Why do diesels accelerate so slowly even with high torque?

[Cerano]

I thought torque is the turning force that pushes the car off the line? So with so much torque how come they're still slower?

 

1.Diesel engines, because they have much higher compression ratios (20:1 for a typical diesel vs. 8:1 for a typical gasoline engine), tend to be heavier than an equivalent gasoline engine.

2.Diesel engines also tend to be more expensive.

3.Diesel engines, because of the weight and compression ratio, tend to have lower maximum RPM ranges than gasoline engines (see Question 381 for details). This makes diesel engines high torque rather than high horsepower, and that tends to make diesel cars slow in terms of acceleration.

4.Diesel engines must be fuel injected, and in the past fuel injection was expensive and less reliable.

5.Diesel engines tend to produce more smoke and "smell funny."

6.Diesel engines are harder to start in cold weather, and if they contain glow plugs, diesel engines can require you to wait before starting the engine so the glow plugs can heat up.

7.Diesel engines are much noisier and tend to vibrate.

8.Diesel fuel is less readily available than gasoline.

 

http://auto.howstuffworks.com/question399.htm

[Yeobh]

Looks like the write-up is ( is abit out of date) applicable to those diesel engines designed with cast iron cylinder heads, for industrial and construction applications/ machineries and are not "high speed diesel ". They are using the old diesel fuel multi injection pumps and not the common rail type.

Present days High speed automotive diesel engines behave almost like petrol injection engines.

Edited May 26, 2010 by Yeobh

[Evoluzio]

I thought torque is the turning force that pushes the car off the line? So with so much torque how come they're still slower?

 

1.Diesel engines, because they have much higher compression ratios (20:1 for a typical diesel vs. 8:1 for a typical gasoline engine), tend to be heavier than an equivalent gasoline engine.

2.Diesel engines also tend to be more expensive.

3.Diesel engines, because of the weight and compression ratio, tend to have lower maximum RPM ranges than gasoline engines (see Question 381 for details). This makes diesel engines high torque rather than high horsepower, and that tends to make diesel cars slow in terms of acceleration.

4.Diesel engines must be fuel injected, and in the past fuel injection was expensive and less reliable.

5.Diesel engines tend to produce more smoke and "smell funny."

6.Diesel engines are harder to start in cold weather, and if they contain glow plugs, diesel engines can require you to wait before starting the engine so the glow plugs can heat up.

7.Diesel engines are much noisier and tend to vibrate.

8.Diesel fuel is less readily available than gasoline.

 

http://auto.howstuffworks.com/question399.htm

 

 

All the above don't address the question. It's the right foot, dude.

[ER-3682]

Today's Diesel are not slow at all,look at the newer Taxis,Kias & Mercs,all very fast.

[Rawsushi]

Umm.. you know diesel powered cars have been winning Le Mans endurance races for many many years already?

[Boyboy]

heavy flywheel, long stroke. so it's much harder to pick up revs in general. the torque is still there to haul a$$ but heavy duty diesels will still have poor pickup. top speed can be excellent still, though. just look at those huge buses flying along NSH

 

but for smaller commonrail turbo, the pickup can be awesome. especially from 1.5krpm to abt 4k rpm. after that the torque drops off drastically.

 

my 0-70 is seriously damn amazing, 70-100 tapers off somewhat so the century sprint timings are just under 10s only. on paper looks like crap but still can out accelerate most turbo or large cc cars for the first 100m at least. of course they will disappear into the distance eventually but in SG, initial pickup rocks

[Joseph22]

heavy flywheel, long stroke. so it's much harder to pick up revs in general. the torque is still there to haul a$$ but heavy duty diesels will still have poor pickup. top speed can be excellent still, though. just look at those huge buses flying along NSH

 

but for smaller commonrail turbo, the pickup can be awesome. especially from 1.5krpm to abt 4k rpm. after that the torque drops off drastically.

 

my 0-70 is seriously damn amazing, 70-100 tapers off somewhat so the century sprint timings are just under 10s only. on paper looks like crap but still can out accelerate most turbo or large cc cars for the first 100m at least. of course they will disappear into the distance eventually but in SG, initial pickup rocks

 

I was thinking, maybe they have excellent Torque cruve(acceleration) but losy BHP Cruve( Top speed)?

Meaning, they can accelerate but their speed are limited by the top speed.

 

Something like you have a car that have the potential to reach 100km/hr in 3 sec but its top speed is only 50km/hr??

[Cerano]

I was thinking, maybe they have excellent Torque cruve(acceleration) but losy BHP Cruve( Top speed)?

Meaning, they can accelerate but their speed are limited by the top speed.

 

Something like you have a car that have the potential to reach 100km/hr in 3 sec but its top speed is only 50km/hr??

 

but diesels can go up to over 200kmh

 

its true their top end is crap... but their low end acceleration like 350nm TDI takes 8.1 seconds

 

http://www.themotorreport.com.au/30082/vol...25kw-tdi-engine

 

VW sciroco GT 350nm takes 8.1 secs thats not very fast given its 350nm torque

Edited May 27, 2010 by Cerano

[Joseph22]

but diesels can go up to over 200kmh

 

its true their top end is crap... but their low end acceleration like 350nm TDI takes 8.1 seconds

 

http://www.themotorreport.com.au/30082/vol...25kw-tdi-engine

 

VW sciroco GT 350nm takes 8.1 secs thats not very fast given its 350nm torque

 

that is turbo induce leh...new type of Diesel engine is like petrol engine liao.

Anyway i am refering to Bhp Cruve not top BHP. I was thinking if thier initial BHP cruve is very crappy but surge upward at slightly higher rev.

[Mini-itx]

Diesel engines have rather poor power curve due to lack of RPM. But they have lots of torque.

 

Btw, you can just look at engine for acceleration. Gear ratios and final drive plays a very important part as well.

[Cerano]

that is turbo induce leh...new type of Diesel engine is like petrol engine liao.

Anyway i am refering to Bhp Cruve not top BHP. I was thinking if thier initial BHP cruve is very crappy but surge upward at slightly higher rev.

 

but diesels cannot rev much. their redline very low leh

[Cerano]

Diesel engines have rather poor power curve due to lack of RPM. But they have lots of torque.

 

Btw, you can just look at engine for acceleration. Gear ratios and final drive plays a very important part as well.

 

okay so... if the peak torque isnt for acceleration then it doesnt count for much....

[Boyboy]

I was thinking, maybe they have excellent Torque cruve(acceleration) but losy BHP Cruve( Top speed)?

Meaning, they can accelerate but their speed are limited by the top speed.

 

Something like you have a car that have the potential to reach 100km/hr in 3 sec but its top speed is only 50km/hr??

 

something like that... BHP still is the factor for top speed.

[Boyboy]

but diesels cannot rev much. their redline very low leh

 

not say very low lah..

 

mine is 5.5k rpm? but for max pickup, i think 4.5k i upshift liao. will only reach the really high rpm in 5th gear at close to max speed .

 

with torque mostly at low end, not only is there no point revving so much, but also there's really no need to

 

[Celicar]

Today's Diesel are not slow at all,look at the newer Taxis,Kias & Mercs,all very fast.

 

I agree with this observation. I've seen a Mercs cab accelerate from stationary very very quickly. Dun play play.

[Cerano]

not say very low lah..

 

mine is 5.5k rpm? but for max pickup, i think 4.5k i upshift liao. will only reach the really high rpm in 5th gear at close to max speed .

 

with torque mostly at low end, not only is there no point revving so much, but also there's really no need to

 

oic because articles all say very low hmm....

 

but how's your acceleration bro? does the torque make a diff

[Kwchan]

put in more gears for top speed lor

 

[Joseph22]

but diesels cannot rev much. their redline very low leh

 

You dont get what i mean.. nevermind.

 

think will just try one last attemp.

 

Assuming Rev at various rpm

rpm Torque Bhp Top Speed

1000 200 50 30km/hr

1200 200 55 35km/hr

2000 200 60 50km/hr

2500 200 80 80km.hr

3000 200 120 150km/hr.

 

something like that??

Edited May 27, 2010 by Joseph22