BP Ultimate--worth it?

Well that's carbs rather than injection and they do have a small tank.

OK. I bought an old Audi 100 with LPG conversion a couple of weeks ago and am quite impressed with how well the system works. Mind you, I'm still on the first tankful, so haven't calculated the economy yet.

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!

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.

Mathew

Forgot to mention, since May '06 I've been using nothing but Optimax (or V-Power as it's called now) - first it was to see if there's a difference but now, again, it's habit. My graph shows now change in results hence I'm reasonably certain it's not helping (fuel consumption wise) hence I probably ought to get back to regular!

Mathew

Hmm, will have to do a few tests. I use it 'cos it's the only thing that stops my car pinking like a b@stard.

I used Optimax in mine for a while and did notice a difference but it wasn't worth the trip to the filling station so I usually used BP standard since that's all that's available locally. I did fill up with Tesco 99 and expected to notice something but I couldn't tell any difference whatsoever and that may explain it. My engine does have knock sensors and adjusts the timing for the octane level.

I simply don't do enough miles on that car to cover the cost - even if I was keen.

I'm not sure I'd relish the poorer performance, either.

In message , Mathew Newton writes

I calculated a moving % Optimax for each fill and then calculated the Kendall correlation coefficient between mpg and % Optimax. Probably not a suitable approach for the way you've done it, as you've fuelled it in blocks.

You could use a Mann-Whitney U-test to compare medians between groups (I'd still go for a non-parametric test on the grounds that it's more conservative and that the frequency distribution is probably not normal) Just eyeballing the data, if you sort your columns by mpg, you will see that the lowest third of mpgs are exclusively 95RON, with the Optimax/V- Power all in the top 2/3.

I get U=1246 for N1,N2 = (121,28). Using a normal approximation, that gives Z = -2.18, which would be significant. However, because of the way that you've used the different fuels, there's no way of saying whether that's because of the age of the engine or the time of year or changes in the way that you drive.

As this is a UK hierarchy NG, could you post in English please? :-)

Chris

In message , Steve Walker writes

Could you run that past me again. I lost you after you said "I calculated..."

Willy Eckerslyke proclaimed to uk.rec.cars.maintenance ...

Same findings with my Celica - had to knock 5 degrees off my timing table to deal with the pinking. Opti back in and all is well again.

Dave Plowman (News) proclaimed to uk.rec.cars.maintenance ...

If set up correctly you dont get a drop in performance. It does require the SGI kits though which are far more expensive and harder to install.

Weatherlawyer proclaimed to uk.rec.cars.maintenance ...

Maybe they're late? I'm always late for something, I just have too many things to do in each day - I wish I could amble to work and enjoy the weather!

Incidentally I hope thats just the one pint youre having :)

Can't have read about those then - every road test I've seen of a converted vehicle mentions the poorer performance.

Dave Plowman (News) proclaimed to uk.rec.cars.maintenance ...

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.

Anyway, SGI kits all the way. Know someone who drives a van converted for work and couldnt tell the difference when it was on petrol or LPG.

Coyoteboy ( snipped-for-privacy@hotmail.com) gurgled happily, sounding much like they were saying :

And that's why you see a drop in performance - because of the lower 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.

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.

I know exactly what you mean. I was half tempted with my P6 (4-cyl), but 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!

Perhaps the main reason I like the SD1 is that it goes when you tell it. 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. ;-)