a few 4A questions......
 

im a nu b so im going to ask....just got my car 01 z28, since i got it i've been driving with the [D] a few days ago i put it in D, which i believe is overdrive, and the car feels different. does it really matter which one i drive in??? is one better than the other?? sorry for my ignorance..its my first ls1.

yes the [D] is overdrive. I mainly use it for the highway, anything over 45. The tranny will tend to down shift more than I like if I drive in O.D., so if I am just driving around town i keep it in D. The RPMs my stay a little higher than if I kept it in O.D., but I will pay a little more for gas rather than pay for a new tranny that much more sooner.

Just my opinion and preference

ok i had it wrong, [D]=overdrive and D=drive. since i got the car i've been driving it in overdrive, so today i drove it in D. I felt a difference, it seems like im over working the engine. and it also sounds different, engine as well as the exhaust.

Anything over about 45-50 mph and I switch from D to [D] (drive to overdrive). Keeps the RPMs down...

Overdrive is what should normally be driven in. The car will have the 4th gear to shift into while cruising, which keeps the RPMs down, therefore saving a bit more gas.

The reason it feels different in D is because you're keeping your revs higher. Do 40 or 50 mph in Overdrive and then do the same thing in D. Notice how many more RPMs you're turning? That's because in D, the engine is only using 3 gears and can't upshift to the 4th gear (overdrive). It is working the engine a bit harder by forcing it to turn more RPMs. The reason it sounds different is also because of the increase in RPMs; it will be a bit louder. As your speed increases while driving in D, you'll notice that when you take your foot off the pedal, the car will feel like it's "dragging" a bit and want to slow itself down quicker. This is simply the engine and transmission trying to drop the RPMs as a result of only using 3 gears.

Drive around town in overdrive. But if you want to floor it, drop the car into D, then punch it a second later. This is healthier for the transmission.

driving it in manual D also raises the line pressure in the tranny and applies more clutches particularly the overrun clutches which normally only come on in decel to give engine braking so in 3rd gear you have overun clutches,forward clutches, and 3-4 clutches applied so it may shift a little different in manual D just because of the line pressure issue

What if you are vacuum modded?

I would not manually down shift the tranny. The way I look at it, is that the tranny is a AUTOMATIC, therefore i let tranny automatically down shift itself. When the car is in [D] and just cruising around town, it tends to down shift with out giving it a whole lotta gas, that's why I like it in D.

He means put it down into D (3 for Pontiacs) before going WOT to prevent the 4-2 downshift.

your manual valve will set it in the boost position so yes even if vacumm modulated

ok, so youre saying its better to cruise in [D] instead of D? I did notice the dragging as well as the gas comsuption as well. and its better to puch it in D? im abit confused ...why would you punch it in D, if its over working the engine (and tranny i assume). which is better for the engine and tranny?? ispend the entire day driving in D yesterday, didnt go higher than 45.

thanks for the help

It also depends on whether you have 2.73 or 3.32 gears. If you have 2.73's, you may find leaving it in D makes for better driveability at lower speeds. With 3.23's you will probably be best just putting it in [D] (overdrive). Don't worry about what gear you're in when you punch it. Just punch it.