Technical To optimize fuel efficiency....

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Technical To optimize fuel efficiency....

mqsash

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Hi,

Manufacturers say that for best mileage, you should shift into higher gears as soon as possible. I interpret this as "maintain your speeds but at the lowest possible rev's and you'll be consuming less fuel"
( After all driving at 80kph in 5th has lower engine revs than doing so in 3rd, and Fiat says shift to 5th ASAP !! )

So thats how I generally drive, with as low revs as possible to maintain the speed. I'm usually into 5th by the time speedo is showing 45-50kph.
Dont have a tacho, but I recon that keeps me in the about 1500-2000 rpm range.

Then I read somewhere that engines are most fuel efficient at a certain rpm's. :confused: and certainly are less efficient towards idle or the red line :bang: .

If this is so, then what would be the ideal rpm's to keep the Uno most fuel efficient?
BTW - mine is a 2001, 1242cc SPFI.

If thats the case, then I certainly would love to get a tacho installed :idea: .

I'm more concerned about the down shift. e.g I can go down to almost single digit speeds in 3rd gear, as a result I tend to keep it in 3rd even near zero.
To speed up from there I shift to 2nd only if I need to pull away quickly, else I prefer to add a little bit more throttle while still in the higher gear and build the speed slowly.
(same thing for down shifting from other gears).
Would this down shifting pattern be less efficient?

mqs
 
Last edited:
Hmm......
Basically the question is whether the engine is most efficient in a certain rpm range, and if so what that range would be for the Uno, and would it be same for all engine types of the uno's.

mqs
 
what's your current milage ?

Use of good petrol is more advisable than to do all this shifting trouble. ..

Anyway who the hell cares of milage ? even if u drive real hard, u will still get around 15KMPL....

Bettter u go in for a bajaj CT100 if u r so milage concious hehe ..but then it is missing 2 wheels he heh...(kiddin--;) )

So many members from India is popping up - nice to see:)


Rajeev
 
Hi Rajeev ,

On the expressway between Pune-Mumbai, if I keep the speed steady at about 80 - 90kph, I can manage about 20kmpl, maybe more (A/c OFF).
But I'm usually much higher than that and manage around 17 kmpl ( with A/c )

In the city I get only about 11 kmpl :bang: ( A/c on 50% of the time )

A CT-100 you suggest....... hmm..... (n) naaahhhhh no way, and not because it has only two wheels.
I'm a reasonable guy, and I am open to options, but It has to be a Fiat and it has to be an Uno :D

Actually the intension of the post was not so much about mileage, but rather about driving style. Basically, should one drive with the engine in a certain rpm band? if so, why? and what would that range be for the Uno?

mqs
 
hellow,

how can u keep the rpm in a certain range if u r driving in mumbai on rush hours !!

Well there must be a best rpm range considering the power to milage ratio is acceptable and more than that, drivable..in any conditions..

but I dont know the optimum rpm range, I am out for max power, so used to rev hard and i found that the real power lies in high rpm --may b round 3-4000rpm..

dont have a tacho, fancy one or ages, may get one soon..

Well here r u located..seems u r in mumbai..

How's ur experience with yr car..means I have seen lots of disappointed ppl in and around here, bcoz of the bad service provided by fiat, and the lack of spares/experienced mechanics...

I have been keepin one alive for the last 9 years, spending lacs and lacs..

now my engine heads are of for some oil seal change, and belive, it took me 4 days to find the correct one !After long journeys from opera house market..I live at New bombay..

Those who sells spares,dont even know what's in which model...even fiat dealers couldnt help me without a sample !!

Rajeev.
 
If this is so, then what would be the ideal rpm's to keep the Uno most fuel efficient?
BTW - mine is a 2001, 1242cc SPFI.
If you can find the specifications for that engine, it will say the peak torque figures. It should also tell you what rpm that figure is achieved at. That is your most efficient engine speed.
H
 
hmm....
Max Torque Nm @ rpm : 92 @ 3,250

So thats the target then, 3250 rpm.

Did some basic math to calculate the speeds at 3250 rpm, taking into consideration the rolling radius and gear ratios. here it is
Gear - Speed @ 3250rpm
1 - 24.73 Kph
2 - 42.26 Kph
3 - 66.96 Kph
4 - 93.96 Kph
5 - 115.38 Kph

Need to get a tacho installed now to verify my math.....:cool:
 
MQUASH,

seems u r a genius on maths..

but if that has to be believed, u should change to 5th only after 115 km/h....

;)

Rajeev.
 
Rajeev: The speeds are not exactly the shifting points - or maybe they are :confused: .
I would think of these speeds as the ideal "cruising" speeds in the given gear.
So one might shift into gear whenever he likes, but ideally should maintain the said speed...... then again only if you have the same gear ratios as mine !!
And I'm still not 100% convinced about this method... read on below

hmallett:
After sending that post last night, I was wondering about the engine being most efficient at the rpm which delivers most torque.
I'm no expert in this field, so please excuse me if I've missed some basic reasoning, but come to think of it, wont the generation of "MAX" torque actually use up "MAX" fuel?

BTW - did the 0-100km run today and also got it on video. The only downside is that the test was conducted on a gradient :( .
Did a total of 4 runs each way. Haven't timed the videos using a stop watch, but going by the ye old wrist watch, the timings are pretty consistent. 20 sec while going uphill and 15 sec on the way down. Will be posting more details and the video on the "0-100 km timings" thread, later tonight.

mqs
 
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