Are high RPMs bad for a turbo diesel?

teednab-el · 14-07-2011 12:56AM

Slightly off topic but I hate the way they rev the sh*t out of diesel cars at the NCT centre. What exactly are they looking for, surely emissions can be detected at lower RPMs? I had a nct mechanic an a*shole rev my car about 4 times at max revs for a minute each time and I didnt even recognise my own car engine. It sounded very bad for a car that I keep very well. So wrong.

Sobanek · 14-07-2011 02:13AM

teednab-el wrote: »

Slightly off topic but I hate the way they rev the sh*t out of diesel cars at the NCT centre. What exactly are they looking for, surely emissions can be detected a t looer RPMs? I had a nct mechanic (a*shole) rev my car about 4 times at max revs for a minute each time and I didnt even recognise my own car engine. It sounded very bad for a car that I keep very well. So wrong.

I felt the same when the V50 was passing its first NCT.

R.O.R · 14-07-2011 08:21AM

I think there is a better chance of the emissions being lower the higher the engine temperature, so if it's not looking good at low revs the NCT guys will rev the balls off the engine to raise the temperature to give it a better chance of passing.

14-07-2011 08:56AM

teednab-el wrote: »

Slightly off topic but I hate the way they rev the sh*t out of diesel cars at the NCT centre. What exactly are they looking for, surely emissions can be detected a t looer RPMs? I had a nct mechanic (a*shole) rev my car about 4 times at max revs for a minute each time and I didnt even recognise my own car engine. It sounded very bad for a car that I keep very well. So wrong.

R.O.R wrote: »

I think there is a better chance of the emissions being lower the higher the engine temperature, so if it's not looking good at low revs the NCT guys will rev the balls off the engine to raise the temperature to give it a better chance of passing.

The test states to being the diesel to the red line or rev limit whatever the term is. With a diesel the higher the revs the more smoke. Hardly the NCT staff's fault that they have to test the diesels this way.

Petrol cars are at idle and at 3000rpm ish iirc.

Mar4ix · 14-07-2011 09:21AM

my new vw polo i was unable rev more then 1.5 k., while parked.

keithclancy · 14-07-2011 09:29AM

The Volvo V50 2.0D Engines Turbo only kicks in at 1800 RPM and tops off at about 3200RPM.

I change at about 3000 driving briskly and about 2200 - 2500 driving to save fuel.

Depends on the engine really, but generally I'd change 3/4s of the way through the Turbo band.

Its what your used to I think, personally I think whatever is best for the job, i.e. 1.0Litre Petrol for around the City and a 2.0D for long distance.

Couldn't afford to run a Petrol, low road tax but 1.78 / liter, at 40,000km / year thats allot

snowman707 · 14-07-2011 09:58AM

if you have yo look at the rev counter to a drive any vehicle you may as well return to the L plates

the rpm will depend on the circumstances, I find most small diesel engines are happy about 2500 rpm, larger ( tractors with different ratio gearboxes etc) about 1800 rpm , a 'happy ' engine will last longer and is far more fuel efficient

4000 rpm changing gear is idiotic

EPM · 14-07-2011 10:00AM

Mar4ix wrote: »

my new vw polo i was unable rev more then 1.5 k., while parked.

Yeah, 3k revs on mine and it wont go any higher.

keithclancy · 14-07-2011 10:07AM

snowman707 wrote: »

if you have yo look at the rev counter to a drive any vehicle you may as well return to the L plates

Handy to know so you have a reference point for what sounds like high revs.

Otherwise your just guessing

I.E. changing at 16000 - 17000 RPM on a 250CC inline 4 would be normal
Getting a 125CC two stroke moving requires about 8000 RPM.
A 1.9 TDI will take off without any throttle at 900-1000RPM
A 1 liter petrol requires around 2000 - 2500 to take off.

If none of them had rev counters and it was your first time driving it you wouldn't have a clue (especially with 2 stroke engines, sound like their going to blow up)

ThisRegard · 14-07-2011 10:20AM

Just as a matter of interest, what's the thinking behind dropping the clutch and revving just before changing gear in a modern car with a modern gearbox ? I understand it may be a throwback to older gearboxes but why do some young lads still do it who probably have never driven an older car, is it the sound they like ?

ShiresV2 · 14-07-2011 10:24AM

ThisRegard wrote: »

Just as a matter of interest, what's the thinking behind dropping the clutch and revving just before changing gear in a modern car with a modern gearbox ? I understand it may be a throwback to older gearboxes but why do some young lads still do it who probably have never driven an older car, is it the sound they like ?

It's called rev-matching gear changes and you do it when going down the box. Makes for a smoother trip. Google it.

ThisRegard · 14-07-2011 10:42AM

I know what it is but with modern synchromesh there's no need for it or double clutching.

alanmc · 14-07-2011 10:50AM

keithclancy wrote: »

Handy to know so you have a reference point for what sounds like high revs.

Otherwise your just guessing

I.E. changing at 16000 - 17000 RPM on a 250CC inline 4 would be normal
Getting a 125CC two stroke moving requires about 8000 RPM.
A 1.9 TDI will take off without any throttle at 900-1000RPM
A 1 liter petrol requires around 2000 - 2500 to take off.

If none of them had rev counters and it was your first time driving it you wouldn't have a clue (especially with 2 stroke engines, sound like their going to blow up)

My first few cars didn't have rev counters.

Matt Simis · 14-07-2011 10:53AM

crosstownk wrote: »

As stated in many earlier posts, on a modern TD changing at approx 2,000rpm is optimum for most driving conditions. Yes it may clog the DPF but they're designed to clog. A regen cycle will have to be done at some stage. There's no point in redlining a TD as torque drops off rapidly.

Um, I find it hard to believe that changing gear at 2000RPM is "optimum" for anything other than saving fuel.
For fast driving you should change gear at 2/3 the max RPM for a diesel in my experience. On a 2.4JTD engine thats about 3800rpm, but its a lot less suck ass than more diesels.

The problem with changing low down on diesels wasnt clogging the DPF, it was causing excessive vibrations (on an already chuggy engine) to rapidly accelerate wear on the DMF (not DPF). Just cos you can change gear low doesnt in anyway mean you should.

Thatnastyboy · 14-07-2011 10:58AM

I dunno about those dirty muck burners,

but

I change gear at 9200rpm :P

Seriously though, the power range in a diesel is very short, but with huge amounts of torque. Wherever the power is, use that rev range.. simples.

I read a very good article explaining it all a while back ill try dig it out.

The article basically said, that if it was possible to get a diesel to make proper power efficiently and stay stable at high rpms, they would trounce any petrol engine..

But they can't, and won't!

ShiresV2 · 14-07-2011 10:59AM

ThisRegard wrote: »

I know what it is but with modern synchromesh there's no need for it or double clutching.

It's not directly related to concepts like to synchromesh and double declutching. See here:

http://tinyurl.com/67k7qbs

14-07-2011 11:00AM

dev100 wrote: »

Well that is unless you a real petrol head with a high performance car then i bow to ya

He is

You may take a bow

keithclancy · 14-07-2011 11:21AM

alanmc wrote: »

My first few cars didn't have rev counters.

Of course ... then its trial and error, rev counter can be handy though.

I hopped on an Aprilia RS125 Extrema, stalled it about 7 or 8 times before I got it to even move

ThisRegard · 14-07-2011 11:21AM

ShiresV2 wrote: »

It's not directly related to concepts like to synchromesh and double declutching. See here:

http://tinyurl.com/67k7qbs

As I said, I know what it is, but on modern cars whilst just driving around changing gear at the appropriate time there's no need for it, unless you're into traffic light gran prix.

TestTransmission · 14-07-2011 04:24PM

einheisserschre wrote: »

dev100 wrote: »

Well that is unless you a real petrol head with a high performance car then i bow to ya

He is

You may take a bow

Lol,I luv you too

crosstownk · 14-07-2011 08:15PM

Matt Simis wrote: »

Um, I find it hard to believe that changing gear at 2000RPM is "optimum" for anything other than saving fuel.
For fast driving you should change gear at 2/3 the max RPM for a diesel in my experience.

I agree. Changing at 2,000 RPM will have a fuel saving advantage assuming that the vehicle is being driven 'gently'. Naturally for a more spritely performance changing at higher RPM will have relevant advantages.

In most driving situations the gentle approach is sufficient (for me anyway) but I do wait for a higher RPM before changing in situations like overtaking.

Squall19 · 14-07-2011 10:35PM

Matt Simis wrote: »

Um, I find it hard to believe that changing gear at 2000RPM is "optimum" for anything other than saving fuel.
For fast driving you should change gear at 2/3 the max RPM for a diesel in my experience. On a 2.4JTD engine thats about 3800rpm, but its a lot less suck ass than more diesels.

.

I think your right there Matt.

Any powerful diesel I have ever driven like 330d, Alfa 2.4, Octavia Vrs needed changing at around 4000rpm and actually a little over that for the bmw , to make the quickest progress, they were all mapped except the Alfa which might have helped them rev.

1.3 diesel Corsa I had as rental in portugal was finished at 3500rpm.

Squall19 · 14-07-2011 10:49PM

Thatnastyboy wrote: »

I read a very good article explaining it all a while back ill try dig it out.

The article basically said, that if it was possible to get a diesel to make proper power efficiently and stay stable at high rpms, they would trounce any petrol engine..

But they can't, and won't!

They are getting closer though, a fellow on the pistonheads forum, had his BMW 335D making very good power at 5000rpm, it's power curve was very turbo petrol like with torque and bhp rising to near red line, was very impressive stuff.

I test drove the 2011 Mitsubishi Lancer 1.8 150bhp diesel with variable valve timing ( first for a diesel apparently ) and it was a very smooth drive for a diesel, it drove almost like a petrol with good torque at 3000rpm and max bhp is made at 4000rpm.

Imagine the sport varient?

Mitsu are supposedly using that tech for the next EVO, going all out with a 300bhp, 600nm torque ,2.5 diesel DiD lump that will do close to 40mpg and 60 in under 5 secs.If they achieve that it would be amazing imo.

Thatnastyboy · 14-07-2011 11:38PM

Squall19 wrote: »

They are getting closer though, a fellow on the pistonheads forum, had his BMW 335D making very good power at 5000rpm, it's power curve was very turbo petrol like with torque and bhp rising to near red line, was very impressive stuff.

I test drove the 2011 Mitsubishi Lancer 1.8 150bhp diesel with variable valve timing ( first for a diesel apparently ) and it was a very smooth drive for a diesel, it drove almost like a petrol with good torque at 3000rpm and max bhp is made at 4000rpm.

Imagine the sport varient?

Mitsu are supposedly using that tech for the next EVO, going all out with a 300bhp, 600nm torque ,2.5 diesel DiD lump that will do close to 40mpg and 60 in under 5 secs.If they achieve that it would be amazing imo.

Good points, and yes they are getting closer, no doubt, i had a spin of a 535d about a year ago and i really couldnt get over the power of it, it really went like fook.

But, it is a 3l 6cyl with 2 turbos, It would want to be powerful in fairness.

The equivelent in a petrol powered engine would put out much more power than the diesel imo, it would maybe be lacking the giant wall of torque, but it would rev properly and make noise to boot.

I'm in no way diesel bashing, if i was to buy a new car i'd buy a diesel: a diesel bmw.

But, since my hobby is buying old cars, i buy n.a petrol motors. much more fun to drive i reckon.

Re: The diesel evo, sounds good, but i dont think it would be as much fun as a petrol, i think it would lack the revs, and the noise.. 2 very important fun factors in my idea of a sports car.

Needler · 14-07-2011 11:52PM

ThisRegard wrote: »

I know what it is but with modern synchromesh there's no need for it or double clutching.

Maybe to prevent wear on the synchros but I dunno if this helps

Are high RPMs bad for a turbo diesel?

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