Well, I'd always suspected it, but now I know for sure.

My Olds has a drinking problem.

Now, we all know how ingenious addicts can be, how well they can hide their addictions and look for all the world like they are consuming the same amount as everyone else. My Olds was no exception, keeping its fuel gauge unreliable, but not actually erratic, never seeming like it wanted another gallon too badly (well, there was that one time when it ran out of gas with the gauge showing over a quarter full, when I knew I had gone nearly to empty a number of times, but, well, it made me feel like that was my fault, and I bought it some more...). I tried to take it easy, to go one day at a time. I'd put in a little bit more gas, just for today.

So, finally, last week, I went on a bit of a bender and filled it all the way up. The next day, I noticed that the Olds's rear end seemed to be dragging a bit, but I didn't think anything of it. I drove the car around, having a good time, not thinking about tomorrow. Today, it seemed like it was time to pay the piper, so, with the gauge on two thirds, I pulled into a gas station and filled 'er up again.

She took 18.5 US gallons. Hmmmm... that gauge again...

I added up the miles since last week's fill-up: 175.

So I did the math: 175miles ÷ 18.5gal = 9.4mpg



Now, if this were the typical 455-powered, 4,300 pound '73 Delta I'd just shrug it off, but this is a 4,300 pound '73 Delta powered by a 110hp 260 from a '78 Cutlass, through a TH375 and a 3.08 rear, which does zero to sixty in about a minute and a half, being driven sedately (because there is no other way to drive it) on smooth back country roads with mellow hills and essentially no stop-and-go, at speeds between 40 and 60 mph.

Anyone have any ideas on what sort of intervention might save this lost soul?
Any of you '70s fullsize 455 drivers keep track of your MPG?

I've got the parts of a number of big and small blocks at this point, and plan to build it a decent engine, but that's not happening now, as I've got plenty to do, so I've got to make do with this one for a while.

Thanks,

- Eric

 

I dunno, it sounds like you could get better milage with a 455! Are you sure it's not time to do the swap yet?

John

 

X2.

Is the choke off completely or not running rich in other ways?
I did not know such a tiny engine could even move such a big car!

 

Yes, choke completely off and properly adjusted, carb gone over, float level correct, timing as advanced as it can be and still start (about 22°BTDC at idle, if I recall), new HEI module and Delco wires.

... And if you were riding in the car, you still wouldn't know it was moving .

- Eric

 

The 260 is NOT the sledgehammer approach to 73 Delta 88's. That's why Olds never made them with a little engine that can't in the first place.

9.4 mpg? Well buddy I can only say this. From the sounds of it you never really tracked your mileage or mpg from the start. So now that you are, you shouldn't be surprised. You know that 260 is working way harder than it was designed to with a car that big. I'm with John and Rob, sort of. Slap in at least a 350.

FWIW, the fuel gage in those cars will read nearly full until you go at least 150 miles. (hiway - at least my 73 Custom Cruiser would - but it had a 455 in it that would move the car nicely) Then it drops off like the grand canyon.

If your rear end is sagging ( I mean if the car's rear end is sagging ) check that back suspension. You da car guy and know all this stuff we're spoutin....

 

My two cents-the Olds 455 gets better mileage than a properly tuned 250 in my 72 Chev PU-sorry, it is along the same line of thought

Ted

 

You're working that 260 to death. It has to gulp fuel to move that bigass Delta around. Ethanol-laced fuel ain't helping any.

Even after I built the 468 for my 73 ragtop it would deliver 14-15 mpg on the road. Before that, the car with 2.73 gearing and a 455 with a burnt valve would get 16 OTR and about 12 in town.

Yank that teeny engine, save the valve covers, timing cover, oil pan and crankshaft (it'll fit a 350), and let it get recycled into a Toyota.

Yah, I know full-size 221/260/289 Fords and 265/283 Chevys did OK, but cars were not as heavy in those days as they were by the early 70s, nor were they strapped with power-robbing emissions devices. Well- maybe you could call a cast iron PowerGlide a power-robbing device.

 

Yeah, that's what I was thinking as well. I think this is funny as hell, really, I mean a tiny BS engine sucking down more gas than a 455.

Another guy just posted tonight that his '75 Delta convertible (not sure if it's a 350 or 455) got almost 14mpg on the highway driving 400-something miles today from PA to the South.

And, like I say, this is on back roads in high gear at "optimum MPG" speeds .

Maybe this will get me motivated to actually start building a motor .

- Eric

 

The valve covers are 5-hole, so they go in the trash, too.

- Eric

 

Are you sure your speedometer is clocking miles properly? Is it calibrated correctly?

Other than that, you're close to the mileage my 500 HP 468 gets with 3.42 gears. I would go for the swap, even my mild 455 gets 12-14 mpg.

 

SO far on the Adventure home I have been getting 13.8 while averaging 70mph.

 

I did consider that question. A buddy of mine tore his hair out over a 12mpg '72 1300cc Beetle for about 3 years before he realized his odometer was off.

I will check it, but since the speedometer reads EXACTLY correct by both GPS and roadside radar signs, I doubt that the odo is too far off.

- Eric

 

Drill 5 more holes in the valve covers, and slip a 500 HP BBO underneath. It will still get 9-10 mpg, won't idle, won't want to go much over 6000 rpm, but you won't care about those little things any more. lol.

 

I get 7-9 with my 468 around town, however my fun pedal is...well...ummm...more fun!

 

Heck, if you are gonna burn a lot of gas, you need to make sure you have the fun to go along with it. Yank that little engine!

 

I think Rocketraider hit the nail on the head. You are working the little 260 to death. It is straining every muscle it has (not many) to just move that big car. It is time to turn the 260 into rebar.

 

Eric,

This just goes to prove that weight of the car (and weight of your right foot) are far more important to gas mileage than engine size.

 

I agree with all above.

Just checked the odometer - drove the same route to drop off and then pick up child at high school (finals week) 4.9 miles in '98 BMW with correct sized tires, 4.9 miles in Olds.

I did the math - if I drive this car about 3,000 miles a year (it'd be more if it had a roof ), and gas costs about $4.00 a gallon (we've been lucky this week, but I doubt that'll hold), and I can squeeze 15mpg out of her with the 350 I have most of the parts for, then I will save $500 a year .

So I actually save money by swapping in a bigger motor !

- Eric

 

I would imagine if it's reading the correct MPH then it's clocking miles correctly too...unless it's broken internally.

This is sounding more and more like the precursor to why I just built a 455 for the convertible. If I'm going to get 12 MPG w/ a 350 2BBL I might as well swap in a 455 and have more fun driving it. lol!

 

Sooner you git at 'r, sooner you can start driving it more....Won't it be nice to actually press the gas and get a response?

 

I'm not quite sure why someone would put a 260 in a giant car anyways . hmmmm

 

Speaking of crappy motors , my parents had a 81 CS with a 231V6 in it ! Great Motor .... NOT ! The thing had to be rebuilt after like 70,000 miles , and had absolutely no power what so ever . Finally my dad blew the head gasket which mixed oil and coolant together from gunning it in the driveway to get un stuck in the snow . ( he was old and disabled ) and that was the end of that car .

 

Try this, maybe good for 1 mpg, may 2, ha ha.
Taller filter, flip the lid, she'd breath a little, maybe
catch her breath. Couldn't hurt, might help? If that
doesn't help, drop in the 455...

 

A classic case of engine abuse...kinda like putting a 229 V6 into an '82 Impala...wait, GM DID do that...still...

 

I had an '81 Olds Cutlass Supreme too. This one had a 267 V8. I threw that out and put in a 400 sb chevy.

I used to call it my gutless Cutlass until I got rid of the 267. A couple years later I put a 455 in it. Then you should have seen what it would do to tires!

I ended up putting the 400 sb in an 81 Z28.

 

Eric, if you could find some performance parts for that 260 you might be able to save it and build a nice lawn mower or golf cart with it.

 

I like your fuzzy math, I believe it would be the difference in the future increase vs current, plus the cost of the mod! I rationalize too, isn't it fun to try and make the numbers dance to the toon of the singing voices in your head!