nonhog

I recall years back having a 1970 Cutlass with a 2bbl 350. Ran good and got 19 mpg. It was all stock with a low cylinder.
Wondering if others have good results with 350 Olds for MPG.
Has me wondering if a 350 is in my future?

72 w29 all green

I had a '70 Cutlass S 350 2v 2.56 rear that got 18mpg on the highway and had #6 cylinder with only 40psi because of a burned exhaust valve.

By comparison, before i swapped for a 3.42 ratio, my '72 442 with 455 4v and 2.73 rear would do no better than 15mpg hwy .

defiant1

My 350 2BBL got 19/20 mpg on the interstate (500 mile trip). I have the 2.56 peg leg as well. It was a workout to keep a steady speed w/o cruise control.

d1

Big Blue 72

When I was driving mine daily (10+ years ago). I would get 10-15 combined MPG on average. SBO350 with 4bbl. I was young and tended to drive around on all 4 barrels pretty consistently. Not the best thing for MPG, but I was young and dumb!

jensenracing77

i get 16 consistently in my Rallye 350. the engine is a little more than stock but not much. 4bbl, 3.42 gears.

lshlsh2

350 2bl 2.56 rear I get 14/15 in my conv. with the top down. Probably would be better with the top up but has never had the top up long enough to check. Besides what is the point of driving a conv. with the top up.
Larry

Lady72nRob71

When I brought my vert home from SC, I got a little over 19 for the whole 1800 mile trip. Some had AC on and a hundered miles in the mountains.
THis is about normal. New v6 minivans and mid size suvs get about the same.

Around town i get 15-16.
Overall, not bad.

JamesPDX

It would seem that by keeping the power range constant, you would get better millage. If the major part of your driving is in town where the speed is lower, then a 3.42 rear might help MPG. However, it would be better to have 2.56 for hi-way trips were your main stay. It would be dependent also upon the type of roads traveled. Local driving in San Francisco might benefit with the 3.42 gears, whereas Iowa might benefit more with 3.08 gears. You would need to calculate the trans gears for this also.

Aceshigh

I have a VERY healthy 1970 350 with ~300hp / 420ft lbs and with my 2.78 peg leg I averaged 14mpg with 90% city driving.
That was with a 600cfm Holley 1850 4BBL

Since then I put in a 12 Bolt Chevy posi with 3.73 , and 18" rims, drag radials, and an Edelbrock 750cfm 4BBL
Needless to say my MPG suffered but it's faster. Those cute 14" doughnuts just did sit n spins.
Now it grabs and launches hard.

f-85

Thats because you live in the sticks! No stop signs or stop lights. You never have to hit the brakes. LOL

Aceshigh

Just my opinion but......

Don't get a neutered 350 with a 2 BBL.
What good is a V8 if you can't even beat a Honda Accord ?? Just my .02

If you're going to get an American V8 with some actual power in it, get one
of the stronger one's from 1970, throw a 4 BBL on it, cam it up and enjoy it.

If MPG is your concern, get an OVERDRIVE transmission.
Don't neuter the engine when those are so plentiful and fairly inexpensive.

Willidog

I guess that if I ever get the chance I need to find out whats wrong with my car, I have the 350 original 2 BBL now a 4 BBL Holley 650 with a Edelbrock Performer intake, factory cam, electronic ignition and I was getting 11-12 MPG. Something must be wrong. Haha

nonhog

Thanks for all the reply's!
I'm weeks away from having my 455 back. It will be interesting what kind of MPG I can extract from that. Yes of course there will be many tanks that will suck because I just couldn't keep my foot out of it.
I'm 46 years old so I could run a tank or two well behaved. I figure the better the MPG the more I'll drive it.
I have a 33 MPG Scion XB but its 5 years old and I'm sick of it. My 08 Silverado gets 18-19 MPG (mixed city/freeway) with the 4.3. Not bad for a truck.
My point is I'd rather drive the wheels of the Cutlass and park the truck for when I need to haul something. 1st things 1st. Seeing where I am at with the 455. Not expecting big numbers for MPG. If its low teens building a 350 for high teens would be a waste.
Was hoping to hear someone did a 350 with O/D and was in the mid 20's?

Seems possible.

InfoJunkie

Years back a friend of mine with a 260CID 1980 Cutlass in a drag race lost pitifully lost to a Hyundai Pony.

My 70 Cutlass S 350 4bbl 2.78 gear got 25mpg (Canadian gallons) highway in 1974 on a 300 mile trip. It had only about 40K miles on it at the time.

fourtwenty

my 70 last year got 25 mpg (canadian) on a trip to the coast through the mountains and the honda didn't win 350 2 bbl.

MDchanic

25 Imperial mpg ≈ 21 US mpg, so those numbers are in keeping with the others.

- Eric

Aceshigh

I know a guy with a STOUT 454 Chevelle that had a T-56 6 speed claiming 20mpg highway.
Mind you that is a double overdrive manual modern transmission with a .50 final gear.
I don't remember his tire height or rear gear ratio though. IIRC 3.73's.
So yes, it's most definitely possible.

In my opinion......
Your just not going to achieve those figures without an overdrive transmission unless it's a very weak motor.
Alot of people hear "350" and go WOW that must be a powerful motor!!! Wrong.....many were pigs.
I think Chevy had the lowest HP I remember for a 350 which was the LG3 with 135hp.
Yep.....1978 http://www.transdatsys.com/Bird%20Pa...gine_specs.htm

If you get 20mpg highway out of a 350 with a 3 speed transmission it's going to be a total pig off the line,
and if you ask me there's no point in bothering with a V8 if it's going to be a total pig 25 second ET 1/4 mile turtle.

455man

Years ago i had a 350 in a 72 Cutlass Supreme, 4bbl, stock intake, headers into 2 1/2 exhaust that stopped before the rearend. 2.78 gears and got 20mpg hwy and ran a 15.6 1/4 mile. I would think an overdrive tranny with a 3.42 gear would get above 20 but not sure how much more.

When i dropped in my stock 455 with a slightly bigger cam (456/470 lift) MPG dropped to 15 hwy. Also I had the crossover welded shut. 14.0 1/4 in second gear. Damn highway gears.

455man

I'm also interested in hearing how a 350 with overdrive would do. I plan on trying this later with 3.73 gears. Then I'll be dropping in the 455

Shizzy

Am I the only one who has never bothered checking the MPG? Ive owned the car 16 years now and never once did the math.

But seriously, its not just the rear gears, transmission or engine. Its the combination. you want the engine to be spinning at its peak efficiency where you do most of the driving. this includes accelerating as well as constant speed.

nonhog

I think lots of people don't. I got it from my dad, he always does. He had a 69 Toyota Corolla that he had wide open freeway early in the a.m. and could get 45 plus MPG out of that 1200cc bomb.
I got it from him later and could only muster 35. Still great MPG. but I am unwilling to do 45 mph on the freeway

JamesPDX

Again, Shizzy and I are in agreement. His comments herein agree with what I have stated in several threads. The intended purpose of the vehicle under given conditions is the primary concern in building any combination. Power, economy, efficiency, reliability, environment, etc. all contribute to the design, and should be taken into account for individual driving pleasure. Often, there will be trade offs that must be dealt with when it comes to deciding on which way to go.

bccan

My combo is running right @ 15 mpg in easy local & mixed driving. Haven't done a long highway ride that would give me a possible increase though I usually drive about 75 (2500 rpm). Small cam, OD trans, conservative converter (lockup only on open road 55+), well set up Qjet. Car is 4000 lbs w/ me in it. Not a 350 but still a small block.

Drove 100 miles on back roads to Lebanon Valley a few weeks ago, took about a dozen runs, knocked down a bunch of low 12's & drove 100 miles home on just a hair over 3/4 tank.

Combo is working well, if I can get my trans shift calibration down I'm hoping for 12 flat in the fall, MAYBE it's got a high 11 if I were to uncork it & hit everything just right!

These cars can give you a bit of both worlds with some harmonious component selection & tuning. That is if you consider 15 mpg decent.

Bayou Olds

Just got my "new" 350 out the shop and home. I am running a 3.23 rear, a 750cfm Q jet, and a .485/.490 lift 268/280 degree duration cam, Performer RPM manifold and of course with headers. I will be happy with 15mpg combined. If I were looking for gas mileage I would have bought an MGB.

Aceshigh

Well said. Totally agreed.

Bayou Olds

Just got time to take a couple of pics (Boy Blackberry cameras suck) of the new engine. Wish I could load an audio clip, it sounds Badddddd.

goatwgn

Need to install an overdrive in my '74 Cutlass Supreme, but I think I may replace the 350 with a fresher one whenever I do. Present engine has 490,000 miles on it and gets about 15 on the highway with a 3.08 rear and 27.5 inch tires. Still runs good and only recently started to use a little oil, don't have the heart to pull it out yet. By comparison, the 455 Pontiac with RAIV cam advanced 4 degrees in my '66 Tempest wagon with 3.42 rear and 2004r transmission I installed 4 years ago gets 20mpg on the highway(I am very happy with that). You barely have to touch the gas to maintain 65mph. When I convert my "daily driver" Cutlass to overdrive and install a slightly higher (numerically) rear end ratio, I expect to better the Pontiac in mileage, with decent acceleration. I beleive 22-25 is possible with the Olds 350 and overdrive. If anyone has done this, I hope they chime in. The gas mileage is really just a side benefit of the overdrive, however. I like overdrives because of the speed you can travel on the highway while barely taching anything, offset with being able to gear for better off line performance.

mfgusa

It's REALLY hard driving my motorcycle enough to offset the thirst of a happy 455 w/ 3:91's. Really hard.

442scotty

My old 65 cutlass with a 305 chev, 700R4 OD and 256 gears got me almost 37 highway MPG canadian on a 1500 mile trip to the rockies 15 yrs ago ...It wasnt doing too much over 1400 rpm at 65 mph

442scotty

The same car this year will try it with a mild 455 built for torque and a 2004r...Im hoping to get at least 30 mpg highway or about 25 US mpg

Redog

1985 Delta 88 with a 1968 Olds 350 and th400 trans with 3.42 gears out back.

MPG avg'ed between 5 and 8 MPG

JamesPDX

442scotty,
If your new 455 is built for torque, it must have a cam and/or stroke. I think it would tend to drink more, and not give you much better than 15 MPG, even with the 200-R4 OD and 2.56 gears. A low rpm on the flats is good for MPG with 2.56 gears, but you will need that power range rpm to get up the hills with any kind of load.

I'm thinking of changing my 3.08 gears to 3.42 to get better use of my 200-R4 OD in town, and maybe better MPG. My hi-way driving would gain ~450 rpm in OD at 65-70 mph, but would easily take the hills without down shifting (manual talk).

Aceshigh

LOL.....this is a motorcycle year for me too bud.

Gas prices are so high, I'm doing the samething I did in 2009.
Car's are on in full modification status, and both my Hayabusa and Harley will be the 2011 summer entertainment.

I will drive my LS1 powered 78z though here and there.

Not to be pessimistic but that's just not gonna happen without you going downhill out of the Rockies with a massive tailwind......in neutral.

And maybe cylinder deactivation of some kind....lol

442scotty

Ha ha....you are probably right...cant wait to see how much it drinks..I have never owned a big block before I got my 2 65's....I did get 15mpg driving the 442 back from Boston at 70mph...323 gears, original Auto trans/motor so I was hoping the other car with a fresh 455 and OD, 256 gears would do a lot better...(might wish I had the old 305 back)

...It hauls pretty good up some of the steep hills around here but I have a new 3.08 rear end ready to swap over if it needs it...Its got to be better than my truck...geez...

Im now spending more on gas a month then I do on food...

455man

The 455 has plenty of torque for any hills. The 256 might be too high geared for the overdrive tranny. I got 15mpg on highway with a 455 and a TH400 so an overdrive will do better than that. Not sure how much better but I'll find out in a few years.

nonhog

? Not sure what your saying "cam and/or stroke". Cam as in not stock?
stroke as in stroker crank? Odd phrasing cam and stroke together.
Just curious.

A BBO not having enough power or torque to get up hills @ low rpm's?
Seems like anything less than a high rpm race only cam could handle that?

Not trying to be combative just not sure I'm following you.

JamesPDX

It is true that the 455 BB has plenty of torque without any after market work, and that the engine needs to be in its power range to pull the hills (especially with high end gears), and that big torque subjected to the transmission under any situation might be too much with 2.56 gears. The axles would be the next consideration if you install lower gears. This is a real trade-off that needs to be considered.

My comment “it must have a cam and/or stroke“ is an old school term and should be well understood by most builders. The simplest expressed solutions to gain torque with the same block, are to change the rocker ratio, the cam lift, and the crank stroke.

Again, it comes down to building an engine with a specific purpose (race/driver/costs) and environment (city/hi-way/hills/temp/etc.) in mind. There is a real cost/benefit trade-off that needs to be kept in mind. The real priorities to you are the most important keys to the design before the build. After the build, it is a done deal, and you may necessarily need to live with your decision (good, bad, or in between). If you choose and have the funds, this project could be considered as a fun trial-and-error test. You’ll be further ahead, if you do your homework, research the facts, check the technology, and have a full understand what you are planning, before you actually build. Remember this is only my opinion. There are many comments and opinions out there, and it is a fact that some of those are completely off base and wrong.

JamesPDX

The engine, gears, and other vehicle combinations must all be considered when determining the statistical outcomes. The same engine in different vehicles will produce different values, etc..

A larger displacement ceteris paribus (with all other things being equal or held constant) can produce more power and torque, but will require more air & fuel, and hence lower your MPG. Changing gears under various conditions may help to offset some of the decreased MPG.

goatwgn

I highly recommend it.I had 3.08 gears before in my '66, and when I installed the 2004r, the 3.08 gear was too much of a good thing. The engine was practically idling down the road at 65 mph. The 3.42 gear made it much better with the overdrive, and rpm is still down quite a bit compared to the 3.08 with TH 400. The 3.08 acted like a 2.06 in OD, the 3.42 acts like a 2.29. Even a 3.73 gear would only "act" like a 2.50 ratio with OD. The smaller engines such as 403's, 350's and 330's I think would be better with the 3.73 if you are running OD. The 3.42 seems to be perfect for the larger engines IMO.

JamesPDX

Good suggestion goatwgn. My hesitation has primarily been with getting good economy (acceptable MPG). I have plenty of grip off the line in the city with the 410.6 (.040 over) that I built for my '87 Brougham (heavy as it is), and the MPG currently is 14-17. As we discussed, the 200-R4 OD with 3.42 gears should improve the MPG on the hi-way, and if played right, in the city as well. Thanks,

What do you think Aceshigh?

Well, I started a new page (something that I've learned)!?!