Mpg

GeoffCapes

Centenary Club
Messages
7,477
#41
I think a few people would be interested to improve mpg and improve the range of the vehicle when cruising through France.
I can only assume you are referring to a non Le Mans trip. As based upon last year, the aim of travelling through France was at the highest possible speed, making as much noise as possible and sod the MPG.

:)
 
Messages
25,971
#42
I honestly think its more placebo effect using a higher octane rated fuel in a car that isnt mapped for it. Yes im sure the additives help clean the fuel system which is why i chuck a tank full in from time to time.

You expect the car to be a little quicker and sharper having just paid about 50p a gallon more for the higher octane fuel. You then pay more attention to the responce and speed of the car and probably push a little harder to test if it is. Reality is its slower as your now lugging an extra 80 kg / ltrs of fuel around that were not in the car when you pulled into the garage on empty.
Completely agree. There was a 5th gear thing that showed one car (I think it was a turbo) had a small power increase, but didn't effectively answer the question of if it was going to be noticeable. They told VBH which fuel was which and sent her out on track which basically plays into all the biases.

At the end of the day, if the map can take advantage of the additional octane, then there may be some benefit. If it can't there's no real point.

C
 
Messages
187
#45
I have owned my 2002 manual 3200GT for seven years. Over that entire period it has averaged 17mpg, with upper and lower bounds of 22mpg and 13mpg. I keep a spreadsheet of the mileage and litres to brim every time I fill it up. The mpg is calculated from that data so it's accurate.
I also have a 2008 Jaguar XF-SV8, which has the supercharged 4.2 litre V8 as used in the XK8. This has also averaged 17mpg with upper and lower bounds of 23mpg and 13 mpg.
However, the Jag has a poxy little 70L tank - I can't tell you how annoying that is!

Steve.
 
Messages
3,556
#46
And another thing lots of people forget, you don't need 400hp to do 90mph..

In 6th the old 3200GT is rolling along at about 2500rpm at 85mph, working out the body drag and the friction of the wide tires its most probably useing no more than about 60bhp!

I used get 25mpg on a run down to the South of France, until I got to Dijon!


Dave
 

Zep

Moderator
Messages
1,429
#47
While I would never disagree with the verdict VBHs perfectly (at the time) formed bottom, there are benefits to using higher octane fuel. My manual states that you should not use fuel with less than 95 RON, to my mind this is not a statement that the engine is mapped for 95, but that the knock limiting function of the ECU will not work well below 95 RON.

The Bosch ME7.1.1 manual states as much: "In principal, the comprehensive dependency of internal torque on cylinder charge, engine speed, Lambda, ignition timing and cylinder individual fuel cut-off could be described in a five dimension map. The decisive step to simplify this dependency is the introduction of two central reference values:

•the optimal spark advance „sa_opt“ and
•the corresponding optimal internal torque „tqi_opt“,which reaches it’s maximum value at optimal spark advance. In some operating points the optimal spark advance is a theoretical value, because of the engine knock limit.

In short, an engine creates maximum torque at optimal ignition advance. That advance is governed by a map which is almost certainly optimised for more than 95 RON (otherwise this would be the maximum, not the minimum) and the ECU retards the ignition timing back from optimal based on the input from the knock sensors. While VBHs **** and a dyno run in a hot environment (a hot inlet charge also lowers the knock limit) may have not shown a measurable improvement, this doesn't mean there isn't one in my opinion.
 
Messages
3,556
#48
While I would never disagree with the verdict VBHs perfectly (at the time) formed bottom, there are benefits to using higher octane fuel. My manual states that you should not use fuel with less than 95 RON, to my mind this is not a statement that the engine is mapped for 95, but that the knock limiting function of the ECU will not work well below 95 RON.

The Bosch ME7.1.1 manual states as much: "In principal, the comprehensive dependency of internal torque on cylinder charge, engine speed, Lambda, ignition timing and cylinder individual fuel cut-off could be described in a five dimension map. The decisive step to simplify this dependency is the introduction of two central reference values:

•the optimal spark advance „sa_opt“ and
•the corresponding optimal internal torque „tqi_opt“,which reaches it’s maximum value at optimal spark advance. In some operating points the optimal spark advance is a theoretical value, because of the engine knock limit.

In short, an engine creates maximum torque at optimal ignition advance. That advance is governed by a map which is almost certainly optimised for more than 95 RON (otherwise this would be the maximum, not the minimum) and the ECU retards the ignition timing back from optimal based on the input from the knock sensors. While VBHs **** and a dyno run in a hot environment (a hot inlet charge also lowers the knock limit) may have not shown a measurable improvement, this doesn't mean there isn't one in my opinion.
Defiantly Zep, the factory quoted 375hp for the standard 3200GT, but there's some late cars out there producing well over 400hp!

So something must have changed


Dave
 
Messages
25,971
#50
While VBHs **** and a dyno run in a hot environment (a hot inlet charge also lowers the knock limit) may have not shown a measurable improvement, this doesn't mean there isn't one in my opinion.
Ummm. Yes... ;)

Probably not *quite* what you meant, but the test was ****. Without knowing what the map *allows* for spark advance range we'll never actually know.

C
 

Corranga

Junior Member
Messages
595
#53
there are benefits to using higher octane fuel....
...
...
...
and the ECU retards the ignition timing back from optimal based on the input from the knock sensors
I agreee. There are benefits, if your engine has knock sensors.
/Elise S1 /Rover K-Series /No knock sensors ;)
 

allandwf

Centenary Club
Messages
6,964
#54
Also you need to find the sweet spot of the engine, unfortunately, for UK, this seems to be cruising around the 90mph mark.