Driving in D

[Stone]

I know this is a silly question, but what is the diffrence between driving in "D" and using the D overdrive? Some one told me that unless your on the highway you should just put in D around the city.

thanks
Mike

 

[buzzman]

Driving around town, you should be in the D overdrive, the D that is nearest the dash, if you are racing, put it in the bottom D.

 

[GNBeswick]

I was curious about this as well, why normal drive while racing? Isnt normal drive just 3rd gear, and overdrive is like 4th? 60mph in 3rd gear just sounds off to me, sounds like the engine is reving way to high, tho I know its not because the rpms show otherwise. Does drive go up to the same speed as overdrive? What is the advantage of racing in drive as opposed to overdrive?

 

[boosted3]

I always use Drive up to 45 mph and anything over that i shift to overdrive. The reason you shift to Drive(3rd) is............ #1) it is one less gear you have to downshift when you flatfoot it which is good for the tranny and ....#2) it brings the RPMs up higher so your boost comes in quicker and you can take off faster. I always downshift to at least 3rd when i race on a roll depending on the speed. sometimes i will go as low as second. And ...yes you can go faster in OD...it is another gear....1st....2nd...3rd...4th....Mostly a highway gear or a 4th if you run out of gear at the end of the track... Hope I helped you out!!

 

[GNBeswick]

Do you know what the top end of 3rd gear is?

 

[77tech9]

Originally posted by GNAsuka
Do you know what the top end of 3rd gear is?

WOT in my car 3rd ends at about 100 mph

 

[murphster]

The reason you keep it in Drive (not Overdrive) at the track is because it will shift into overdrive (4th gear) usually before the end of the 1/4 mile. The shift into overdrive can come early before 3rd gear is finished winding out and hurt your times.

For most people it is no problem to leave it in Drive during a 1/4 mile run, however the faster cars (say mid/low 12's and faster) can run out of gear and get too high of an rpm while in 3rd before the end of the 1/4 mile. Bigger tires like 28" will help reduce the rpms in 3rd so its not a problem. The very fast cars may have different gear ratios (?) and the rpms can probably go much higher due to engine work done.

For off track driving, the benefit of leaving it in Drive is that the response will be better since you don't have to downshift from overdrive to drive when giving it some gas. On the other hand, the higher rpms may be annoying on the highway and certainly isn't good for gas mileage.

 

[GNBeswick]

Very interesting, thanks for the detailed reply. Ill be sure to keep that in mind next time I hit up the track.

 

[2 SLOW]

OK, first the tranny was designed to be left in overdrive on the street for normal driving. If you can only go 100mph in third you have a problem with the motor. Probably weak valve springs. You should be able to go at least 115mph in third. I've gone almost 129mph on 26" tires with a lockup converter in 3rd gear. If you can go over 115mph in the quarter you will be in the 11's and making good power. If you shift into overdrive you will eventualy wipe out the weak clutches in 4th gear. It wasn't designed for that kind of abuse. The load of 4th gear will increase the risk of detonation and taking out the head gaskets. And it will slow your times down. I have a friend with a low 10 second car that goes 136-137mph on 28" tires with a non lockup and shifts into 4th at about 132. Its a beefed up tranny.

 

[BLACK6PACK]

Yeah, what 2 slow said.

Mine's always in OD unless I'm at the track. With my 26" nittos, I cross the 1/4 mile line at round 5300-5500 rpm at around 115 in 3rd.

Driving in the city at 45mph in OD I can pretty much idle at that speed. Bet I could get 50 mpg at 45-50mph. I would have to blow a bunch of stoplights and stopsigns though.

 

[Red Regal T]

I'm done at 110 in third. My stock cam has about 200K on it. I'm going to upgrade soon.

 

[Ormand]

OK, first the tranny was designed to be left in overdrive on the street for normal driving

As I remember the OD was an "add on" to the TH series, to help GM meet CAFE requirements. Not sure that it was "designed to be left in OD". The owners manual says to use D when increased performance is needed, such as on hilly rodas or when towing. But it does say to use OD for MOST normal driving. Around town, up to 45 or 50, I believe that D is needed for increased performance. If you are in OD, and need to accelerate, you have to floor the pedal, and get the downshift, which can cause problems if the road is damp or dirty. (Also takes time to happen) In D, the throttle response is much better, and violent downshifts can be more easily avoided. Since many of us have improved the response and power of the engine, I'm thinking that the use of OD would also have changed somewhat from "showroom stock".

 

[scottyb]

Leave it on OD for daily driving use. Not unly will it help your mileage, but running a lower RPM means less wear on the engine. Also, I notice mine downshift sooners when in drive under normal driving conditions, so this means more shifting when slowing for corners and engine braking = more wear. I only put it in drive when "playing".