I drove my kid sister's Impreza turbo yesterday. Mint condition, 
unmodified W-reg with 30K miles. Very nice, very secure feeling, very 
comfortable, quick on boost, but Jesus, appalling turbo lag. For all the 
guff about 'peaky' VTEC engines, if you boot my Civic at 30mph in 6th, 
it accelerates. Not terribly quickly, but smoothly and without 
labouring. Try the same thing in 5th in the Impreza and *nothing*, 
literally *nothing* happens. Are they all like that? I thought driving 
round turbo-lag was a 1980's pastime?

-- 
Steve Walker

Steve Walker (steve@otolith.demon.co.uk) gurgled happily, sounding much 
like they were saying :


> For all the guff about 'peaky' VTEC engines, if you boot my Civic at 
> 30mph in 6th, it accelerates. Not terribly quickly, but smoothly and 
> without labouring. Try the same thing in 5th in the Impreza and 
> *nothing*, literally *nothing* happens.


Umm, why on earth would you want to plant it at 30 in top?

"Steve Walker"  wrote in message
news:WtUsS2Xwtz$CFwaL@otolith.demon.co.uk...

> I drove my kid sister's Impreza turbo yesterday. Mint condition,
> unmodified W-reg with 30K miles. Very nice, very secure feeling, very
> comfortable, quick on boost, but Jesus, appalling turbo lag. For all the
> guff about 'peaky' VTEC engines, if you boot my Civic at 30mph in 6th,
> it accelerates. Not terribly quickly, but smoothly and without
> labouring. Try the same thing in 5th in the Impreza and *nothing*,
> literally *nothing* happens. Are they all like that? I thought driving
> round turbo-lag was a 1980's pastime?


Turbos need engine revs to give boost.
I wouldn't expect any turbo to give much boost, given the low revs of an
engine in 5th at 30mph.
I think maybe you're expecting too much.
Driven normally, my Celica turbo has no noticeable lag. Of course more power
comes in as the revs rise, but it's smooth and progressive. I would expect
an Impreza turbos delivery to be very similar.
Mike.

Adrian wrote:

> Steve Walker (steve@otolith.demon.co.uk) gurgled happily, sounding
> much like they were saying :
>
>> For all the guff about 'peaky' VTEC engines, if you boot my Civic at
>> 30mph in 6th, it accelerates. Not terribly quickly, but smoothly and
>> without labouring. Try the same thing in 5th in the Impreza and
>> *nothing*, literally *nothing* happens.
>
> Umm, why on earth would you want to plant it at 30 in top?


Becasue in a sensible car with torque instead of nutty rev levels you can 
happily put it in 5th at 25 and leave it there all the way to 150+...

Steve Walker wrote:

> I drove my kid sister's Impreza turbo yesterday. Mint condition, 
> unmodified W-reg with 30K miles. Very nice, very secure feeling, very 
> comfortable, quick on boost, but Jesus, appalling turbo lag. For all the 
> guff about 'peaky' VTEC engines, if you boot my Civic at 30mph in 6th, 
> it accelerates. Not terribly quickly, but smoothly and without 
> labouring. Try the same thing in 5th in the Impreza and *nothing*, 
> literally *nothing* happens. Are they all like that? I thought driving 
> round turbo-lag was a 1980's pastime?


In a turbo'd engine, the compression ratio is often lowered, this means 
that a turbo'd engine produces even less torque at low revs than a 
similar capacity normally aspirated one.

At low revs there is not enough exhaust gas to push a usefully sized 
turbo hard enough to make it push more air into the engine.  In fact, 
turbos are actually a restriction in the exhaust and the inlet at low 
(and high) revs.

I'm not sure I would class what you describe as lag.  Try driving 
something turbo'd from the 1980s for more details. (c:  I'd describe lag 
as the delay between being off boost but at revs within the range of the 
turbo, flooring it, and waiting for full boost and the turbo 'kick'.  On 
older cars, the delay is quite marked and could easily take an 
inexperienced driver by surprise.

Many modern turbo'd engines seem to have this delay engineered out to 
some extent, by using clever turbos and electrickery, but I don't think 
there's a lot they can do to improve driveability at really low revs.

Douglas

"Mike G"  wrote in
news:42ff40d7$0$1316$ed2619ec@ptn-nntp-reader02.plus.net: 


> 
> "Steve Walker"  wrote in message
> news:WtUsS2Xwtz$CFwaL@otolith.demon.co.uk...
>> I drove my kid sister's Impreza turbo yesterday. Mint condition,
>> unmodified W-reg with 30K miles. Very nice, very secure feeling, very
>> comfortable, quick on boost, but Jesus, appalling turbo lag. For all
>> the guff about 'peaky' VTEC engines, if you boot my Civic at 30mph in
>> 6th, it accelerates. Not terribly quickly, but smoothly and without
>> labouring. Try the same thing in 5th in the Impreza and *nothing*,
>> literally *nothing* happens. Are they all like that? I thought
>> driving round turbo-lag was a 1980's pastime?
> 
> Turbos need engine revs to give boost.
> I wouldn't expect any turbo to give much boost, given the low revs of
> an engine in 5th at 30mph.
> I think maybe you're expecting too much.
> Driven normally, my Celica turbo has no noticeable lag. Of course more
> power comes in as the revs rise, but it's smooth and progressive. I
> would expect an Impreza turbos delivery to be very similar.
> Mike.
> 
> 

Like Mike says, you need to gear the car correctly. At 30 in fifth, you 
don't have enough revs to spin the turbo and it's just labouring the 
engine. When you have an engine speed of approx 2500rpm, the point at 
which a turbo begins to have real effect, try putting your foot down 
then. Then you can measure the true turbo lag. The real advantage of the 
turbo is the high torque output at relatively low revs. My S70 T5 hits 
maximum torque at about 2500 and sustains the same torque all the way to 
5100. That means I can accelerate rapidly from 40 to 80mph whilst 
remaining in third gear. Great for overtaking!


-- 
Stuart Sharp

> Becasue in a sensible car with torque instead of nutty rev levels you can
> happily put it in 5th at 25 and leave it there all the way to 150+...
>
>


Im my 307 D-Turbo put it in 5th at 25 and you'll stall the engine! Gotta be
doing at least 35-40 before engaging 5th just to make sure the engine is
above 1100RPM then it'll pull all the way. Could really do with a 6 speed
box to help things mid range but not enough pennies to buy a new model.

Chris

"PC Paul"  wrote in message
news:VxHLe.4172$P.3450@fe3.news.blueyonder.co.uk...

> Adrian wrote:
> > Steve Walker (steve@otolith.demon.co.uk) gurgled happily, sounding
> > much like they were saying :
> >
> >> For all the guff about 'peaky' VTEC engines, if you boot my Civic at
> >> 30mph in 6th, it accelerates. Not terribly quickly, but smoothly and
> >> without labouring. Try the same thing in 5th in the Impreza and
> >> *nothing*, literally *nothing* happens.
> >
> > Umm, why on earth would you want to plant it at 30 in top?
>
> Becasue in a sensible car with torque instead of nutty rev levels you can
> happily put it in 5th at 25 and leave it there all the way to 150+...


Without sacrificing good acceleration?
Most cars would still be comparitively gutless, regardless of how much
torque the engine had.
Mike.

Mike G wrote:

> "PC Paul"  wrote in message
> news:VxHLe.4172$P.3450@fe3.news.blueyonder.co.uk...
>> Adrian wrote:
>>> Steve Walker (steve@otolith.demon.co.uk) gurgled happily, sounding
>>> much like they were saying :
>>>
>>>> For all the guff about 'peaky' VTEC engines, if you boot my Civic
>>>> at 30mph in 6th, it accelerates. Not terribly quickly, but
>>>> smoothly and without labouring. Try the same thing in 5th in the
>>>> Impreza and *nothing*, literally *nothing* happens.
>>>
>>> Umm, why on earth would you want to plant it at 30 in top?
>>
>> Becasue in a sensible car with torque instead of nutty rev levels
>> you can happily put it in 5th at 25 and leave it there all the way
>> to 150+...
>
> Without sacrificing good acceleration?
> Most cars would still be comparitively gutless, regardless of how much
> torque the engine had.
> Mike.


Well obviously if you want *good* acceleration, change down.

But for pottering on A and B roads being able to put it in 5th and leave it 
makes for a relaxing drive.

My Carlton had better acceleration in 5th at 40 than my Astra (1.4i) had in 
3rd...

"Douglas Payne"  wrote in message
news:42ff468a$0$18644$14726298@news.sunsite.dk...

> Steve Walker wrote:
> > I drove my kid sister's Impreza turbo yesterday. Mint condition,
> > unmodified W-reg with 30K miles. Very nice, very secure feeling, very
> > comfortable, quick on boost, but Jesus, appalling turbo lag. For all the
> > guff about 'peaky' VTEC engines, if you boot my Civic at 30mph in 6th,
> > it accelerates. Not terribly quickly, but smoothly and without
> > labouring. Try the same thing in 5th in the Impreza and *nothing*,
> > literally *nothing* happens. Are they all like that? I thought driving
> > round turbo-lag was a 1980's pastime?
>
> In a turbo'd engine, the compression ratio is often lowered, this means
> that a turbo'd engine produces even less torque at low revs than a
> similar capacity normally aspirated one.


Yup. My Celica has a 8.5 to 1 comp ratio.
If there is less torque at low revs, it's not something that is apparent in
normal driving.


> At low revs there is not enough exhaust gas to push a usefully sized
> turbo hard enough to make it push more air into the engine.  In fact,
> turbos are actually a restriction in the exhaust and the inlet at low
> (and high) revs.
>
> I'm not sure I would class what you describe as lag.  Try driving
> something turbo'd from the 1980s for more details. (c:  I'd describe lag
> as the delay between being off boost but at revs within the range of the
> turbo, flooring it, and waiting for full boost and the turbo 'kick'.  On
> older cars, the delay is quite marked and could easily take an
> inexperienced driver by surprise.


I understand the Sierra Cosworths are like that. Boost comes in so quickly
that on a wet road, you can easily lose the back end.
Mate had a  '90 Saphire Cosworth in excellent nick. I could have baught it
for 1500 a couple of years ago, but the turbo delivery characteristics were
enough to put me off, so I got a Celica turbo instead. Not as quick, but
better equipped and more rewarding to drive OMO.


> Many modern turbo'd engines seem to have this delay engineered out to
> some extent, by using clever turbos and electrickery, but I don't think
> there's a lot they can do to improve driveability at really low revs.


My Celica GT4 turbo is a 1990. Turbo delivery comes in so smoothly and
progressively, that I doubt anyone who didn't know would realise that it had
a turbo. Poodling around town, it feels like, and is just as driveable as
any non-turbo car.
Mike.

In message , 
Adrian  writes

>Steve Walker (steve@otolith.demon.co.uk) gurgled happily, sounding much
>like they were saying :
>
>> For all the guff about 'peaky' VTEC engines, if you boot my Civic at
>> 30mph in 6th, it accelerates. Not terribly quickly, but smoothly and
>> without labouring. Try the same thing in 5th in the Impreza and
>> *nothing*, literally *nothing* happens.
>
>Umm, why on earth would you want to plant it at 30 in top?


Curiosity, principally.

-- 
Steve Walker

In message <42ff40d7$0$1316$ed2619ec@ptn-nntp-reader02.plus.net>, Mike G 
 writes

>
>"Steve Walker"  wrote in message
>news:WtUsS2Xwtz$CFwaL@otolith.demon.co.uk...
>> I drove my kid sister's Impreza turbo yesterday. Mint condition,
>> unmodified W-reg with 30K miles. Very nice, very secure feeling, very
>> comfortable, quick on boost, but Jesus, appalling turbo lag. For all the
>> guff about 'peaky' VTEC engines, if you boot my Civic at 30mph in 6th,
>> it accelerates. Not terribly quickly, but smoothly and without
>> labouring. Try the same thing in 5th in the Impreza and *nothing*,
>> literally *nothing* happens. Are they all like that? I thought driving
>> round turbo-lag was a 1980's pastime?
>
>Turbos need engine revs to give boost.
>I wouldn't expect any turbo to give much boost, given the low revs of an
>engine in 5th at 30mph.
>I think maybe you're expecting too much.


After the slagging I've heard people give VTEC units in favour of 
sporting blown engines, I was expecting to see some of the flexibility I 
keep hearing about.


>Driven normally, my Celica turbo has no noticeable lag. Of course more power
>comes in as the revs rise, but it's smooth and progressive. I would expect
>an Impreza turbos delivery to be very similar.


Oh, it's fine when it comes in, a bit less frenetic than what I'm used 
to. I got the impression one could very easily lose one's license 
without having any fun in the process. Nice car, though.

-- 
Steve Walker

"PC Paul"  wrote in message 
news:VxHLe.4172$P.3450@fe3.news.blueyonder.co.uk...

> Adrian wrote:
>> Steve Walker (steve@otolith.demon.co.uk) gurgled happily, sounding
>> much like they were saying :
>>
>>> For all the guff about 'peaky' VTEC engines, if you boot my Civic at
>>> 30mph in 6th, it accelerates. Not terribly quickly, but smoothly and
>>> without labouring. Try the same thing in 5th in the Impreza and
>>> *nothing*, literally *nothing* happens.
>>
>> Umm, why on earth would you want to plant it at 30 in top?
>
> Becasue in a sensible car with torque instead of nutty rev levels you can 
> happily put it in 5th at 25 and leave it there all the way to 150+...
>
>
>


Ever considered an automatic...?

In message , Stu 
 writes


>Like Mike says, you need to gear the car correctly. At 30 in fifth, you
>don't have enough revs to spin the turbo and it's just labouring the
>engine. When you have an engine speed of approx 2500rpm, the point at
>which a turbo begins to have real effect, try putting your foot down
>then.


Oh, I understand that, it's just I'd been led to expect something more 
flexible and driveable than a VTEC unit, and it just isn't.

By the way, apologies for posting this here, I meant to post it to 
uk.rec.cars.misc, and fucked up.

-- 
Steve Walker

Steve Walker wrote:

> I drove my kid sister's Impreza turbo yesterday. Mint condition,
> unmodified W-reg with 30K miles. Very nice, very secure feeling, very
> comfortable, quick on boost, but Jesus, appalling turbo lag. For all
> the guff about 'peaky' VTEC engines, if you boot my Civic at 30mph in
> 6th, it accelerates. Not terribly quickly, but smoothly and without
> labouring. Try the same thing in 5th in the Impreza and *nothing*,
> literally *nothing* happens. Are they all like that? I thought driving
> round turbo-lag was a 1980's pastime?


That's not lag, that's just off-boost. At low RPM there's not enough exhaust 
gas flowing to spin up the compressor. Turbo lag is the delay from hitting 
the accellerator at a speed where it is capable of spinning the compressor - 
say 3000rpm, and the turbo spooling  up to pressure.


-- 
re-configure the solar matrix in parallel for endothermic propulsion

Steve Walker (steve@otolith.demon.co.uk) gurgled happily, sounding much
like they were saying : 


> After the slagging I've heard people give VTEC units in favour of 
> sporting blown engines, I was expecting to see some of the flexibility
> I keep hearing about.


I don't think anybody - or at least anybody sane - would ever suggest a 
"conventional" turbo lump would be as flexible as an equivalent power big-
capacity normally aspirated lump.

I've driven VTEC civics in the past - the original shape one, 1.6/160bhp, 
about L-reg - and they went like shit off a shovel. But only really once 
they hit loonyrevs. Below that, they were just... unexciting.

Likewise, no turbo off-boost will be all that, as the CR has to be lowered 
to stop the thing eating itself.

If you want to make a turbo "flexible" on- and off-boost, then you've got 
to start either managing the boost electronically or using lower boost 
pressures. For example, the petrol turbo in my Cit XM manages the boost to 
allow the use of a relatively high CR - as a result, the absolute power's 
fairly unexceptional for a turbo'd 2.0 petrol (150bhp), but the off-boost 
performance is good, with a ludicrously flat torque curve - 180lb/ft peak 
is reached across a range of about 3,000rpm

In message , 
Adrian  writes

>Steve Walker (steve@otolith.demon.co.uk) gurgled happily, sounding much
>like they were saying :
>
>> After the slagging I've heard people give VTEC units in favour of
>> sporting blown engines, I was expecting to see some of the flexibility
>> I keep hearing about.
>
>I don't think anybody - or at least anybody sane - would ever suggest a
>"conventional" turbo lump would be as flexible as an equivalent power big-
>capacity normally aspirated lump.
>
>I've driven VTEC civics in the past - the original shape one, 1.6/160bhp,
>about L-reg - and they went like shit off a shovel. But only really once
>they hit loonyrevs. Below that, they were just... unexciting.


They aren't like that now. You have to bear in mind that the 1.6 litre 
VTi Civics were in the market against 2.0 litre naturally aspirated 
lumps giving about 150 bhp. Of course they lacked torque relative to 
something like a 16V Astra GTE. The 2.0 i-VTEC engine gives similar 
low-rev torque to any other normally aspirated two litre.

-- 
Steve Walker

Mark W wrote:

> "PC Paul"  wrote in message
> news:VxHLe.4172$P.3450@fe3.news.blueyonder.co.uk...
>> Adrian wrote:
>>> Steve Walker (steve@otolith.demon.co.uk) gurgled happily, sounding
>>> much like they were saying :
>>>
>>>> For all the guff about 'peaky' VTEC engines, if you boot my Civic
>>>> at 30mph in 6th, it accelerates. Not terribly quickly, but
>>>> smoothly and without labouring. Try the same thing in 5th in the
>>>> Impreza and *nothing*, literally *nothing* happens.
>>>
>>> Umm, why on earth would you want to plant it at 30 in top?
>>
>> Becasue in a sensible car with torque instead of nutty rev levels
>> you can happily put it in 5th at 25 and leave it there all the way
>> to 150+...
> Ever considered an automatic...?


Yep. But when I'm not in a relaxed all-day-in-5th mood I tend to be in a 
'steering with the throttle' sort of mood and a manual works far better at 
that point... ;-)

In article , 
nobody@home.com says...

> That means I can accelerate rapidly from 40 to 80mph whilst 
> remaining in third gear. Great for overtaking!
> 

Try 25-70 in 3rd. Celica zoom time.
-- 
Carl Robson
Car PC Build starts again. http://smallr.com/rz
Homepage: http://www.bouncing-czechs.com

In article <42ff516a$0$97139$ed2619ec@ptn-nntp-reader03.plus.net>, 
metier@lycos.co.uk says...

> My Celica GT4 turbo is a 1990. Turbo delivery comes in so smoothly and
> progressively, that I doubt anyone who didn't know would realise that it had
> a turbo. Poodling around town, it feels like, and is just as driveable as
> any non-turbo car.
> 

Bit boring though.
I miss the "lag, lag, boom, oh jesus£ boost of my old Saab.
Mind you it was fun arround the derbyshire lanes yesterday, at the 
Bubble Inn charity car meet.
-- 
Carl Robson
Car PC Build starts again. http://smallr.com/rz
Homepage: http://www.bouncing-czechs.com

Tim S Kemp wrote:

> 
> Steve Walker wrote:
> > I drove my kid sister's Impreza turbo yesterday. Mint condition,
> > unmodified W-reg with 30K miles. Very nice, very secure feeling, very
> > comfortable, quick on boost, but Jesus, appalling turbo lag. For all
> > the guff about 'peaky' VTEC engines, if you boot my Civic at 30mph in
> > 6th, it accelerates. Not terribly quickly, but smoothly and without
> > labouring. Try the same thing in 5th in the Impreza and *nothing*,
> > literally *nothing* happens. Are they all like that? I thought driving
> > round turbo-lag was a 1980's pastime?
> 
> That's not lag, that's just off-boost. At low RPM there's not enough exhaust
> gas flowing to spin up the compressor. Turbo lag is the delay from hitting
> the accellerator at a speed where it is capable of spinning the compressor -
> say 3000rpm, and the turbo spooling  up to pressure.


Modern turbo installations use a bypass valve downstream of the turbo in 
addition to the wastegate. This allows the turbo to maintain spin while the
throttle is closed. This dramatically reduces the turbo lag.

On Sun, 14 Aug 2005 13:51:16 GMT, "PC Paul"  wrote:


>My Carlton had better acceleration in 5th at 40 than my Astra (1.4i) had in 
>3rd...


Which you pay for with high fuel consumption.

Peter Hill wrote:

> On Sun, 14 Aug 2005 13:51:16 GMT, "PC Paul"  wrote:
>
>> My Carlton had better acceleration in 5th at 40 than my Astra (1.4i)
>> had in 3rd...
>
> Which you pay for with high fuel consumption.


Never claimed otherwise.. but (at the time) it was worth it.

"PC Paul"  wrote in news:Lo6Me.1155$Wq4.379
@fe1.news.blueyonder.co.uk:


> Peter Hill wrote:
>> On Sun, 14 Aug 2005 13:51:16 GMT, "PC Paul"  wrote:
>>
>>> My Carlton had better acceleration in 5th at 40 than my Astra (1.4i)
>>> had in 3rd...
>>
>> Which you pay for with high fuel consumption.
> 
> Never claimed otherwise.. but (at the time) it was worth it. 
> 
> 
> 

Let's face it, turbocharging sacrifices economy just as much. My S70's 
handbook still has a little card with the Volvo mpg figures on it. Combined 
mpg for my T5 is 25.2. A modern, normally aspirated 2.3l engine would do 
much better than that. Basically, more power equals less mpg. The only way 
to improve speed without sacrificing fuel economy is to reduce weight (i.e. 
get a motorbike).


-- 
Stuart Sharp

Stu wrote:

> "PC Paul"  wrote in news:Lo6Me.1155$Wq4.379
> @fe1.news.blueyonder.co.uk:
>
>> Peter Hill wrote:
>>> On Sun, 14 Aug 2005 13:51:16 GMT, "PC Paul"  wrote:
>>>
>>>> My Carlton had better acceleration in 5th at 40 than my Astra
>>>> (1.4i) had in 3rd...
>>>
>>> Which you pay for with high fuel consumption.
>>
>> Never claimed otherwise.. but (at the time) it was worth it.
>>
>>
>>
> Let's face it, turbocharging sacrifices economy just as much. My S70's
> handbook still has a little card with the Volvo mpg figures on it.
> Combined mpg for my T5 is 25.2. A modern, normally aspirated 2.3l
> engine would do much better than that. Basically, more power equals
> less mpg. The only way to improve speed without sacrificing fuel
> economy is to reduce weight (i.e. get a motorbike).


When I was looking into getting a bike to save money while maintaining 
performance, I found it was going to cost about the same to run as the car, 
once you include servicing it every 3000 miles, a new rear tyre frequently, 
etc.

And fuel economy was crap compared to what I expected! Almost all only had 
an average of  35-40 mpg.

"PC Paul"  wrote in
news:N37Me.1373$Wq4.1337@fe1.news.blueyonder.co.uk: 


> Stu wrote:
>> "PC Paul"  wrote in news:Lo6Me.1155$Wq4.379
>> @fe1.news.blueyonder.co.uk:
>>
>>> Peter Hill wrote:
>>>> On Sun, 14 Aug 2005 13:51:16 GMT, "PC Paul"  wrote:
>>>>
>>>>> My Carlton had better acceleration in 5th at 40 than my Astra
>>>>> (1.4i) had in 3rd...
>>>>
>>>> Which you pay for with high fuel consumption.
>>>
>>> Never claimed otherwise.. but (at the time) it was worth it.
>>>
>>>
>>>
>> Let's face it, turbocharging sacrifices economy just as much. My
>> S70's handbook still has a little card with the Volvo mpg figures on
>> it. Combined mpg for my T5 is 25.2. A modern, normally aspirated 2.3l
>> engine would do much better than that. Basically, more power equals
>> less mpg. The only way to improve speed without sacrificing fuel
>> economy is to reduce weight (i.e. get a motorbike).
> 
> When I was looking into getting a bike to save money while maintaining
> performance, I found it was going to cost about the same to run as the
> car, once you include servicing it every 3000 miles, a new rear tyre
> frequently, etc.
> 
> And fuel economy was crap compared to what I expected! Almost all only
> had an average of  35-40 mpg.
> 
> 
> 

Not to mention the fact that you're far more likely to die. My mate at 
work is now looking at buying a TVR, after a near-death experience with 
his Kawasaki Ninja. The largest remaining piece of the bike was the fuel 
tank!



-- 
Stuart Sharp

Stu wrote:

> 
> "PC Paul"  wrote in news:Lo6Me.1155$Wq4.379
> @fe1.news.blueyonder.co.uk:
> 
> > Peter Hill wrote:
> >> On Sun, 14 Aug 2005 13:51:16 GMT, "PC Paul"  wrote:
> >>
> >>> My Carlton had better acceleration in 5th at 40 than my Astra (1.4i)
> >>> had in 3rd...
> >>
> >> Which you pay for with high fuel consumption.
> >
> > Never claimed otherwise.. but (at the time) it was worth it.
> >
> >
> >
> Let's face it, turbocharging sacrifices economy just as much. My S70's
> handbook still has a little card with the Volvo mpg figures on it. Combined
> mpg for my T5 is 25.2. A modern, normally aspirated 2.3l engine would do
> much better than that. Basically, more power equals less mpg. The only way
> to improve speed without sacrificing fuel economy is to reduce weight (i.e.
> get a motorbike).


If you drive normally, a turbo actually saves fuel. This is because of the
positive displacement effect; the turbo makes a small engine behave like
a larger engine, but without the extra friction losses of the larger engine.
The spin of the turbo wheel is almost for free. In practical terms, you can
reduce the rpm and drive in higher gear, just as if it was a bigger engine.

"Johannes H Andersen"  wrote in message
news:43010FE1.67379839@sizefitter.com...

>
>
> Stu wrote:
> >
> > "PC Paul"  wrote in news:Lo6Me.1155$Wq4.379
> > @fe1.news.blueyonder.co.uk:
> >
> > > Peter Hill wrote:
> > >> On Sun, 14 Aug 2005 13:51:16 GMT, "PC Paul"  wrote:
> > >>
> > >>> My Carlton had better acceleration in 5th at 40 than my Astra (1.4i)
> > >>> had in 3rd...
> > >>
> > >> Which you pay for with high fuel consumption.
> > >
> > > Never claimed otherwise.. but (at the time) it was worth it.
> > >
> > >
> > >
> > Let's face it, turbocharging sacrifices economy just as much. My S70's
> > handbook still has a little card with the Volvo mpg figures on it.
Combined
> > mpg for my T5 is 25.2. A modern, normally aspirated 2.3l engine would do
> > much better than that. Basically, more power equals less mpg. The only
way
> > to improve speed without sacrificing fuel economy is to reduce weight
(i.e.
> > get a motorbike).
>
> If you drive normally, a turbo actually saves fuel. This is because of the
> positive displacement effect; the turbo makes a small engine behave like
> a larger engine, but without the extra friction losses of the larger
engine.
> The spin of the turbo wheel is almost for free. In practical terms, you
can
> reduce the rpm and drive in higher gear, just as if it was a bigger

engine.

No in 90% of cases.

the turbo acts as a restriction in the exhaust so the engine is breathing
with a clogged lung effectively, and as petrol turbo motors tradtionally ran
with a lower CR- thermodynamic efficiency is lower than a NA higher CR
engine would be, so again it will use more fuel.

A petrol engine tradionally operates at 14.7:1 fuel air mix, if you add more
air, you have to add more fuel- mpg decreases, so allowing the turbo to
boost is not good.

However if you look at the very latest crop of low or medium blow turbo's
with 10:1 CR's, and lean burn technology, and direct injection, such as
VAG's 2.0l FSI turbo motor, they give very nearly as good mpg as the
equivilant NA engine, but only when running at little or no positive boost.

Diesels are another matter. Almost without exception, if you take a stock NA
diesel, and turbo it, leaving the fuelling as stock, or even increasing it
slightly, the turbo will present better mpg's.

PSA's XUD 70ps vs the XUDT 90ps motors are a very good example.

Tim..

"Tim.." wrote:

> 
> "Johannes H Andersen"  wrote in message
> news:43010FE1.67379839@sizefitter.com...
> >
> >
> > Stu wrote:
> > >
> > > "PC Paul"  wrote in news:Lo6Me.1155$Wq4.379
> > > @fe1.news.blueyonder.co.uk:
> > >
> > > > Peter Hill wrote:
> > > >> On Sun, 14 Aug 2005 13:51:16 GMT, "PC Paul"  wrote:
> > > >>
> > > >>> My Carlton had better acceleration in 5th at 40 than my Astra (1.4i)
> > > >>> had in 3rd...
> > > >>
> > > >> Which you pay for with high fuel consumption.
> > > >
> > > > Never claimed otherwise.. but (at the time) it was worth it.
> > > >
> > > >
> > > >
> > > Let's face it, turbocharging sacrifices economy just as much. My S70's
> > > handbook still has a little card with the Volvo mpg figures on it.
> Combined
> > > mpg for my T5 is 25.2. A modern, normally aspirated 2.3l engine would do
> > > much better than that. Basically, more power equals less mpg. The only
> way
> > > to improve speed without sacrificing fuel economy is to reduce weight
> (i.e.
> > > get a motorbike).
> >
> > If you drive normally, a turbo actually saves fuel. This is because of the
> > positive displacement effect; the turbo makes a small engine behave like
> > a larger engine, but without the extra friction losses of the larger
> engine.
> > The spin of the turbo wheel is almost for free. In practical terms, you
> can
> > reduce the rpm and drive in higher gear, just as if it was a bigger
> engine.
> 
> No in 90% of cases.
> 
> the turbo acts as a restriction in the exhaust so the engine is breathing
> with a clogged lung effectively, and as petrol turbo motors tradtionally ran
> with a lower CR- thermodynamic efficiency is lower than a NA higher CR
> engine would be, so again it will use more fuel.


Because of the hot gas temperatures. The high volume of expanded gas is as
much restricted as in a NA engine. In the turbo, the gas works against the
turbo wheel instead of the exhaust. After the thermodynamic work on the turbo
wheel, the gas becomes cooler and denser and flows throw the exhaust at lower
speed than for a NA. Hence the loss due to the turbo restriction is minimal.  
 

> A petrol engine tradionally operates at 14.7:1 fuel air mix, if you add more
> air, you have to add more fuel- mpg decreases, so allowing the turbo to
> boost is not good.


Not if you use a lower rpm. Since you add both air and fuel, you can end
up with the exact same volume and mix (power) but at lower rpm. This is the
'positive displacement' effect. The engine does the same as before, but at
a lower rpm, hence less friction and pumping losses. 


> However if you look at the very latest crop of low or medium blow turbo's
> with 10:1 CR's, and lean burn technology, and direct injection, such as
> VAG's 2.0l FSI turbo motor, they give very nearly as good mpg as the
> equivilant NA engine, but only when running at little or no positive boost.


If you use the engine as a 'performance' engine, then yes you will naturally
use more fuel. If you just use the engine as usual, then the turbo will be
more economical.


> Diesels are another matter. Almost without exception, if you take a stock NA
> diesel, and turbo it, leaving the fuelling as stock, or even increasing it
> slightly, the turbo will present better mpg's.


Yes, but the same principle can be applied to petrol turbo, e.g. Saab's light
pressure turbos.  


> PSA's XUD 70ps vs the XUDT 90ps motors are a very good example.
> 
> Tim..

In article , 
nobody@home.com (Stu) wrote:


>  turbocharging sacrifices economy just as much.


Except in a diseasel.

The Turbo Escort Diesel has BETTER fuel economy than the non-turbo, and 
20 hp more to boot.

-- 
Paul Cummins - Always a NetHead
Wasting Bandwidth since 1981