Volvo 850 - gas type?

If the turbo is kicking in then you aren't getting any economy.

 

Therein is the crux. Drive a turbo conservatively and it naturally
tends to be inefficient. Driving in a way that makes the turbo work is
not necessarily conducive to better mileage (though thermal efficiency
will be improved).



--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name

 

Well I can say with certainty that using the turbo frequently will not
increase mileage regardless of what it does for thermal efficiency. I once
managed 13 mpg average for a tank of gas in my 240T. Best I've ever gotten
was just over 24mpg highway.

 

I'll just stick with my premium 91 then... MUCH easier, almost worth the few
dollars per tank not to have to do all that work.

 

Have you tried 100 octane AvGas. If you want to blow money, you might
as well do it right.

 

We don't have that here... I'm in Ontario, Canada... the highest i've seen
is 95 Octane at a Pioneer station and 94 Octane at a Sunoco.

If you think "blowing" money on a car that can use premium fuel is the
correct term, that's your opinion... If the manual is recommending 91 then
why not use it, I'm not going to have my timing retarded and performance
reduced just because at the absolute minimum 87 Octane will function in the
engine... Not after going to the dealer and having the service guy say to me
"that's probably one of the nicest running 10 year old cars i've ever worked
on"

Where do I get this "AvGas" anyways??

 

From any small airfield, it's aviation fuel, used in piston engine aircraft.

 

Doesn't it still contain lead? Or at least did recently.

 

I dunno, only time I've ever heard of people running it in cars was for race
cars.

 

You could buy racing fuel at most any track too...
What does Cam-2 go for now days anyone know?

I admit I was wrong, I read my owners manual it does say premium. I just
put in ~10 gallons in the ~17 gallon tank, saw no performance change, 2 or 3
more tanks will tell...

To everyone I told 87 was ok, I am sorry, I might have been wrong. I will
report on my result in a few weeks.

 

It's reasonable for a turboed car to return poorer mpg than it's
equivalent N/A car, but it is surprising to see the variation in
mileage you get. 24 mpg is an improvement of nearly 85% over 13 mpg.
That is far better than my best-over-worst figure in a N/A 740 (not
entirely a fair comparison, since I run on LPG). My best mileage is
about 30% better than my worst; I don't think any of my 200s did any
better. Presumably the big difference you see is down to the turbo
doing it's stuff when it's on boost.


--

Stewart Hargrave


For email, replace 'SpamOnlyToHere' with my name

 

Yes, it's called 100LL for "low lead".

 

I think the overiding factor as to why a turbo car returns worse fuel
consumption will alwys be the 'grin factor' a turbo car has. I have a 99S70
T5 SE and have had a worst consumption of 22mpg (UK gallons) and a best of
38mpg.... The former on country lanes whilst grinning like a Cheshire cat
and the latter whilst on motorways cruising in traffic at 40-60mph with
virtually no stop start stuff (very rare that happens in the UK!)... Both
were over a distance equivalent to 1/2 tank of fuel so not entirely
definitive...

As for turbo cars being less efficient when driven gently, this is a common
myth. A turbo car can be more economical than an equivalent non turbo car as
it can provide air to the engine without the engine having to draw it in
(that vacuum reading has to be worked for by the engine). As the turbo
utilises otherwise waste energy contained in the still rapidly expanding
exhaust gasses it relieves the engine of the need to 'suck' air into the
combustion chamber. Unfortunately for a petrol engine this applies to a very
narrow range of engine operating speeds and is typically a few hundred revs
near where the turbo provides positive pressure to the inlet manifold (and
positive pressure over around 2psi is where economy suffers). If you look at
the diesel world (ok, so its a different principle involved but some of the
concepts hold), the turbo diesel engine almost always seems to be more
economical than the non-turbo equivalent.

To be fair to the turbo engine though we should compare apples with apples
and not apples with pears. If we look at the power outputs of a turbo engine
and an equivalent power output NA engine the NA engine almost always loses
out. This is because a larger engine has inherently more frictional losses
than a smaller one (larger bores, longer strokes and/or more cylinders),
thus a small engine with lower losses and a turbo will generally be more
economical than a larger higher friction one.