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BP Ultimate--worth it?
Cars Maintenance General car maintenance (uk.rec.cars.maintenance)
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#31
 
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Re: BP Ultimate--worth it? -
04-24-2007
, 02:54 AM
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Most kits rely on a restrictive "mixer" in the intake like a gas ring. The modern ones have nice injected (liquid IIRC) gas and there's no reason why youd see a drop in performance as they create no restriction and can supply all the air and fuel you might want, plus it mixes better for a better burn. And its higher Octane, not that that'll help on most cars, but if you have a programmable ECU you could make use of it - somewhere up around race-fuel levels IIRC but you have to account for the lower calorific value. |
calorific value. You can get the performance back up, but only by getting
the timing to take advantage of the extra octane (somewhere around 110,
IIRC).
Mind you, since few people use full power - and even then usually only
infrequently - the fact that the vast majority of LPG conversions remain
able to run on petrol means you can just switch back to petrol when the
power's required.
#32
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Mind you, since few people use full power - and even then usually only infrequently - the fact that the vast majority of LPG conversions remain able to run on petrol means you can just switch back to petrol when the power's required. |
this Audi (5-cyl 2 litre) was when climbing a particularly steep hill -
when changing down was just as easy as switching to petrol. On the flat,
it's not an issue for me, but then I haven't run it sufficiently on
petrol to know what I'm missing.
#33
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With LPG at 40p per litre, aren't you tempted to have it converted? I simply don't do enough miles on that car to cover the cost - even if I was keen. |
it'd take at least three years to pay for itself, by which time the
price advantage may have disappeared. Psychologically though, it does
make a difference. I can almost persuade myself that LPG is cheap enough
to be practically free, which makes me feel much better about taking the
long way home, etc.
Mind you, since the Audi 100 with LPG kit and a year's MOT cost me less
than 300 quid, I can persuade myself that the car itself was practically
free too!
#34
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Mind you, since few people use full power - and even then usually only infrequently - the fact that the vast majority of LPG conversions remain able to run on petrol means you can just switch back to petrol when the power's required. That's my view of it too. The only time I noticed a lack of power from this Audi (5-cyl 2 litre) was when climbing a particularly steep hill - when changing down was just as easy as switching to petrol. On the flat, it's not an issue for me, but then I haven't run it sufficiently on petrol to know what I'm missing. |
Most buy LPG conversions to save money and therefore won't be much worried
about less performance. If I wanted an economical SD1 they did do a
diesel. IIRC, the fastest one on the UK market when introduced. ;-)
--
*Ambition is a poor excuse for not having enough sense to be lazy *
Dave Plowman dave (AT) davenoise (DOT) co.uk London SW
To e-mail, change noise into sound.
#35
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Could you run that past me again. I lost you after you said "I calculated..." |
I've got a spreadsheet with 20,000 miles or so of fills, mileage and
whether it was Optimax or 95RON. So, knowing the volume of the tank, the
composition of the petrol in before filling and the type of petrol
added, I can calculate what % Optimax the car was running on for that
fill.
It's then possible mathematically to work out whether high values of %
Optimax are associated with high values of miles per gallon more often
than can be explained just by random coincidence. One such test is
Kendall's correlation coefficient. It's part of a branch of statistics
called "nonparametric statistics", which deals with data by ranking it
rather than by looking at the actual values. The main advantage of
nonparametric methods is that they make fewer assumptions about the
underlying data and are less likely to "see things that aren't there".
IOW, they're generally more conservative.
Anyway, applying that tells me that the more Optimax was in the tank,
the more likely I was to get higher mpg. Taking a bit of a liberty and
using another statistical method to fit a straight line to the data
tells me that it's only worth an extra 1.6 miles per gallon at 100%
Optimax, and that there's a shit load of scatter. So I'd only see that
extra 1.6 miles per gallon averaged out over thousands of miles, and it
wasn't worth the difference in the price of Optimax.
You can't do the same analysis for Matthew's data, because while I
randomly stuck the odd tank of Optimax in, he more or less used nothing
else for 12 months. So an alternative approach is to divide his data
into two groups, tanks of 95RON and tanks of Optimax/VPower. You can
then use a different statistical method to determine whether any
difference in miles per gallon between them is likely to be down to
chance. A suitable non-parametric test for this is called the
Mann-Whitney U-test. You basically put both lists of mpg numbers
together, sort them and number them with their rank. Then you separate
them, throw away the raw number and keep the rank, like this:
95RON 30, 29, 33, 28, 31
Optimax 30.5, 32, 34, 36
mpg rank fuel
28 1 95
29 2 95
30 3 95
30.5 4 Opt
31 5 95
32 6 Opt
33 7 95
34 8 Opt
36 9 Opt
95 RON 1,2,3,5,7 sum = 1+2+3+5+7 = 18
Optimax 4,6,8,9 sum = 4+6+8+9 = 27
You then add the ranks up for each group and plug the sum of the ranks
and the number of items in each group into a formula and end up with a
number you can look up in a statistical table. By comparing the number
you found with the number in the table, you can determine the
probability that using Optimax or 95RON actually made no difference to
fuel consumption, and any apparent difference was just down to chance.
For Matthew's data, it's less than 1 in 20. So we can be 95% sure that
Matthew's car gave better mpg when he was running it on Optimax than
when he was running it on 95RON.
But, there's a problem; there is no control for all of the other factors
which could affect fuel consumption. Almost all of the Optimax data is
from May 2006-April 2007, 47000-58000 miles. Maybe it's just because by
then the car was fully run in. Maybe his pattern of journeys or his
driving style changed. Maybe the weather was milder. Who knows?
Clear as mud?
--
Steve Walker
#36
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Could you run that past me again. I lost you after you said "I calculated..." Sorry, that was a bit opaque. OK, for the Civic Type-R I used to own, I've got a spreadsheet with 20,000 miles or so of fills, mileage and whether it was Optimax or 95RON. It's then possible mathematically to work out... snip |
Quote:
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Clear as mud? |
Ummm... I'm with Paul. I think. Can you come back to me in a bit when I've
remembered what day it is? Thanks.
#37
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In message <k+mg$jAE4PLGFwMu (AT) 10 (DOT) 0.0.3>, Paul Giverin paul (AT) giverin (DOT) co.uk> writes Could you run that past me again. I lost you after you said "I calculated..." Sorry, that was a bit opaque. OK, for the Civic Type-R I used to own, I've got a spreadsheet with 20,000 miles or so of fills, mileage and whether it was Optimax or 95RON. So, knowing the volume of the tank, the composition of the petrol in before filling and the type of petrol added, I can calculate what % Optimax the car was running on for that fill. It's then possible mathematically to work out whether high values of % Optimax are associated with high values of miles per gallon more often than can be explained just by random coincidence. One such test is Kendall's correlation coefficient. It's part of a branch of statistics called "nonparametric statistics", which deals with data by ranking it rather than by looking at the actual values. The main advantage of nonparametric methods is that they make fewer assumptions about the underlying data and are less likely to "see things that aren't there". IOW, they're generally more conservative. Anyway, applying that tells me that the more Optimax was in the tank, the more likely I was to get higher mpg. Taking a bit of a liberty and using another statistical method to fit a straight line to the data tells me that it's only worth an extra 1.6 miles per gallon at 100% Optimax, and that there's a shit load of scatter. So I'd only see that extra 1.6 miles per gallon averaged out over thousands of miles, and it wasn't worth the difference in the price of Optimax. You can't do the same analysis for Matthew's data, because while I randomly stuck the odd tank of Optimax in, he more or less used nothing else for 12 months. So an alternative approach is to divide his data into two groups, tanks of 95RON and tanks of Optimax/VPower. You can then use a different statistical method to determine whether any difference in miles per gallon between them is likely to be down to chance. A suitable non-parametric test for this is called the Mann-Whitney U-test. You basically put both lists of mpg numbers together, sort them and number them with their rank. Then you separate them, throw away the raw number and keep the rank, like this: 95RON 30, 29, 33, 28, 31 Optimax 30.5, 32, 34, 36 mpg rank fuel 28 1 95 29 2 95 30 3 95 30.5 4 Opt 31 5 95 32 6 Opt 33 7 95 34 8 Opt 36 9 Opt 95 RON 1,2,3,5,7 sum = 1+2+3+5+7 = 18 Optimax 4,6,8,9 sum = 4+6+8+9 = 27 You then add the ranks up for each group and plug the sum of the ranks and the number of items in each group into a formula and end up with a number you can look up in a statistical table. By comparing the number you found with the number in the table, you can determine the probability that using Optimax or 95RON actually made no difference to fuel consumption, and any apparent difference was just down to chance. For Matthew's data, it's less than 1 in 20. So we can be 95% sure that Matthew's car gave better mpg when he was running it on Optimax than when he was running it on 95RON. But, there's a problem; there is no control for all of the other factors which could affect fuel consumption. Almost all of the Optimax data is from May 2006-April 2007, 47000-58000 miles. Maybe it's just because by then the car was fully run in. Maybe his pattern of journeys or his driving style changed. Maybe the weather was milder. Who knows? Clear as mud? |
To get any reasonabe comparisions you need to factor in several other
things, weather conditions , wind , ambient temperature , load of
vehicle , traffic conditions , tyre pressures aircon on or off journey
distance , driving style , infact thiers so many variables its almost
imposible to get a true reading
--
#38
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I would be surprised if that's a real effect. I found a small, statistically significant increase in mpg with Optimax over 95RON in my Civic Type-R, but that was based on almost 20,000 miles worth of data. There's a tremendous amount of scatter and as a result the trend is barely visible by eye. The scatter is the key thing - I've been monitoring my consumption for nearly 60,000 miles... Indeed the longer I do it the less easy it is for me to stop! http://www.newtonnet.co.uk/permanent/consumption.xls Anyway, the range is around 4-5mpg and it goes up and down like nobody's business. Hence, unless I get over this amount then any improvement will be just lost in the noise... Furthermore, as mentioned elsewhere if you're testing with something in mind then who knows what effect it'll have on your driving style. As things stand I measure consumption out of habit hence I'm as unbiassed as you could probably get. |
#39
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I've recently tried BP Ultimate unleaded in my Nissan Primera 2.0i There seems to be about 5 miles per gallon improvement, maybe slight increase in power It costs around 99p+ per litre---anyone have experience / comments on this fuel? |
not just greater MPG. The main reason I use it in my Mondeo ST220 is that it
is supposed to keep the inside of the engine sparkly and new. Probably a
load of BS, but it works for me!
#40
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If you believe the hype from Shell, the advantages of Optimax/V-Power are not just greater MPG. The main reason I use it in my Mondeo ST220 is that it is supposed to keep the inside of the engine sparkly and new. Probably a load of BS, but it works for me! |
engine?
--
*Preserve wildlife - Go pickle a squirrel*
Dave Plowman dave (AT) davenoise (DOT) co.uk London SW
To e-mail, change noise into sound.
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