set up for chevy, it's a budget driver, I have dual pattern trans and the cutlass is a plain jane 78.

Other Details:
I will travel roughly 42 miles roundtrip a day.

I have a Olds 330 engine that I can put in car but since I will be putting some miles on it, it may not be the best cost effective option since its a high compression engine and high octane fuel needs to be used. Haven't found many ppl who run these engines in gbodies or daily drivers but if you have with good results, please chime in on your mpg averages. I have averages from Olds owners that still run the 330 in their 60s Olds.

I have a 200-4r trans (its dual pattern)
The car has a 2.56 peg leg rear but I have a 3.73 rear that I can swap.
Have dual exhaust set up if needed
I do not need power, the more mpgs the better, however a nice balance would be desired
I'm looking for low budget solution.

Please chime with your advice, thoughts, combinations, mpg, etc.
 

King_V

Master Mechanic
Jul 17, 2013
307
5
18
Sicklerville, NJ
I suppose it depends on what you have on hand to swap in that's feasible, and what sort of money you have to put into the project.

My first thought would be maybe the LS series engines, but 4.8L or 5.3L varieties. Decent power, and modern system should give better fuel economy.

On the other hand, maybe using your 330, but getting heads off a 350 with larger combustion chambers can bring the compression low enough to use regular fuel.

I'm taking more from theory and guesswork than practical experience, though.
 
Oct 14, 2008
8,806
7,746
113
Melville,Saskatchewan
Get either the .028" or .041" head gaskets if you want to drop compression a bit. Probably needs all new gaskets anyhow. A modern cam like a Lunati high efficiency cam and dual exhaust would help. A HEI with an Accel super coil, better module, recurve and as much vacuum advance as it can stand. A late 70's Qjet off a 350 with APT notched and a thread in plug, so you can lean out the part throttle mixture to the mx. Igot 20 imperial no problem with 88 CSC, 8 to 1 403, 2004R and 2.56 gears. When I added headers and diuals, mileage was the same, just way more power. I lost a couple of mpg going to 3.42's but the car felt better everywhere. A LS might gain a few mpg's over an Olds, a carbed sbc won't.
 

online170

G-Body Guru
Oct 28, 2010
726
319
63
Here are the combo's I've had. Not all in a G-body. The Aerodynamics unfortunately play a huge role.

1) Best was a 350 chev, with 250hp, and a T56. Holley Dbl pumper with 4 corner idle. I drove 60mph @ 1400rpm, and got 33mpg ONCE! After that I couldn't get much over 24mpg, and was about 16mpg City. This is in a aerodynamic Fbody.
2) My friend has a 350 chev with TPI, trickflow heads, roller cam in the 227ish* duration, with a T56 and 4.11 gears, and he can regularly get 27-30mpg highway! And close to 20mpg city. This is in a Gbody.
3) Also had excellent luck with Buick and Olds engines. Either a Qjet or a 2jet with about 2.73 gears and TH350 is perfect. Or a 3.08 3.23 with OD would work well also. In the 20ish MPG mark.


least costly to most costly is #3 ---> #1.
Most mpg to least mpg is #1 --- #3.
 

QS442

Master Mechanic
Sep 20, 2011
294
148
43
DE
2) My friend has a 350 chev with TPI, trickflow heads, roller cam in the 227ish* duration, with a T56 and 4.11 gears, and he can regularly get 27-30mpg highway! And close to 20mpg city. This is in a Gbody.

WOW!! I would drive car ALL the time with that MPG! I really want to park my truck and not touch my Omega during winter. So, I am up to making good mpg but don't want to break the bank.
 

565bbchevy

Geezer
Aug 8, 2011
9,591
12,612
113
Michigan
I know a lot of people would like to see you put something in there besides a sbc but if this is going to be a budget build then the obvious choice is a sbc.
SBC is probably one of the most affordable engines to build or buy new and there is nothing more budget friendly than an engine that drops directly in place of your current engine with every bracket and accessory bolting right on.

And if you really want to save some money Summit Racing has GM crate engines with free truck shipping at the moment.
Here is the most affordable long block:
http://www.summitracing.com/parts/nal-1 ... /overview/
Something simple like this with a dual plane intake and maybe a carb with around 600 cfm, along with the overdrive trans and a mild gear should get pretty good mileage.
 
Oct 14, 2008
8,806
7,746
113
Melville,Saskatchewan
Unless you put on a mpfi setup the sbc will NOT get better mileage then anything else. Guys seem to kick butt with the LS in power and mpg, even carbureted. I got 32 mpg out of an 81 Delta 88, 307, TH350C and 2.41 gears. Great and decent power. If you have all the accessory brackets, put in the 330.
 

DRIVEN

Geezer
Apr 25, 2009
8,062
14,479
113
*CENSORED*
My '79 has a stock 305. Originally was a TH200/2.29 but I swapped in a 200-4R/3.42. So, my cruise RPM stayed the same. Over the life of the car it's gotten 20-23mpg. Years ago, when fuel was actually gasoline instead of ethanol blends, it did better than now.

If you were to follow the formula that most manufacturers use for max MPG, you would use the following:
-Long stroke
-Small bore
-Long intake runners
-High compression
-EFI
In essence, build for torque and gear accordingly. Gbodys aren't very aerodynamic and not too light either. There's no way to make them compare to newer, sleeker vehicles in the fuel economy department. If you can get mid 20s you're doing great.
 

azmalibuwagon

Master Mechanic
Sep 18, 2009
277
2
18
Phoenix
FWIW -

MPG is highly related to your engine rpm, so putting in a 3.73 most likely won't be a good thing. My wagon had that same 305/2.56/200 4R combination, with an electronic Q-Jet. Best I could get was 20 mpg, averaged 17 mpg. But the engine would bog at highway speeds; the car was gutless until I got it up to about 85 mph. I replaced the 2.56 with a 3.73 and got instant fun while the mpg went down to 15.5 average, a best of a little over 17. Worth it for me, but not good for mileage.

For better mpg, a 3.08 might help a little by reducing the bogging, but if you're ok with the performance now, you should probably leave the 2.56 in there. Just my 2 cents.
 
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