Fuel Economy (or rather, the lack there of)

[Guest Mr. Solutions]

Boys & Girls

Kinda silly asking this question AFTER I have had the engine rebuilt... but anyway!

As mentioned, my 263 has been rebuilt to original factory specs. Carb & fuel pump & all that is also all standard.

Is there anything that can be done to make these beasts lighter on fuel consuption. I seem to recall from my VW Beetle days that I changed the needles in the carb at the expense of power. Are things like this feasible at all? What has anybody else done in this regard?

Now admittedly I only have the engine pre-rebuild as a reference point, and consumption was horrible in the city, and only marginally better on the open road @ a steady 60-70MPH.

Thanks

Johan

[Matt Harwood]

Hey, <span style="font-style: italic">you're</span> the one named Mr. Solutions!

Seriously, though, have you fully tuned the carburetor and set the timing? That's probably the most challenging part of getting a new engine to run, and one that a lot of people don't expect. They want to just drop it in and go. Check both of those easy things.

Since the engine is fresh, it will tend to be a little thirsty. Once it's broken in, I'm sure you'll see an improvement with no other changes. And if your only reference is pre-rebuild, I think it will be notably better.

As a last resort, perhaps you could go to a steeper gear in the differential to drop RPM at cruise.

Hope this helps.

[NTX5467]

As Matt mentioned, tuning can be a key issue . . . especially after the original settings to do the initial fire-off with.

The fuel economy issue can depend upon how well the rings were seating before the rebuild. If the ring seal was good, you might not see much improvement. Still, getting fresh ring/bore interfaces as well as fresh valve/valve seat interfaces would seem to help efficiency somewhat as it's all freshly done.

I don't know about changing the carb calibrations to "leaner" jetting. Typically, even the older pre-smog controlled engines would click off an air/fuel ratio of about 14.8 to one at "cruise" (which is where it needs to be for optimum fuel economy and lower emissions). Unless there's an altitude situation where the vehicle will be operated, staying with the factory specs on the carb might be advisable . . . until you get several thousand miles on the new engine and have the time and parts to get involved with taking the carb apart several times.

You CAN set the idle mixture screws toward the leaner side of things, though, which might help low-speed economy (low speed = less than 1000 rpm). Once you get the hot idle mixture for "best lean idle" and "highest manifold vacuum", then you might see if you can lean the mixture about 1/4 turn or so (on each idle mixture screw) and then tweak the idle speed screw a little to regain the few rpm lost. This might work, but at least you knew things will be a little better this way. Or you can go for a 20rpm drop with each mixture screw, from the max vacuum at the specified hot idle rpm. Nothing major, must some tweaking and tinkering toward the leaner side of things.

Spark can be as important and fuel, too. You might "J-gap" the plugs to mimic how many of the newer plugs' ground electrodes only overhang the center electrode by about 1/2 its diameter. This can expose more of the spark kernel to the mixture. Might make some difference, might not, but it's a cheap modification if you have an hour or so to invest.

Of course, fuel economy on the road is a mix of tire rolling resistance and wind resistance. Plus the lubes in the rear axle, trans, and such. No real "fixes" there, but all of them together might help some.

Key thing is to make sure that everything's at factory specs to start with as a baseline.

If you really want to get involved, you might find a speed shop with a chassis dyno. You can rent time from them (something like $100/hr base rate?). What you'd be looking for is "road load cruise air/fuel ratio monitoring" to see where things are at a 60mph cruise and a 30mph cruise at "road load" on the chassis dyno. Once you know where the air/fuel ratios are under those conditions, THEN you might consider -- key word -- seeing if you might find some different jets or something for the carb. You might include a short "power" check, but only to see if the carb's power mixture is happening when it needs to. Best economy is at or near 14.8 and best power is at or near about 13.0 (maybe as low as 12.0 in some cases).

What you might discover is that with modern fuels, the air/fuel ratios might already be toward the leaner side of things, so little could be gained in thar area from a carb recalibration/rejetting. One of those things you never know where things might be until you investigate them.

Just some thoughts.

Best of luck!

NTX5467

[Bill Stoneberg]

The best bet is to change the rear end gears, you are probably looking at 4:11 OR 4:46 TO 1 on your car. Great for torque and pulling stumps, not so good for cruising and gas milage.

[Guest brh]

This is an issue for anyone that owns a lead sled, I have also found that the lack of fuel quality has dropped my mpg. Other than the usuals--proper tire inflation, and keeping the engine in tune is about it. You can cautiously go down the road of leaning the engine out as NTX points out, but follow his recomends as an engine running too lean is not a good thing. The only other small things are putting on a less restrictive exhaust system, pulling the intake manifold and having it polished along with having the ports lined up. I think they call it "blueprinting" an engine. But I seriously doubt ya want to go that direction as the engine has just been done. If you recall the 70's just about every gizmo known to man was offered for better gas mileage, well none of em worked. Once that engine breaks in you should see some better mileage.

[The Old Guy]

The center sections of the Buick rear axles will interchange from 1940- 1955 in all but the 90 series. The V8 dynaflow Buicks have 3,3 to 3.6 ratios. I installed a 3.4 in my 40 in place of the 4.4, and gained 3-5 MPG