Cruising on the highway at 75-80mph, my engine is reaching 4000rpm. I hear of people cruising at 2-2.5k; What must be done to reduce engine RPM at high speed. I went from 13(185x60)'' to 14'' sbp cop wheels and that seemed to help. 225 with a 727 ; 3 on tree; 150#s in all cylinders, reaching 300k miles; smooth~

you need to change your rearend gears. It sound like you are running 3.91's. I'm running 3.23's and 235/60R14's, I turn 3000rpm at 75 mph.
when I was running 2.76's and 225/75R14's I would turn 2400rpm at 75mph.

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Not to ask the question, but when you changed rims, did you change tire size and did you change the speedo gear in the tranny to compensate for tires/etc...?


Someone on here should have a conversion chart/ reference to help out.



good luck,



-D.Idiot

No, I did not change the speedometer gear, infact after i removed the insturment panel to replace bulbs, my speedometer doesnt even work. I've tried to clean and grease it but nope. Is there any info on fixing those or installing a new one? Anyways I dont know the exact gear ratio but its a 69' 7 1/4 with what i eyeballed at around 2.75

I got my speedometer to work correctly now (that was harder than it should've been) And that 3800rpm speed is at 80-85..maybe thats why my gas mileage is so bad. 25'' dia rear tires. 2.76 gears. 727 3spd tree.

65 Valaint 3.23 gears 235/60/14 tires, 2350RPM at 83 mph,,,,, .70 overdrive.

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Yeah....Im the one who destroyed this rare, vintage automobile.....