Difference between 1.9TDI 90Hp and 150Hp
- Thread starter indiemike
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As previously mentioned, the 90bhp was on a 5 speed box, and the 150bhp on a 6 speed box
I would suggest its all very very different where the clutch is concerned, due to the huge difference in Torque delivered from the engines.
BHP is nothing without Torque
I would suggest its all very very different where the clutch is concerned, due to the huge difference in Torque delivered from the engines.
BHP is nothing without Torque
Ah. Somebody torqueing bollox again. Time to dust off the old lecture.
Power(bhp)=Torque(lb-ft) x rpm/5252
If you have power, you have torque. No way around it. The reason diesel engines need heftier clutches is to do with spec sheets (no, really!).
Torque is a measure of the amount of push the charge in the cylinder is giving to the crankshaft. In technical terms this is BMEP (Brake Mean Effective Pressure) - a measure of the pressure generated in the cylinder head when the fuel-air charge burns. How much bang it makes, if you like.
A car's maximum bhp, the figure on the spec sheet, is found at the top end of the rev range (notice that rpm is a factor in the equation above). Provided torque, i.e. the bang from the fuel/air mixture burning in the cylinder, doesn't drop off, peak rpm is limited by mechanical factors, often valve bounce.
In a petrol car, rpm can be increased to ridiculous levels (20,000 or more in F1 engines) provided all the whirling bits are balanced very well, the gas flow all through the engine is good and the ignition can keep up. Increasing rpm is a prime factor in getting more rated power out of petrol engines. Of course this means you have to wring its neck to get that power and go around sounding like a banshee out of hell.
Diesels are limited by the fact that diesel fuel burns more slowly than petrol. Above about 4000 rpm the cylinder charge doesn't completely burn before the exhaust valve opens - the flame front hasn't got to the edges of the cylinder - so unburned and partly burned fuel gets pushed out of the exhaust valve, leading to lots of smoke, and a sudden downturn in power: the bang has been let out of the cylinders.
So a diesel's max bhp is always measured at less rpm than a petrol engine's.
The reduction in power as the rpm reduces is roughly linear. So at the sorts of rpm where you're starting off, say 1500 rpm or so, the diesel is generating *more power* than the equivalent petrol car, and the clutch has to be able to absorb that power.
Some figures to back that up.
Notice the diesels are generating similar amounts of torque but at lower rpm, hence the difference in max power.
BUT, if you look at the max torque situation for each engine (the area of performance where starting off and gearchanges happen) things look very different.
That's why the TDI 130 needs a better clutch
For TDI 90 vs 150 the figures are:
almost half as much *POWER* again.
The crude way of looking at all this is that power=how big a bang you can make X how soon you can make another one.
It's all down to the fact that diesels make bigger bangs than petrol cars. Those bigger bangs are what the clutch has to deal with when starting from stationary and when changing gear.
Oh, er, to answer the original question, the TDI 90 has ordinary distribution pump injection, a simple wastegate turbo and conservative mapping. It's the oldest of the TDI engines still in mass circulation, almost always attached to a five-speed box.
The TDI 150 has PD injection, a bigger variable vane turbo generating more boost, and mapping to match, and always attached to a six-speed box. Remember what I said above about rev limits: diesels have narrower power bands than petrol engines, and extra speeds in the box help. But they have to be tough enough to absorb the power generated at low revs.
Clutches, as has already been mentioned, have to match the gearbox input shaft and the six-speed box will need a different clutch for that reason.
Power(bhp)=Torque(lb-ft) x rpm/5252
If you have power, you have torque. No way around it. The reason diesel engines need heftier clutches is to do with spec sheets (no, really!).
Torque is a measure of the amount of push the charge in the cylinder is giving to the crankshaft. In technical terms this is BMEP (Brake Mean Effective Pressure) - a measure of the pressure generated in the cylinder head when the fuel-air charge burns. How much bang it makes, if you like.
A car's maximum bhp, the figure on the spec sheet, is found at the top end of the rev range (notice that rpm is a factor in the equation above). Provided torque, i.e. the bang from the fuel/air mixture burning in the cylinder, doesn't drop off, peak rpm is limited by mechanical factors, often valve bounce.
In a petrol car, rpm can be increased to ridiculous levels (20,000 or more in F1 engines) provided all the whirling bits are balanced very well, the gas flow all through the engine is good and the ignition can keep up. Increasing rpm is a prime factor in getting more rated power out of petrol engines. Of course this means you have to wring its neck to get that power and go around sounding like a banshee out of hell.
Diesels are limited by the fact that diesel fuel burns more slowly than petrol. Above about 4000 rpm the cylinder charge doesn't completely burn before the exhaust valve opens - the flame front hasn't got to the edges of the cylinder - so unburned and partly burned fuel gets pushed out of the exhaust valve, leading to lots of smoke, and a sudden downturn in power: the bang has been let out of the cylinders.
So a diesel's max bhp is always measured at less rpm than a petrol engine's.
The reduction in power as the rpm reduces is roughly linear. So at the sorts of rpm where you're starting off, say 1500 rpm or so, the diesel is generating *more power* than the equivalent petrol car, and the clutch has to be able to absorb that power.
Some figures to back that up.
Code:
An LC produces 180 bhp at 5900 rpm, by generating 160 lb-ft of torque.
My TDI110 produces 110 bhp at 3750 rpm, by generating 154 lb-ft
and
A TDI 130 produces 130 bhp at 4000 rpm, by generating 171 lb-ftNotice the diesels are generating similar amounts of torque but at lower rpm, hence the difference in max power.
BUT, if you look at the max torque situation for each engine (the area of performance where starting off and gearchanges happen) things look very different.
Code:
The LC produces 173 ft-lb at 2000 rpm, generating 66 bhp
My TDI 110 produces 173 ft-lb at 1900 rpm, generating 63 bhp. I'm the equal of the LC here.
A TDI 130 produces 229 ft-lb at 1900 rpm, generating 83 bhp.That's why the TDI 130 needs a better clutch
For TDI 90 vs 150 the figures are:
Code:
155 lb-ft at 1900 rpm for 56 bhp
vs
236 lb-ft at 1900 rpm for 85 bhpalmost half as much *POWER* again.
The crude way of looking at all this is that power=how big a bang you can make X how soon you can make another one.
It's all down to the fact that diesels make bigger bangs than petrol cars. Those bigger bangs are what the clutch has to deal with when starting from stationary and when changing gear.
Oh, er, to answer the original question, the TDI 90 has ordinary distribution pump injection, a simple wastegate turbo and conservative mapping. It's the oldest of the TDI engines still in mass circulation, almost always attached to a five-speed box.
The TDI 150 has PD injection, a bigger variable vane turbo generating more boost, and mapping to match, and always attached to a six-speed box. Remember what I said above about rev limits: diesels have narrower power bands than petrol engines, and extra speeds in the box help. But they have to be tough enough to absorb the power generated at low revs.
Clutches, as has already been mentioned, have to match the gearbox input shaft and the six-speed box will need a different clutch for that reason.
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muttley, you need to get out more.
haha but very interesting non the less! learn something new every day n that!
FSiLeonMike wrote
muttley, you need to get out more.
It's mostly cut-and-paste, I've posted similarly before (a while ago mind).
There was another Power-vs-torque, petrol-vs-diesel ding-dong going on and I got to thinking about exactly why diesels behave differently to petrol cars at commuting/going shopping speeds. Already knew that power was related to torque, so the persistent misapprehension that they were somehow mysteriously different irritated me.
It really is down to diesels making a bigger bang, but not being able to make another one as soon as a petrol engine can
muttley, you need to get out more.
It's mostly cut-and-paste, I've posted similarly before (a while ago mind).
There was another Power-vs-torque, petrol-vs-diesel ding-dong going on and I got to thinking about exactly why diesels behave differently to petrol cars at commuting/going shopping speeds. Already knew that power was related to torque, so the persistent misapprehension that they were somehow mysteriously different irritated me.
It really is down to diesels making a bigger bang, but not being able to make another one as soon as a petrol engine can
That Was Brilliant Muttley
I've herd so many people try to explain it and fail badly (not saying ive been successfully)
its that kind of post that needs to be stickied
Thank you for a very informative post!
I've herd so many people try to explain it and fail badly (not saying ive been successfully)
its that kind of post that needs to be stickied
Thank you for a very informative post!
I don't follow.... Surely if power is what determines which clutch you need isn;t it just as straight forward as saying the tdi150 needs a clutch capable of 150bhp? Even though it produces less than 236ft lb at max power ~ 4000rpm?
I would have thought that if an engine makes a massive bang (high BMEP) but say, only twice a minute, therefore producing almost zero power, the clutch would still slip if the bang was more than the friction force of the clutch?
I hope my question makes sense! Sorry if I'm being thick!
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RLyons wrote
I don't follow.... Surely if power is what determines which clutch you need isn;t it just as straight forward as saying the tdi150 needs a clutch capable of 150bhp? Even though it produces less than 236ft lb at max power ~ 4000rpm?
No, the problem is not the maximum power that the engine can produce, it is the power at the rpm-range you will be expecting to engage the clutch - which tends to be around the max-torque range. Starting from stationary in the diesel you'll be revving to 1500-2000 rpm, and when changing up you'll be perhaps at 2500. The contrast between diesel and petrol is stark: LC 66bhp, TDI 150, 85bhp.
And remember, power and torque at a given rpm have a fixed relationship, so you can say the diesel has higher torque at starting-off-revs than the petrol engine, but this inevitably means it also has higher power.
I would have thought that if an engine makes a massive bang (high BMEP) but say, only twice a minute, therefore producing almost zero power, the clutch would still slip if the bang was more than the friction force of the clutch?
Well yes, but
1) Your almost-zero-power example breaks some of the assumptions I've made (and left unexplained, for simplicity's sake). Note that I've compared petrol and diesel at the same rpm (1900-2000) for the low-speed, max torque case, which removes the rpm variable. Another way of looking at it is that the TDI goes from start to max power in 2000 rpm wheras the petrol engine takes twice as long, 4000 rpm, during the first bit of which it's producing LESS power than the diesel. This is why racing drivers keep the rpm up as high as possible
2) very low-revving engines typically do produce comparatively low power: they are employed in areas where they are expected to keep going for days or weeks at a time (ship propulsion, pumping stations etc.) They are started in gear, and may not even have a clutch in the drive train.
(Anybody out there with a BSA Gold Star, one bang every other lamp-post, just keep out of this, will you? Your clutch is a massive multi-pate wet thing in any case, and you've got a cush drive on the engine sprocket)
3) If the end result is almost zero power, then the bangs can't be that big. The reason I blamed spec sheets for the confusion is that we tend to rate engines by the "max power" figure without considering how that's arrived at. Petrol engine max power is always got at high rpm, and is rarely approached in daily use because it's uncomfortable (loud and shaky). Diesels, with their narrower power band, spend more time on a daily basis closer to their max power, which is also less boisterous than an equivalent petrol car.
An LC comes off the line producing less power than a TDI 150, and has to wind through more rpm to get to its max power rev range. The diesel driver has to change up earlier because they run out of power-band sooner, and the LC starts to turn the tables. Once both cars are rolling, a competent LC driver will keep the revs up (and thus the power close to maximum) and leave the TDI behind. The extra weight of the diesel will also tell against it.
I don't follow.... Surely if power is what determines which clutch you need isn;t it just as straight forward as saying the tdi150 needs a clutch capable of 150bhp? Even though it produces less than 236ft lb at max power ~ 4000rpm?
No, the problem is not the maximum power that the engine can produce, it is the power at the rpm-range you will be expecting to engage the clutch - which tends to be around the max-torque range. Starting from stationary in the diesel you'll be revving to 1500-2000 rpm, and when changing up you'll be perhaps at 2500. The contrast between diesel and petrol is stark: LC 66bhp, TDI 150, 85bhp.
And remember, power and torque at a given rpm have a fixed relationship, so you can say the diesel has higher torque at starting-off-revs than the petrol engine, but this inevitably means it also has higher power.
I would have thought that if an engine makes a massive bang (high BMEP) but say, only twice a minute, therefore producing almost zero power, the clutch would still slip if the bang was more than the friction force of the clutch?
Well yes, but
1) Your almost-zero-power example breaks some of the assumptions I've made (and left unexplained, for simplicity's sake). Note that I've compared petrol and diesel at the same rpm (1900-2000) for the low-speed, max torque case, which removes the rpm variable. Another way of looking at it is that the TDI goes from start to max power in 2000 rpm wheras the petrol engine takes twice as long, 4000 rpm, during the first bit of which it's producing LESS power than the diesel. This is why racing drivers keep the rpm up as high as possible
2) very low-revving engines typically do produce comparatively low power: they are employed in areas where they are expected to keep going for days or weeks at a time (ship propulsion, pumping stations etc.) They are started in gear, and may not even have a clutch in the drive train.
(Anybody out there with a BSA Gold Star, one bang every other lamp-post, just keep out of this, will you? Your clutch is a massive multi-pate wet thing in any case, and you've got a cush drive on the engine sprocket)
3) If the end result is almost zero power, then the bangs can't be that big. The reason I blamed spec sheets for the confusion is that we tend to rate engines by the "max power" figure without considering how that's arrived at. Petrol engine max power is always got at high rpm, and is rarely approached in daily use because it's uncomfortable (loud and shaky). Diesels, with their narrower power band, spend more time on a daily basis closer to their max power, which is also less boisterous than an equivalent petrol car.
An LC comes off the line producing less power than a TDI 150, and has to wind through more rpm to get to its max power rev range. The diesel driver has to change up earlier because they run out of power-band sooner, and the LC starts to turn the tables. Once both cars are rolling, a competent LC driver will keep the revs up (and thus the power close to maximum) and leave the TDI behind. The extra weight of the diesel will also tell against it.
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