millage per gal

I have a 41 8 cyl with 47k on it I had it rebuilt when it had 45k. comp is 100psi. I have overdrive and on the hiway I only get 12mpg. Tires are at 23 psi. I use 30w oil (NAPA). Vac is at 19 psi off manifold. any suggestions what I can do to get it higher? I hear people are getting 15-18 mpg.


  • GlowplugGlowplug Posts: 1,975Expert Adviser
    Let the have you broken  in the engine?  New engine builds are notorious for rotten mileage
  • tenbroecktenbroeck Posts: 16Member
    what is the best way to brake it in? 
  • GlowplugGlowplug Posts: 1,975Expert Adviser
    Breaking in an engine buy driving it... 
  • tenbroecktenbroeck Posts: 16Member
    well I have done that I have put 2k on it 
  • onerare39onerare39 Posts: 1,046Expert Adviser, Moderator
    edited August 2019
    23 psi tire pressure seems really low.  That may have some role in your MPG.
  • Ken U-TxKen U-Tx Posts: 3,958Senior Contributor
    There are many factors involved in determining the cause of poor fuel  mileage. The carburetor is the carburetor correct? Is it jetted correctly with correct metering rod? Is the float level set to compensate for modern gasoline? Are thefloat needle and seat good? Are the brakes dragging? Is the front wheel alignment within specs? Are the wheel bearings in good shape, not set too tight and well greased? Is ignition timing set with a bit more advance for running modern gas with higher octane than what was used in 1941? Is the vacuum advance on the distributor working? Is the distributor in good shape with the centrifugal advance not worn out, sticking, broken springs, etc? Are the points new and the DWELL set to specs? LOTS of things to check out.
  • tenbroecktenbroeck Posts: 16Member
    I was incorrect on the tire pressure the are 32 psi. Carb was rebuilt by a person in Calf he does them all cannot remember his name right now. Front end was reworked by a person here that has been in business many years and does old cars. just frontend work. Brakes were adj this year. everything in dist is free but not sure how to tell if it is worn. Points and cond are new and set with feeler gauge not dwell not sure what dwell should be. Timing is set to spect not sure how much to advance it.  Wheel bearings  not tight I will check the grease. I do not have a vac advance on my dist. there was never one. car has been in the family since the 40's.  thanks for all the info I will double check what I can.    
  • squirrelsquirrel Posts: 169Member
    How fast do you drive on the highway?

    On the ignition can advance it a bit if it does not ping, try from 4 to 10 degrees.

  • terraplane8terraplane8 Posts: 537Senior Contributor
    You may need an analyser to see what your mixture is, especially if you are some way above sea level or your mixture will be too rich. Maybe your timing is too retarded - using the vacuum gauge you can adjust that to get the max reading at idle then back it off a little then road test it for pinging. My '33 Terraplane 8 got 18.9mpg on the open road with mixed hills and flats, averaging 51.6mph calculated by time/distance with no overdrive.
  • tenbroecktenbroeck Posts: 16Member
    on state hwy I do 55. 
  • tenbroecktenbroeck Posts: 16Member
    what type of spark plug do you use? right now I have champion J8c

  • KdancyKdancy Posts: 2,446Senior Contributor
    also, what type of gas are you using? go to non-ethanol if not using it already. 
    as noted above, increase timing and back off if pinging is heard. 
  • tenbroecktenbroeck Posts: 16Member
    can not get non ethanol 
  • cheyenne7271cheyenne7271 Posts: 126Member
    I guess I should be thankful I can get non-ethanol fuel here in west Texas. More freedoms taken away I guess, but we won’t go there.....
  • joe53HHjoe53HH Posts: 62Expert Adviser shows the locations for non-ethanol in the US and Canada.
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