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Im running 390 4 barrel holley on stock engine , as mentioned before the car is located in the middle east where temp gets real hot. what type of oil would you run? and also man my girl drinks gas like a thirsty horse what is the normal miles per galllon a 1968 6.4 390 on holley 4 barrel should get?
 

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I haven't done a real mpg check (I will soon), but just based on miles driven and the gas gauge, I'm guessing 10-11 on my new 390/300. (3:50 rear doesn't help.)

The best mileage I ever got on an FE motor was when my original engine (352/250) was about ready to die.

Mileage was easily 14-15.
 

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I haven't done a real mpg check (I will soon), but just based on miles driven and the gas gauge, I'm guessing 10-11 on my new 390/300. (3:50 rear doesn't help.)

The best mileage I ever got on an FE motor was when my original engine (352/250) was about ready to die.

Mileage was easily 14-15.
Jerry what weight oil are you running?
 

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I run 10w40. In that heat, I might consider a 50 or even 60 weight oil though.

I'm gonna say you have the standard cast exhaust manifolds. With those, I was getting ~10 around town, ~13 on the freeway. Now, with long tube headers and a couple other things, the car gets ~20 on the freeway and ~15 around town; with a 780cfm Quickfuel carb.
 

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Not sure how '64 compares to '68 but i get about 15 on the highway, bored .040 over and RV cam. I used straight 30 weight oil up until just a few years ago but changed to 10w40 because 30 was getting too hard to find for some reason plus probably better i switched anyway. I have the 4v original carb
 

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My 352 gave 8.6 mpg, my rebuilt 390 gives about the same. Probably the carburetor is to blame. I gained an mpg after rebuilding the transmission but lost it by downshifting around town.

If if gets cold at night, stay with multiweight oil. Maybe add a thickener, like Motor Honey to keep the oil pressure up when the oil gets hot.
 
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