Gear Changing in vRS

[rainbow-walker]

Hiya all,

If we ignore economy, and smoothness of ride, and assume that the aim is to reach cruising speed as quickly as possible, what are the best revs to change up ?

Is it at peak torque, or peak power, or somewhere in the middle ?

Peak power is at 4000rpm
Peak torque is at 1900rpm

In practice, when accelerating briskly I tend to change between 3-3,500 rpms.

What says you ?

Cheers.

RBW.

[WW_VRS]

If it is standard (i.e. not remapped, and no green filter/PD160 air intake), then it pretty much is over by 3800rpm, revving higher won't gain much if anything.

I sure wouldn't waste much time in 1st gear, i.e. as soon as you are moving sufficiently drop into 2nd, it will go very nicely. Depending on target speed, pull through to 3800ish in 3rd then drop into 4th, or if you're nearly there anyway, just drop it into 4th and then stick into 5th/6th

Remapped you can pull through higher, mine tails off when it hits the red so it seems but it may differ depending on map.

The thing to remember is the torque at the wheels, and having sufficient power to offset the resistance of pushing the car forward at a particular speed

[rainbow-walker]

Good point about lower gears, yes 1st gear isnt really usable at high revs is it, lots of wheel spin !

mmmm @ Quaife LSD... what sort of power is yours kicking out WW_VRS ? (and I dont mean the A2 !).

[WW_VRS]

About 160-170ish (once fixed again) at a minimum but it's not been RRed (ever). It has a phase 1 custom code remap on it + propane injection.

However Jason (Devonutopia) has a fairly similar setup and he's running 200+ bhp at the moment IIRC.

The Limited Slip Diff is excellent as it really helps put the power down

(PS the A2 isn't too bad considering it is a 1.4 TDI that was remapped too )

[vindaloo]

Without a remap there seems to be a flat spot around 3K rpm, so holding on to the death (4K+ rpm) in lower gears so you drop back higher up in the rev range is worthwhile.

J.

[ScoobyChris]

I found that on the vRS taking it to 4k from 2nd upwards seemed to be the best way of accelerating briskly although it does seem to run out of steam above 3.5k.....

Obviously remapped/tuning boxed, it will pull right up to the red line so it's harder to feel the right point to change as the power just keeps coming!

Chris

[WW_VRS]

When it hits the red I tend to drop in the next up cogs though

[adamC]

If i am giving it some tend to get out of 1st asap then take it to 3k in each gear as it seems that if you change gear at 3 k you start the next at the 2k mark so get the full torque again. Maybe just me but tends to see of a few

[wja96]

The torque will fool you into changing up early. Don't be fooled. Change up at the red-line for maximum acceleration. Use good diesel and teh engine will remap itself a little to make better use of the better fuel at the high-end.

[WW_VRS]

I'd avoid pulling too much over 3800 rpm unless you've remapped it though, it gets VERY slow getting higher up the rev range. It runs out of air/boost/derv pretty sharpishly at that point.

The learning ECU is very true though, it does adjust with driving, although in my case that's actually not a good thing as I tend to cruise at pace and/or do economy run (during office hours/rush hours there is hardly ever a point in going that fast ). Then when I want to have a bit of fun the learning ECU gets in the way a little (for a while )

[jjj84]

Always change after max power. No matter what car or how much power or torque, always rev at least to peak power.

If peak power is at 4000rpm best place to change would be around 4000-4200rpm.

If you rev it too much (like 4500rpm) it wouldnt do any good because next gear would be giving you more power at that speed.

Simple physics...

If you have dynographs of your own engine, from there you can calculate best shiftpoints...

[wja96]

Originally Posted by WW_VRS

I'd avoid pulling too much over 3800 rpm unless you've remapped it though, it gets VERY slow getting higher up the rev range. It runs out of air/boost/derv pretty sharpishly at that point.)

It just feels like it's slowing down because you're not getting the torque shove any more. It takes much longer to change gear than to red-line it and revs x gears = speed so you get there quicker if you keep the foot planted. One of the main reasons the vRS has such a crappy 0-60 time is the gearing. You have to change up to 3rd to hit 60mph. If second gear was longer it would have worse 0-50 times but a better 0-60 time.

And my unchipped motor positively flies round to the red line. in 1st, 2nd or 3rd which makes 90 mph all too easy to reach very fast.

[wja96]

Originally Posted by jjj84

Always change after max power. No matter what car or how much power or torque, always rev at least to peak power.

If peak power is at 4000rpm best place to change would be around 4000-4200rpm.

If you rev it too much (like 4500rpm) it wouldnt do any good because next gear would be giving you more power at that speed.

Simple physics...

If you have dynographs of your own engine, from there you can calculate best shiftpoints...

What you say is absolutely true assuming you can pick your own gear ratios. This is why 'close ratio' gearboxes are good for fast accelleration but bad for fuel economy. The Fabia vRS gearbox is a compromise so it's not a true 'close ratio' box but it's not bad. In a standard car, you have the gear ratio's you got from the factory so you want to change gear at the point that the next gear will be allowing the engine to develop the most power.

What happens in reality is that you need to be going as fast as possible in each gear to do this. You can check this for yourself in a Golf TDI with the DSG gearbox. It actually accelerates faster than the standard car because even an expert driver cannot out-shift the DSG 'box and it revs to the red line to do it.

[rainbow-walker]

Interesting info, so the fastest way is to rev to peak power...

Except in 1st gear, 2nd gear etc..

Cheers.

RBW.

[Schern]

You can definitely feel it come on peak power at 4k, but theres definitely a lull between 3500-3900, then it picks up again as it hits peak power. It always surprises me a little bit as you think its all done, and then it picks up its skirts for one last surge!

[P-A]

Originally Posted by adamC

If i am giving it some tend to get out of 1st asap then take it to 3k in each gear as it seems that if you change gear at 3 k you start the next at the 2k mark so get the full torque again. Maybe just me but tends to see of a few

Spot on! In order to get the best out of diesel engines it's the torque range (not max BHP) that you need to think about. Peak torque is between 2-3k rpm so it's best to change gear at around 3k rpm. Leaving it later with see the torque tail off quite quickly. People used to petrol engines will always change as late as possible, diesel driving requires a different driving style.

[jjj84]

Originally Posted by P-A

Spot on! In order to get the best out of diesel engines it's the torque range (not max BHP) that you need to think about. Peak torque is between 2-3k rpm so it's best to change gear at around 3k rpm.

Wrong...

Horsepower vs torque (everyone should read this article)

"The classic mistake is to conclude that the fastest way down, let's say, a 1/4 mile drag strip is to keep the engine RPM at the torque peak (or as close as possible)."

"Isn't your acceleration greatest at the torque peak? Yes, it is! But only within that gear. The next gear down will give you even greater acceleration at the same speed, unless the vehicle speed is too high for that gear."

"There are no exceptions; a car running at its (net) power peak can accelerate no harder at that same vehicle speed. There is no better gear to choose, even if another gear would place the engine closer to its torque peak. You'll find that a car running at peak power at a given vehicle speed is delivering the maximum possible torque to the tires (although the engine may not be spinning at its torque peak). This derives immediately from first principles in physics."

"If you exceed the maximum traction available from the tires, then additional power doesn't help. That's why it's sometimes no loss at all to shift early when the tires break loose, and in fact it can be a benefit." This is why in fabia rs you would like to change gear before redline in first gear.

I hope that noboby after this will claim that using torque is the most fastest way to accelerate..

[franv8]

Originally Posted by wja96

It just feels like it's slowing down because you're not getting the torque shove any more. It takes much longer to change gear than to red-line it and revs x gears = speed so you get there quicker if you keep the foot planted. One of the main reasons the vRS has such a crappy 0-60 time is the gearing. You have to change up to 3rd to hit 60mph. If second gear was longer it would have worse 0-50 times but a better 0-60 time.

And my unchipped motor positively flies round to the red line. in 1st, 2nd or 3rd which makes 90 mph all too easy to reach very fast.

Can mostly agree with that! Back in '86 the auto Corvettes were 0.3 sec FASTER to 60 than the manuals, and I have to say I've taken many faster cars while they were busy chaging gear!

I used to have some electronics book that showed you how to build a very crude G-meter (Listen up all G-Tech owners!) - and then suggested you plot acceleration charts for each gear, then you can easily see where you need to change to keep the 'G' highest for the longest.