Overdrive Off Button Use On Free Way..

[kidafa]

Hi All,

Just wondering if you guys use the overdrive off button very much if at all on your S1 Stags. I had a play with it for the first time today on the drive to work(I live in eastern suburbs and work at mt barker).

So i drive up the freeway each day and my EBC gives me the boost pressure read out (usually have it set on low for this drive). Anyway more to the point. Going up the freeway from adelaide to mt barked is pretty much a slight uphill the entire time. So if i let the car use the overdrive (4th gear) it pretty much sits on a bit of boost somewhere between 2 and 3 psi for most of the trip and at about 2.5/3000 rmp.

If i click the od off button it sits at higher rev range but use's alot less boost if any at all. My SAFC only starts to bend the fuel ratios about 3000rpm so im wondering which would be better to cruise on on my way to work with overdrive on or off.

Hope that makes sene :S? PS ive had a search and none of the previous threads really suit my quesiton.

[Johnny]

I used to turn the overdrive off and let it run in 3rd gear on roads which have a slight incline. Definitely fine: more revs but less load on the engine and less fuel.

[Xmetal]

Makes for a good kick-down button too for overtaking.

[Tangles]

always using my auto as a manual(ish)

[KiwiRS4T]

The overdrive button is a throwback to the eighties when jap autos used to have three speed + overdrive instead of a proper 4 or 5 speed auto. I would be interested in the basis for people's assertion that they use less fuel by driving around in third gear. The whole point of higher gearing is to save engine wear and fuel. It is true that some underpowered and overgeared cars may use more fuel because you have to have the foot flat all the time to make progress but I don't find that with my Stagea. Normally the most economical driving style is to accelerate briskly to your desired cruising speed and then maintain that with the minimum throttle opening at which point your Air/fuel ratios should be at their most economical (around 14 to1).

Having said that it is possible that under unusual circumstances, such as the continuous uphill referred to above, third gear might be more economical but I would try a week in third and a week in 4th accurately measuring the fuel consumption each week to get a true comparison.

[zoomzoom]

if its a hill where i know i need to accelerate quickly ill put it into overdrive, but leaving it top gear should be more efficient if youre not in a hurry. more revs means more energy lost through heat.

the point about it being "on" boost isnt really the proper way to think about it. the rate at which the engine uses fuel is proportional to the rate at which the mass of air is going into the intake.

x revs at y psi of boost will draw the same mass of air if you increase the revs and lower the intake pressure. not to mention pressure also is affected by heat as well as mass in a volume.

the difference is that lower revs and forcing more air into the cylinders should increase thermal efficiency...same mass of air as a larger NA engine would normally draw in, with less cylinder surface area to lose heat

freeway speeds.....definitely let it go into top gear.

[KiwiRS4T]

if its a hill where i know i need to accelerate quickly ill put it into overdrive [i guess you mean you'll push the "overdrive off" button, thus putting it into third gear], but leaving it in top gear [i guess you mean "overdrive" or 4th gear] should be more efficient if youre not in a hurry. more revs means more energy lost through heat.

the point about it being "on" boost isnt really the proper way to think about it. the rate at which the engine uses fuel is proportional to the rate at which the mass of air is going into the intake.

x revs at y psi of boost will draw the same mass of air if you increase the revs and lower the intake pressure. not to mention pressure also is affected by heat as well as mass in a volume.

the difference is that lower revs and forcing more air into the cylinders should increase thermal efficiency...same mass of air as a larger NA engine would normally draw in, with less cylinder surface area to lose heat

freeway speeds.....definitely let it go into top [4th or " overdrive" ] gear.

It would be simpler if they had just put in a 4 speed auto. When I bought my car the only manuals were the RS260 at about 4 times the price of a RS4T but now there are quite a few "S" (manuals) for sale at about twice the price of an RS and if I were buying today I would definitely buy a manual.

[zoomzoom]

i have a bad habit of saying "putting it into overdrive" when i mean "out" of overdrive.

although an auto trans bugs me from a performance standpoint it does make it easier to drive around town given the size of the car that it is.

probably better in snow too as the torque delivery is smoother than a manual in its operation, but im yet to back that up by taking the stagea out to the snow

[Sydneykid]

It would be simpler if they had just put in a 4 speed auto.

It is a 4 speed auto, the button simply stops it from shifting into 4th. It also stops, rather it delays (for a long time), the torque converter lock up, so you get slip.

You also have the option of only using 1st and 2nd via the selector.

Plus by selecting snow mode you eliminate 1st and it starts in 2nd.

Overall a very useful auto gearbox, especially when coupled with the best 4wd system.

As for using less fuel in 3rd gear, not based on what I have seen in the injector duty cycle. Which after all is a far more accurate method of determining fuel economy than looking at a boost guage.

Cheers

Gary