1000rpm for cruising at 30mph?

[blahblop123]

i had a 1l petrol daihatsu which is used to cruise at 20-30mph in 5th gear. in return it gave me 50+ mpg and a smooth/quiet cruise. I tried the same thing with my 1.4tdi Ibiza but it started making knocking sounds at just over 1000rpm. surely an engine with so much torque low end would make easy meal of cruising at 30mph in 5th gear in comparison to a tiny 1l with peak torque at 4000rpm.

[devnull]

life is hard.

[jamieduff1981]

You're probably below turbo threshold at 1000rpm, so your torquey engine quite possibly has bugger all torque at 1000rpm!

[Gixer]

Maybe the gear ratios are different. Who cruises at 20-30mph anyway

[HaloGen8]

Just why??

Oil flow?
Pick up if needing to react to a situation?

[JakeT]

In the vast majority of cars I would say 4th is the highest gear you want for 30 and not to be running at below 1500RPM. No engine bar a bus/truck will make a lot of torque that low.

[Lost soul]

JakeT said:

In the vast majority of cars I would say 4th is the highest gear you want for 30 and not to be running at below 1500RPM. No engine bar a bus/truck will make a lot of torque that low.

My A5 3lt TDI is quite happy at 30 at around 1100rpm in 4-5th

[Greg_D]

I'll bet you're a hit with the ladies!!!

[Pappagallo]

Pistonheads: Juddering along in 5th Matters.

[Lost soul]

Greg_D said:

I'll bet you're a hit with the ladies!!!

Its a discussion mate , go on off you go now

[Mr2Mike]

blahblop123 said:

i had a 1l petrol daihatsu which is used to cruise at 20-30mph in 5th gear. in return it gave me 50+ mpg and a smooth/quiet cruise. I tried the same thing with my 1.4tdi Ibiza but it started making knocking sounds at just over 1000rpm. surely an engine with so much torque low end would make easy meal of cruising at 30mph in 5th gear in comparison to a tiny 1l with peak torque at 4000rpm.

1) The gear ratios will be considerably different between the petrol and the diesel.
2) Diesels have very high compression ratios, and high peak cylinder pressures. This means the crankshaft undergoes more violent acceleration/deceleration as the engine turns and this will be amplified at low RPM. These are ideal conditions to destroy a dual mass flywheel very quickly.
3) Lugging an engine at very low RPM will not give the best economy. The slower an engine runs, the more time is available for the combustion process to lose heat into the cylinder and combustion chamber.

[SMcP114]

Most boring thing I've ever read in my life.

[kambites]

Both the Elise and the Octavia will do it, at least until you encounter a hill, but it's pretty horrific for fuel economy.

[Lost soul]

SMcP114 said:

Most boring thing I've ever read in my life.

Then don't fking read it

[Greg_D]

Lost soul said:

Greg_D said:

I'll bet you're a hit with the ladies!!!

Its a discussion mate , go on off you go now

already gone...

to smoke fags with the cool kids not juddering along holding everyone up...



PS, you do realise that the OP probably isn't a girl, don't you???

Edited by Greg_D on Wednesday 16th July 14:17

[blahblop123]

haha, holy sh*t there are trolls on pistonheads ?

thanks you, to those that gave legitimate responses.

[andy-xr]

Flywheel wont like it at those revs, the petrol probably didnt care, the diesel will. I'm part sure that's what killed off the DMF in my Mondeo, too much trying to accelerate away at 1100 rpm in 4th

[Pappagallo]

Lost soul said:

SMcP114 said:

Most boring thing I've ever read in my life.

Then don't fking read it

To be fair, he'd have had to read at least once to work out that it's boring.

[CallorFold]

Being a Diesel would be my first suggestion.

I'm currently driving a MK3 Diesel Focus (Courtesy car) which is filling in for my MK2 Petrol Focus.

My Petrol Focus can happily sit at just over 30 in 5th pootling along but the Diesel doesn't even really like being in 4th at 30, there's a small judder, it's much more comfortable in 3rd.

[Bradley1500]

Why would you want to sit at 1000RPM?

As others have mentioned it could potentially cause damage and won't be great for your fuel economy.

IIRC the optimum RPM for fuel economy on a diesel is circa 1500-1600 and 1800-2000 on a petrol, obviously varying dependent on your car.