[hrishig]

( Mods pl merge / move the thread if needed )

Here is the graph that I found while surfing







Does this mean that

1) All 3 engines should perform similar below 3000 - 3500 rpm?

2) The advantage of i-vtec over vtec can be seen only after 5000 rpm?

[ashthedivx]

Is the said difference is on paper only or the New Honda City loaded with i-vtec is literally so much lethal ??

[Guna]

Doesnt look very accurate. i-Dsi is supposed to have better torque at low RPMs then VTechs.

[alpha1]

^ You might be comparing two different engines in that case.

The only difference between a vtec and non-vtec engine is experience above ~4500 RPMs. So all the torque/power curves below should be same.

[hrishig]

Originally Posted by Guna

Doesnt look very accurate. i-Dsi is supposed to have better torque at low RPMs then VTechs.

??
Is this true? Is there any source / link which can confirm this?

[Guna]

Originally Posted by hrishig

??
Is this true? Is there any source / link which can confirm this?

I remember having read about this, probably in Autocar, but can't seem to get the same source.
Here is another article I found which says "Compared to the 88ps I-DSI engine, the VTEC engine delivers in the upper mid to high rpms. Indeed, at rpms below 3,000, the VTEC actually delivers less torque (i.e. less power) than the I-DSI, consistently 0.2kgm across the relevant rpm range."

Source: Honda City | Automobile and Car Review India

[ImmortalZ]

Guys, discussing the differences between VTEC, i-VTEC and i-DSI is opening a big can of worms.

Honda has used the VTEC nomenclature for large number of different technologies for their heads dealing with creative valve timing.

Get a big cuppa coffee and settle down for a read of the wikipedia page or if you really want a technical discourse, the Temple of VTEC Asia articles.

It is all very confusing, but very revealing.

[sujaylahiri]

Well Honda actually cheat a bit on their VTEC/i-VTEC valvetrains.

They only have that system on the intake valves, not on both intake and exhaust, like what Mitsubishi or Toyota or a ton of other companies have.
But there's nothing wrong with it, as long as it works.

But what it basically is that they have two different camshaft profiles on the camshaft, so depending on your "requirement", it is chosen by the ECU.

The two different profiles mostly affect the valve lift (only the intake in a VTEC). So if you gun it, it switches to the more aggressive profile and the valve opens more and for a longer time and hence more fuel+air is injected in the cylinder.

Whereas in economy mode, the opposite happens.

I'd guess that the i-DSI works in a similar way, but I could be wrong.

Most of the different manufacturers have their own version of VTEC, where they vary the different aspects of the intake and exhaust stroke to achieve different characteristics (like valve overlap, ignition delay etc.)

[Guna]

Originally Posted by sujaylahiri

I'd guess that the i-DSI works in a similar way, but I could be wrong.

One thing about i-DSI is, it has dual spark plugs which ignite with a fractional delay, supposedly resulting in better combustion.

Whatever the curves show, I have felt the new i v-tech to be more lively and responsive in the low end also, compared to i-DSI

[hellspawn]

Well if you observe the i-dsi has an almost flat torque curve between 2000-4000rpm.This is why its easier to drive in the city.

[Shan2nu]

Well Honda actually cheat a bit on their VTEC/i-VTEC valvetrains.

They only have that system on the intake valves, not on both intake and exhaust, like what Mitsubishi or Toyota or a ton of other companies have.

The two different profiles mostly affect the valve lift (only the intake in a VTEC). So if you gun it, it switches to the more aggressive profile and the valve opens more and for a longer time and hence more fuel+air is injected in the cylinder.

Firstly, VTEC doesn't only vary the lift but also the duration of the valves.

2ndly, Honda does have engines that use VTEC on the intake as well as the exhaust valves (mostly DOHCs). Even the B16s had this.

U can read more about the different types of VTEC engines here - VTEC

Shan2nu

[sujaylahiri]

Originally Posted by Shan2nu

Firstly, VTEC doesn't only vary the lift but also the duration of the valves.

Shan2nu

If you read my post again carefully, you'll see that I've talked about it as well.

"valve opens more and for a longer time and hence more fuel+air is injected in the cylinder"


I didn't know exactly what engines have VTEC on both intake and exhaust, but some of the more popular ones these days don't.

[ImmortalZ]

K20A - Civic Type-R, Integra Type-R, Accord Euro-R (225BHP)
K20A2 - RXS - S (200BHP)

The K20A2 I believe is one of the most sought after swaps for Honda cars in the world. People swap it into anything from a 88 to 2009 Civic, Prelude, Del Sol and even Fits. Some bolt the head to a K24A8 Accord engine to get a frankenstein torque monster.

Nice info here.

[hrishig]

After reading various article on net regarding the idsi and vtech comparision it is for sure that the idsi max torque is near 2800rpm and for vtech it is somewhere near 4500 rpm. The bad thing is both these cars have same rpm meter which is perfect for vtech but not so perfect for idsi.

Means for idsi , most of the buys will not cross 4500 mark as car starts screeming , yet the max rpm value is around 7-8k So for i-dsi the additional values are useless.