350 gas mileage, same 10mpg city AND highway

That's pretty good, must have been a careful driver.

We did a lot of work with a 73 350 Malibu, driver adjustable power piston stop and vacuum advance. The key was to get it to shift early, we would adjust the power piston stop to max Vacuum then lean it 1 1/2 or so. Then advance the timing till we heard knock.

Would do somewhere in the 20s, not sure exactly.

Hoop

 

x-2 you might want to look into a fuel/air ratio meter (check e bay for them)to tune the carb. they use a wide band O2 sensor in the exhaust and allow you to check air/fuel ratio on the fly. this will tell you what circuit is lean or rich. might need a metering rod or jet change or possibly a power valve spring change. also with a Q jet check to see if the spun in aluminum plugs under the main jets are leaking that's a common problem with Q jets. if they are seal them up with some JB weld. get a timing tape for the balancer and check the advance curve in the distributor. the curve may not be quick enough or may not advance fast enough. you also might want to check the vac advance to see if its working. a bad adv. canister or frozen linkage that doesn't allow advance would shoot the hell out of mpg. good luck the 350 should get much better mpg than 10!!!

 

Have you done anything with this issue? Find a solution yet? 10MPG is not acceptable. It should do way better. However, since several other examples of mileage and vehicle have been posted, my 8600# Dmax gets 17MPG empty if I cruise it at 2100RPM. Yes, empty it weighs Eighty Six Hundred pounds.

Not nearly the same due to aluminum heads, OD and EFI, our old OT T/A did 26MPG at 78-80 with the AC on. It too was a 350 so it's possible to wring out some decent mileage from an engine that size. The challenge is in doing it "mechanically".

 

I just drove my "new" G-body wagon 1750 miles home after purchase. 355, factory aluminum intake with a new Q-jet [found carb receipt in car], headers and low restriction mufflers, 3.07 gears in the teeny 7.5" 10 bolt, stock 350 turbo converter. Has a low restiction K&N filter. I inflated tires to 32 psi before leaving and on my way home I weighed it on a log truck scale...went 3540 with me in it and fulla gas.
I expected 12-13 MPG but on 2 separate tankfulls, I got 19.3 and 19.7 MPG! One tank was on 2 lane, keeping the car under 60 MPH and the other was on I-80 at closer to 70 mpg between Wendover and Salt lake city.
I've never gotten that good of mileage with a 350...color me happy.

 

I had a 78 chevy truck with a Target Master 350 like you have....10 was all it got city or highway...I also had 76 ford 351 in a van...it was like new low mileage.....10 was all it got.

My 51 ford I sold had a 305, turbo 350, 2.79 rear, custom built quadrajet by me and my mechanic, and it got 18mpg in the city and 24.6 mpg on the highway running 70 plus....IN THE MOUNTAINS....I think 350's just love gas.

 

3 words, calibration, calibration, calibration.

 

Not trying to be a fly in the ointment but a couple things about that engine.

That Goodwrench engine is probably a GM P/N 10067353, which is a service replacement for a multitude of GM car and truck models using a 350 from about the mid 70's through about mid 1980's. The camshaft installed is 14060651, which is the replacement for 3896929. Intake lift is 390, Exhaust lift is 410 with both having a duration of 296 .

The GM Performance engine 12499529, the 350/290 HP uses a 3896962 which is the old Hi-Po cam going back to 1973, that was the hydraulic replacement for the solid lifter cam used until 1972. That has an Intake lift of 450, Exhaust lift of 460, and share a 222 duration. And the 290 HP is an 8:1 c.r. engine. Both of those 350's are based on the same engine platform, the "universal" GM replacement engine as it accept the oil dipstick on either side. Both should share 1.94 intake/1.50 exhaust valves.

The 290 is timed at 10 degrees base,32 degrees total.`

GM Performance recommends a 670 CFM carburetor and GM P/N 10185063 intake manifold to attain the 290 HP rating.

All that being said, I have sold a lot of the 350/290 engines in the course of my employment and have never had a complaint on that engine of fuel mileage. Wanting a little more "oomph" not uncommon and that can be improved by the 64cc Vortec heads and a camshaft swap.

One other factor, in the late 70's GM used a Snap-On optical(?) timing setup that had a tubular deal that the probe slid into. IIRC the timing marks on the balancer were in a different location. Could there be is mismatch of early pointer and late balancer? Or the ring that walked on the hub? That just came to mind.

 

It would be interesting to know what kind of vacuum it's pulling on the highway.

 

I had a '70 El Camino with a 300HP/350 & a turbo 350 Trans not sure of the gear ratio. Had 900 miles on it when I left Long Beach for Pocatello, Idaho. Ran flat out through Nevada & got 20 MPG With a Q-Jet.