VTEC - Page 2 - SV650.org

BillyC · 11-09-05, 08:33 PM

VTEC.... Honda's brand of Variable Valve Timing and Lift.

The Honda VTEC engines rev high (not exactly motorbike revs) because that's how they're made - light and revvy, but their talk and power delivery is also like an I4 bike engine - nothing low down, but all the power kicking in high up.

For the first few thousand RPM, an S2000 has little more power than a Ford Fiesta

No really!

In fact, the 2 litre Honda lumps power claim is a bit dodgy... the 200bhp or whatever it's supposed to make doesn't come until 8000 rpm, and the red-line is somewhere just the other side of 9000 rpm.

There are many engines that benefit from VVT&L... and it's simply a way of delivering power, when it's really required. It might work well on the 650 Vee... and help remove some of the snatchy power delivery that is associated so much to the SV.

Sid Squid · 11-09-05, 08:36 PM

All IC engines benefit from appropriate valving, the timing, lift and duration off the cam's lobes are always set as a compromise between the optimum settings for differing engine speeds, some systems actually change those settings, that's variable valve timing. There are several cars with this sort of system, I think that Suzuki made a few small fours like this too.
Honda do things slightly differently with their VTEC system, the VFR has four valves per cylinder and at low engine speed only one inlet and one exhaust open, this means that the gas flow passes through a smaller area and thus travels faster, (for any given volume), going faster means that the gas has greater momentum, and this improves the volumetric efficiency and cylinder scavenging.

There's no engineering reason why you couldn't do it to any four-stroke engine, but of course you'd need to examine the economics, I doubt it would make much sense, (as the technology stands now, won't be long I'm sure), for smaller simpler motors.

11-09-05, 08:56 PM

VTEC------SPEETEC! Pah! Where would I be without the hammering and banging from my desmodronics??

11-09-05, 10:56 PM

I read about it in a magazine...the fact I've heard nothing else seems as though it has been dropped.

The idea of V-TEC is to give optimum performance at low revs, then changing to optimum performance at high revs. This could work on a bus like the CB1300 but it would be banging on and off on a SV.
A Hayabusa is designed to go 180mph+ and so would be ineffecient at 30mph...cut the number of valves and power and Hey Presto...more effecient at 30mph...better fuel economy.

Why you would buy a big bike and ride at 30mph is another matter.
I can't imagine riding a bike on Spanish roads...it makes our roads look sane.

11-09-05, 11:12 PM

the VTEC doenst go down very well with many honda owners, its a common mod to disable it.

11-09-05, 11:27 PM

I'm sure the V-Tec will join the linked brakes and automatic gearbox in the Honda museum of 'answers to questions no-one asked'.

12-09-05, 08:47 AM

Quote:

Originally Posted by The Basket

Why have VTEC? No purpose I can think of. An answer to a question no-one asked. And on a small engine? Especially a revvy one? Adds complexity, increases service costs,

I agree , according to the VFR owners i know, it don't seem to help the low end that much , and the transition in the 7000rpm range can be disturbing, especially mid-corner.

northwind · 12-09-05, 02:22 PM

I think judging VTEC on how well it works in the VFR would be a bit unfair... it seems to be a pretty common concensus that it's just done badly on that particular bikes. VVT of some sort is finding its way into quite a few different applications, after all.

Sid Squid · 12-09-05, 05:35 PM

The VTEC system fitted to the Honda VFR is not a VVT system.

northwind · 12-09-05, 05:47 PM

That would be a question of definitions, I think? After all, VTEC stands for "Variable Valve Timing and Lift Electronic Control"

11-09-05, 08:33 PM	#11
BillyC Moderator Mega Poster Join Date: Nov 2003 Location: The exiles of Kent Posts: 2,184	VTEC.... Honda's brand of Variable Valve Timing and Lift. The Honda VTEC engines rev high (not exactly motorbike revs) because that's how they're made - light and revvy, but their talk and power delivery is also like an I4 bike engine - nothing low down, but all the power kicking in high up. For the first few thousand RPM, an S2000 has little more power than a Ford Fiesta No really! In fact, the 2 litre Honda lumps power claim is a bit dodgy... the 200bhp or whatever it's supposed to make doesn't come until 8000 rpm, and the red-line is somewhere just the other side of 9000 rpm. There are many engines that benefit from VVT&L... and it's simply a way of delivering power, when it's really required. It might work well on the 650 Vee... and help remove some of the snatchy power delivery that is associated so much to the SV. __________________ SV650 K3 - Gone. Now a member of the SV650.org Kawasaki brigade!

11-09-05, 08:36 PM	#12
Sid Squid No, I don't lend tools. Mega Poster Join Date: Jul 2003 Location: Skunk Works, Nth London Posts: 8,680	All IC engines benefit from appropriate valving, the timing, lift and duration off the cam's lobes are always set as a compromise between the optimum settings for differing engine speeds, some systems actually change those settings, that's variable valve timing. There are several cars with this sort of system, I think that Suzuki made a few small fours like this too. Honda do things slightly differently with their VTEC system, the VFR has four valves per cylinder and at low engine speed only one inlet and one exhaust open, this means that the gas flow passes through a smaller area and thus travels faster, (for any given volume), going faster means that the gas has greater momentum, and this improves the volumetric efficiency and cylinder scavenging. There's no engineering reason why you couldn't do it to any four-stroke engine, but of course you'd need to examine the economics, I doubt it would make much sense, (as the technology stands now, won't be long I'm sure), for smaller simpler motors. __________________ If an SV650 has a flat tyre in the forest and no-one is there to blow it up, how long will it be 'til someone posts that the reg/rec is duff and the world will end unless a CBR unit is fitted? A little bit of knowledge = a dangerous thing. "a deathless anthem of nuclear-strength romantic angst"

12-09-05, 02:22 PM	#18
northwind Moderator Mega Poster Join Date: Jan 2004 Location: In the garage where I belong Posts: 17,083	I think judging VTEC on how well it works in the VFR would be a bit unfair... it seems to be a pretty common concensus that it's just done badly on that particular bikes. VVT of some sort is finding its way into quite a few different applications, after all. __________________ "We are the angry mob, we read the papers every day We like what we like, we hate what we hate But we're oh so easily swayed"

12-09-05, 05:35 PM	#19
Sid Squid No, I don't lend tools. Mega Poster Join Date: Jul 2003 Location: Skunk Works, Nth London Posts: 8,680	The VTEC system fitted to the Honda VFR is not a VVT system. __________________ If an SV650 has a flat tyre in the forest and no-one is there to blow it up, how long will it be 'til someone posts that the reg/rec is duff and the world will end unless a CBR unit is fitted? A little bit of knowledge = a dangerous thing. "a deathless anthem of nuclear-strength romantic angst"

12-09-05, 05:47 PM	#20
northwind Moderator Mega Poster Join Date: Jan 2004 Location: In the garage where I belong Posts: 17,083	That would be a question of definitions, I think? After all, VTEC stands for "Variable Valve Timing and Lift Electronic Control" __________________ "We are the angry mob, we read the papers every day We like what we like, we hate what we hate But we're oh so easily swayed"

11-09-05, 08:56 PM	#13
Peter Henry Guest Posts: n/a	VTEC------SPEETEC! Pah! Where would I be without the hammering and banging from my desmodronics??

11-09-05, 10:56 PM	#14
The Basket Guest Posts: n/a	I read about it in a magazine...the fact I've heard nothing else seems as though it has been dropped. The idea of V-TEC is to give optimum performance at low revs, then changing to optimum performance at high revs. This could work on a bus like the CB1300 but it would be banging on and off on a SV. A Hayabusa is designed to go 180mph+ and so would be ineffecient at 30mph...cut the number of valves and power and Hey Presto...more effecient at 30mph...better fuel economy. Why you would buy a big bike and ride at 30mph is another matter. I can't imagine riding a bike on Spanish roads...it makes our roads look sane.

11-09-05, 11:12 PM	#15
Warren Guest Posts: n/a	the VTEC doenst go down very well with many honda owners, its a common mod to disable it.

11-09-05, 11:27 PM	#16
The Basket Guest Posts: n/a	I'm sure the V-Tec will join the linked brakes and automatic gearbox in the Honda museum of 'answers to questions no-one asked'.

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