ding chavez

I got a 99 z28, mostly stock despite a few bolt ons including exhaust and lid. Gears are stock. I have the stock a4 tranny, and never thought twice about using D opposed to [D]. I read in the manual the drive provides more power; perhaps if someone is towing or traveling uphill. I have been driving in regular drive recently and noticed a nice increase in performance, and a lot more power in any gear, especially at low RPMs. There have been times when I punched my car in overdrive, and watched the RPMS slowly rise instead of exploding and the car throwing me down the road. However, in regular drive, I have more power at the command of my foot. Is this normal? I know the only downside of driving in regular drive is lower fuel economy, but its just more fun. When i descend down hills my exhaust rumbles, and it sounds sick! So whats the difference? Is overdrive simply an extra gear for the car to travel in, because i feel like in regular drive my car doesnt downshift as much. Please discuss how you drive your a4

twitchtwice

iTrader: (12)

it depends on how fast you are going, if you are going highway speeds the reason it blasts forward is probably because the car is in third gear and doesn't downshift from 4th.

joecar

In OD or [D] the available gears are: 1st, 2nd, 3rd, 4th.

In D the available gears are 1st, 2nd, 3rd.

4th gear has ratio 0.696 (keeps engine RPM lower for a given MPH).
3rd gear has ratio 1.000 (keeps engine RPM higher for a given MPH).

3rd gear usually keeps engine RPM in the engine's torquey region, that's why 3rd gives quicker acceleration than 4th.


When in [D] you punch the throttle, there are two situations (keeping it simple):

- your MPH is sufficiently low to allow the PCM to shift the trans from 4th to 3rd (the RPM should jump up and your MPH should rise quickly);

- your MPH is above the downshift threshold, so the PCM keeps the trans in 4th (your RPM rise slowly as does your MPH).

shtnfrds

iTrader: (1)

anything above 45 i use OD, keeps the tranny from shifting so much and lasts longer IMO.

CoolAid

Race in [D] or 4th or overdrive or whatever it is in Mullets. Racing in 3rd engages the overrun clutches and is no bueno.

TXZ28LS1

iTrader: (5)

i keep it in OD for everything.

blackfang

iTrader: (2)

That is what I heard too.

I race mine in OD and on the highway over 45-50. If I am under those speeds or stop n go, I have it in D

PedaltoMetal

In manual 3rd the overrun frictions are applied (but only in 3rd) that's why your getting compression braking. (That rumble you hear when you let off the gas).

Why is racing in 3rd bad? Bringing on the overrun frictions adds support to the input sprag.

CHRRRIS

I was told by many in a previous thread that when I hit the strip to race in D. I leave it in D around town as well since I cruise around 45mph and that's about the speed the tranny can't decide between 3rd and 4th. If I'm gonna be on the highway then I'll pop it in OD but that's about it.

FLT

iTrader: (1)

I fully agree with this statement. Personally if you are going to race on the highway dropping it down in D3 first will help with the band release. Then punch it and let the computer do the work. When going fast and it is time to get into OD under full throttle, just bump the shifter into OD and keep going. To me it just makes sense.

As far as what the OP has posted, I wonder if what is stated on the owners manual has something to do with the computer programming. Basically making reference to things like TQ management and timing here. Might be something to consider. Vince B