Hey guys my vrs mk1 is boosting fine low revs but as I get to higher revs it seems to lose boost any idears?

any lights glowing on the dash? any codes in ecu? has it been mapped? **** map maybe

If it's standard sounds like it's ok,there is little point going over 3000rpm with a standard set-up

It's normal that you run out of torque around 3800-4000 revs if mapped

I don't know about standard if it goes to redline

Its been maped but other than that engine wise is standerd

It used to pull all the way through to next gear change but now it seem to lose boost then over rev

Over rev?

Is the clutch slipping?

Would also make it feel like it's losing power when it starts to slip.

Lose boost and over Rev sounds like clutch slipping.

I dont know clutch seems ok I will have a proper look at it today could it be a boost leak by any chance?

No a boost leak would lose boost all the time,and you would have a whooshing/air escaping noise.

And it wouldn't do the over rev symptom you described.

If it's standard sounds like it's ok,there is little point going over 3000rpm with a standard set-up

Why do people keep on stating this? The car makes maximum torque at 1900rpm but maximum power at 4000rpm and revving the car all the way to the redline drops you higher up the power band in the next gear when you change, plus speed is revs x gearing so more revs always equals more speed.

If you limit yourself to 3000rpm then you're driving a 110bhp car because that's all the power it makes at 3000rpm.

Yes, I completeky understand that when the torque drops away it feels like it's not accelerating as fast, but it is. Honest.

Why do people keep on stating this? The car makes maximum torque at 1900rpm but maximum power at 4000rpm and revving the car all the way to the redline drops you higher up the power band in the next gear when you change, plus speed is revs x gearing so more revs always equals more speed.

If you limit yourself to 3000rpm then you're driving a 110bhp car because that's all the power it makes at 3000rpm.

Yes, I completeky understand that when the torque drops away it feels like it's not accelerating as fast, but it is. Honest.

More revs equals more speed yeah, but if the revs are not rising as fast as they could be in a higher gear you are accelerating slower.

Not a chance the standard set up is accelerating as fast at high revs with low torque.

The cross over point between torque and bhp is the best place to change gear, and that is not 4000rpm!

Errrr I think you probably need to differentiate between the torque that you FEEL as acceleration and actual acceleration, which is done by power, not torque. Your butt-dyno is lying to you.

Errrr I think you probably need to differentiate between the torque that you FEEL as acceleration and actual acceleration, which is done by power, not torque. Your butt-dyno is lying to you.

if your car has a significantly higher torque figure than bhp (most turbo dervs) the fastest way to accelerate is to keep the engine in the torque power band, not rev it out where the torque has all but disappeared.

So you reckon on a 1/4 mile run you would cover the 1/4 mile faster by revving the engine to 4000rpm before changing gear rather than changing earlier and keeping in the high part of torque band in a standard pd130 engined car?

if your car has a significantly higher torque figure than bhp (most turbo dervs) the fastest way to accelerate is to keep the engine in the torque power band, not rev it out where the torque has all but disappeared.

So you reckon on a 1/4 mile run you would cover the 1/4 mile faster by revving the engine to 4000rpm before changing gear rather than changing earlier and keeping in the high part of torque band in a standard pd130 engined car?

If you think about what I'm saying you will see I'm correct.

Compare the old 2.0TFSi Skoda Octavia vRS with the equivalent CR170. There were two versions of the TFSi engine. One had 280Nm torque and 197PS and the other had 350Nm torque and 211PS.

The CR170 always had 170PS at 4200rpm and 350Nm at 2200rpm.

Irrespective of the torque both petrol cars were substantially faster in a standing start race because they had more power. Try suggesting to the TFSi 211PS car driver that he should shift up at anything less than 6500rpm maximum revs and he'll just laugh at you. 350Nm torque or not.

The torque is the length of the lever but you still need power to do the work.

Or the CR170 with the DSG gearbox. In sport mode, if it genuinely was faster to short shift, don't you think the people who made the car would have programmed the gearbox to shift up early? I think they would have, instead of which it revs all the way to the red line before it shifts up. Because that's fastest. Petrol or diesel.

On my SLK CDi250 it has 500Nm torque at 2000rpm. It's full automatic. In Sport mode, when do you think it changes up? Yep, you guessed it, at the 4400rpm red line.

Sorry, but unless you know something that all the automotive engineers in the world apparently don't know then I suspect that you are just repeating something that feels fast rather than what actually IS fastest.

Kev is right, if peak torque is at 1900 rpm and the close ratio gearbox drops 1000 rpm between gears then changing at 2900 rpm will provide the greatest acceleration, the only reason to hang on to a gear longer is if you happen to be cornering and changing gear will upset the handling due to the momentary unweighting of the back end. Some cars will achieve their best top speeds in fifth rather sixth if top gear is an overdrive. Other than that, no.

If you think about what I'm saying you will see I'm correct.

Compare the old 2.0TFSi Skoda Octavia vRS with the equivalent CR170. There were two versions of the TFSi engine. One had 280Nm torque and 197PS and the other had 350Nm torque and 211PS.

The CR170 always had 170PS at 4200rpm and 350Nm at 2200rpm.

Irrespective of the torque both petrol cars were substantially faster in a standing start race because they had more power. Try suggesting to the TFSi 211PS car driver that he should shift up at anything less than 6500rpm maximum revs and he'll just laugh at you. 350Nm torque or not.

The torque is the length of the lever but you still need power to do the work.

Or the CR170 with the DSG gearbox. In sport mode, if it genuinely was faster to short shift, don't you think the people who made the car would have programmed the gearbox to shift up early? I think they would have, instead of which it revs all the way to the red line before it shifts up. Because that's fastest. Petrol or diesel.

On my SLK CDi250 it has 500Nm torque at 2000rpm. It's full automatic. In Sport mode, when do you think it changes up? Yep, you guessed it, at the 4400rpm red line.

Sorry, but unless you know something that all the automotive engineers in the world apparently don't know then I suspect that you are just repeating something that feels fast rather than what actually IS fastest.

Just to make you feel like a racing driver it revs right up there!

Watch the speedo and rev counter slow down once you pass the peak torque point, I'm talking from driving experience.

Just cause your m8's down Mcd's tell you its fastest to bounce off the limiter in each gear doesn't mean it is

Just to make you feel like a racing driver it revs right up there!

Watch the speedo and rev counter slow down once you pass the peak torque point, I'm talking from driving experience.

Just cause your m8's down Mcd's tell you its fastest to bounce off the limiter in each gear doesn't mean it is

I race cars at a reasonably high level (I've finished top 3 in historic rallies) and I promise you, no one is short shifting. If a racing driver revs all the way, that's because it's fastest.

And yes, if I rev-limit your PD130 and i don't Rev-limit mine I will be faster over the quarter mile.

Do people talk about power to weight ratio, or torque to weight ratio? :think:

 

Some good ideas about the physics here from 'Stingray' on page 1.

 

Edit:  my favourite bit of what he says,

 

" In a given gear, the instantaneous acceleration is highest at the torque peak. At a given speed, a vehicle allowed to select any gear ratio will have the highest instantaneous acceleration at the power peak. If that sounds contradictory, try reading it a couple of times. The first condition has you choose a gear and vary speed. In the second, you fix speed and vary the gear ratio"

 

[my emphasis].

I race cars at a reasonably high level (I've finished top 3 in historic rallies) and I promise you, no one is short shifting. If a racing driver revs all the way, that's because it's fastest.

And yes, if I rev-limit your PD130 and i don't Rev-limit mine I will be faster over the quarter mile.

 

I can categorically assure you that it is your butt-dyno which is deficient:

 

http://physics.stackexchange.com/questions/57800/calculating-the-acceleration-of-a-car

 

Forget the quarter mile or any other standing start scenario with a fixed terminal speed, if you and kev are in identical standard VRS's next to each other and you're both rolling side by side and you both accelerate as hard as possible to Vmax then kev will win comfortably using his technique. End of.

 

That's why you're a driver and I'm an engineer.

I race cars at a reasonably high level (I've finished top 3 in historic rallies) and I promise you, no one is short shifting. If a racing driver revs all the way, that's because it's fastest.

And yes, if I rev-limit your PD130 and i don't Rev-limit mine I will be faster over the quarter mile.

This thread was about a pd130 vrs, not a high revving low torque rally car.

I race cars at a reasonably high level (I've finished top 3 in historic rallies) and I promise you, no one is short shifting. If a racing driver revs all the way, that's because it's fastest.

And yes, if I rev-limit your PD130 and i don't Rev-limit mine I will be faster over the quarter mile.

Well done you race cars. You are forgetting that on a race/rally engine they have been tuned to the maximum potential, most likely costing of high lift cams and the like, thus shifting the power and torque bands further up the rev range meaning high rpm gear changes are better suited in this situation.

We are talking about a run of the mill factory standard road car which has economy in mind when it was produced.

I can categorically assure you that it is your butt-dyno which is deficient:

http://physics.stackexchange.com/questions/57800/calculating-the-acceleration-of-a-car

Forget the quarter mile or any other standing start scenario with a fixed terminal speed,

But why should the fastest not always be the fastest? Car engineers don't program the gearboxes on DSGs to shift up early for the simple reason that revving them to the red line IS faster.

if you and kev are in identical standard VRS's next to each other and you're both rolling side by side and you both accelerate as hard as possible to Vmax then kev will win comfortably using his technique. End of.

There was a thread a few days ago where someone was remembering the Skoda advertising blurb from the early days of the vRS and quoting how it was faster than a Lotus Elise or a Porsche Turbo. It was, just under specific gear and speed conditions.

As an engineer, please explain why when Shark or any other tuner remap a DSG gearbox they don't remap it so it short shifts as this would make them super-fast, surely?

This thread was about a pd130 vrs, not a high revving low torque rally car.

Have you seen the torque curve on a SAAB 96 V4? 1.85l revving to a maximum of 6700rpm and more torque than a Fabia vRS. Only a 4 speed gearbox though.

The fact is you haven't given ANY satisfactory response to the simple question I posed. IF, AS YOU SAY, THE FASTEST WAY TO DRIVE A LOW REVVING, HIGH TORQUE, DIESEL IS TO SHORT-SHIFT, WHY DO THE MANUFACTURERS PROGRAM THE DSG GEARBOXES TO CHANGE UP AT THE RED LINE?

The answer is simple. It's ultimately the power that does the work and they make the power higher in the Rev range so you rev past the maximum power so when you drop back it's closest to maximum power which gives to maximum acceleration.

For you to be correct, EVERY car manufacturer and remapper in the world would have to be wrong.