3spd / 4spd OD swap ?s

USC87

Member
Joined
Feb 17, 2006
Please bear with me, I have *very* limited trans knowledge. I'm redoing a car currently and getting to the trans phase of things. I'll be doing alot of driving when I'm done as this car will be both highway transportation and a cruiser for show nights.

Currently it has a th350 in it, and I'm thinking of going to a 200-4r. Its already got relatively high gears in the rear end as of right now (guess they call it highway gearing), and as it sits, I used to average in the 22-26mpg range on the highway. Seeing how I'm replacing the trans anyways, and with gas prices where they are headed, I'm hoping putting in the OD unit might bump it up?

I have heard what may just be misinformation that if you have high gearing in the rear end the OD might actually hurt your mileage, and drop your final drive ratio down so low it'd also be worse for the engine as well. If it helps this is a fairly low horsepower application this is NOT a SFI turbo car). Curious for any input on this at all? Like I said, not too knowledgeable on the subject. Thanks.
 
Trans 3 or 4

You didn't say what year it was. Most cars were designed to give the best gas mileage in the late 70' early 80's as we had gas problem then. A 82 Regal had a 350C with 2.41 ratio. It would take along time to get up to speed. You would be right about having to much gear as you could spend most of the time in 3rd of a 4 speed trans. I did put a slightly larger tire on my car at that time, stock tire 195/75/14 to 205/75/14.
If you are after gas mileage use the 350c with the lockup clutch.
Diver
 
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