Small turbos?

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Tue 1 Apr 2014 18:02
Small turbos? - P3t3r

I've noticed some very powerful small turbo engines recently. Eg. Ford 1.0 gives upto 123bhp, which is similar to their 1.6, but has much better economy. On paper, it sounds amazing, but I wonder what they are like in the real world. Is their performance that good and is their fuel consumption comparable to a normal engine?

The only turbo I have driven is a Fiat TwinAir. I didn't really enjoy driving it and owners were reporting high fuel consumption. If I remember correctly you had to either completely abuse it for good performance (and high consumption) or you had to labour it and have no power, there seem to be nothing in the middle which is what I want for every day driving.

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Tue 1 Apr 2014 19:45
Small turbos? - skidpan

Bought a Seat Leon 1.4 TSi last June. It is 140 PS which is about the same as most 2 litre petrols but it has 184 ft lbs of torque at 1500 rpm which easilly beats them.

It is an amazing engine, power from tickover, no turbo lag, quiet and the economy is brilliant, I have been getting an average of 45 mpg since I bought it, seen as much as 52 mpg on a run. They are calculated figures and not those taken form the dash display.

Would I buy a N/A 2 litre again, no way.

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Tue 1 Apr 2014 19:53
Small turbos? - daveyjp
I test drove a C class with the new 1.6 turbo and auto box. It was very sprightly and did 40mpg from cold on a largely urban trip of about half an hour.
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Tue 1 Apr 2014 20:02
Small turbos? - cockle {P}

My experience pretty much mirrors skidpan.

I bought the 1.0 Focus to replace my 1.6, the 1.0 out performs my old 1.6 noticeably, no perceivable turbo lag, torque bands are in slightly different places which took a bit of getting used to; would say it drives a bit more like my turbo diesel van than a petrol. Currently averaging about 42mpg around town, SWMBO has a bit of a heavy right foot.....

Will be interesting to see how the reliability pans out but these engines have been around for a while in some of the smaller models.

3500 miles in I'm well impressed.

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Tue 1 Apr 2014 21:52
Small turbos? - the_bandit

Tiny engines with turbos are aimed only at reducing CO levels and little to do with the economics of ownership.

Good news for the garages and parts trade whilst they service and repair thrashed engines and turbos that have been going like the clappers trying to haul heavy cars round!

Tiny engines belong in tiny cars!

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Wed 2 Apr 2014 00:18
Small turbos? - SteveLee

Tiny engines with turbos are aimed only at reducing CO levels and little to do with the economics of ownership.

Good news for the garages and parts trade whilst they service and repair thrashed engines and turbos that have been going like the clappers trying to haul heavy cars round!

Tiny engines belong in tiny cars!

As long as the engine block and mounts have been designed well enough to avoid flexing the block under the load of dragging heavy bodyshells around there's no reason why the small engines shouldn't be perfectly reliable. Okay they will perform more revs per given mile (which will reduce ultimate longevity) but then they'll warm up quicker too - which is good for petrol engine life. If you sepnd all day on the motorway - bigger will be better, for mixed urban driving you spend a surprising amount of time off the throttle - at which point the little low compression turbo petrol will be under very little mechanical strain with the turbo off boost.

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Wed 2 Apr 2014 01:15
Small turbos? - unthrottled

Okay they will perform more revs per given mile

Why? A typical 1.4 turbo will make more torque at 1500 RPM than an n/a 2.0 will at 4000. You can downspeed as well as downsize. Cooling is a big issue for petrol turbos but I'm fairly sure that was worked out in the development stage.

Sounds like a re-run of the early 1970's when British Leyland and Hugh Gardner pooh poohed turbos on diesel engines as a short term fad. Scania and Cummins disagreed. Guess who is still going-and who is just a footnote in commercial diesel history?

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Wed 2 Apr 2014 02:12
Small turbos? - SteveLee

Okay they will perform more revs per given mile

Why? A typical 1.4 turbo will make more torque at 1500 RPM than an n/a 2.0 will at 4000. You can downspeed as well as downsize. Cooling is a big issue for petrol turbos but I'm fairly sure that was worked out in the development stage.

Sounds like a re-run of the early 1970's when British Leyland and Hugh Gardner pooh poohed turbos on diesel engines as a short term fad. Scania and Cummins disagreed. Guess who is still going-and who is just a footnote in commercial diesel history?

But lugging tall gearing will encourage petrol turbo engines to make boost which will do nothing for fuel economy - this was the reason behind the low pressure turbo fad in the late 90s, the LPT engines made enough power on light throttle openings (by having relatively high compression engines) to cruise without making significant fuel guzzling boost. To achieve the same aim with a small capacity engine requires revs. Better cruise economy will be achieved with these small petrol turbos by revving them hard enough to make sufficient horsepower to cruise without turbo boost, avoiding the heat and fuel penalties associated with constant high levels of boost.

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Wed 2 Apr 2014 10:50
Small turbos? - unthrottled

I'd pretty much agree with your whole post Steve.

But the smaller petrol turbos tend to be geared around 2500 RPM @ 70mph-which isn't really lugging the engine down.

An 'interesting' aside about turbos on petrols is that they can produce boost against a partially closed throttle since the turbo only sees total airflow and cannot differentiate between an engine at WOT at 1500 RPM and at part throttle at 3000 RPM. So the compressor boosts against an almost closed throttle-leading to a pretty nasty pumping loss-which was part of the motivation for downsizing in the first place!

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Wed 2 Apr 2014 03:47
Small turbos? - Collos25

Tiny engines with turbos are aimed only at reducing CO levels and little to do with the economics of ownership.

Good news for the garages and parts trade whilst they service and repair thrashed engines and turbos that have been going like the clappers trying to haul heavy cars round!

Tiny engines belong in tiny cars!

Not born out with facts.

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Wed 2 Apr 2014 00:11
Small turbos? - SteveLee

Daihatsu were making 100+bhp from a one litre turbo over 25 years ago - that engine was perfectly reliable without today's ultrasophisticated engine management systems.

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Wed 2 Apr 2014 00:23
Small turbos? - Wackyracer

Daihatsu were making 100+bhp from a one litre turbo over 25 years ago - that engine was perfectly reliable without today's ultrasophisticated engine management systems.

IIRC The Daihatsu Charade diesel turbo also did 99mpg too.

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Wed 2 Apr 2014 09:55
Small turbos? - skidpan

Okay they will perform more revs per given mile (which will reduce ultimate longevity)

That does not apply to my Seat Leon 1.4 TSi. At 70 mph in 6th it is doing 2500 rpm, our Mondeo 2,0 TDCi 130 did exactly the same revs at 70 mph.

It is by far the slowest reving petrol I have ever owned. The nearest I have owned as far as revs goes was a Cooper S and at 70 mph it did about 3100 rpm. 1800 cc petrol Golfs and Nissans were doing about 3500 rpm at 70 mph, way more revs per mile.

But lugging tall gearing will encourage petrol turbo engines to make boost which will do nothing for fuel economy -

If that were true how come my Leon has averaged 45 mpg in mormal use and I have seen 52 mpg on a run. Its as good as most diesels I have owned.

Edited by skidpan on 02/04/2014 at 09:57

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