cuttysupreme72

I have a 72 cutlass with the 350 rocket and a 72 quadrajet 750 cfm on it. It has the TH350 tranny. I have rebuilt the qjet myself, and have a good tall 14" air cleaner on it. Stock intake manifold. And i'm running the stock points style ignition setup. And true dual exhaust with no cats and flowmaster 40 knockoffs. Also recent tune up, and new mechanical fuel pump, fuel filter, and cap and button. What all can I do to get the best possible fuel economy? And yes I realize I will probably never see over 20mpg. But I would like to get as close to 20 as possible. Last I checked i'm getting like 15.6 mpg. Doing about 75% highway and 25% city.

Allan R

If your car is all tuned and mechanically sound? You're already where you should be. That rating you have is about what they got when they were new.

The only other ways to get better mpg out of your car is to drive like an old man, or put some of those horrendous 2:56 gears in it. If mileage is important to you, practice good fuel sense driving habits. IMO, You're about the only variable that can make any significant difference to your mileage at this stage.

cuttysupreme72

Ah that sucks. Do you think headers or a light cam or a different carb setup or an aftermarket intake would help at all?

1969w3155

My '71 with 3:42's got 12mpg highway, the '71 that I had 25 years ago with the 2:56's gave me 18 mpg highway.

cuttysupreme72

I see. lol So I guess by standard mine gets "good" fuel economy. Oh well. Its worth it to me.

ah64pilot

WOW! You get 15.6 MPG! Holy crap! That's awesome! I get 6 in the silver car and 11 in the convertible

cuttysupreme72

Ouch! lol I am rather decent at rebuilding and tuning carbs : By the way Your silver one is absolutely beautiful.

ah64pilot

Thank you! I paid the bodyshop myself lol! But I did put it all back together after it was painted

cuttysupreme72

It really looks sweet! Mine needs the body gone over. One of the previous owners did a frightening bondo job on it. It looks like they slapped it on in a few places then took a wood file to it, and spray painted over it. Gotta love ugly bondo craters.

DoubleV

If you're looking for better MPG you can never go wrong with an overdrive trans with a lockup coverter.

jensenracing77

the best thing you could do is rear end gears and a 200 4R transmission. if you are getting 15.6 now, the OD transmission alone will put you very close to 20 and maybe over if the lock up converter is hooked up.

cuttysupreme72

I was actually debating on a 700r4 because I have one hanging out in my garage, but it come off of a 350 chevy. So I dont know if the bell housing pattern would match up, or the drive shaft for that matter. And What is a lockup? Are you talking about a stall converter? I know alot about engines, but I'm only familliar with manual trannys. This is the first automatic I have had for longer than two weeks. Also isn't a 200r4 a "weaker" tranny? I had always heard that they dont hold up as well. Ironically enough I have heard the same about the 700r4.

DoubleV

You can build a 2004r to take way more punishment then you'll most likely ever going to give it. In stock form it's not the most durable trans, but one of the better ones ( like from a 80's 442, GN, or Monte SS ) should be good enough.

Easier to just google 'what is a lockup converter' than explain it in detail but in simple terms, a converter is always slipping a little and a lockup converter will eliminate this slipping when cruising around in OD.

Olds64

Perhaps you could change to a 2 barrel intake and carburetor. My dad owned a 69 Delta 88 with a 455 and a Rochester 2 jet on it. Of course, the first thing we did was ditch the 2 jet and go to a 4 barrel but he wasn't concerned about fuel economy.

brownbomber77

With a rebuilt Q-jet, street dominator intake, headers, stock everything else, and a 2.73 gear, my brother got 22mpg goin 70 on a '77 coupe...

oldcutlass

I had a friend of a friend's aquaintence, that said his brother's 3rd cousin, twice removed, who passed on that his father told him that his grandads ol 72 got better than that.

My car gets 7-8 mpg average, going uphill, downhill, headwind, tailwind, etc.. Feel Better!

brown7373

That's about what I get with my 72. I think a Q-jet will get better fuel mileage than a 2 bbl if you drive conservatively because the primaries on a 4 are smaller than on a 2. A lot of the 2 bbl also had higher rear gears than the 4 bbl, but mine is 4 bbl with 2.73, so how much do you gain with a 2.56?

I think the main reason newer cars get better mileage is electronics, lower weight (plastic) and more efficient transmissions and gearing. I've thought about transmission changes too, but how many miles of driving more efficiently do you have to do to pay for the cost of changing transmission and or rear gears? Maybe if and when I need a transmission rebuild it would make sense.

Rickman48

FYI - the Q-jet WILL get better MPG - the primaries are smaller!
Just keep your foot out of it.
[proven in a sbc, 30 yrs ago]

OldsManNJ

I have a 71 S 350/TH350 with a Edelbrock cam/lifter set with edelbrock intake and carb - Headers and 2.5 dual exhaust - and I get no where near 15.6 - I would be happy with that if I where you. - I drive my car every day and average 12-13 mpg - except car show weekends when I tend to kick it a bit more - then I get 10 - so driving style is probably your best tweak at this point - you won't get much better than what you are already.

380 Racer

My car gets <2 mpg which costs around $8.00 a gallon......there you all feel better? LOL

Octania

There ya go, just remove that little link from the primary to secondary throttle shaft. In earlier carbs, 1968??, it was even detachable with a clip!

oldcutlass

Not really, yours has a bit more fun pedal in it! Though I get to drive mine everyday! So maybe mine is a bit more fun overall!

nonhog

Check out ecomodder.com they are into saving fuel much like musclecar fans are into going fast. I'm all for a little of both.

Another MPG thread. https://classicoldsmobile.com/forums...stion-mpg.html

be careful IIRC it has MG content.

455man

My 72 CS with 350, TH350, 2.73 gears and headers would get 20mpg on the highway. Overdrive tranny would help, reducing weight, cold air intake, fuel injection, headers. Depends on how much you want to spend or how far you wanna go. You wont get 30mpg but you could do better than 15.

henryk8398

I agree with the others. It sounds like you've got the 350 tuned as well as you can and good job, too! Besides driving like there is an egg under your foot, the next step would be overdrive. With a 200-4R or 700-R4, you will get better acceleration of out of hole, too. If you have a mild 350, I think a 200-R4 would be a great choice.

hookem horns

Current MPG is better than most of us see. Enjoy as-is or get a beater econobox as a daily driver for cheaper than improving what you have now. Maybe even a miata if secure in your manhood and want something fun to drive.
http://austin.craigslist.org/cto/3193303686.html

cuttysupreme72

Its because of the 2.73 gear. I'm wanting to keep my setup stock short of converting it to a muncy 4 speed.

cuttysupreme72

lol whats funny is our cars aren't that out of par with the newer ones as far a weight goes. My car is a cutlass sedan hard top. according to the DMV it weighs 3600lbs. Were as a 2003 crown victoria weighs in at just over 4000lbs

cuttysupreme72

Hey thanks alot! And yeah I may give the 700R4 a try. But will it bolt up to the 350 rocket? The one I have came off of a chevrolet truck with a 350 in it.

cuttysupreme72

lol Well Whats funny is.. I drove a miata 5 speed for years

henryk8398

No, you will need an adapter. I'd go for the 200-4R. It usually not as strong in stock form as the 700, but can be upgraded. It is a bolt-in and should have the BOP bolt pattern. The driveshaft will also fit. I beleive you will need to move your crossmember down the frame to the th400 position. The holes should already be in the frame and can easily be drilled if not. Lots have done the swap. Search the forums and see what you can find.

ah64pilot

I sure wish I had met you when I was in Dallas...you crack me up!

Well you know what? I've got a buddy that has a car that gets 8 gallons per 1000 ft so now don't YOU feel better lol! Guess who that is





My neighbor has a 2011 SS Camaro that weighs in at 3970 w/ him in it (240 lbs) and a half a tank of gas. Compare that to my silver car that weighs 3750 with me in it (240 lbs) and a FULL tank of gas.

Plastic weighs less, but the copper doesn't God bless those computers for helping the older cars keep up by mere weight savings lol!

jensenracing77

i am assuming you are not hot roding this car much? a good stock 200 4R will hold up for easy every day driving. all 200 4R transmissions have the dual bellhousing so no adapter plate needed. the 700 R4 will have to have the adapter plate. there was never a 700 R4 with the BOP bellhousing. if you plan to play, you will have to have the 200 4R beefed up to hold up.

cuttysupreme72

I dont rag it a whole lot, but occasionally I will start feeling froggy and take her up to 7000 rpms

captjim

And before you do all that work, do some math. How long will it take to save $2,000 (cost of new trans and converter, conservatively) in gas?

I also agree a 4bbl is better than a large 2 bbl.

ah64pilot

And this is a mostly stock 350? Either your tach is broke or something's fishy

jensenracing77

if it got him to 20 MPG even, it would take him 52,000 miles to brake even at $3.50 per gallon. that is if he got a continual 20 MPG but that won't happen in stop and go. i understand what you are saying but that is why i ask if he was hot roding it. if not he could get a good used one for less than $300 and go with it. don't take that long to pay for $300.

the diesel truck guys make fun of my 8.1 gas truck. i get 14 MPG and they get 18-19. they paid $4000 more at least for there truck and .50 to $1.00 more for fuel. what i am getting at is that captjim is right. if you have to pay much to increase your mileage, you are just shooting yourself in the foot.

if you don't drive this car much, it will be best to go as you are now.

380 Racer

OK Steve.......Tony wins the fuel consumption contest. Along with the expense part........LOL.

oldcutlass

I'm waiting for someone to throw down the my dad can kick your dads butt card, here in a few more posts, LOL!

Steve I really wanted to meet up with you guys! Someday we can all get together.

cuttysupreme72

I already have the tranny and the torque converter sitting in my garage. All I would have to but is a adapter plate, and maybe shorten the drive shaft.