someone verify? (or falsify?)

[chevyguy502]

i know using drive instead of od gives better pickup, but will it affect anything, besides gas economy? will it affect the speed in the higher gears? i dont think it will, but i wanted to make sure

[Ridenour]

Well the only thing using drive does instead of overdrive ( on an automatic assuming) is that it locks out overdrive; so your tranny doesn't lock into overdrive at cruising speeds. It won't effect anything; except keeping the tranny out of OD; so when you stomp on it it won't have to come out of od, and then downshift. At WOT, the tranny won't lock into od anyways. I would never disable od except for at the track, really. Unless your driving agressively in traffic, and don't want it unlocking and then downshifting when womping on it; then locking it out would be understandable.

[curtis73]

It will cause you engine to spin about 24% faster which is "harder" on it. I put that in quotes because its not usually 24% harder. Some combos have such a tall ratio on the highway that OD is too high. I had an Oldsmobile with an ovedrive and a 2.73 rear axle ratio. At 65 it was spinning at about 1400 rpms. That was too low. Contrast that with a Pontiac I have with an OD and 3.73s. Its not a high enough gear and the big engine is spinnng too fast for my comfort even in OD.

The good news is that its sometimes better for the tranny depending on its design.

[jveik]

hell i have a turbo 400 that dont even have overdrive!!!

[CBFryman]

is ite technically over drive if the differential ratio is so high it is no longer actually overdrive, or does it only refer to the over drive of the transmission?
anyway, OD off, as has already been stated, is for when racing or driving aggresively at speeds which the tranny may switch into overdrive thinking its going to stay cruising OR when you are towing and dont want it going in and out of OD while going up hills.

[curtis73]

Overdrive only applies to the tranny, but some mistake it for a cure-all for final drive ratio.

I currently have stock 3.08s in a car and after I swap in a 6-speed I'll put 4.10s in. People ask me why and I just have to do the math for them. The stock OD is .76. The 6-speed's OD is .50. So the stock final drive is 2.34. After the swap, the final drive will be 2.05. After the swap I'll have lower highway RPMs with 4.10s, but its hard for some to grasp that.

The bottom line is that it all depends on your final drive ratio. Some overdrives put RPMs in the basement while others barely keep it below redline.