Mid speed acceleration and rev's

[chisler]

Hello, with the holidays over, traffic increasing, and less room to test things out, thought I should ask some diesel experts (you guys), how acceleration best works.

I've been driving a new skoda rs tdi for almost 2 weeks now, and still unsure what Rev's are best to accelerate.

accelerating with high revs, (say about 4000) seems to work pretty much the same as a petrol car, speed gradually increases.
though when accelerating with low revs (say about 2000) theres always like this short pause, then BANG! my car shoots off, and my body feels like its been forced back, like I'm fighting gforces or something :eek:

it feels like acceleration is faster at low revs, so I would like to know "is low rev acceleration faster"? or am I being tricked here? is that short pause just making the acceleration feel more dramatic than it really is?

thanks in advance :driver:

[xvr6]

chisler
That is called turbo lag. You plant your foot and the turbo takes a few moments to spin up and, as you are telling the ECU that you want full noise, that when the turbo is up to speed and delivering a healthy boost it happens very quickly. This is the TDI rush and is part of the enjoyment, but it makes the traction control work hard and does shred tyres very quickly.
You will learn to tame it and anticipate it and then the rattly diesel will surprise people when you blow them in the weeds at the lights.

[Greg Roles]

Hey mate,

It's just the same as a petrol car, except the usable powerband is smaller, and more concentrated! 1800-3500rpm is where the fun is at, and as correctly pointed out above, the "rush" is simply turbo boost. Personally I think it's a very very good thing!

Below 1800rpm the engine isn't producing enough exhaust to spin the turbo to provide boost, so this is where the turbo "lags" or takes time to get it's speed up. Best to downchange gears and get higher in the revs. It will accelerate below this, but you're into a thing called "surge" and making the turbo work very hard and inefficently staying here too long, such as sitting on 80kph on the highway on cruise in 6th, where your revs are down below 1800rpm. You'll get a feel for it.

Over about 2000rpm the turbo will spin up very quickly when you demand it, and the more exhaust flowing, and thus revs, the quicker it's already spinning when you demand it. After about 3500 to 4000 rpm on the TDI the power drops off, and you're really just making noise, so try and keep the engine between 2000-4000 if you want power. In a manual you are pretty busy in traffic, but once you get a feel for it, you'll be fine. Listen to the motor, how it's performing, it's pretty obvious at either end of the rev range where it isn't happy.

It's a different driving style for sure, but I know going back to driving a manual turbo diesel has made me a FAR better driver than I was in an auto falcon where I was basically just steering.:driver:

[Buller_Scott]

X2.

it will take you a while to learn how to drive a TDi, but once you've got the hang of it, it'll be awesome fun- so much more entertaining than driving a NA petrol car.

just be careful to warm it up properly (until warm, rev to 2500 only, when warm, rev to atleast 3000rpm), and never jam your foot down on the loud pedal under 2000rpm, as this forces the turbo to boost close to limit, and (from my understanding) can be detrimental to the engine internals in some cases (big boost + lots of torque @ low revs = BAD).

Have fun.
scott

[chisler]

thanks everyone,
my car is DSG auto, and I've been switching from normal auto mode (which changes gears faster than I can blink), to Sports auto mode (which won't change gears until 4000 or so rpms)

I'll start using the manual triptronic system for the next few 1000k's, which hopefully will make it easier to figure out how my car will perform best.

still not sure I understand the 6th gear 100%, I did read its for economy as opposed to power.
but lets say in the following "hypothetical" scenario, I'm cruising down the road at say 150kph in 6th, and my rpm's are sitting at 2500, and I wish to accelerate, would it be best to still go down a gear? or it wouldn't matter at that point?

[VW Convert]

still not sure I understand the 6th gear 100%, I did read its for economy as opposed to power.
but lets say in the following "hypothetical" scenario, I'm cruising down the road at say 150kph in 6th, and my rpm's are sitting at 2500, and I wish to accelerate, would it be best to still go down a gear? or it wouldn't matter at that point?

It wouldn't matter really, your rear view mirror would probably be full of flashing blue and red lights! j:

I'm not sure your hypothetical is viable, as I would have thought that at 150 Ks the engine would be doing more than 2500 but in general terms, 6th gear will not give the best possible acceleration.

Cheers

George

[gregozedobe]

If you want absolute full tilt max acceleration from a TDI you want the engine between 3,000 and 3,600 rpm (any higher and you will get better acceleration in a higher gear).

Most people find a TDI pulls that well from 2,500 rpm onwards that they don't need to change down a gear as often as you would in a petrol. It is called surfing the torque curve. As long as the engine isn't lugging at too low a revs you can get away with higher gears than you would expect (and get better fuel economy to boot).

[gldgti]

thats all about right....

i would say to the hypothetical question - once you get to 180-190 6th will be the best ;-)

i have found as i get lazier and do mroe city driving that 3rd is my favorite gear, because i can go between 40km/h and 100km/h in that gear without too much effort :-)

ofcourse, thats probably more like hte coffee drinking gear for me, im not usually that lazy.... but you get my point

[Buller_Scott]

thanks everyone,
my car is DSG auto, and I've been switching from normal auto mode (which changes gears faster than I can blink), to Sports auto mode (which won't change gears until 4000 or so rpms)

I'll start using the manual triptronic system for the next few 1000k's, which hopefully will make it easier to figure out how my car will perform best.

still not sure I understand the 6th gear 100%, I did read its for economy as opposed to power.
but lets say in the following "hypothetical" scenario, I'm cruising down the road at say 150kph in 6th, and my rpm's are sitting at 2500, and I wish to accelerate, would it be best to still go down a gear? or it wouldn't matter at that point?

at that speed, personally, it wouldnt matter to me how fast i got from say 150kph to 180, as id be more concerned with getting busted for speeding, but yes- my understanding too, is that top gear is engineered for economy.

Alot of guys in the states/canada who mod the CRAP outta their earlier tdi's, are modding their 5th gears such that they are taller(i think) and more fuel efficient.

[chisler]

reading my posts again, I sound like some young hoon lol :drinkbeer:

but it was seriously a hypothetical, my last 14 years of driving has only been with company cars, so have always been very A to B driving in my thinking.
though I've recently found that dropping 40k on a new car, not only gets you sexy spoilers, but also come with free desire to understand how a car actually works :biggrin:

switching to the manual system, is helping alot to understand how my car best performs, for both performance and economy.

actually I'm becoming a bit of a fan of manual, never really understood why people liked manuals over auto's until now.
though I wonder.... is using a stick you only have to push a little forward or back (well not back much, cause gears automatically drop when slowing down) considered manual driving? :driver:

[gregozedobe]

My definition of a "manual" gearbox is "Where a human brain is the only thing that makes any decisions and directly controls actions relating to gear changes, clutch operation and engine revs".

Anything else I regard as some form of "auto" (and yes, that includes computer operated pseudo-manuals such as DSGs - you go make up your own definition if you don't like mine ;) )

So according to me, yes you are "manual driving", just not with a manual gearbox :)

And congratulations, you are well on the way to becoming a car enthusiast and actually enjoying your driving.

[Buller_Scott]

Hear Hear.

After my last car, i swore to myself that i would never drive auto again. Manual is just too much fun.