[honeybee]

Originally Posted by Aroy

OK a slight modification.
"For the same state of tune a higher displacement engine will have more low end torque compared to a smaller displacement engine."

Aren't both engines of the same displacement, i.e. 1.1 Litre?

[devansn]

Good thread! I think Spark is an exception in the small cars. I feel Spark's low end torque is amazing - just reminds me of Palio 1.2 - slot in 2nd and slowly release the clutch... But yes, as anshuman pointed out, the refinement is not comparable to the ones having poor low end torque.

BTW, what is the relation between low end torque and refinement?

[oxyzen]

Low end torque is all about idle RPM. The current trend is to reduce the idle RPM to such a level till the engine chokes to death. So what we have to resort to is give more and more gas. On the other hand if you set the idle RPM 200 above the usual you will never stall. (the Yeti needs it badly)
The other factor is ignition timing. You can be at idle with a little bit of retard. A little tap in the throttle should enable an advance in timing and provide instant pep.
However both of these are done for FE improvements.
But the fundamental fact remains we are shifting to oversquare engines. We are designing intake manifolds to provide more high end torque which will result to better power. And power sells cars.

[dhanushs]

Originally Posted by oxyzen

Low end torque is all about idle RPM.

huh? Could you please explain?

Originally Posted by oxyzen

The current trend is to reduce the idle RPM to such a level till the engine chokes to death.

What is the current trend for idle rpm? I mean figures

Originally Posted by oxyzen

The other factor is ignition timing...
... We are designing intake manifolds to provide more high end torque which will result to better power.

How much does ignition timing affect torque?. What was the older trend, and whats the new trend?

How much effect does a proper intake manifold design (not CAI) have in engine power/torque characteristics? Also, what was the previous trend and how badly modified are newer cars (design wise)

And power sells cars.

I agree completely that figures do help sell cars.

[quadmaniac]

Overall, I'd +1 the fact that the Chevy Beat has good low end torque, since I drive one.

Over speed bumpers et al, I never have to downshift at all. Once I remember, while taking a U turn from a complete dead halt, I stalled my car. Then I cranked the engine again and started slowly releasing the clutch and proceeding, and was able to make the turn succesfully. AFTER all that was over, I realized that I was in 2nd gear all along! (that being the reason for the stall)

[oxyzen]

Originally Posted by dhanushs

huh? Could you please explain?
What is the current trend for idle rpm? I mean figures

For a petrol it depends. Is it a 3 cylinder or 4. Does it have cast iron Block or aluminum. But you can safely assume a 900 RPM for 3 cylinder & 750-800 for a proper 4 cylinder. Some manufacturers aven push it down to 650.

Now the problem is in such a case you dont have any margin of error. If the RPM goes down by another 200 you are most likely to stall. And off-course you will find more pep in 750 RPM than 650.

Originally Posted by dhanushs

How much does ignition timing affect torque?. What was the older trend, and whats the new trend?

Earlier (some manufacturers) used to set a retarded ignition angle (for steady state). And advance it as soon as you need power. The net result- spontaneous response- a mild push in the back just after pressing the accelerator.
Current trend - always set is at max torque point or trace knock point.

Originally Posted by dhanushs

How much effect does a proper intake manifold design (not CAI) have in engine power/torque characteristics? Also, what was the previous trend and how badly modified are newer cars (design wise)

I have seen increase in 5 Nm at the midrange with a 3-4 Nm drop at the top end. Just by changing a manifold. So that is a little less than 10% which is by no means insignificant.
I wont say they are badly modified. You see, these days even power (specially petrol) is struggling to sell cars. There is a new kid in town & that is ARAI approved FE. And since better midrange helps achieve it, so yup some manufactures are looking into it.

[rednikhil]

A majority seem to be of the opinion that improving FE is one of the major reasons for poor low end torque in modern petrol engines. If an engine has poor low end torque, wouldn't it equate to gunning the engine to higher RPMs to get things moving, implying holding on to lower gears till higher RPMs? Would this not actually lead to lower FE figures rather that improving upon it, as everyone seems to be suggesting?

A car having good low end torque, allowing early up-shifts would any day prove to be more fuel efficient since it would allow the engine to operate in the optimum RPM range, the so called "green band". Just my two bits.

[Dr.Suraj]

WOW!

I had a bit of my own Permutations & Combinations going along in the recent past.

But this NEVER occurred to me !

Thank you so much for posting.

I myself was leaning towards the Nano
&
was awaiting the Nano diesel option too.

While keeping my eyes & ears peeled for the Chevrolet Electric vehicle due in 2012
&
what the Mahindra R&D comes up with next since XUV 500 is already out.

But - definitely a very interesting thought!

Now to find a good used Reva !
&
a mechanic who can take care of it at regular intervals.

[Aroy]

Originally Posted by rednikhil

A majority seem to be of the opinion that improving FE is one of the major reasons for poor low end torque in modern petrol engines. If an engine has poor low end torque, wouldn't it equate to gunning the engine to higher RPMs to get things moving, implying holding on to lower gears till higher RPMs? Would this not actually lead to lower FE figures rather that improving upon it, as everyone seems to be suggesting?

A car having good low end torque, allowing early up-shifts would any day prove to be more fuel efficient since it would allow the engine to operate in the optimum RPM range, the so called "green band". Just my two bits.

Actually the sweet spot for any engine is the peak torque. That is where the engine is running at maximum efficiency, that is lowest specific fuel consumption.

So if you are at a very low torque at a low engine speed, you will be consuming more fuel that you would at a higher speed/higher torque portion. That is why some petrol cars give better FE when revved up a bit compared to low RPM driving.

You have to tune the engine to produce the best torque in the RPM band that is used the most. For city driving it is at the lower end and on highways it is at higher end, hence there is always a trade off between city and highway drivability.

Regrading Low torque vs FE.
All things being equal, FE increase with decrease of the engine displacement, while HP will increase at higher RPM. So to increase FE you are decreasing the engine displacement. To increase HP you are designing the engine to rev higher, which essentially boosts the HP. Hence an engine with peak torque of "X" at say 4000 RPM, will have less HP compared an engine which has a torque peak of 10% less than "X" at 5000 RPM. If a normal torque curve is reasonably flat between 2K and 4K RPM, and usable range till 5K, when you tune the engine for higher peak torque, you are
. Pushing the peak towards 4K+
. Reducing the torque at 2K
. Increasing usable RPM to 6K
In effect you have more HP, but less low end torque. Fine if you want to race, but a let down for B2B traffic.
At one time in the 30's, a lot of manufacturers produces monster 5L+ straight 8 engines, with a flat torque from practically start to the end of the range. The manufacturer would claim that you could start and drive the 2 ton vehicle in the top gear.

[cijo]

From my experience in driving a ford ikon flair 1.3 rocam for 5 years , when i compare it with other 1.3 it have a high torque at lower rpm , but the car does not perform well in higways.There is no point in accelerating rocam beyond 3500 rpm because there is no considerable increase in speed beyond 3500 rpm and my car gave me low fuel efficiency (11kmpl).I think new age cars are tuned such a way that they have better fule efficiency and have better torque and power distribution over broader rpm range .

[aaggoswami]

Short stroke engines, well I don't agree with the point that the newer engines are getting shorter stroke which results into poor low end torque.
Take for example the engine mentioned here, the K10.
K10
Bore : 73.0mm
Stroke : 79.5 mm

Bore/Stroke Ratio : 0.91

The F8D/F10D
Bore : 68.5mm
Stroke : 72.0mm

Bore/Stroke Ratio : 0.95

G16
Bore : 75.0mm
Stroke : 90.0mm

Bore/Stroke Ratio : 0.83


The engines that have ratio of around .95 to 1.03 are considered square engines.
K10B is not a square engine and going only by dimensions, its an undersquare unit. Still F8D/F10D had better torque than F8D/F10D. So its not entirely upon Bore/Stroke, but it goes deeper than that.

Lets now consider K12M:
Bore : 73.0mm
Stroke : 71.5mm

Bore/Stroke Ratio : 1.02
So here again we can call it square unit or going by dimensions, an oversqaure unit. But K12M does not feel as lifeless as K10B which happens to be undersquare.

Last example in this post, the Ikon 1.6
Bore : 82.0mm
Stroke : 75.5mm

Bore/Stroke ratio : 1.086.

This was an oversquare unit, but had what we can say one of the best bottom end torque.

Again, I do believe that even ignition timings cannot make a significant difference. What can make a difference is Variable valve timing. The valve overlap can help here, but not ignition timings. The reduced valve overlap helps in better lower end torque, but the top end suffers.

The modern day motors take other things into consderation like emissions norms ( which might be playing havoc with low end grunt ), need for higher power and respectable FE. Moreover, the electronics are also playing a major role in modern engines.

I think that its not easy to arrive at a conclusion that lower stroke or anything is cause of this problem. Its rather a compromise for achieving higher volumetric efficiency as power is required more ( to beat competition ? ) and may be the families are having more highway trips.

Whatever be the reason, the end result is that its getting very tough to drive cars with low bottom end grunt in city traffic.

-> Drove my cousin's kappa i10. 1500 rpm, any gear except first, floor the pedal you are not moving anywhere. If you keep the pedal floored for even 2-3 seconds, may be an overloaded 100cc bike would zoom past you. Cars like Santro, M800 and old Waggie would have zoomed off with the amount of throttle I was giving.

-> K10 Waggie that we have. Each bump can ensure that you work out your gearbox. And if you driving this car after driving M800, Santro, old Waggie, etc., you are bound to have stalled car in middle of traffic. I faced this.

-> Honda Jazz. What a great mill it is, but in traffic, one has to be judicious else one will have stalled car.

We have M800 and Baleno at home along with Waggie ( K10 ). When it comes to driving in dense traffic in city, I prefer the 1.3 lakh kms. non ac M800. Yes, it can be that irritating.

The compromise is too much to handle given the increasing traffic.

[morphique]

Do we have a dedicated thread where we have listed (manual) cars that are easiest to drive in bumper to bumper traffic with good low end torque?
If not, can everyone here, in addition to their opinion about low end torque of today's small cars, also provide their opinion about cars that do not suffer from this disease?

[d_himan]

Interesting! Maybe a few exceptions though.

However, my 1997 Zen was really slow in the city with the Santro being far more perky in bumper to bumper traffic. I feel my current i10 1.2 VTVT feels far more livelier than the Zen. Again, I remember the Corsa Sail 1.4 being really slow.

[scuderiaferrari]

I think Baleno is a brilliant car in this respect. Great low end torque, combined with good high end power. And it revs freely too.. it can chug along from as low as 800 rpm, without struggling much.

All this with pretty long gearing. So if you look at it, the engine has a lot of real low end grunt, to overcome the tall gearing.

For low end pulling power, you can always have a shorter gearing, which would give a better response at the low speeds (since you are in a relatively higher rpm in any given gear than a taller geared one). However, this would result in much higher rpms at highways speeds. Which would impact the FE then. Santro/ i10 1.1 are examples of these.

In contrast, Swift (1.3) and all were really tall geared cars.

The companies are interested in:

1. claiming better FEs (highway numbers can really turn the averages here)
2. refinement (lower rpm means better feeling of refinement)

So, they tend to move towards taller gearing, which impacts drivability.

[srishiva]

I think all automakers have finally caught up with Honda's engine refinement and torque characteristics.