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-   -   Max kmpl , and how to achieve it (https://www.team-bhp.com/forum/technical-stuff/28072-max-kmpl-how-achieve-4.html)

Engine block heaters are already used to ease cold startup here in the U.S. Wouldn't it be helpful ? It runs on AC power though.

Yup I could feel it nowadays and raising/reducing gears based on it. But in 5th gear beyond 60 or more, I couldn't feel much may be due to racing sound of engine, that's why I had to ask this question !!

Oops! I heard it somewhere as well (outside of TBHP) and I didn't believe due to this reason: my car SX4's peak torque is at 4200 RPM and in 5th gear I would be beyond 110 kmph or so at this rpm (because, 80 kmph is around 2500 RPM), does it give best FE at this speed? It's hard for me to believe because, in 2 long drives, I got best mileage (16 kmpl) when I stayed within 80 kmph (whereas got 14.75 kmpl when I crossed 100 many times).

I am missing to understand something here, please help me understand.

Sathya, your observation is correct - stay below 80 kmph and you will get the best FE.
Other things like gradual acceleration, gentle braking (wherever possible, and using gears to decelerate), optimal gear, etc. have already been covered.
And no you're not 'missing to understand' anything.

I do not think it should be peak torque, it would rather be in the right torque band. Typical example may be on a slope you could stay in gear 3 straining the engine but still pulling or stay in gear 3 with less pressure on gas. You may want to consider this scenario with various loads: only driver in the vehicle you can shift pretty early say 10, 20, 35, 45 and 50+ KMPH. On a fully loaded one you may want to shift a little late to get enough pull (torque) say: 15, 25, 40, 60 and 80 KMPH. These are not absolute figures, it depends on where you feel enough pull for given load and gear and shift at the right point. Its to get minimum required work done by the engine for a given load.

Gurus, please feel free to correct if my fundas seem wrong, do not flame me though lol:

Driving with window/s rolled down induces drag on the car - leading to poor FE.
Under-inflated tyres are no help either.
Has anyone got any figures for a) windows down, no AC and b) windows rolled up, AC on? Which would give better FE?
(Turbosam,? please)

at max torque the engine is most efficient as heat exchanger as well as pump. ull be getting max performance in minimum fuel consumed.
kmpl efficiency on the other hand , wil be achived at much lower rpm/speed. ull be getting better kmpl figures @ 60-90kmph of steady driving in top gear with minimum input from accelerator input-just barely to maintain the momentum(even though the engine is less efficient at that rpm )
if u have an engine who has massive flat torque from as low as 1000-1500 rpm to @4000-5000 rpm then ur sitting in a gold mine ull get a road muncher at a fraction of a liter examples --most of the maserati 's especially bora,khamsin ,ghibli engines-4.9l redline at 5500 power rated 320 bhp torque 481.4 Nm, POWER BAND 800-5500 RPM..but then
maserati is maserati...:Frustrati

[quote=sathya_nars;560460]Oops! I heard it somewhere as well (outside of TBHP) and I didn't believe due to this reason: my car SX4's peak torque is at 4200 RPM and in 5th gear I would be beyond 110 kmph or so at this rpm (because, 80 kmph is around 2500 RPM), does it give best FE at this speed? It's hard for me to believe because, in 2 long drives, I got best mileage (16 kmpl) when I stayed within 80 kmph (whereas got 14.75 kmpl when I crossed 100 many timees)

Windows rolled down with no AC is better than AC with windows up. AAA in U.S recommends this and its tried and tested.

yes , any thing which adds drag will hamper fuel efficiency too.
all ground effect spoilers, gurney flaps, wings ,wide tyres, big exposed wheel arches,plow like design of rear bumper<unfortunarely on all indian cars>roof mounted racks all add to drag .. drag means more poerr to overcome resictence means more fuel (in an extreme case top f1 cars has down force is of @ 3 tons at 330kmph that means equivalent of moving 3 tons more at that speed)
fuel consumption in a/c depends upon ur car interior material, compressor size, its gear ratio to engine ,desired temp setting ,sunshades fitted,cabin volume,car colour.....
u can save some fuel by switching the a/c on only while coasting and breaking once the comfortable temp is achived . it also adds the life to a/c clutch which otherwise keeps engaging and disengaging continously and suddenly at high rpm which saps compressor life too

Thanks Turbosam. Awesome.
Another query: If handling and 'grip' are not important, would it be advisable to slightly over-inflate tyres for better FE?

if handlng and grip is not imp plus if u are ready to accept a bit noisey and a bit of harsher ride then, tyres inflated to the max- 1 to-2 psi recomanded by the tyre manufacturer will give you @ 5-15% more distance per lit . apard from lesser rolling resiestence, the tyre will deflect lesser so EFFECTIVE rolling radious will be more by @ 5-7% this difference will NOT show on the guage as number of revolutions will be translated in kms covered but when meter says 100 kms actually u have travelled 105 +kms as with larger radius, u will be needing lesser revolutions to cover the same distence .
its as god as fitting taller tyres ..

@ TURBOSAM..

It has been a pleasure to read your posts, as they come from an "unassuming" & knowledgeable person (as is evident from all the above posts) - rather than from those of us who think "they are the most knowledgeable" or from those whose each sentence is full of spite & sarcasm.

I hope that more people such as yourself would come forward with "knowledgeable answers" to address queries of members who are keen to know things but don't know whom to ask.

Kudos to you. No offense meant to any fellow member

Cheers

Makes perfect sense! Thanks. I presume the effects described are mainly for tubeless.

it hsa boosted my moral even higher . thanks

those effects are for both tubeless as well as tube types as long as they are radial types .
in bias ply tyres the tyre will be ovel or round if over inflated as there is no mechanism to maintain the near-flat contact patch .
it will reap even better milage benifits in bias ply tyres, but the contact patch will be too small to safely stop the car .plus it will over agriviate the tyre centre line wear.:Shockked:

Hi TURBOSAM,

I agree with Ricky_63 about pleasure in reading your post.I do feel that it comes from direct experience and sharing without any expectation.I too felt many times the depth of the subject presented in a very simple way.I appreciate your effort.