overdrive?
- Thread starter Guled22
- Start date
krly79
Member
it just locks up your converter and pulls down your rpms to get better gas mileage. You should leave it off for racing (unless you redline well before the lights, which I don't think that you will) because when it locks up then it goes 1:1 and thats not good for performance. I'm not sure how the 4r70w's are, but the 700r4's won't hold 4th at WOT unless they are built to do so.
RIP 112
New Member
O/D is exactly what what it says, OVERdrive. It's an extra gear to get better mileage, something to make the car run normal speeds than a 4speed. You can turn it off during heavy loads like climbing in Colorado, etc. But when racing at the track, you'll never hit overdrive in a 1/4, or even 4th for that matter. All turning O/D off will do is shut the 5th gear out and use 4th as a primary.
RIP 112
New Member
It all depends on the driver. I have a 03 GT 4R70W and I always leave it off until I get in the powerband and then turn it on as needed. But that's only my opinion. It works for me. A prelude has gobs of top end power, but I wouldn't let one beat me, I'd have to turn into Mario Andretti!!!!haha Another thing, if your timing is real good, I would manually shift the car from 1, then 2 into O/D off, then O/D on. It will let you be in control of the car and shift when you like. 4R70W's have a weird way of shifting, it's almost too early. I don't know if it's like that for your 97...
triggz
Founding Member
overdrive = 4th gear. simple as that.
the reason you are able to turn it off is, like was stated, climbing hills or pulling something so the trans doesnt keep trying to get into too high of a gear. (same reason you can select 1st/2nd)
the 4r70w is a 3speed + overdrive trans.
the planetary gear set in the transmission make up the 3 speeds, while overdrive is actually a 'band' instead. this band is not designed to be engaged at full-throttle. its just not that tough. around town, all youre doing is keepin it from going past 3rd gear...
if you're gonna be doing some highspeed racing, overdrive doesnt actually come into play until around 115-120mph (in a stock geared 99+ anyway)
with the 'lude catching up to you deal, thats probably due to the 97's poor head design for high rpms.
the reason you are able to turn it off is, like was stated, climbing hills or pulling something so the trans doesnt keep trying to get into too high of a gear. (same reason you can select 1st/2nd)
the 4r70w is a 3speed + overdrive trans.
the planetary gear set in the transmission make up the 3 speeds, while overdrive is actually a 'band' instead. this band is not designed to be engaged at full-throttle. its just not that tough. around town, all youre doing is keepin it from going past 3rd gear...
if you're gonna be doing some highspeed racing, overdrive doesnt actually come into play until around 115-120mph (in a stock geared 99+ anyway)
with the 'lude catching up to you deal, thats probably due to the 97's poor head design for high rpms.
RIP 112
New Member
3 speed w/ O/D?? Is there something I'm missing? I thought the 4r70w was a 4speed w/ O/D. Unless you're talking about the planetary being three speeds and two bands.
SN95StangMan
New Member
so when overdrive is on does it actually change the gear ratio's of the car or does it just turn the 4th gear off and on. It seems like the car accelerates much faster with it off. and too rip 112 when you said "I would manually shift the car from 1, then 2 into O/D off, then O/D on." At what RPMs do you shift into each gear, and should I start in neutral and rev it up and put it into first?
RIP 112
New Member
Guled22 said:
I manage about 4700rpm because it feels like the powerband peaks around 4500. You need an advance for the handshift because it takes the car a little time to function to the next shift. I suggest you test your car by taking it to a back road, shifting it in first and running it through the entire rpm range. Feel for the car to surge(mine usually starts about 4900-5000rpm) and find you a comfortable shift point. Do the same with 2nd. O/D can be shifted back on when you get to a good range in your final gear, anywhere's from 4500-4700. But I never make it there because My axle starts hopping at 125mph and it scares the crap out of me. I can't even imagine trying 150!! Since our cars are different You just have to find your preference. Play around with it a little. Hope this helps. Oh, I wouldn't suggest revving the car and then engaging into 1st because it will mess with your U-Joints and converter. I already cracked a pinion on the rear differential by doing that. Don't take any chances like that.
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krly79
Member
Guled22 said:
It actually just locks the converter up to slow it down and bring your rpms down. It isn't actually a gear per-say, but just slows down your converter and it seems like it shifted, but your converter just locked up and slowed your rpms down.
jstreet0204
Active Member
Overdrive is simply a 4th gear designed for highway cruising speed to reduce gas consumption. When drag racing in 1st, 2nd, and 3rd, it makes no difference to the car's performance whether the OD button is turned on or off. I leave it off just to make sure the car does not accidently shift into OD during the 1/4 mile. I trap at 130 mph in 3rd gear with 4.10's and 28 inch slicks. The lock-up feature of the torque converter is something totally different than OD. The converter can lock-up in 2nd, 3rd, or OD, depending on your speed and how the computer is programmed.Guled22 said:
Dark Knight GT
I can't get it up......ok that didn't sound right.
jimfitzgerald said:
What he said. I'm also going to be the jackazz in this thread and remind everyone of something......o/d is a BAND, not a GEAR.
J/K 
trinity_gt
10 Year Member
My god, I can't believe it took till post #13 to get this...
Overdrive is a gear ratio that results in the output shaft of the transmission spinning faster than the input shaft. That's it. It has nothing to do with torque converters. There can be more than one O/D gear in a trans: The 6-speed manual in a 2009 Corvette will actually have two overdrive gears; 5th gear is 0.71:1 while 6th is 0.57:1.
It's a highway gear. It's intended to reduce highway RPM to reduce fuel consumption and engine noise getting into the cabin. Your car feels slow in O/D because it is: With an O/D gear ratio, the torque at the output shaft of the transmission is actually less that that at the crankshaft. Contrast this with 1st gear where you get a multiplication. The 4R70W has a 1st gear of 2.84:1, meaning the input shaft spins 2.84 times the output shaft speed and you see a 2.84 times torque multiplication. So if your engine makes 300ft-lbs at 4000RPM, you'd see 852 ft-lbs of torque (300*2.84) at the output shaft of the trans which would be spinning at just over 1400RPM (4000/2.84).
Now go into overdrive: At 4000RPM your engine still makes 300ft-lbs but the O/D gear ratio is 0.70:1, meaning you'd see just 210 ft-lbs (300*0.7) at the trans output though it'd be spinning at 5714RPM (4000/0.7). You can see the obvious here: You're going to be going quite fast but the car is going to feel very, very sluggish.
And what if the car goes into O/D in town when you're puttering along at 1200RPM, where the engine is making 80ft-lbs of torque? 80*0.7 = 56-ftlbs: You couldn't even tighten a lugnut with that. No wonder the car feels sluggish and slow with O/D on. Indeed, some of the world's most powerful cars top out at a lower speed in O/D simply because even they don't have the torque to overcome what the O/D takes away. They do better with a lower gear where the RPM climbs some but so too does the torque.
A "band" is simply a device in the transmission designed to control the rotation of a drum. If you've ever used a band-type oil filter wrench, you get the idea of a band in a transmission. When a band is active, a piston moves causing the band to tighten over its drum, stopping the drum from turning. Depending on what other components are driven -- all switched with clutches etc -- the output shaft can end up turning faster than the input shaft, giving an overdrive.
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