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Diesel turbo lag?

139 posts & 47 voices | Started 1 year ago by ziggy | Latest reply from Surf-Mat

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ziggy - Member

Got a hire car while I wait for a payout on my car someone thoughtfully smashed into, it's a Renault Laguna diesel.

Just seems to have loads of turbo lag, is this how most diesels are? It's spanking new with only 200 miles on it if that makes any difference.

Seem to be changing gear all the time, not helped by having 6 gears. If I try to use the torque using higher gears it just takes ages to move. Was looking at diesel for my next car, not so sure now, although it would be a VAG engine, any better?

Posted 1 year ago #
tron - Member

Turbo lag in diesels doesn't tend to be that bad - my old 110 HDI 406 had a bit of lag, but it wasn't terrible.

They do tend to do absolutely nothing below 1500 rpm, and have pretty narrow powerbands. Keeping things above 1500rpm is the answer. And not trying to rev round to the redline.

The only time you really noticed it in the 406 was pulling out of T junctions on fast roads - you'd get nothing nothing nothing followed by the front end scrabbling for grip.

Posted 1 year ago #
skidsareforkids - Member

My Tdci Focus is a bloody nightmare for that! I have just gotten used to "blipping" the throttle before the off, but it can't be good for the clutch, and I must look like a tit. I'm never getting a diesel again...

... Actually, I would get a Cummins diesel, but that's it...

Posted 1 year ago #
chvck - Member

If you actually think about it you probably lose say 10 minutes on a long run due to a bit less acceleration? How much do you gain in MPG though?

Posted 1 year ago #
amplebrew - Member

We got a new Transit van in work which on paper was more powerful than the older one.

It's nowhere near as nice to drive though, all Ford have done is put a bigger turbo on the same engine to give it more power; but giving it loads of lag.

It needs constant gear changes to keep it on the go.

Posted 1 year ago #
tron - Member

If you actually think about it you probably lose say 10 minutes on a long run due to a bit less acceleration?

I doubt it very much. Averaging 80 instead of 75 doesn't make that much of a difference, even over what most people would consider a long run.

Similarly, driving flat out on twisty roads doesn't seem to make up that much time - normally because someone will always be in your way.

Ultimately it's an irritation. A car where every control responds quickly and properly to your inputs is a pleasure to drive, even if it's a slow one.

Posted 1 year ago #
john_drummer - Member

my Saab 9-3 is a little bit sluggish at first, and first gear is very narrow - but that's probably due to it being a GM Saab (Vauxhalls have very narrow first gear too, from experience).

once moving and above about 1200rpm it's great. I don't do that much stirring of the gears, as it's a diesel with way more torque than a weedy petrol engine

my previous car, a BMW 320D was much better, but I guess you get what you pay for

I wouldn't have petrol again for my car, although Mrs_drummer's C4 1.6 petrol is quick enough

Posted 1 year ago #
amplebrew - Member

I think some manufacturers use bigger turbos to get more BHP from an engine rather than increasing the engine size.

The problem with a bigger turbo, is that you often get more lag.

When Ford first brought out the Escort Cosworth they fitted it with big turbo, they later changed it for a smaller one to make it drive better. (Obviously this wasn't a diesel though)

Posted 1 year ago #
uponthedowns - Member

A proper modern diesel with variable turbo vane geometry should not exibit turbo lag and should not have a narrow power band. My BMW 320d drives just like a petrol engine (except with more torque) with smooth power delivery throughout the rev range. Likewise Mercedes turbo diesels have no discernable lag. A Ford diesel I drove about 4 years ago (in a Jag X type) didn't have any turbo lag but had a very narrow power band. Hopefully they've sorted that out now. I've always thought French cars are crap.

Posted 1 year ago #
ziggy - Member

Forgot to mention the electronic handbrake, whilst great on inclines needs quite a few revs and slow with the clutch on steeper hill starts, can't do the clutch much good!

Glad it's not just me then, had a Type R previously so thought it might just need getting used to. Petrol all the way for the next car.

Posted 1 year ago #
2unfit2ride - Member

I must say I was shocked by the lack of torque on my passat 170 sport estate, talk about having to work a gearbox
The only redeeming feature is the turn of speed when laden, the ride is horrid as well, and believe me there is no redeeming features about the ride quality. I bought it on the strength of using an A6 2.5 auto diesel for a couple of weeks, shite MPG, but good ride & low down torque, you live & learn eh.

Posted 1 year ago #
amplebrew - Member

My best mate has got a BMW 530d which is really nice, but it's a world away from the Ford, Vauxhall, Citreon etc diesels I've driven.

It seems that you need to buy an expensive one to get a nice one

I'd still have a petrol everytime though.

Posted 1 year ago #
amplebrew - Member

ziggy - Member
Forgot to mention the electronic handbrake, whilst great on inclines needs quite a few revs and slow with the clutch on steeper hill starts, can't do the clutch much good!

Our new Transit has hill start fitted and it's a nightmare. You have to really rev the engine if you're after a quick getaway.

Posted 1 year ago #
tron - Member

My BMW 320d drives just like a petrol engine

Have a look at the dyno plots for the 2l BMW Diesel and compare with a 2l Petrol engine. They're very different. Petrol engines tend to have a usable rev range of 5-7000 revs, with power and torque increasing almost all of the way up the range. Diesels are lucky to have a useful range of 3000 revs, with torque reaching its maximum very early.

If anything, a big old non-turbo diesel is closer in feel to a petrol engine than the current common rail lumps.

But with either, the throttle response and weight distribution is considerably worse.

Posted 1 year ago #
uponthedowns - Member

Ok diesels don't rev so high as petrol engines but I find having to rev the crap out of an engine to make rapid progress frankly tiresome. I'll revise my remark then. My BMW 320d drives just like a petrol engine (except with more torque) up to its maximum revs which from memory are about 4000 rpm.

Posted 1 year ago #
chvck - Member

haha

Posted 1 year ago #
uponthedowns - Member

haha
:?:

Posted 1 year ago #
Penrod Pooch - Member

A VAG with a remap will pull smoothly through from well under 1500 to well over 3500, There is virtually no lag lower down the revs, but cruising at 90 you feel a fair bit before it boots you up to 100, albeit very bloody quickly....

Posted 1 year ago #
thv3 - Member

Got a Civic 2.2CDTI, not problems with lag here.

Then again, I like diesels, wouldn't go back.

Posted 1 year ago #
singlecrack - Member

My Tdci Focus is a bloody nightmare for that! I have just gotten used to "blipping" the throttle before the off, but it can't be good for the clutch, and I must look like a ****. I'm never getting a diesel again.

In contrast my Focus Tdci is excellent,, seems to have loads of torque and hardly any turbo lag

Posted 1 year ago #
tron - Member

My BMW 320d drives just like a petrol engine (except with more torque) up to its maximum revs which from memory are about 4000 rpm.

Keep telling yourself that. If you back to back drove a 320d and 3 with a petrol engine with the same power output, you'd notice considerable differences.

Posted 1 year ago #
uponthedowns - Member

Whatever

Posted 1 year ago #
Flaperon - Member

Just ordered a STS kit for my Passat which will take it from 130 - 170HP. Also frustrated with the lack of response below 2000RPM, but it's a turbo, and as the chipping bloke said, "What do you expect?"

Looking at the dyno plots for my car the chip has absolutely no effect below 1800RPM anyway, but delivers massively improved torque and power right up to the red line. Looking forward to uploading it into the car's brain.

Posted 1 year ago #
tron - Member

BTDT with chipping diesels. There's a lot of difference to be made at the top end, but I can't help but feel there's a reliability compromise.

Posted 1 year ago #
uponthedowns - Member

the chip has absolutely no effect below 1800RPM anyway

Probably because its just turning up the boost on the turbo.

Posted 1 year ago #
bruneep - Member

thv3 - Member

Got a Civic 2.2CDTI, not problems with lag here.

Then again, I like diesels, wouldn't go back.

same here

Posted 1 year ago #
2unfit2ride - Member

I want to chip my 170, not to make it quicker, but to make it more linear, any recommendations?
Same goes for the suspension, anyone gone from silly stiff 'sport' to something a a tad more compliant?

Posted 1 year ago #
Flaperon - Member

uponthedowns - completely agree, just highlights the point that diesels are incredibly turbo dependent. As regards reliability, I accept that it's almost certainly going to need a clutch in the next 50k, and I'd prefer to have the extra oomph in the short term. Can't really see the life of any other component being adversely affected.

Posted 1 year ago #
Poggy - Member

Diesels will always have a drag compared to petrol due the combustion process...

Diesel Air/Fuel/Pressure = Combustion
Petrol Air/Fuel/Ignigion Spark = Combustion

What ever turbo is added will only be a reflection on the initial combustion & as it's a slower process, drag will always be secondary & noticeable...

OMG! Sounds like i know what i'm talking about! 'Apprentice Diesel Engineer' Lucas

Posted 1 year ago #
Poggy - Member

Saying all that...

Since itroduction of common rail diesel & removal of diesel pumps, things are an awful lot quicker... I think it's just getting used to driving a diesel engine harder than a petrol '& you can' as they're much much more hardy, as the pressures they have to withstand are so much bigger!

Give them some stick!!!

Posted 1 year ago #
tron - Member

Diesels will always have a drag compared to petrol due the combustion process...

It's more the fact that the pistons, crank and flywheel all need to be a lot stronger than in a petrol engine, so they're heavier. So they take longer to spin up. The rotating weight stuff really applies here as we're talking in thousands of RPMs.

A petrol engine squeezes the charge just like a diesel does, just not to the same extent (11:1 would be a high compression petrol engine, easily double that for a diesel). Combustion before the piston reaches top dead centre is not good in any engine!

Posted 1 year ago #
Poggy - Member

Errrrm.... it's the combustion process! Fact...

Posted 1 year ago #
ziggy - Member

Think I've just found the issue with this particular car, it may have a 1.5 108bhp engine, I'm surprised it moves at all. Either that or a 148bhp 2 litre.

Posted 1 year ago #
PeteG55 - Member

Got to laugh at the 'give it some stick' and the like comments here. Diesels demand a different driving style from a petrol engine. Diesels require a different style of driving to a petrol engine, the lower rev range and torque delivery mean driving using the torque rather than the BHP. Revving the tits off it will do it or you no favours at all.
Modern diesel engines do have narrower power bands hence we have pretty much every car with 6 speed gearboxes. But petrol engines are also going that way due to emissions, to keep them in their most efficient rev range. Its why we're seeing 7 and 8 speed manual and automatic gearboxes from the likes of Lexus and Mercedes. Both petrol and diesels are getting more 'sweet spot' dependant.
I'd say give it a chance. Get used to driving it, then tell me it isn't as good as a petrol engine, especially when your returning 55+MPG.
Also I can't comment on the Renault diesel engine, but current VAG cars with the variable geometry turbos drive brilliantly. BMW used 2 turbos of different sizes to achieve the same effect on the 2.0 4 pot and 3.0 6 pot engines. Those BMW engines are now also single turbos with variable vanes technology.

Posted 1 year ago #
PeteG55 - Member

Oh and turbos do change the power delivery of an internal combustion engine and do indeed help particularly so on diesels. However, with tighter and more stringent emissions controls we're looking at the death of normally aspirated engines with 5-10 years. Forced induction makes all automotive engines more efficient.
Also, although the bottom end of diesel engine is required to be stronger than a conventional petrol engine because of the high compression ratio, they're actually not that much heavier than a normal production petrol engine. This is mainly because the diesel engine doesn't spin anywhere near as fast as a petrol engine and therefore doesn't need to cope with the piston speeds of a petrol engine. With modern dual mass flywheels (as fitted to near enough all cars now)included, I'd be willing to bet that the difference in weight in the bottom end components is negligible.

Posted 1 year ago #